JPH053911B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to the resonant frequency at a stationary point of an element or a circuit in which a certain physical quantity changes with a stationary point in response to frequency fluctuations. Regarding detection method.

(Prior Art) Resonance phenomena generally exist widely in the natural world, but they are particularly important phenomena in electric circuits, and are frequently used in a variety of circuits and devices.

Therefore, it is an essential technology to accurately measure the resonant frequency of these electric circuits or circuit elements, but in general, resonant circuits are easily affected by the surrounding environment, and the input terminal of a measuring device such as a frequency counter is If it comes into direct contact with a resonant circuit, the frequency will fluctuate and accurate measurement is often impossible.

Conventionally, the resonant frequency measurement method in such cases is to absorb the oscillation energy of a variable frequency oscillator placed non-contact near the resonant circuit under test at the same frequency as the resonant circuit under test. A method using phenomena, the so-called dip meter method, was common.

To briefly explain the principle of this dip meter, as shown in FIG. If the circuit under test 4 consisting of an inductance L ₁ and a capacitor C ₁ is approached and the frequency of the oscillator 2 is changed from ₁ to ₂ , the frequency at both ends of the coil 3 and the voltage of the voltmeter are as shown in FIG. As shown in the figure, the ground of the voltmeter changes to a minimum at the resonant frequency of the circuit under test, which is ₀ . As mentioned above, this occurs because the energy of the oscillator 2 is absorbed by the resonant circuit under test, which has a lower impedance. By adjusting the frequency, the frequency at that point can be detected.

However, such a conventional resonant frequency measurement method using the level dip method detects the minimum level value or converts this into a current to detect the maximum current value, and therefore accurate measurement is difficult.

That is, the minimum voltage value at the dip point mentioned above changes depending on the ratio of the resistance and reactance of the resonant circuit to be measured, the so-called Q (quality factor), or the mutual inductance between the circuit and the antenna coil 3, etc. It is difficult to identify it unambiguously because it differs from case to case, so there was a flaw in the lack of a measurement system.

(Object of the Invention) The present invention has been made in order to solve the deficiencies of the conventional resonance frequency measurement method as described above. The purpose of this invention is to provide a method for detecting resonant frequencies with extremely high precision.

(Structure of the Invention) In order to achieve the above-mentioned object, the present invention has the following structure.

That is, applying a carrier wave signal frequency-modulated by a required low frequency signal to the circuit under test, and demodulating the amplitude distortion that the carrier signal receives at the resonant frequency of the circuit under test and its vicinity. The resonant frequency is detected by the following.

(Example) The present invention will be described in detail below based on an illustrated example.

Before that, we will give a specific example of measuring the resonant frequency of a non-measuring circuit with a contact as described above, and briefly explain the drawbacks of the conventional dip meter method.

In recent years, in order to measure the temperature of various parts of the body for the purpose of cancer treatment, etc. in biological and medical research, wires have been used to connect unpowered probes implanted in the body for long periods and measuring instruments outside the body. A method has been proposed to measure temperature without having to connect the device.

The above-mentioned temperature measurement method involves surgically implanting a probe with a crystal oscillator connected to an antenna coil at a desired location within the body, or passing it into the digestive tract and injecting electromagnetic waves at the desired frequency from outside the body. A method of emitting energy and applying it to the crystal resonator via the antenna coil and observing the energy absorption when it resonates, that is, by detecting the resonance point of the probe using the dipmeter method described above, the internal temperature can be determined. It is common to measure

However, the coupling between the probe implanted in the living body and the external device is extremely loose, and as mentioned above, the minimum level at the dip point varies depending on the measurement conditions, so detection of the resonance point is extremely difficult. It was difficult.

In order to eliminate such drawbacks, in this embodiment, the resonant frequency detection method of the present invention is applied to provide an in-vivo temperature measurement method configured as follows.

That is, FIG. 1 is a block diagram showing one embodiment of the in-vivo temperature measuring device according to the present invention.

In the figure, 5 is an in-vivo probe composed of a crystal oscillator X and an antenna coil _L3 ,
As an in vitro device, the output of a voltage controlled oscillator (VCO) 7 subjected to FM or PM modulation using the output of a low frequency oscillator ₆ is applied to the antenna coil L 4 facing the probe, and the antenna coil L ₄ An AM detection circuit 8 is added to the synchronous detection circuit 8, the output of which is inputted via an amplifier 9 to a synchronous detection circuit 10 which uses the output of the low frequency oscillator 6 as a synchronous signal, and the oscillation frequency of the VCO 7 is controlled by the output thereof. This is what I did.

The in-vivo temperature measuring device configured as described above operates as follows.

That is, FIG. 2 is a waveform diagram showing the state of AM modulation distortion that the irradiated electromagnetic wave is subjected to in the vicinity of the resonant frequency ₀ of the probe.

Now, the low frequency signal is 80Hz, and the frequency deviation is ±
When the 2KHz electromagnetic wave frequency is variable from 19MHz to 21MHz and the resonant frequency of the probe is □ ₀ =20MHz, the frequency-modulated electromagnetic wave is vibrated at a period of 80Hz over ±2KHz from its center frequency.

Therefore, the center frequency is △ on the resonance characteristic curve of the probe including the resonance point ₀ .
The AM modulation distortion when located at three points: a low point A, a point B that is the same as ₀ , and a high point C exhibits waveforms as shown by the arrows in the figure, respectively.

That is, when the resonance point ₀ of the probe is included in the deflection frequency of the electromagnetic wave, AM modulation distortion twice as high as the deflection frequency occurs with the resonance point as a boundary. This double distortion has a phase difference of 180° above and below ₀ , and when the center frequency of the electromagnetic wave coincides with ₀ , the double distortion described above is shifted in terms of direct current, but becomes a sine wave.

This is because the electromagnetic energy is absorbed by the resonant circuit of the probe, and at this time, both ends of the coil _L4 of the external device facing the probe are
AM modulated waveforms as shown in d and e appear.

FIG. 3 shows the signal waveforms of each part of the block diagram shown in FIG. The signal waveforms c, d, and e applied to the coil _L4 are the waveforms generated at both ends of the coil _L4 in the probe resonance characteristic curves A, B, and C shown in FIG. 2, respectively.

Furthermore, when these waveforms c, d, and e are subjected to AM detection, the aforementioned AM modulation components generated as a result of energy absorption by the probe are extracted, as shown in f, g, and h of the figure, respectively.

Therefore, by detecting this change by some means, it is possible to identify at which point on the resonance characteristic curve of the probe the center frequency of the electromagnetic wave at that time is located.

In this embodiment, the thus demodulated waveform is subjected to synchronous detection using the low frequency signal as a reference in the synchronous detection circuit 10, and then the waveform is shaped into the respective waveforms as shown in FIG. 3 i, j, and k. A rectangular wave corresponding to AM modulation distortion is obtained, the duty ratio of the rectangular wave is detected, and the duty ratio at the resonance point ₀ of the probe is 1:1. It is used to detect and measure the temperature inside the living body.

Further, if the rectangular wave is integrated and then converted into a DC voltage, a DC voltage corresponding to the above-mentioned duty ratio is obtained, and this value corresponds one-to-one to each point on the resonance characteristic curve of the probe.

That is, at ₀ , the relative value is 0.5V, the lower side than ₀ is 0.5V or less, and the higher side is 0.5V or more.

Therefore, if the above-mentioned DC voltage is configured to control the frequency control voltage of the VCO, each of these blocks forms a closed loop, and the center frequency of the electromagnetic wave can be automatically adjusted to the resonance point ₀ of the probe. .

In other words, if the closed loop is operated so that the aforementioned DC voltage is 0.5V, or this DC voltage output is input to a comparator with 0.5V as the reference voltage, and the difference becomes 0, the servo control loop system can be activated. This can be used to automatically measure the frequency of the resonance point ₀ of the probe as it moves in accordance with the temperature.

If a lock loop system is constructed using the present invention in this way, it will be possible to construct a lock loop system using the present invention.
It has the following characteristics compared to the one using .

In other words, a conventional PLL detects the phase of a signal in a closed loop and converts the difference into a DC signal to construct a servo system, and generally a large level signal is required to extract phase information. On the other hand, since the present invention extracts AM distortion occurring in FM waves, this is possible even with relatively low level signals.

Also, if you compare the loop sensitivity and lock range of the two, the relative ratio of the lock range and full scale is The stability of the system is greatly influenced by the stability of the circuit elements that make up the system, but in the present invention, the above-mentioned frequency deviation, for example ±2KHz, is the full scale, and the modulation signal frequency within that 2 times for example
Extract 160Hz or waveform duty ratio 1:
It is sufficient to detect 1, and the aforementioned lock range and full scale ratio become small, and it can be understood that the control of the system is extremely easy compared to the conventional PLL.

It should be noted that the above embodiment is one specific example of the present invention, and the present invention is not limited thereto, and it is clear that there are various other implementation methods. For example, the low frequency signal may be a left-right symmetrical wave such as a triangular waveform, and the synchronous detection circuit may also be a synchronized phase detection circuit.

Furthermore, the present invention is not limited to detecting the resonant frequency of a circuit under test, but also detects what happens when the characteristic changes with a stationary point of maximum or minimum value and that change is replaced with a change in frequency. something, such as a stopping point of impedance or current,
It will be obvious that the invention can be applied to any stationary point detection of voltage changes or other physical changes.

As another application example of the present invention, for example, an element or a circuit whose resonant frequency changes depending on pressure is used as the probe, and the resonant frequency is adjusted using a device configured similarly to the block diagram shown in the above embodiment. If detected, the pressure can be detected by the same method as explained above, and in this way, in the same way as the temperature measurement in the living body, the pressure in various parts of the living body, such as the pressure in the brain, or the pressure inside the container can be measured. Extremely effective for measuring pressure, etc.

Further, although the above example shows a case where a dip point of a resonant circuit is detected, the present invention is not limited to this, and it is also possible to detect a maximum point of a change in a physical quantity.
At this time, the antenna coil of the external circuit and the AM
By making the detection circuit resonate in series and lowering its impedance, it is possible to detect the maximum point of the physical quantity change exhibited by the circuit under test.

(Effects of the Invention) Since the present invention is configured and functions as explained above, when a certain physical quantity changes with a stationary point in response to frequency fluctuation, the frequency at the storage point can be precisely detected. This method is suitable for various methods, and is extremely convenient for automating this detection.

In particular, it is extremely effective in accurately detecting weak information on physical changes, such as when extracting temperature information from an implanted probe for measuring temperature or pressure inside a living body.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figures 2 and 3 are waveform diagrams for explaining the operation of each part of the block diagram shown in Figure 1, and Figures 4 and 5 are principle diagrams showing the conventional resonant frequency measurement method. . DESCRIPTION OF SYMBOLS 1... Voltmeter, 2... Oscillator, 3... Antenna coil, 4... Circuit under test, 5... Probe, 6... Low frequency oscillator, 7... Voltage controlled oscillator circuit (VCO), 8... ...AM detection circuit, 9...amplifier, 10...synchronous detection circuit, 11...duty ratio detection circuit.

Claims (1)

[Claims] 1. When detecting the frequency at a stopping point of an element or circuit, etc., in which a change in a physical quantity such as voltage, current, or impedance has a stopping point in response to a change in frequency, the frequency can be determined by using a required signal. Extracting the duty ratio of the carrier demodulated waveform at the stopping point when the center frequency of the carrier signal is changed while causing the modulated carrier signal to be wirelessly connected to the element or circuit via an antenna coil. A method for detecting a resonant frequency, characterized in that the frequency at the stationary point is detected by: 2. The resonant frequency according to claim 1, wherein the frequency of the stationary point is detected by converting the carrier demodulated waveform into a rectangular wave, integrating this, and converting it into a DC voltage. Detection method. 3. Claim 2, characterized in that the frequency of the stationary point is automatically detected by configuring a closed loop so that the center frequency of the carrier signal is controlled by the DC voltage. How to detect the resonant frequency of.