RU2795044C2 - System of inductive reading of electromagnetic signals from the body - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention provides a system for magnetically inductive sensing of electromagnetic signals emitted from a body in response to electromagnetic excitation signals applied to the body. A group of inventions relates to a system and method for inductive reading of physiological parameters for reading electromagnetic signals emitted from a body in response to electromagnetic excitation signals transmitted to the said body. The system contains a loop resonator, a means for generating a signal, and a means for signals processing. The resonator contains a loop antenna and a capacitor electrically connected to it. The antenna loop has one turn with a circumferential length l. In this case, the normalized radial frequency

≡ω/ω_ref electromagnetic excitation signals is from 0.025 to 0.50, whereω_ref = 2πc/l , π is the ratio of the circumference of a circle to its diameter, and c is the speed of light. The process is as follows: a loop resonator is excited to generate electromagnetic excitation signals having a radial frequency ω. The signals are sent to the body. A resonator is used to establish inductive coupling with electromagnetic signals emitted from the body in response to excitation signals. Read electromagnetic signals emitted from the body based on the detection of electrical changes in the loop antenna, indicating changes in the measured inductance in the loop, while the loop generates excitation signals. Process the signals received at the antenna. The frequency of the signals is reduced by mixing each signal with a reference waveform of a different frequency. A differential filter is applied to extract an output signal having a frequency being the difference between the frequency of the waveform and the received signal. In this case, the normalized radial frequency

≡ω/ω_ref electromagnetic excitation signals is from 0.025 to 0.50, whereω_ref = 2πc/l , π is the ratio of the circumference of a circle to its diameter, and c is the speed of light.

EFFECT: by the increased power of detected electromagnetic signals received from the body during inductive reading, and reduced noise level in them, the accuracy of the analysis is increased, by reducing the frequency of signals by mixing each signal with a reference waveform of a different frequency, applying a differential filter to extract the output a signal having a frequency being the difference between the frequency of the oscillating and received signals.

14 cl, 12 dwg

Description

FIELD OF TECHNOLOGY

The present invention relates to a system for inductively sensing electromagnetic signals from a body, and more particularly to a sensor for establishing inductive coupling with a body for sensing electromagnetic signals.

BACKGROUND OF THE INVENTION

Inductive reading can be used as a means of non-invasively investigating body properties.

In one preferred application, inductive reading can be used as a means for non-invasively investigating physiological characteristics, in particular heart and lung dynamics. Inductive sensing is based on magnetic induction and has several advantages over conductive and capacitive sensing.

The advantage over conductive readings such as bioimpedance measurements is that there is no need for adhesive electrodes; reading can be done without contact and/or through non-conductive material such as textiles and plastics.

The advantage over capacitive sensing is that inductive sensing is based on magnetic fields rather than electric fields, and as a result is more sensitive to changes at greater depths of penetration into the body than those types of sensing that only occur at skin level. This is because magnetic fields penetrate deeper into the body than electric fields, and thus magnetic fields can be used to measure changes in properties inside the body at greater depths, while electric fields are mainly useful only for measuring effects on skin surface, such as changes in skin properties (eg, permeability) or skin movement (skin proximity).

Coil-based inductive sensors function by establishing an inductive coupling with electromagnetic signals (i.e. electromagnetic waves or oscillations), with the propagation of signals through the coil resulting in a change in the current passing through the coil, which can be measured and used to determine the properties of the propagating signal (including, for example, frequency spectrum, amplitude, and phase image).

An electromagnetic excitation signal may be transmitted to the body to be examined. The electromagnetic excitation signal causes magnetic induction in the body, i.e. generation of eddy currents in body tissue due to the application of an external magnetic field. These eddy currents, in turn, generate electromagnetic signals propagating from the body, which interact with the applied fields in such a way that they can be read by the coil.

Movement of tissue in the body can manifest itself as changes in the volumes of local areas of the tissue and as changes in the conductive or dielectric properties of the tissue. These changes then cause amplitude and/or phase modulations of the electromagnetic signal emitted from the body in response to electromagnetic stimulation. By monitoring these changes, the movement and size changes of elements within the body can be detected and tracked, as well as changes in conductivity and dielectric properties. For example, heart contractions manifest themselves mainly as the movement of blood, and breathing manifests itself mainly as changes in the conduction of the lung.

For 50 years, since the first two studies in this area in 1967 (Vas et al.) and 1968 (Tarjan et al.), active research, and many publications appeared every decade. In particular, one active goal has been to obtain strong cardiopulmonary signals using an inductive sensor. As a rule, strong signals were the target.

However, current research has not led to the adoption of this technology for commercial applications because the signals received from inductive sensors remain notoriously weak and often saturated with noise.

Increasing the strength of the magnetic signals received from the body during inductive sensing is therefore a very important area for development. In known systems, the signal strength remains unacceptably low, which prevents effective commercial application of this technology.

It is an object of the present invention to increase the signal strength of detectable electromagnetic signals received from the body during inductive sensing.

DISCLOSURE OF THE INVENTION

The present invention is defined in the claims.

According to an aspect of the invention, there is provided an inductive physiological sensing system for sensing electromagnetic signals emitted from a body in response to electromagnetic excitation signals transmitted to said body, the system comprising:

a loop resonator for establishing inductive coupling with said electromagnetic signals radiated from the body, wherein the resonator comprises a loop antenna and an electrically connected capacitor, and the antenna loop has only one turn with circumferential length l, and

, для передачи в указанное тело,signal generating means configured to drive the resonator to generate electromagnetic drive signals having a radial frequency

, for transmission to the specified body,

электромагнитных сигналов возбуждения составляет от 0,025 до 0,50, где

и с = скорость света.while the normalized radial frequency

electromagnetic excitation signals is from 0.025 to 0.50, where

and c = speed of light.

To avoid uncertainty, s = 3 × 108 m/s.

электромагнитных сигналов возбуждения является одним из наиболее важных параметров при определении мощности сигнала, считываемого системой (а также абсолютной частоты f).The invention is based on the results of a significant research program carried out by the inventors, as a result of which it was found that the above parameter of the normalized radial frequency

electromagnetic excitation signals is one of the most important parameters in determining the power of the signal read by the system (as well as the absolute frequency f).

ниже 0,025 отношение сигнал-шум считываемого электромагнитного сигнала значительно уменьшается, что приводит к более высокой чувствительности к движению. Более конкретно, ниже данного уровня мощность сигнала значительно снижается и в большинстве вариантов практического применения насыщается шумом, исходящим от электронного шума, электромагнитных помех и шума от емкостной связи с поверхностью тела (т.е. прямой связи посредством электрических полей и зарядов, индуцируемых электрически).More specifically, studies have shown that at values

below 0.025, the signal-to-noise ratio of the electromagnetic signal being read is significantly reduced, resulting in higher motion sensitivity. More specifically, below this level, the signal power is significantly reduced and, in most applications, saturated with noise from electronic noise, electromagnetic interference, and noise from capacitive coupling to the body surface (i.e., direct coupling through electrical fields and electrically induced charges) .

However, despite the highly significant signal strength advantages that the inventors have been able to achieve with this invention, such high frequencies as claimed have never been explored in the art. It is highly likely, in view of the prevailing belief prevailing in the art, that (absolute) frequencies above about 10-29 MHz lead to a significant reduction in the achievable penetration depth due to skin reactions. The anticipated reduction in penetration depth would render the system ineffective for investigating physiological parameters. However, the inventors have found that this prevailing prejudice is a misconception because, although skin reactions are real, they only become unfavorable at much higher frequencies than those used in the present invention.

является наивысшим физически возможным при достижении эффективного индуктивного считывания. Это максимально возможная нормализованная частота первого резонанса в (одной) рамочной антенне, которая является резонансом, при котором ровно половина длины волны совпадает по окружности петли.In addition, it was found that the value of 0.50 for

is the highest physically possible while achieving efficient inductive sensing. This is the maximum possible normalized frequency of the first resonance in a (single) loop antenna, which is the resonance at which exactly half the wavelength coincides with the circumference of the loop.

Above the first resonance, a highly irregular current is induced in the resonator loop and the loop will perform a stationary sequence of oscillations of the accumulated charges. This accumulated charge interference pattern is typically capacitively coupled to the body surface, thereby inducing surface charges on the subject's skin surface.

ниже значения 0,5, мощность сигнала может быть поддержана на уровне, подходящем для практического применения.In this case, the sensor is brought into a highly sensitive state with respect to the movement of the body surface, where even very slight movements induce parasitic signals that completely drown out the perceived inductive signal (namely, the magnetic inductive signal emanating from under the body surface). This puts the inductive sensor in an inefficient state in most applications. Therefore, by saving

below a value of 0.5, the signal strength can be maintained at a level suitable for practical applications.

, предлагаемый в настоящем изобретении, таким образом, максимизирует мощность сигнала, которая является достижимой при магнитном индуктивном считывании.Range of values for

, proposed in the present invention, thus, maximizes the signal power that is achievable with magnetic inductive sensing.

ввиду емкостной связи между обмотками. Это, в свою очередь, ограничивает доступное увеличение мощности сигнала.In addition, the study found that, contrary to expectations, increasing the number of coil windings (coil turns) N above unity (one loop) does not provide a noticeable increase in signal power. Moreover, increasing the number of windings is actually disadvantageous for the purpose of maximizing signal strength, since increasing the number of windings limits the maximum realizable value

due to the capacitive coupling between the windings. This, in turn, limits the available increase in signal strength.

диапазона и антенны с одной катушкой, следовательно, являются фундаментально взаимосвязанными. Когда антенна содержит более одной петли (N>1), максимальная частота

может быть использована с петлей значительно уменьшенной ниже

ввиду паразитных емкостей между петлями и большей общей длиной провода катушки

. Это делает невозможным достижение предпочтительного нормализованного частотного диапазона, заявленного в настоящем изобретении, и сопутствующего увеличения мощности сигнала. Следовательно, только путем уменьшения количества витков катушки до одной возможны предпочтительно более высокие

значения.The two salient features of the above

band and single coil antennas are therefore fundamentally related. When the antenna contains more than one loop (N>1), the maximum frequency

can be used with a loop significantly reduced below

due to parasitic capacitances between the loops and the longer overall length of the coil wire

. This makes it impossible to achieve the preferred normalized frequency range of the present invention and the accompanying increase in signal strength. Therefore, only by reducing the number of turns of the coil to one, preferably higher

values.

However, limiting a coil winding to one is contrary to the prevailing assumptions in the art, which generally assume that multiple coil windings increase signal strength by increasing inductive coupling. This has further contributed to the reluctance in the art to investigate frequencies in the range claimed in the present invention.

Multiple windings also add to the cost and complexity of the sensor. Reducing to a single loop simplifies the design and operation of the device and reduces the form factor.

, заявленный в настоящей заявке, был затем определен на основании моделирования и экспериментов.A more detailed physical explanation and rationale for the specific defined range will be provided below. Briefly, however, the claimed invention is based on the discovery that reflected inductance (antenna inductance resulting from eddy currents induced in the body in response to electromagnetic stimulation) is a key factor in determining the resulting received signal strength at the antenna. First, by normalizing this quantity to make it effectively size-independent, and then by simulating the variation of the various parameters on which it depends, it was found that the normalized radial frequency of the sensed signals is the most significant parameter in determining the reflected inductance. The optimal range of values for

, declared in this application, was then determined based on simulations and experiments.

The system according to the present application is a system for inductive reading of a physiological parameter. Therefore, the system is designed to read electromagnetic signals received from the subject's body in response to electromagnetic excitation signals applied to the subject's body.

The system may in particular be a system for reading vital signs. Vital signs may include, for example, heart rate, pulse rate, tidal volume, respiratory rate, systolic volume, systolic volume variation, cardiac output, or aortic or arterial pulse height/pressure/diameter modulation.

It should be noted that, despite the fact that the present application is directed to the reading of physiological parameters, the inventive concept implemented in the invention, in principle, is not limited to the measurement of physiological parameters (such as vital signs). The inventive concept is applicable in a broader sense to any system for inductive reading. Examples will be described in the next section.

, могут быть сгенерированы путем возбуждения резонатора на радиальной частоте

. Под этим может подразумеваться возбуждение резонатора для резонанса на частоте

. Под этим, в частности, может подразумеваться индукция в антенне резонирующего тока, имеющего радиальную частоту

.Electromagnetic excitation signals having a radial frequency

, can be generated by excitation of the resonator at the radial frequency

. This may mean excitation of the resonator for resonance at the frequency

. This, in particular, may mean the induction in the antenna of a resonant current having a radial frequency

.

. Собственная резонансная частота резонатора может быть установлена путем соответствующего выбора емкости конденсатора.This can be achieved by providing a resonator having a natural resonant frequency equal to

. The natural resonant frequency of the resonator can be set by appropriate selection of the capacitance of the capacitor.

, может быть достигнуто путем возбуждения резонатора с током частоты

.Additionally or alternatively, excitation of the resonator to induce in the antenna a resonant current having a radial frequency

, can be achieved by excitation of the resonator with a current of frequency

.

электромагнитных сигналов возбуждения зависит от радиальной частоты

электромагнитных сигналов возбуждения и эталонной частоты

антенны (которая является радиальной частотой, на которой окружная длина l петли равна одной длине волны в свободном пространстве (т.е. где λ свободного пространства = l)).Normalized Radial Frequency

electromagnetic excitation signals depends on the radial frequency

electromagnetic excitation signals and reference frequency

antenna (which is the radial frequency at which the circumferential length l of the loop is equal to one wavelength in free space (i.e. where free space λ = l)).

Therefore, embodiments of the invention may require that the antenna, capacitor, and/or signal generating means are together configured such that the normalized radial frequency is within a certain range.

, и выбора антенны с правильной окружной длиной l. Там, где резонатор имеет заданную собственную резонансную частоту, он может быть индуцирован резонировать на данной частоте путем его возбуждения, например, с использованием генератора колебаний, работающего автономно (без фиксированной или вынужденной частоты колебаний).As an example, this can be achieved, for example, by providing a resonator with a capacitance chosen such that the natural resonant frequency of the resonator is set to

, and choosing an antenna with the correct circumferential length l. Where a resonator has a given natural resonant frequency, it can be induced to resonate at a given frequency by exciting it, for example, using an oscillator operating autonomously (without a fixed or forced oscillation frequency).

The system, in accordance with the present application, may be designed to read electromagnetic signals emitted from the body of the subject, i. physiological, diagnostic or medical system for reading. However, in a broader sense, the system is applicable to the perception of electromagnetic signals received from any body, where the body should be understood in a broad sense as a term meaning any physical object or entity, or any area of such an object or entity.

для передачи в тело.The readout system comprises means for generating a signal for driving a resonator for generating electromagnetic signals of radial frequency.

for transmission to the body.

By excitation of the resonator, a resonant current is induced for a reciprocating flow through the loop antenna into the capacitor.

The resonator can be excited by applying (alternating) current through the antenna to stimulate the generation of oscillatory electromagnetic signals (waves).

могут быть сгенерированы электромагнитные сигналы возбуждения с частотой

.By excitation of the antenna at a current with a frequency

electromagnetic excitation signals with a frequency can be generated

.

, т.е. возбуждения антенны переменным током частоты

. Активационное средство может быть, например, генератором колебаний.The means for generating the signal may comprise an activation means for excitation of the antenna, for example at a radial frequency

, i.e. excitation of the antenna by alternating current frequency

. The activation means may be, for example, an oscillator.

The same antenna is used to generate the excitation signals as it is used to read the electromagnetic signals received from the body in response.

For the avoidance of doubt, “electromagnetic excitation signals” simply means electromagnetic signals to be transmitted into the body to excite or stimulate the generation of eddy currents in the body, in order to in turn stimulate the emission of electromagnetic signals back out of the body, which can be perceived by the system for reading .

By "electromagnetic signals" can generally be understood to be electromagnetic radiation or electromagnetic oscillations and/or electromagnetic waves.

сигналов возбуждения может составлять от 0,025 до 0,25.According to one set of implementation options, the normalized radial frequency

excitation signals can range from 0.025 to 0.25.

= 0,25, амплитуда тока изменяется в большей степени по петле антенны. Фаза тока также является относительно постоянной вокруг петли антенны. Данные факторы являются значительными ограничивающими факторами в достижении высокой мощности сигнала и высокого качества сигнала.Within this range, the current amplitude when reading signals received back from the body is substantially constant (uniform) across the antenna loop. Higher

= 0.25, the current amplitude varies more along the antenna loop. The phase of the current is also relatively constant around the antenna loop. These factors are significant limiting factors in achieving high signal strength and high signal quality.

In particular, non-uniform currents are extremely disadvantageous because they lead to the accumulation of charges in the antenna loop, which, in turn, leads to capacitive coupling with the medium under study. Capacitive coupling with the medium is the main source of signal distortion (motor artifacts) in inductive sensors.

сигналов возбуждения может составлять от 0,025 до 0,20. Ниже верхнего предела 0,20 для

сопротивление излучения поддерживается на оптимально низком уровне (<0,5 Ом), фаза тока относительно постоянна по петле антенны, и равномерность амплитуды тока дополнительно улучшена (разность амплитуды тока между любыми двумя точками на окружности петли <20%).According to one set of implementation options, the normalized radial frequency

excitation signals can be from 0.025 to 0.20. Below the upper limit of 0.20 for

radiation resistance is kept optimally low (<0.5 ohm), the phase of the current is relatively constant across the antenna loop, and the uniformity of the current amplitude is further improved (difference in current amplitude between any two points on the loop circumference <20%).

= 0,20 начинают возникать некоторые электрические эффекты, в результате чего катушка становится чувствительной к составляющей электрического поля электромагнитных (ЭМ) сигналов, принимаемых обратно от тела (что создает помехи при считывании сигналов магнитного поля). Ниже

= 0,20 было обнаружено, что система считывания остается индуктивно сильно чувствительной к индуцированным электромагнитным сигналам, исходящим от тела без накопления значительных электрических зарядов вдоль одного провода петли антенны.This range is also particularly advantageous because the higher

= 0.20, some electrical effects begin to occur, causing the coil to become sensitive to the electric field component of the electromagnetic (EM) signals being received back from the body (which interferes with the reading of the magnetic field signals). Below

= 0.20, it was found that the reading system remains inductively highly sensitive to induced electromagnetic signals emanating from the body without the accumulation of significant electrical charges along one wire of the antenna loop.

сигналов возбуждения может составлять от 0,04 до 0,25. Нижний предел 0,04 является предпочтительным, поскольку это дает более высокую мощность сигнала (чем 0,025, например), в то же время, сохраняя преимущества очень низкого сопротивление излучения (~0,01 Ом), фазы постоянного тока по петле антенны и амплитуды постоянного тока над петлей антенны.According to one set of implementation options, the normalized radial frequency

excitation signals can range from 0.04 to 0.25. The lower limit of 0.04 is preferred as it gives higher signal power (than 0.025 for example) while still retaining the benefits of very low radiation resistance (~0.01 Ω), DC phase over the antenna loop, and DC amplitude current over the antenna loop.

выше 0,04 обеспечивает достаточно мощный уровень сигнала, чтобы сигнал был надежно защищен от шума в широком диапазоне вариантов практического применения. В некоторых сценариях (однако не во всех) электромагнитные сигналы ниже данной нормализованной частоты могут оказаться искажены артефактами шума, происходящими ввиду емкостной связи с поверхностью ткани (т.е. электрического соединения с поверхностью тела ввиду зарядов, индуцированных электрическим образом). Было обнаружено, что для датчиков традиционного размера, например, с радиусом от 1 до 3 см, мощность сигнала является удвоенной по сравнению с сигналами, использующими нормализованную радиальную частоту около 0,025. В частности, было обнаружено, что сигналы дыхания (сигналы, указывающие на функцию дыхания) имеют значительно более высокие мощности сигналов. Это будет объяснено более подробно в следующем разделе.It was found that the normalized radial frequency

greater than 0.04 provides a strong enough signal level that the signal is well protected from noise in a wide range of applications. In some (but not all) scenarios, electromagnetic signals below this normalized frequency may be distorted by noise artifacts due to capacitive coupling to the tissue surface (i.e. electrical connection to the body surface due to electrically induced charges). It has been found that for traditional sized sensors, for example, those with a radius of 1 to 3 cm, the signal strength is twice that of signals using a normalized radial frequency of about 0.025. In particular, respiration signals (signals indicative of respiratory function) have been found to have significantly higher signal strengths. This will be explained in more detail in the next section.

с генерированием сигналов возбуждения, имеющих радиальную частоту

.As noted above, in the examples, the signal generating means may be configured to drive the resonator to resonate at the radial frequency

with the generation of excitation signals having a radial frequency

.

для способствования возбуждению резонатора на радиальной частоте

, и, пр необходимости, конденсатор выбран для настройки собственной радиальной частоты резонатора на

.A resonator (circuit) having a natural radial frequency can be provided

to help excite the resonator at the radial frequency

, and, if necessary, the capacitor is chosen to tune the natural radial frequency of the resonator to

.

The system may include signal processing means configured to process signals received at the antenna. The signal processing means may be configured to read changes in the natural resonant frequency of the resonator (ie, resonator detuning) and use these changes to extract an output signal. The signal processing means may, in addition or alternatively, read changes in the damping factor of the resonator circuit and use these changes to extract an output signal.

Reading changes in natural resonant frequency may be advantageous because measuring changes in damping factor requires measuring the imaginary part of the reflected inductance, which may require additional complexity in the electronic circuitry of the signal processing means. However, the measurement of the imaginary part, and hence the damping factor, is possible according to one or more embodiments.

In accordance with at least one set of implementations, the system may comprise signal processing means configured to process signals received at the antenna to reduce the frequency of the signals by mixing the signals with a reference waveform of a different frequency, and applying a differential filter to extract the signal. , having a frequency that is the difference between the frequency of the reference and received waveform.

The goal of such implementations is to reduce the power consumption and processing power required of any signal processing performed by the system. In particular, digital dividers and counters (to process the received signals for analysis) consume a current proportional to the operating frequency. Therefore, in order to save power, according to the present embodiments, the frequency of received signals is first reduced, which allows subsequent signal processing to be performed at lower power consumption.

The advantage of the proposed particular implementation, initially mixing the second signal and then detecting the difference frequency signal, is that the mixing does not result in a loss of resolution. This is in contrast to, for example, dividers (which can also be used to reduce frequency), which do reduce resolution. However, the invention is still compatible with the use of dividers in other implementations.

The frequency of the reference waveform is preferably very close to the frequency of the received signals. In preferred examples, the frequency of the waveform and the frequency of the received signals are separated by 10 to 20%.

, т.е. радиальной частоте электромагнитных сигналов возбуждения.As explained above, the received signals will typically have a frequency equal to

, i.e. radial frequency of electromagnetic excitation signals.

According to one or more embodiments, the signal generating means may be configured to control the antenna to generate electromagnetic excitation signals at a frequency of 30 MHz to 1000 MHz.

.The frequency here refers to the absolute frequency f, not the radial frequency

.

и

, соответствующее требование предъявляется к

, что означает, что окружная длина

петли антенны должна быть выполнена с возможностью достижения желаемого значения f. В частности, данные варианты реализации требуют

According to these embodiments, an absolute frequency requirement is provided. Accordingly, since

And

, a corresponding requirement is placed on

, which means that the circumferential length

the antenna loop must be designed to achieve the desired f value. In particular, these implementations require

The application of excitation signals to the body at such high frequencies is not known in the art. This is because it is generally understood in the art that frequencies above about 30 MHz result in a significant reduction in the achievable penetration depth while increasing the operating power required. However, the present inventors have found that a decrease in penetration depth does not interfere with inductive readings (particularly physiological readings) until much higher frequencies are reached. This is especially true for applications applicable to the study of respiratory function. Therefore, these embodiments improve signal strength without impeding reduction in penetration depth.

This frequency range is preferred because the signal power becomes much higher than f = 30 MHz. This is especially true for comparatively smaller loops (radii in the range of 1-3 cm). In this case, when, for example, the signal is measured by changing the resonant frequency of the resonator (as described above), the frequency shift signal (the real part of the reflected inductance) quickly becomes much stronger when entering this range, by increasing in signal power, as well as moving in the phase of the reflected inductance in the direction of the real part.

This frequency range is also particularly advantageous when using a signal processing means in the form of a frequency converter with a counter. Absolute changes in the resonant frequency of the resonator due to, for example, breathing when using f < 30 MHz can be below 1 kHz. When using a slope counter, the quantization noise of the number of samples in the signal is easily visible at a given operating frequency.

With an increase in the absolute frequency above f > 30 MHz, the effect of quantization noise on the signal in most cases will cease to be problematic. This is described in more detail below.

In addition, it is preferable to keep the frequency below 1000 MHz to optimize the penetration depth. At frequencies above 1000 MHz, the penetration depth of electromagnetic signals begins to become unacceptably small for measuring physiological parameters, such as lung or heart signals.

According to one or more embodiments, the signal generating means may be configured to drive the resonator to generate electromagnetic drive signals having a frequency of 100 MHz to 1000 MHz.

At frequencies above 100 Hz, the penetration depth is still quite deep, while the signals become much stronger. In particular, it has been found that cardiopulmonary signals become much stronger. In addition, the phase of the reflected inductance moves further towards the real part. This is advantageous when the signal generating means is capable of measuring changes in the resonant frequency of the resonator, which requires measuring the real part of the reflected inductance.

In addition, above a frequency of 100 MHz, quantization noise, for example, means for processing the slope counter signal (for example, with an integration time of about 0.05 seconds), is practically negligible relative to the signal strength. This is described further below.

According to one or more embodiments, the signal generating means may be configured to drive the resonator to generate electromagnetic drive signals having a frequency of 30 MHz to 500 MHz.

This absolute frequency range optimizes the depth of penetration, particularly for muscles. The signal strength at 500 MHz remains very high while the penetration depth is maintained relatively large (~5 cm for muscle - and higher for other media).

This frequency range may also be preferred where power consumption is a concern, such as battery-powered sensors. Below 500 MHz, the frequency is low enough not to contribute significantly to signal processing power consumption.

According to one or more embodiments, the signal generating means may be configured to drive the resonator to generate electromagnetic drive signals having a frequency of 100 MHz to 500 MHz.

This combines the advantages of the 100 MHz lower limit and the 500 MHz upper limit described above.

The excitation of the resonator to generate signals of the above frequencies can be performed in accordance with the examples of the methods set forth above.

In particular, in preferred examples, the antenna loop may have a radius of 15 to 20 mm.

In still other preferred applications, the antenna loop may have a radius of 90 to 110 mm.

Loop radii of 15 or 20 mm are desirable because larger loops have been found to be more sensitive to the movement of objects in the environment since the distribution of the electromagnetic field is proportional to the size of the loop where the relative frequency is kept constant. Loops with radii smaller than 15 mm are possible, but the received signal strength is reduced.

Antenna loops with a radius of 90 to 110 mm are advantageous, for example, in cases where reading over a relatively long distance is required. For example, an antenna of this size could be embedded in a mattress or chair and allow reading through furniture materials. An antenna loop having a radius of 100 mm has been tested and found to be advantageous, for example, in similar applications.

According to one or more embodiments, the system may include means for processing signals read by the antenna to extract one or more physiological parameters.

In the examples, in accordance with a further aspect of the present invention, there is provided a method for inductively sensing physiological parameters, comprising sensing electromagnetic signals emitted from a body in response to electromagnetic excitation signals transmitted to said body, the method comprising:

excitation of the loop resonator for generating electromagnetic excitation signals and directing the signals to said body, wherein the resonator comprises a loop antenna and a capacitor electrically connected, and the loop antenna has only a single-turn loop with circumferential length l; And

using a loop resonator to establish inductive coupling with electromagnetic signals emitted from the body in response to excitation signals,

электромагнитных сигналов возбуждения составляет от 0,025 до 0,50, где

и с = скорость света.while the normalized radial frequency

electromagnetic excitation signals is from 0.025 to 0.50, where

and c = speed of light.

All terms should be interpreted in accordance with the above description regarding the aspect of the system for reading, in accordance with the present invention.

In accordance with at least one set of implementation options, the method may include processing signals received by the antenna to extract information about physiological parameters.

электромагнитных сигналов возбуждения может составлять от 0,025 до 0,25.In accordance with one or more implementation options, the normalized radial frequency

electromagnetic excitation signals can range from 0.025 to 0.25.

Any of the options or embodiments set forth above with respect to the aspect of the reading system according to the present invention may also advantageously be applied or included in the aspect of the present method of the invention by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the present invention will be described in detail, by way of example only, with reference to the accompanying drawings, in which:

in FIG. 1 shows chest stimulation of a subject in close proximity to a resonator consisting of a loop antenna and a capacitor;

in FIG. 2 shows the dependence of the respiratory component in the characteristic reflected inductance on the normalized radial frequency of electromagnetic excitation signals, modeled for a homogeneous medium;

in FIG. 3 shows the dependence of the respiratory component in the characteristic reflected inductance on the normalized radial frequency of electromagnetic excitation signals, modeled for an open lung;

in FIG. 4 shows the structure of a simulated multilayer lung;

in FIG. 5 shows the dependence of the respiratory component of the characteristic reflected inductance on the normalized radial frequency of electromagnetic excitation signals, modeled for the multilayer lung of FIG. 4;

in FIG. 6 shows an example of a reading system according to an embodiment;

in FIG. 7 shows an example of a reading system processing scheme, according to an embodiment;

in FIG. 8 shows another example of a reading system processing scheme, according to an embodiment;

in FIG. 9 shows the change in current amplitude around the pickup coil in an example readout system for various normalized radial frequencies of electromagnetic signals;

in FIG. 10 shows the change in the phase of the current around the measuring loop in an example system for reading for various radial normalized frequencies of electromagnetic signals;

in FIG. 11 shows the dependence of the unprotected loop impedance at normalized radial frequency; And

in FIG. 12 shows the penetration depth of excitation signals as a function of signal frequency for signals propagating through different media.

IMPLEMENTATION OF THE INVENTION

The invention provides a magnetic inductive system for reading electromagnetic signals emitted from a body in response to electromagnetic excitation signals applied to the body. The generation and reading of electromagnetic signals is carried out by the same loop resonator, which contains a single-turn loop antenna and a tuning capacitor. The resonator loop antenna and the signal generating means for driving the resonator for generating the drive signals are jointly configured to optimize the value of the ratio between the radial frequency of the generated electromagnetic drive signals and the reference frequency of the antenna, where the reference frequency is the frequency for which one wavelength of the generated drive signals (waves ) corresponds to the circumferential length of the antenna. This ratio, which corresponds to the normalized radial frequency of the generated excitation signals, is maintained between 0.025 and 0.50.

применяемых электромагнитных сигналов возбуждения является ключевым параметром при определении силы сигналов, считываемых антенной (где

является радиальной частотой сигналов возбуждения,

, а l представляет собой окружную длину одновитковой петли антенны).The invention is based on the results of a research program undertaken by the inventors, as a result of which it was found that the normalized radial frequency

applied electromagnetic excitation signals is a key parameter in determining the strength of the signals read by the antenna (where

is the radial frequency of the excitation signals,

, and l is the circumferential length of a single-turn antenna loop).

The theoretical background of the invention will now be explained with reference to FIG. 1-5.

Embodiments of the invention operate on the principle of inductive coupling, wherein the coil or wire induces a potential difference through itself due to the action of a time-varying magnetic field. Embodiments of the present invention use this principle to measure the strength of electromagnetic signals generated within areas of the body by reading changes in the inductance of a coil placed in close proximity to the body, where these changes are detected based on changes in the resonance characteristics of the coil circuit.

Any electrical conductor exhibits the property of self-induction. Self-induction is a property of an electrical conductor in which a change in the current flowing through the conductor leads to the induction of an electromotive force in the conductor. According to Lenz's law, the induced electromotive force tends to oppose the changing current that induces it. Therefore, the generally accepted term for it is "back EMF". Self-induction can be understood as arising from the magnetic flux induced as a result of a change in current (Ampère's law). This flux then interacts with the conductor itself to induce a back emf (Faraday's law of induction and Lenz's law).

The relationship between the self-inductance L of the circuit, the voltage, v(t), and the current, I(t), can be expressed as:

By using Faraday's law of induction to express v(t) as dΦB/dt (where ΦB is the magnetic flux) and integrating over time (assuming L is a time constant), the free space self-inductance L for a coil having N turns can be be expressed as:

Embodiments of the present invention use a resonator comprising a single loop loop antenna to stimulate or excite the body with electromagnetic signals (waves) and to sense signals radiated back from the body in response to these excitation signals.

The coil can be driven with alternating current to generate excitation signals for transmission to the body.

When the coil is close to the body, the inductance L receives an additional reflected inductance component, L _r , due to the eddy currents induced in the stimulated body as a result of the application of the excitation signals. This is shown schematically in FIG. 1, which shows, as an example, a loop antenna 12 driven by alternating current in the vicinity of a subject's chest 16 to transmit electromagnetic signals 22 to the chest.

As a consequence, eddy currents 18 are induced in the chest. Eddy currents occur naturally due to Faraday's law of induction, according to which an electromotive force (EMF) is induced in a conductive medium in response to the presence of a time-varying magnetic field.

These eddy currents, in turn, effectively contribute to the inductance of the loop antenna 12. This is because they themselves generate a time-varying magnetic flux 24 of a frequency equivalent to that generated by the antenna feed 12. These eddy current fluxes combined with the feed flux of the antenna, resulting in a larger induced back EMF in the antenna and hence a larger measurable effective inductance.

The additional inductance component due to eddy currents is listed as "reflected inductance", L _r . The total inductance L _t of the antenna 12 with the coil can be expressed as:

where L ₀ is the self-inductance of the loop antenna 12 and L _r is the reflected inductance.

Reflected inductance can be defined as:

представляет собой радиальную частоту электромагнитных сигналов 22 возбуждения (изменяющееся во времени поле, применяемое к телу).where A _r is the reflected part of the electromagnetic vector potential (ie the part that is generated by the eddy currents 18 in the stimulated environment) and I is the coil current. The reflected inductance is closely related to the reflected impedance Z _r . The ratio is L _r =Z _r /iω, where

represents the radial frequency of the electromagnetic excitation signals 22 (a time-varying field applied to the body).

The above integral expression can be understood by applying the relation:

where B _r is the "reflected" magnetic field, and then the application of the Stokes theorem is carried out to re-express equation (4) as:

where N = number of turns. It can be seen that this corresponds to the form of the simplified expression for inductance given in Equation (2) above.

The amplitude of the reflected inductance component gives an indication of the power of the "reflected" electromagnetic signals radiated back from the body. Stronger signals give a higher signal-to-noise ratio, which improves the quality and reliability of the read signals. Thus, by seeking to optimize the power L _r , the signal-to-noise ratio can be maximized.

Typically, the reflected inductance, L _r , is complex and can be expressed as

(7)

(7)

связано с реактивным импедансом рамочной антенны, а

связано с резистивным импедансом катушки.Where

is related to the reactive impedance of the loop antenna, and

related to the resistive impedance of the coil.

The addition of the reflected component of the inductance L _r leads to a detuning of the characteristics of the coil. In particular, both the natural radial frequency of the coil antenna circuit and the attenuation factor of the loop antenna circuit change. By measuring this detuning of the characteristics of the coil, the value of the reflected inductance L _r and the measured reflected signals can be determined.

In particular, the detuning of the characteristics of the coil as a result of the addition of reflected inductance can be expressed as follows:

(8)

(9)

представляет собой незатухающую собственную радиальную частоту схемы катушки в свободном пространстве,

представляет собой собственную незатухающую радиальную частоту схемы катушки в присутствии среды или тела (нижний индекс t означает «общее»),

представляет собой коэффициент затухания в свободном пространстве,

представляет собой (общий) коэффициент затухания в присутствии среды,

представляет собой фактическую часть отраженной индуктивности, определенной в уравнении (7), и

представляет собой мнимую часть отраженной индуктивности, определенной в уравнении (7).Where

is the undamped radial natural frequency of the coil circuit in free space,

is the intrinsic undamped radial frequency of the coil circuit in the presence of a medium or body (the subscript t means "general"),

is the attenuation coefficient in free space,

is the (total) damping factor in the presence of a medium,

is the actual part of the reflected inductance defined in equation (7), and

is the imaginary part of the reflected inductance defined in equation (7).

. Отстроенный коэффициент затухания зависит также от мнимой части отраженной индуктивности

.It can be seen that the detuned natural radial frequency depends only on the real part of the reflected inductance

. The detuned damping factor also depends on the imaginary part of the reflected inductance

.

и отраженная индуктивность

могут быть определены следующим образом:For simplicity, it is preferable to work with geometrically normalized quantities. Accordingly, the "characteristic" self-inductance

and reflected inductance

can be defined as follows:

(10)

(eleven)

не зависит от размера системы и от числа витков в катушке антенны.where l = circumferential length of one coil turn, N = number of coil windings, L ₀ is the free space self inductance (actual), L _r is the reflected inductance (complex), and where L _r is defined as in equation (4 ) higher. The advantage of using geometrically normalized quantities is that

does not depend on the size of the system and on the number of turns in the antenna coil.

Using these characteristic quantities, the detuning of the characteristics of the coil, resulting from the addition of reflected inductance, can be expressed as follows:

(12)

(13)

представляет собой незатухающую собственную радиальную частоту схемы катушки в свободном пространстве,

представляет собой собственную незатухающую радиальную частоту схемы катушки в присутствии среды или тела (нижний индекс t обозначает «общее»),

представляет собой коэффициент затухания в свободном пространстве,

представляет собой (общий) коэффициент затухания в присутствии среды,

представляет собой фактическую часть характерной отраженной индуктивности, определенной в уравнении (9), и

представляет собой мнимую часть характерной отраженной индуктивности, определенной в уравнении (9).Where

is the undamped radial natural frequency of the coil circuit in free space,

is the intrinsic undamped radial frequency of the coil circuit in the presence of a medium or body (the subscript t stands for "general"),

is the attenuation coefficient in free space,

is the (total) damping factor in the presence of a medium,

is the actual part of the characteristic reflected inductance defined in equation (9), and

is the imaginary part of the characteristic reflected inductance defined in equation (9).

These equations have not been obtained before and allowed the inventors to extract new physical concepts, since these quantities provide signal strength measurement factors regardless of the radius of the loop and the number of coils in the antenna.

. Следовательно, стало возможным более фундаментальное физическое понимание.For example, for circular loops in particular, typical intrinsic self-inductance values are around 500-1100 nH/m, regardless of the number of turns and loop radius. To calculate the signal strength, it is only necessary to derive the value of one variable, namely

. Consequently, a more fundamental physical understanding became possible.

From the above, it can be seen that the natural radial frequency of the system changes in the presence of a medium by a factor that depends on the actual part of the reflected inductance L _r , and the attenuation factor changes in the presence of a medium by a factor that depends on the imaginary part of the reflected inductance L _r . These changes can be used to determine L _r and thereby determine the measurement of the strength of electromagnetic signals received from the environment (from the stimulated and read body).

The inventors of the present invention have achieved an increase in perceived signal power by deriving a new and powerful expression for reflected inductance that allows it to be quantified in a new way based on system properties that can be easily tuned and optimized.

Specifically, starting from Equation (4) above and limited to cylindrical symmetry (suitable for the coil antenna used in embodiments of the present invention), the reflected inductance becomes:

(14)

where Ar,ϕ is the azimuthal component of the reflected vector potential, a is the radius of the loop(s) of the loop antenna, N is the number of coil turns, and I is the coil current.

Using the calculations for Ar,ϕ set out in Cheng D.H.S. (1965), Reflected impedance of a circular coil in the vicinity of a semi-infinite medium, Institute of Electrical and Electronics Engineers Research Notes on Instrumentation and Measurement, 14(3), 107-116 (Cheng, D. H. S. (1965), The reflected impedance of a circular coil in the proximity of a semi-infinite medium, IEEE Transactions on Instrumentation and Measurement, 14(3), 107-116), the inventors obtained the following expression for the characteristic reflected inductance:

(15)

и

, a представляет собой радиус петли, h представляет собой расстояние от петли до среды, J₁(x) представляет собой функцию Бесселя первого порядка первого рода,

представляет собой радиальную частоту электромагнитных волн (сигналов), Γ(ξ) представляет собой TE (т.е. s - поляризованный) коэффициент отражения Френеля стимулируемой (многослойной) структуры, и где ξ представляет собой поперечное волновое число в пределах данной среды.Where

And

, a is the radius of the loop, h is the distance from the loop to the medium, J ₁ (x) is the first order Bessel function of the first kind,

is the radial frequency of the electromagnetic waves (signals), Γ(ξ) is the TE (i.e., s - polarized) Fresnel reflectance of the stimulated (multilayer) structure, and where ξ is the transverse wavenumber within the given medium.

The calculation of the TE Fresnel reflection coefficients for a given medium is detailed on page 186 of Sophocles J. Orphanidis' Electromagnetic Waves and Antennas (which is available online at: http://www.ece.rutgers.edu/~orfanidi/ewa/) .

полностью не зависит от числа витков, и поскольку (как показано ранее)

представляет мощность сигнала, следовательно, можно увидеть, что мощность сигнала не зависит напрямую от количества катушек. Из этого можно легко увидеть, что увеличение количества катушек в антенне не оказывает полезного воздействия на мощность сигнала. Since equation (15) shows that

is completely independent of the number of turns, and since (as shown earlier)

represents the signal strength, therefore it can be seen that the signal strength does not depend directly on the number of coils. From this it can be easily seen that increasing the number of coils in the antenna does not have a beneficial effect on the signal strength.

The understanding of reflected inductance represented by Equation (15) above has not been obtained before. This approach provides a powerful quantitative representation of the power of the reflected signal.

The reflected inductance of a loop antenna system over a homogeneous medium can be characterized by five basic geometric properties. They are: the radius of the loop, a, the frequency of electromagnetic signals/waves, ω, the distance between the loop and the medium, the permeability of the medium and the conductivity of the medium.

They can be understood as geometric properties since they refer to the five length scales within the system. Considering the case where the medium is an area of the subject's body, they can be understood as: the radius of the loop, the wavelength in the free space of EM waves, the distance between the loop and the medium, the length of the EM wave inside the medium, and the depth of the skin. It should be noted that although N can be considered a property of the coil, it is not a geometric property, since it does not affect any of these five length scales.

All five length scales can be scaled by a factor of x, so that the resulting fields and eddy currents are also just a scaled copy. The resulting reflected inductance is then also scaled by a factor of x, since the fields remain unchanged while the circumferential length of the loop is increased by a factor of x.

, однако, остается неизменной, поскольку коэффициент масштабирования появляется как в L_r, так и в l, и, таким образом, полностью компенсируется (см. уравнение (11) выше).Characteristic reflected inductance

, however, remains unchanged since the scaling factor appears in both L _r and l, and thus cancels out completely (see equation (11) above).

The way in which the geometric properties need to be scaled to describe the overall increase in size by the x factor is given below.

loop radius →

radial frequency of generated EM signals →

h distance from coil to medium → h

permeability →

conductivity →

reflected →

Normalized geometric properties can be defined that remain unchanged as the size of the x-factor increases overall. They are defined below. They allow you to calculate the characteristic reflected inductance using only four parameters instead of five (for a homogeneous medium). This reduces the complexity of the present model in terms of how system properties affect signal strength.

Normalized loop antenna radius:

Normalized radial frequency of electromagnetic excitation signals:

Normalized distance between loop antenna and medium: ĥ

ĥ = h/a

Normalized permeability:

Normalized conductivity:

Normalized (characteristic) reflected inductance:

In the above expressions, a is the radius of the loop antenna, l is the circumferential length of one winding of the loop antenna, and ω _ref = c/a = 2πc/l is the radial frequency for which one free-space wavelength of EM signals equals the circumferential length l coils. Typically, this is ω _ref = 2πc/l (obtained by setting λ=l in the general ratio for free space waves ω = 2πc/λ). In the particular case of a circular coil, l = 2πa, which allows a simplification to ω _ref = c/a.

частота генерируемых сигналов возбуждения является одним из данных параметров.Therefore, these normalized geometric parameters allow the characteristic reflected inductance to be expressed in 4 rather than 5 parameters by making the values independent of the antenna loop radius. Normalized Radial

the frequency of the generated excitation signals is one of these parameters.

является наиболее сильным определяющим фактором измеренной характеристики отраженной индуктивности

.Using a number of computational models, the inventors found that the parameter

is the strongest determinant of the measured reflected inductance characteristic

.

с фиксированной характерной проводимостью

= 0,056 и фиксированной относительной проницаемостью

. Результаты показывают изменение мощности характерной отраженной индуктивности

при изменении

.FIG. Figure 2 shows the results of computer simulation of electromagnetic stimulation of a homogeneous medium using one turn (N=1) of a coil of fixed radius a, at a fixed characteristic distance from the medium

with fixed characteristic conductivity

= 0.056 and fixed relative permeability

. The results show the power variation of the characteristic reflected inductance

when it changes

.

отсутсв данной простой однородной модели

. Кроме того, было обнаружено, что это является самой сильной зависимостью

от какого-либо из параметров ĥ, a,

или

.From the graph in FIG. 2 it can be seen that a strong dependence on

missing in this simple homogeneous model

. In addition, it was found to be the strongest dependence

on any of the parameters ĥ, a,

or

.

It was found that this strong dependence is also reproduced in more complex models.

в зависимости от

для модели, построенной для представления открытого легкого, под которым подразумевается само легкое, в изоляции от любых слоев жира, мышц или костей, которые его окружают на практике. Для данной модели изменение характерной отраженной индуктивности

между легким при вдохе и легким при выдохе

было смоделировано в качестве функции

. Это изменение

является значимым физиологическим параметром, поскольку позволяет определять характеристики функции легких.FIG. 3 shows the results of computer simulation for

depending on the

for a model built to represent an open lung, by which is meant the lung itself, in isolation from any layers of fat, muscle, or bone that surround it in practice. For this model, the change in the characteristic reflected inductance

between the lung on inhalation and the lung on exhalation

has been modeled as a function

. This change

is a significant physiological parameter, since it allows you to determine the characteristics of lung function.

в зависимости от

было смоделировано для одновитковой рамочной антенны пяти различных радиусов a в диапазоне от 10 мм до 100 мм. На графике показаны отдельные линии 24-32, соответствующие разным размерам радиуса, при этом размер радиуса для каждой линии обозначен оттенком на графике.Change

depending on the

was modeled for a single loop loop antenna with five different radii a in the range from 10 mm to 100 mm. The graph shows individual lines 24-32 corresponding to different radius sizes, with the radius size for each line indicated by a shade on the graph.

от

и, опять же, было обнаружено, что

представляет собой параметр, от которого наиболее сильно зависит

.It can be seen that there is a strong dependence

from

and, again, it was found that

is the parameter on which the most

.

от изменения

для данной модели многослойного легкого была снова рассчитана.In addition to the open lung model, another model was calculated for the multilayer lung, taking into account the layers of fat, muscle, and bone that surround the lung. Addiction

from change

for this multilayer lung model was calculated again.

A schematic illustration of the physical structure of a simulated multilayer lung is shown in FIG. 4. The lung itself is depicted as layer (f) with a simulated height of 20 cm for exhalation and 25 cm for inhalation. Three layers of bone are superimposed on top of the lung: cortical bone (c), spongy bone (d) and cortical bone (e) 0.2 cm, 0.8 cm and 0.2 cm high, respectively. Above the layers of bone - the upper layer of fat (a) 1 cm high and the layer of muscle (b) underlying, 1 cm. Three layers of bone are also modeled under the lung: cortical bone (g), cancellous bone (h) and cortical bone ( i) 0.2 cm, 0.8 cm and 0.2 cm high, respectively, and an additional layer of muscle (j) 1 cm and a layer of fat (k) 1 cm.

A single loop loop antenna with a radius a is shown at a distance h from the multilayer structure.

в зависимости от

были получены для антенны в диапазоне различных радиусов a катушки антенны, варьирующихся от 10 мм до 100 м, при этом каждая из линий 42-50 соответствует полученному результату для одного из размеров радиусов, как указано оттенком на ФИГ. 5.The results of the multilayer lung model are shown in FIG. 5. Values

depending on the

were obtained for the antenna over a range of different antenna coil radii a , ranging from 10 mm to 100 m, with each of the lines 42-50 corresponding to the result obtained for one of the radius sizes, as indicated by the shade in FIG. 5.

от

сохраняется в многослойной модели для всех размеров радиуса несмотря на то, что радиус катушки теперь имеет нетривиальную разницу с полученной направленностью. Однако, что касается других более базовых моделей, было установлено, что

было наиболее значимым фактором при определении

, с отношением между

и

, которое сильнее, чем с любым другим параметром.It can be seen that a strong dependence

from

is preserved in the layered model for all radius sizes, despite the fact that the coil radius now has a non-trivial difference from the resulting directivity. However, for other more basic models, it has been found that

was the most significant factor in determining

, with the relation between

And

, which is stronger than with any other parameter.

, где ω представляет собой радиальную частоту генерируемых электромагнитных сигналов (частоту, при которой осуществляется приведение в действие или возбуждение резонатора катушки), а ω_ref представляет собой частоту, для которой одна длина волны в свободном пространстве равна окружной длине катушки, представляет собой наиболее эффективный подход к оптимизации силы считанной отраженной индуктивности

и, следовательно, оптимизации соотношения сигнал/шум (мощности сигнала).Based on the obtained simulation results, it can be determined that the optimization

, where ω is the radial frequency of the generated electromagnetic signals (the frequency at which the coil resonator is driven or energized) and ω _ref is the frequency for which one wavelength in free space equals the circumferential length of the coil, is the most efficient approach to optimizing the strength of the read reflected inductance

and hence optimizing the signal-to-noise ratio (signal strength).

приводят к более высокой считанной величине

. Однако было установлено, что максимум

, который физически возможен, при этом по-прежнему достигая эффективного индуктивного считывания, составляет

= 0,5. Это связано с тем, что это представляет собой резонансную частоту полуволны петли (т.е. максимальную частоту собственного резонанса).The results show that, in general, higher

lead to a higher reading

. However, it was found that the maximum

, which is physically possible while still achieving an efficient inductive readout, is

= 0.5. This is because this represents the resonant frequency of the loop's half-wave (i.e., the maximum natural resonance frequency).

Above this frequency, a highly non-uniform current is induced in the resonator loop, and the loop will carry out a constant sequence of oscillations of the accumulated charges. This accumulated charge interference pattern is typically capacitively coupled to the body surface, thereby inducing surface charges on the subject's skin surface.

ниже значения 0,5, мощность сигнала может быть поддержана на уровне, подходящем для практического применения.In this case, the sensor is brought into a highly sensitive state with respect to the movement of the body surface, where even very slight movements induce parasitic signals that completely drown out the perceived inductive signal (namely, the magnetic inductive signal emanating from under the body surface). This puts the inductive sensor in an inefficient state for most practical applications. Therefore, by maintaining

below a value of 0.5, the signal strength can be maintained at a level suitable for practical applications.

= 0,025, в дополнение к очень низкой мощности сигнала (как можно увидеть из ФИГ. 2, 3 и 4), чувствительность катушки к электрическим составляющим электромагнитных сигналов становится значительно увеличенной. Ввиду уменьшенной мощности сигнала соотношение сигнал/шум является значительно уменьшенным. В результате, в большинстве вариантов практического применения сигнал является эффективно насыщенным шумом, получаемым в результате электронного шума, электромагнитных помех и шума в результате емкостной связи с поверхностью тела (т.е. прямой связи посредством электрических полей и зарядов, индуцируемых электрически).It was also found that below the value

= 0.025, in addition to the very low signal strength (as can be seen from FIGS. 2, 3 and 4), the sensitivity of the coil to the electrical components of the electromagnetic signals becomes greatly increased. Due to the reduced signal strength, the signal-to-noise ratio is significantly reduced. As a result, in most applications, the signal is effectively saturated with noise resulting from electronic noise, electromagnetic interference, and noise due to capacitive coupling to the body surface (ie, direct coupling through electrical fields and electrically induced charges).

(и, следовательно, на мощность сигнала). Это является неожиданным результатом, и в настоящее время он не известен и не используется в уровне техники. В устройствах и способах уровня техники, как правило, предполагается, что увеличение числа обмоток N увеличит достигаемую мощность сигнала.In addition, simulations performed using all three simulation approaches (homogeneous medium, open lung, and multilayer lung) have been found to demonstrate that increasing the number of coil turns N above one has no effect on the characteristic reflected inductance.

(and hence the signal strength). This is an unexpected result and is currently not known or used in the prior art. In prior art devices and methods, it is generally assumed that increasing the number of windings N will increase the signal power achievable.

от N может быть непосредственно замечена в уравнении (15) выше, которое показывает, что

не имеет зависимости от N. Этот результат, следовательно, возник ввиду нового получения уравнения (15) авторами изобретения.Independence

from N can be directly seen in equation (15) above, which shows that

does not depend on N. This result, therefore, arose due to the new derivation of equation (15) by the inventors.

ввиду емкостной связи между обмотками. Следовательно, путем увеличения N, максимизация

ограничена. В дополнение, даже на более низких нормализованных частотах осуществляется индукция емкостной связи между обмотками многовитковой катушки, которое делает петлю восприимчивой к емкостной связи с тканью. Это, в свою очередь, приводит к искажениям в измеренном сигнале в случае даже небольших величин движения относительно кожи. Данные артефакты движения могут легко доминировать над желаемым индуктивным сигналом, снижая эффективность датчика.Moreover, not only does N not have a positive effect on signal strength, but it is actually unfavorable for increasing signal strength, since it limits the maximum possible physically realizable

due to the capacitive coupling between the windings. Therefore, by increasing N, maximizing

limited. In addition, even at lower normalized frequencies, capacitive coupling is induced between the windings of the multi-turn coil, which makes the loop susceptible to capacitive coupling with tissue. This, in turn, leads to distortions in the measured signal in the case of even small amounts of movement relative to the skin. These motion artifacts can easily dominate the desired inductive signal, reducing sensor performance.

In addition, at high frequencies, the capacitive connections between the turns will exhibit resonances that are very sensitive to offset, and these can severely distort the inductive-sense target signal.

от 0,025 до 0,50, где

и с = скорость света.Based on the above three findings, in accordance with the first set of embodiments of the invention, a system for magnetically inductive reading of electromagnetic signals emitted from the body in response to the transmission of electromagnetic excitation signals to the body is presented, while the system includes a resonator containing a loop antenna formed from a single-turn loop (N=1) with a circumferential length l and in which the resonator is excited to generate excitation signals with a normalized radial frequency

from 0.025 to 0.50, where

and c = speed of light.

An example of a magnetic inductive sensing system, in accordance with one embodiment of the invention, is shown schematically in FIG. 6.

The system 10 includes a loop resonator 11 containing a single loop loop antenna 12 that is electrically connected to the capacitor. The purpose of the antenna is to generate electromagnetic waves or signals for transmission to the body and to establish inductive coupling with electromagnetic signals returned (or reflected) from the body in response to the excitation signals. The capacitor allows you to tune the natural resonant frequency of the resonator circuit. When the resonator is then excited, it will naturally resonate at that frequency, generating electromagnetic signals at that frequency. Therefore, the choice of capacitance of the capacitor allows you to choose the frequency of the generated electromagnetic signals.

Resonator 11 is electrically connected to signal generating means 14 which, in use, is configured to be driven to generate electromagnetic drive signals. According to the present example, the signal generating means is an oscillator that is configured to drive the antenna 12 with an oscillating current so as to generate a sinusoidal electromagnetic signal (sine electromagnetic wave) to be transmitted to the body to be stimulated.

The resonator 11 is also electrically connected to a signal processing means 54 ("Feedback") in the form of a signal processing unit for processing electromagnetic signals received at the antenna 12. In FIG. 6 shows signal processing means connected to the resonator by signal generating means 14 . However, this is not essential: the resonator and the signal processing means can be connected independently.

The signal processing unit 54 analyzes the characteristics of the response signal received at the antenna 12. In particular, the signal processing unit may process the received signals to extract measurements of changes in the attenuation coefficient in the resonator circuit 11 and the natural resonant frequency of the resonator signal. In the present example, it will be assumed that the signal processing block extracts the change measurement of only the natural resonant frequency. This function will be described in more detail below.

System 10 also includes a microcontroller 56 ("MPU") for controlling system components. For example, the microcontroller may control the specific actuation circuit implemented by the resonator drive signal generation means 14 and/or the particular analysis processes implemented by the signal processing means 54 and/or may control the sequence of actuation and analysis operations.

In addition, communication means (not shown in FIG. 6) may be provided to facilitate communication between the microcontroller and an external device such as an external computer or data storage. This can facilitate the transfer of signal processing results obtained by the signal processing means to an external computer. It may also facilitate the transmission of control commands to the microcontroller 56 from an external control means such as a computer.

The data transmission means may comprise a wireless communication means or a wired communication means. The communication means may function or operate in accordance with any suitable communication protocol or medium, such as, for example, Bluetooth, Wi-Fi, Near Field Communication (NFC), ZigBee, or any suitable wired communication protocol.

от 0,025 до 0,50, где

, с = скорость света (3 × 108 м/с), а l представляет собой окружную длину петли антенны. Нормализованная радиальная частота

, следовательно, зависит как от окружной длины l антенны, так и от радиальной частоты

, при которой работает резонатор 11 (частота, на которой осуществляется его возбуждение).System 10 is configured to generate electromagnetic excitation signals with a normalized radial frequency

from 0.025 to 0.50, where

, c = speed of light (3 × 108 m/s) and l is the circumferential length of the antenna loop. Normalized Radial Frequency

, therefore, depends both on the circumferential length l of the antenna and on the radial frequency

, at which the resonator 11 operates (the frequency at which it is excited).

и

.For example, an antenna with a fixed circumferential length l requires the resonator to be excited at a radial frequency between

And

.

может быть реализовано путем выбора емкости конденсатора таким образом, чтобы собственная резонансная частота резонатора 11 была равна

. Когда средство для генерирования сигнала (например, генератор колебаний) затем возбуждает резонатор, оно будет резонировать на радиальной частоте

, генерируя тем самым сигналы возбуждения с частотой

.Excitation of the resonator at a given frequency

can be implemented by choosing the capacitance of the capacitor so that the natural resonant frequency of the resonator 11 was equal to

. When the signal generating means (for example, an oscillator) then drives the resonator, it will resonate at the radial frequency

, thereby generating excitation signals with a frequency

.

In the case of a circular loop antenna with radius a, l is naturally equal to 2πa.

от 0,025 до 0,50.In use, the antenna 12 is in close proximity to the body or medium to be examined, and the antenna is excited by the signal generating means 14 to generate electromagnetic excitation signals with a normalized radial frequency.

from 0.025 to 0.50.

Preferably, the system is used to read physiological parameters and properties, such as air, fluid and/or tissue movement in the subject's body. The system can read vital signs. Preferably, the system can be used in particular, for example, for reading respiratory movements.

In these examples, the system reads movements of air, fluid, and/or tissue (eg, caused by breathing or heartbeat) by reading modulations in the reflected signal inductance caused by those movements.

It should be understood that movements of tissue in the body may include changes in tissue volume, as well as dielectric and conductive properties. These modulations cause amplitude and/or phase modulations of the electromagnetic signal.

The emission of a modulated electromagnetic signal is carried out by the body in response to an electromagnetic excitation signal that is radiated into the subject's body. As described above and shown in FIG. 1, the electromagnetic excitation signal induces magnetic induction, i.e. generating eddy currents 18 in the tissue due to the application of an external magnetic field 22, and this eddy current/electromagnetic signal is modulated by the movement of air, fluid and/or tissue in the subject.

The electromagnetic excitation signal is generated by the antenna 12 of the resonator 11, and the reflected electromagnetic signals (caused by eddy current induction) are read by the same antenna. The generation of this electromagnetic excitation signal is carried out by excitation of the resonator by means 14 for signal generation.

Magnetic fields penetrate deeper into the body than electric fields, and thus magnetic fields can be used to measure changes in properties deeper within the body, while electric fields can be used to measure changes in properties at the skin surface, such as skin permeability. Thus, the properties of antenna 12 and the electromagnetic drive signals generated are preferably designed such that the resonator and antenna are most sensitive to magnetic signals (the magnetic components of electromagnetic signals) and least sensitive to electrical signals, i. such that the behavior of the magnetic field of the emitted electromagnetic signal dominates the behavior of the electric field.

The processing of electromagnetic signals received from the body in response to excitation signals can be performed in several ways.

As noted above, the measurement of signals can be performed based on reading the detuning characteristics of the resonator circuit. In particular, the reading can be performed by measuring changes in (1) the undamped natural radial frequency and (2) the damping factor of the resonator circuit. Changes in these properties have been expressed in equations (8) and (9) and (12) and (13) above.

Changes in one or both of these parameters can be used to determine the received (reflected) signals.

The damping factor depends on both the actual and imaginary parts of the reflected inductance, while the natural frequency only depends on the actual parts. In some cases, it may be preferable to read only the actual part, because reading the imaginary part (related to damping) may require additional circuitry, which can increase the complexity and cost of the system.

In the following, specific examples of signal processing means that use measurement of changes in the natural resonant frequency of the resonator will be presented.

According to the first set of embodiments, the signal processing means may be implemented by an automatic phase control circuit. An example of an automatic phase control circuit that can be used in accordance with this set of implementation options is shown in FIG. 7.

In this embodiment, an automatic phase-locked loop (PLL) circuit is used to drive the resonator 11, and the control signal for the PLL produces an output signal representing the movement of air, fluid, and/or tissue in the subject's body. Therefore, the circuit in FIG. 7 implements the functionality of both signal generating means 14 and signal processing means 54 in the exemplary system of FIG. 6.

FIG. 7 shows a circuit 60 for generating and processing signals for the resonator 11, and includes a reference oscillator 61, a PLL 62, which is connected to the reference oscillator 61 and provides an analog control signal (known as V _tune ) to a voltage controlled oscillator 64 (VCO). The signal V _tune is the result of comparing the signal from the reference oscillator 61 with the signal from the UNO 64. In response to the analog PLL control signal, the UNO 64 generates an excitation signal at the desired frequency and outputs it to the resonator 11, whereby the antenna 12 of the resonator 11 emits electromagnetic (s) excitation signal(s). As noted above, the electromagnetic excitation signal will induce eddy currents in the subject's body, and these eddy currents will induce a magnetic flux that is sensed by antenna 12. This generated flux results in a reflected inductance L _r component in the antenna coil inductance (as explained in detail above). This can be read by tuning the characteristics of the coil, in particular the natural frequency of the coil.

The drive signal is also provided to the PLL 62 as part of the feedback loop. The analog control signal from the PLL 62 is also provided to an analog-to-digital converter (ADC) 66 which converts the analog control signal to a digital signal and this digital signal is provided to the controller 68. The controller 68 determines the digital control signal for the PLL 62 and outputs it to the PLL. 62. As one of skill in the art would know, in a PLL system, if the phase of the REO 54 differs from the phase of the reference oscillator 61, the digital control signal corrects the phase of the REO.

Movements of air, fluid, and/or tissue in the body effectively align antenna 12 (due to reflected inductance), and the digital control signal counteracts this tuning and corrects the phase of the UNO 54. Therefore, the digital control signal carries information regarding the movements of air, fluid, and /or tissue, and the controller 68 determines an output signal 70 from the digital control signal that represents or contains information about the movements of air, fluid, or tissue in the subject's body. Although this output signal 70 does not carry actual phase and amplitude information, physiological characteristics (eg, heart rate, respiration rate) can be clearly observed.

The correction signal V _tune , which is required to maintain the UNO 64 at the desired frequency, is used to measure amplitude and/or phase shifts due to movements of air, fluid and/or tissue in the subject's body. Phase shifts tend to dominate amplitude changes. The PLL correction signal (the digital control signal output by the controller 68 derived from the analog PLL correction signal) is used to determine the output signal 70. For example, the output signal 70 may correspond to a digital control signal with suitable filtering and/or downsampling to improve the signal/total ratio. noise.

Therefore, the output signal carries a signal representing the received electromagnetic signals obtained based on changes in the natural resonance frequency of the resonator 11, which are reflected in the correction signal.

In accordance with yet another set of implementations, an alternative signal processing means is implemented in which the read signals from antenna 12 are first processed to reduce their frequency by mixing them with an additional reference waveform of a different frequency and applying a filter that passes the difference frequency. This allows post-processing of the signal in a much lower frequency range, which reduces power consumption and required processing power.

In particular, in order to reduce the power consumption and the required processing power of the system, the signal processing is preferably performed in the digital domain. Digital dividers and counters draw current proportional to the operating frequency. Therefore, further energy savings are achieved by lowering the frequency in the digital system using a second oscillator reference frequency close to the frequency at which the antenna 12 is driven to generate electromagnetic excitation signals and in which the signals returning from the body are also oscillatory. By mixing the returned high frequency electromagnetic signals (typically around 400-500 MHz) with another signal whose frequency is different but close to that frequency (e.g. +/- 50 MHz from the EM measurement frequency), and applying a low-pass filter, which passes the difference frequency (i.e. f _measurement - f _reference ), signal processing (eg digital counter) can be done in a much lower frequency range, reducing power consumption and required processing power.

One example of this processing scheme is shown in FIG. 8, which shows a related processing scheme.

The system comprises a resonator having an antenna 12 and coupled to a first oscillator ("Osc 1") 74 that generates a drive signal to drive the resonator 11 to generate electromagnetic drive signals for transmission to the body of interest (e.g., the subject's body). The electromagnetic signals radiated back from the body in response are received at the antenna by the inductive coupling element 12, and the resultant signal is output from the resonator having a frequency f1. The second (reference) oscillator (“Osc 2”) 76 generates an oscillatory signal of the second frequency f2, close to the frequency f1, for example, between f2 = 0.8 * f1 and f2 = 1.2 * f1 (i.e. within + // 10% -20% of f1).

A frequency mixer (“Mix”) 78 mixes the two frequencies f1 and f2, and a low pass filter (“LPF”) 80 then passes the difference frequency (ie, f1-f2).

The resulting difference frequency signal is then passed on to additional processing components to extract properties of the signal received from the body, for example, as shown in FIG. 8, counter 82.

In the example shown in FIG. 8, the first oscillator 74 functions as means 14 for generating the system signal 10 (see FIG. 6), and the remaining components shown function as means 54 for processing the system signal.

In all examples of this processing approach, the result is that the RF measurement frequency, typically >200 MHz, is reduced to ~50 MHz, i.e. difference between two mixed frequencies f1, f2. Signals with this frequency can be easily processed by microcontrollers and microprocessors. Such signals can, for example, be directly processed by the counter input of the microcontroller.

Thus, the use of relatively more power-hungry components such as RF phase-locked loop (PLL) circuit systems and digital frequency dividers is prevented. The system therefore needs significantly less current.

Alternatively, the use of a frequency mixer and filter with a low-pass PLL circuit can be implemented to improve system quality, albeit at the expense of higher power consumption.

Another advantage of the present set of implementations is that blending does not result in a loss of resolution. In contrast, using a digital divider does result in this kind of loss. The read signal modulations in the 28 MHz downmix signal (in the example of FIG. 10 above) have the same amplitude (with the same relative gain) as the higher (eg, 405 MHz) frequency modulations.

Then, a physiologically modulated signal with a frequency of 28 MHz is output to processing elements with low current consumption, for example, to the counter input of the microcontroller's frequency counter.

Microcontrollers are widely available that have counter inputs capable of reading the frequency shifts in the range that typically occur in the body.

The use of frequency mixing and filtering in combination with a digital counter makes it possible to measure, for example, physiological parameters such as vital signs, including heartbeat and respiration, with an inexpensive system. The antennas, oscillators and frequency converter in the examples can be built into a printed circuit board (PCB). Flexible circuit technology (eg, floppy disk technology) can also be used to further reduce the size and cost of components and the entire system.

A test system was designed (which can be further optimized) that draws 1 mA per antenna, which is at least 10 times less current than digital systems with similar performance characteristics.

All frequencies shown above are just an example.

Other signal processing means may also be used. One skilled in the art will recognize many standard approaches to measuring signals received at antennas, and any suitable approach may be used. For example, in additional implementations, the counter itself may be used to measure signals.

генерируемых электромагнитных сигналов возбуждения между 0,025 и 0,50. Это обеспечивает улучшение характеристик по сравнению с системами уровня техники, как объяснено выше, по причинам улучшенного соотношения сигнал/шум и оптимизированной восприимчивости к магнитным, нежели к электрическим составляющим сигнала.In the example of FIG. 1 above uses the normalized frequency range

generated electromagnetic excitation signals between 0.025 and 0.50. This provides improved performance over prior art systems, as explained above, for reasons of improved signal-to-noise ratio and optimized susceptibility to magnetic rather than electrical signal components.

ниже 0,025 отношение сигнал-шум считываемого электромагнитного сигнала значительно уменьшено, что приводит к более высокой чувствительности к движению. Более конкретно, ниже данного уровня мощность сигнала значительно снижается и в большинстве вариантов практического применения насыщается шумом, исходящим от электронного шума, электромагнитных помех и шума от емкостной связи с поверхностью тела (т.е. прямой связи посредством электрических полей и электрически индуцированных зарядов).In particular, studies have shown that for values

below 0.025, the signal-to-noise ratio of the read electromagnetic signal is greatly reduced, resulting in higher motion sensitivity. More specifically, below this level, the signal power is significantly reduced and, in most applications, saturated with noise from electronic noise, electromagnetic interference, and noise from capacitive coupling to the body surface (i.e., direct coupling through electric fields and electrically induced charges).

Also, below a given normalized frequency, the oscillator has difficulty oscillating when N=1 (single-turn loop only) due to ohmic losses, which greatly reduce the quality factor of the resonator at low normalized frequencies using N=1.

However, as described above, providing a resonator with N>1 (more than one loop) to increase the quality factor is undesirable because it increases the cost and complexity of the sensor, and also leads to parasitic capacitances between the turns, thereby inducing non-uniform currents in the loop and inducing charges even at low frequencies. This, in turn, makes the sensor more susceptible to noise artifacts due to capacitive coupling between these induced charges in the loop and mutually induced surface charges on the body (induced electric fields, radiated loop charges).

электромагнитных сигналов возбуждения составляет от 0,025 до 0,25.According to a more specific set of implementation options, the magneto-inductive sensing system can be configured such that the normalized radial frequency

electromagnetic excitation signals is from 0.025 to 0.25.

= 0,25 амплитуда тока изменяется в большей степени по петле антенны. Фаза тока также является относительно постоянной вокруг петли антенны. Данные факторы являются значительными ограничивающими факторами при достижении высокой мощности сигнала и высокого качества сигнала.Within this range, the current amplitude when reading signals received back from the body is substantially constant across the antenna loop. Higher

= 0.25 the amplitude of the current varies more along the antenna loop. The phase of the current is also relatively constant around the antenna loop. These factors are significant limiting factors in achieving high signal strength and high signal quality.

. Соответствующие

каждой линии помечены на графике.This is shown in FIG. 9. In FIG. 9 shows the normalized current (y-axis) versus the segment index around the antenna loop (x-axis) for three different signals with different normalized radial frequencies.

. Relevant

each line is labeled on the graph.

= 0,25 однородность тока петли быстро становится очень плохой. Неоднородные токи являются крайне невыгодными, поскольку они приводят к накоплению зарядов, что приводит к емкостной связи с исследуемой средой. Емкостная связь со средой является основным источником искажения (артефактов) для индуктивных датчиков.It can be seen that above the normalized radial frequency

= 0.25 loop current uniformity quickly becomes very poor. Non-uniform currents are extremely disadvantageous because they lead to the accumulation of charges, which leads to capacitive coupling with the medium under study. Capacitive coupling with the medium is the main source of distortion (artifacts) for inductive sensors.

= 0,25 однородность тока и фазы тока значительно улучшается, но при этом достигается максимальная мощность сигнала, поскольку известно, что более высокое значение

дает более высокую мощность сигнала (объяснено выше). Следовательно, это обеспечивает хороший баланс между мощностью сигнала (соотношением сигнал/шум) и однородностью тока и фазы тока.Therefore, by keeping below

= 0.25 the homogeneity of the current and phase of the current is greatly improved, but at the same time the maximum signal strength is achieved, since it is known that a higher value

gives higher signal strength (explained above). Therefore, this provides a good balance between signal strength (signal to noise ratio) and current and current phase uniformity.

сигналов возбуждения может составлять от 0,025 до 0,20. Ниже верхнего предела 0,20 для

, сопротивление излучения является достаточно низким (<0,5 Ом), фаза тока относительно постоянна по петле антенны, и дополнительно улучшается равномерность амплитуды тока (разность амплитуды тока между любыми двумя точками вокруг контура <20%).According to yet another set of implementations, the normalized radial frequency

excitation signals can be from 0.025 to 0.20. Below the upper limit of 0.20 for

, the radiation resistance is quite low (<0.5 Ω), the current phase is relatively constant across the antenna loop, and the current amplitude uniformity is further improved (current amplitude difference between any two points around the loop <20%).

= 0,20, амплитуда тока (ось у) по окружности антенны (ось х) является относительно однородной и имеет значительно большую однородность, чем, например, при

= 0,333.This is shown in FIG. 10. In FIG. 10 shows that when

= 0.20, the current amplitude (y-axis) along the circumference of the antenna (x-axis) is relatively uniform and has a much greater uniformity than, for example, with

= 0.333.

обеспечивает то, что сопротивление излучения сохраняется в пределах оптимально низкого диапазона. Это изображено на ФИГ. 11, на которой показано сопротивление излучения (ось у; Ом) в зависимости от

(ось х). Можно увидеть, что ниже уровня

= 0,2, сопротивление излучения поддерживается на очень низком уровне (ниже 0,5 Ом). Следовательно, 0,2 представляет собой оптимальный компромисс между максимизацией мощности сигнала (соотношения сигнал/шум) путем максимизации

, насколько это возможно, при поддержании контролируемого уровня сопротивления излучения. In addition to the above benefits, the upper level of 0.20 for

ensures that the radiation resistance is kept within an optimally low range. This is shown in FIG. 11, which shows the radiation resistance (y-axis; Ohm) depending on

(x axis). You can see below the level

= 0.2, the radiation resistance is kept very low (below 0.5 ohm). Therefore, 0.2 represents the optimal compromise between maximizing signal power (signal-to-noise ratio) by maximizing

as far as possible while maintaining a controlled level of radiation resistance.

= 0,20 начинают возникать некоторые электрические эффекты, в результате чего катушка становится чувствительной к составляющей электрического поля ЭМ сигналов, принимаемых обратно от тела (что создает помехи при считывании сигналов магнитного поля). Ниже

= 0,20 было обнаружено, что система считывания остается сильно магнитным образом чувствительной, без накопления значительных электрических зарядов вдоль одного провода петли антенны.This range is also particularly advantageous because the higher

= 0.20, some electrical effects begin to occur, causing the coil to become sensitive to the electric field component of the EM signals being received back from the body (which interferes with the reading of the magnetic field signals). Below

= 0.20, it was found that the readout system remains highly magnetically sensitive, without the accumulation of significant electrical charges along one wire of the antenna loop.

сигналов возбуждения составляет от 0,04 до 0,25. Нижний предел 0,04 является предпочтительным, поскольку это дает более высокую мощность сигнала (чем 0,025, например) в то же время сохраняя преимущества очень низкого сопротивление излучения (~0,01 Ом), фазы постоянного тока по петле антенны и амплитуды постоянного тока по петле антенны.In accordance with another set of implementation options, the system 10 can be implemented such that the normalized radial frequency

excitation signals is from 0.04 to 0.25. The lower limit of 0.04 is preferred as it gives higher signal power (than 0.025 for example) while still retaining the benefits of very low radiation resistance (~0.01 Ω), dc phase over the antenna loop and dc amplitude over antenna loop.

выше 0,04 обеспечивает достаточно мощный уровень сигнала, чтобы сигнал был надежно защищен от шума в широком диапазоне вариантов практического применения. В некоторых сценариях (однако не во всех) электромагнитные сигналы ниже данной нормализованной частоты могут оказаться искажены артефактами шума, являющихся результатом емкостной связи с поверхностью ткани (т.е. электрического соединения с поверхностью тела ввиду зарядов, индуцированных электрическим образом). Было обнаружено, что для датчиков удобного размера, например, с радиусом от 1 до 3 см, мощность сигнала является удвоенной по сравнению с сигналами, использующими нормализованную радиальную частоту около 0,025. В частности, было обнаружено, что сигналы дыхания (сигналы, указывающие на функцию дыхания) имеют значительно более высокие мощности сигналов.It was found that the normalized radial frequency

greater than 0.04 provides a strong enough signal level that the signal is well protected from noise in a wide range of applications. In some scenarios (but not all), electromagnetic signals below this normalized frequency may be distorted by noise artifacts resulting from capacitive coupling to the tissue surface (ie, electrical connection to the body surface due to electrically induced charges). It has been found that for conveniently sized sensors, such as those with a radius of 1 to 3 cm, the signal strength is twice that of signals using a normalized radial frequency of about 0.025. In particular, respiration signals (signals indicative of respiratory function) have been found to have significantly higher signal strengths.

In accordance with a further set of implementation options, system 10 can be configured such that the electromagnetic drive signals have a frequency of 30 MHz to 1000 MHz.

Frequency here refers to absolute frequency, not radial frequency.

и

, соответствующее требование предъявлено к

, что означает, что окружная длина

петли антенны должна быть выполнена соответствующим образом.According to these embodiments, an absolute frequency requirement is provided. Accordingly, because

And

, the corresponding requirement is presented to

, which means that the circumferential length

antenna loops must be made accordingly.

This frequency range is preferred because the signal power becomes much greater than f = 30 MHz. This is especially true for comparatively smaller loops (radii in the range of 1-3 cm). In this case, when, for example, the signal is measured by changing the resonant frequency of the resonator (as described above), the frequency shift signal (the real part of the reflected inductance) quickly becomes much stronger when entering this range, by increasing in signal power, as well as moving in the phase of the reflected inductance in the direction of the real part.

This frequency range is also particularly advantageous when using a signal processing means in the form of a frequency converter with a counter. Absolute changes in the resonant frequency of the resonator due to, for example, breathing when using f < 30 MHz can be below 1 kHz. When using a slope counter, the quantization noise of the number of samples in the signal is easily visible at a given operating frequency.

With an increase in the absolute frequency above f > 30 MHz, the effect of quantization noise on the signal in most cases will cease to be problematic. This is described in more detail below.

In addition, it is preferable to optimize the frequency below 1000 MHz to optimize the penetration depth. At frequencies above 1000 MHz, the penetration depth of electromagnetic signals begins to become unacceptably small for measuring physiological parameters, such as lung or heart signals.

In accordance with another set of implementation options, system 10 can be configured such that the electromagnetic drive signals have a frequency of 100 MHz to 1000 MHz.

At frequencies above 100 Hz, the penetration depth is still quite deep, while the signals become much stronger. In particular, it has been found that cardiopulmonary signals become much stronger. In addition, the phase of the reflected inductance moves further towards the real part. This is advantageous when the signal generating means is capable of measuring changes in the resonant frequency of the resonator, which requires measuring the real part of the reflected inductance.

In addition, above a frequency of 100 MHz, quantization noise, for example, means for processing the slope counter signal (for example, with an integration time of about 0.05 seconds), is practically negligible relative to the signal strength.

In accordance with yet another set of implementation options, system 10 can be configured such that the electromagnetic drive signals have a frequency of 30 MHz to 500 MHz.

This absolute frequency range optimizes the depth of penetration, particularly for muscles. The signal strength at 500 MHz remains very high while the penetration depth is maintained relatively large (~5 cm for muscle - and more for other media).

This frequency range may also be preferred when it comes to power consumption, such as battery-powered sensors. Below 500 MHz, the frequency is low enough not to contribute significantly to signal processing power consumption.

In accordance with another set of implementation options, system 10 can be configured such that the electromagnetic drive signals have a frequency of 100 MHz to 500 MHz.

This combines the advantages of the 100 MHz lower limit and the 500 MHz upper limit discussed above.

Application of excitation signals to the body at such high frequencies is not known in the art. This is because it is generally understood in the art that frequencies above about 30 MHz result in a significant reduction in the achievable penetration depth while increasing the operating power required.

, как правило, определяется как:The penetration depth or skin depth is defined as the distance over which the amplitude of an electromagnetic wave is reduced by a factor of 1/e. More specifically, skin depth or penetration depth

is usually defined as:

представляет собой проницаемость среды, а σ представляет собой проводимость среды.where k is the wavenumber of electromagnetic signals in the medium being penetrated, ω is the radial frequency of the signals, μ is the permeability of the medium,

is the permeability of the medium, and σ is the conductivity of the medium.

The supposed loss of penetration depth at high frequencies stems from the so-called skin effect. This effect is seen, for example, when an alternating current flows near the surface of the conductor; the current density seems to be attracted to the surface of the medium, preventing the flow of current under the surface. The higher the frequency of the electromagnetic signal, the stronger the effect. This effect also occurs in biological tissues that are penetrated by an inductive probe: at higher frequencies, the induced eddy currents are effectively “pulled” to the body surface, thereby reducing the penetration of the incoming magnetic field deeper into the tissue. Thus, the skin effect has a decreasing effect on the penetration depth of the inductive sensor.

However, the present inventors have found that the actual reduction in penetration, while real, is much less significant than previously thought. In particular, it has been found that the reduction in penetration depth achieved does not interfere with effective inductive sensing up to frequencies above about 1000 MHz. This is especially true for applications applicable to the study of respiratory function. These embodiments therefore allow greater penetration depths than currently known in the art.

This is shown in FIG. 12, which shows the penetration depth of the generated excitation signals (y-axis; in meters) versus signal frequency (x-axis; in MHz) for signals propagated through four different media. Line 92 represents signals propagating through muscle, line 94 represents signals propagating through cancellous bone, line 96 represents signals propagating through cortical bone, and line 98 represents signals propagating through fat.

The graph shows that the loss of penetration with increasing frequency varies for different media. The waves penetrate fat very well (line 98) even at very high frequencies and relatively well through bone (lines 94 and 96). The waves penetrate muscles less well, but even at frequencies corresponding to and above the previously suggested upper limit of 30 MHz, it can be seen that the penetration depth is still more than 10 cm. Thus, it can be seen that for a typical body containing several layers of skin, fat , muscles and bones, the penetration depth will be more than sufficient to reach internal organs such as the lungs or heart, even at the frequencies used in the present invention.

As noted above, the inductive sensor is based on the connection with the magnetic components of the reflected electromagnetic signals. An electrical (eg, capacitive) connection is undesirable because it masks the desired magnetic fields and saturates the detected signal. Consequently, the signal-to-noise ratio is reduced.

Therefore, in accordance with one or more preferred embodiments, the reading system may further comprise means for shielding the antenna from the electrical components of the reflected electromagnetic signals and/or for blocking the electrical components of the outgoing excitation signals.

Shielding has the advantage that it allows the loop antenna to operate at higher frequencies while ensuring that the sensor is not made more susceptible to capacitive coupling to the body under test. As noted above, the stored electrical charge in the loop may, in some cases, be capacitively coupled to the patient, thereby inducing an electrical surface charge in the patient. This effect is unfavorable because it masks the desired magnetic signal that is generated within the body.

By adding electromagnetic shielding, potentially unfavorable electric fields generated by the loop current will be contained around the loop, preventing connection to the body under test.

Therefore, in one set of implementations, the system may further comprise a blocking screen configured to intercept electromagnetic signals propagating to or from the antenna, the screen comprising an electrically conductive housing to block the electrical components of the incident signals, and wherein the housing delimits at least one non-conductive gap to prevent the induction of eddy currents within the body.

When electromagnetic fields propagate towards or away from the antenna, the components of the magnetic field falling incidentally on any conductive body (including the shield) induce, by means of magnetic induction (Faraday's law of induction), eddy currents within the body. In shielding, this is what provides the magnetic field shielding effect, since eddy currents, in turn, induce a magnetic field in the opposite direction to that which was originally incident (Lenz's law), thereby counteracting or suppressing the original propagating magnetic field oscillations. Thus, the components of the magnetic field are effectively blocked.

Due to the inclusion of conductive gaps in the screen, eddy currents cannot be generated and, consequently, no opposing field components are generated that compensate for the propagating magnetic field fluctuations. Therefore, the magnetic field components of the electromagnetic signals can pass through the screen.

In contrast, the shielding of the components of the electric field, which functions through a different physical principle, continues to occur. Screening of the electric field occurs by redistribution of electric charges inside the screen housing when the components of the electric field of electromagnetic signals occur. The appearance of fields on one side of the screen redistributes the charges in such a way that they cancel the influence of the field components on the other side.

Thus, the shielding approach of the present invention blocks the propagation of electric field components in an efficient manner, while still allowing magnetic field components to pass through. The parasitic effects of the electric fields are thus suppressed and the signal-to-noise ratio of the resulting measurement signal received from the signals received at the antenna is increased.

In one preferred set of embodiments, the antenna loop may be broken with a hole, where the hole is covered by a capacitor to form a resonator, and in which the system includes means for signal processing, the means being electrically connected to the resonator through only one antenna point located on one side of the hole. .

The consequence of this is that the resonator is only freely connected to the signal processing means, with the advantage that the signal processing means does not stress the antenna loop too much. This increases the sensitivity of the signal processing means system to incident electromagnetic signals.

The system has a large number of potential applications.

One particularly advantageous field of application is the examination of the human or animal body. The system makes it possible to measure or otherwise analyze the movement of air or fluid (eg blood) within the body, or the expansion or contraction of organs or vessels such as, for example, the heart, lungs or blood vessels.

The present application is directed in particular to a physiological reading system. The system may include means for processing the signal received by the antenna to obtain one or more physiological parameters.

Embodiments of the invention make it possible to obtain a much higher signal intensity than known systems due to the provided optimization for the normalized radial frequency of the electromagnetic signal strength. Therefore, a powerful system for non-invasive examination of the human and animal body is provided.

Any embodiment of the invention can be advantageously applied to measure vital signs, according to one set of examples. These include, for example, heart rate, pulse rate, respiratory capacity and respiratory rate.

Although the present application is directed in particular to a system for the inductive reading of physiological parameters, the inventive concept is not limited in its application to only the reading of physiological parameters. In general, embodiments of the system described in this disclosure can be used to investigate the intrinsic properties of any body or object that has the ability to generate eddy currents in response to the application of oscillating magnetic fields.

The system can be useful, for example, for studying systems with dynamic cavities, i.e. cavities in which the constituents or segments move or change in size, since such changes and movements cause noticeable modulations in the read signals, allowing measurements and other analysis.

Besides detecting dynamic changes in local volumes of body regions, the system is also very useful for measuring the conductive and dielectric properties of bodies. The system, for example, can be used to measure the conductivity of a liquid through a container wall without direct galvanic contact, or fruit ripeness without the need for galvanic contact with the interior of the fruit.

, где

и с = скорость света.In the above detailed description, the normalized radial frequency is defined as

, Where

and c = speed of light.

This value of the speed of light can be interpreted in a broader sense as the phase speed of light in the environment surrounding the loop, when using it. Thus, the speed of light is usually given as the speed of light in air (since the antenna is typically used in air), but it can be considered more broadly as the phase speed of light in the medium surrounding the antenna. Thus, the invention can equally be applied when the antenna is not surrounded by air, but by another medium.

становится

где Vp представляет собой фазовую скорость света в среде, окружающей петлю при ее использовании.So the equation

becomes

where Vp is the phase velocity of light in the environment surrounding the loop when it is in use.

Other variations of the described embodiments can be understood and implemented by a person skilled in the art in the implementation of the present invention in practice after reading the drawings, description and appended claims. In the claims, the word "comprising" does not exclude the presence of other elements or steps, and singular grammatical indicators do not exclude the plural. The mere fact that certain measures are listed in mutually distinct dependent clauses does not in itself indicate that a combination of these measures cannot be used successfully. No reference signs in the claims should be considered as limiting its scope.

Claims (25)

1. An inductive physiological reading system for reading electromagnetic signals emitted from a body in response to electromagnetic excitation signals transmitted to said body, the system comprising: a loop resonator for establishing inductive coupling with said electromagnetic signals emitted from the body, wherein the resonator contains a loop antenna and an electrically connected capacitor, and the antenna loop has only one turn with circumferential length l, signal generating means configured to drive the resonator to generate electromagnetic drive signals having a radial frequency ω to be transmitted to said body, while the normalized radial frequency

≡ ω/ω _ref of electromagnetic excitation signals is from 0.025 to 0.50, where ω _ref = 2πc/l, π is the ratio of the circumference to its diameter and c = the speed of light, and signal processing means configured to read electromagnetic signals radiated from the body based on detecting electrical changes in the loop antenna indicative of changes in measured inductance in the loop while the loop generates said drive signals, wherein the system comprises signal processing means configured to process the signals received at the antenna and reduce the frequency of the signals by mixing each signal with a reference waveform of a different frequency, and applying a differential filter to extract an output signal having a frequency that is the difference between the frequency vibrational and received signals. 2. The system of inductive reading of physiological parameters according to claim 1, in which the normalized radial frequency

electromagnetic excitation signals is from 0.025 to 0.25. 3. An inductive physiological reading system according to any one of the preceding claims, wherein the normalized radial frequency

electromagnetic excitation signals is from 0.04 to 0.25. 4. An inductive physiological sensing system according to any one of the preceding claims, wherein the signal generating means is configured to drive the resonator to resonance at a radial frequency ω to generate drive signals having a radial frequency ω. 5. The inductive physiological sensing system of claim 4, wherein a resonator is provided having a natural resonant frequency ω to assist in driving the resonator at a radial frequency ω, and wherein, if necessary, a capacitor is selected to adjust the resonator's natural resonant frequency. 6. The inductive reading system of physiological parameters according to claim 1, in which the frequency of the reference oscillatory signal and the frequency of the received signals differ within +/-10-20%. 7. An inductive physiological reading system according to any one of the preceding claims, wherein the frequency of the electromagnetic excitation signals is between 30 and 1000 MHz. 8. System for inductive reading of physiological parameters according to any one of paragraphs. 1-6, in which the frequency of the electromagnetic excitation signals is from 100 to 1000 MHz. 9. System for inductive reading of physiological parameters according to any one of paragraphs. 1-6, in which the frequency of the electromagnetic excitation signals is from 30 to 500 MHz. 10. System for inductive reading of physiological parameters according to any one of paragraphs. 1-6, in which the frequency of the electromagnetic excitation signals is from 100 to 500 MHz. 11. An inductive physiological reading system according to any one of the preceding claims, wherein: the antenna loop has a radius of 15 to 20 mm or the antenna loop has a radius of 90 to 110 mm. 12. An inductive physiological readout system according to any one of the preceding claims, the system comprising means for processing the signals read by the antenna to extract one or more physiological parameters. 13. A method for inductively reading physiological parameters, comprising reading electromagnetic signals emitted from a body in response to electromagnetic excitation signals transmitted to said body, the method comprising: excitation of the loop resonator for generating electromagnetic excitation signals having a radial frequency ω and directing the signals to said body, wherein the resonator comprises a loop antenna and an electrically connected capacitor, and the loop antenna has only a single-turn loop with a circumferential length l; using a loop resonator to establish inductive coupling with electromagnetic signals emitted from the body in response to excitation signals, reading electromagnetic signals emitted from the body based on the detection of electrical changes in the loop antenna, indicating changes in the measured inductance in the loop, while the loop generates said excitation signals; processing signals received at the antenna and reducing the frequency of the signals by mixing each signal with a reference waveform of a different frequency, and applying a differential filter to extract an output signal having a frequency that is a difference between the frequency of the waveform and the received waveform; while the normalized radial frequency

≡ ω/ω _ref of electromagnetic excitation signals is from 0.025 to 0.50, where ω _ref = 2πc/l, π is the ratio of a circle's circumference to its diameter, and c = the speed of light. 14. The method of claim 13, wherein the normalized radial frequency ω of the electromagnetic excitation signals is between 0.025 and 0.25.

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