JPS61120974A - Detection of resonance frequency - Google Patents

Abstract

PURPOSE:To enable highly accurate detection of resonance frequency, by applying to a circuit to be measured a carrier signal FM modulated by a required low frequency signal to demodulate the amplitude distortion incurred at the resonance frequency of the circuit being measured and near it. CONSTITUTION:An in-vivo probe 5 is made up of a crystal oscillating element X and an antenna coil L3. The output of a voltage control oscillator 7 as FM or PM modulated output of a low frequency oscillator 6 is applied to a coil L4 facing the probe 5 as in-vitro unit while an AM detection circuit 8 is added to the coil L4 to input the output to a synchronous detection circuit 10 using the output of the oscillator 6 through an amplifier 9 as synchronous signal to control the oscillation frequency of an oscillator 7 by the output thereof. The waveform demodulated is synchronously detected with the circuit 10 using a low frequency signal as reference, and shaped to obtain a square wave corresponding to an AM modulation distortion, the duty ratio of which is detected with a duty ratio detection circuit 11. Then, the resonance frequency is detected utilizing that the duty ratio will be 1:1 at the resonance point of the probe 5.

Description

[Detailed description of the invention] (Industrial application field) The present invention deals with a physical quantity that corresponds to frequency fluctuations.

(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 all input terminals of measuring instruments such as frequency counters are 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 as follows:
A method using a phenomenon in which the oscillation energy of a variable frequency oscillator placed non-contact in the vicinity of the circuit under test, etc. is absorbed by the resonant circuit under test at the same frequency;
The so-called dip meter method was common.

To explain the principle of this dip meter in a little more detail, the 4th dip meter
As shown in the figure, the voltmeter (V, V) 1? If an antenna coil 3ft connected to the added variable frequency oscillator 2 so as to form a complete parallel resonant circuit is brought close to the circuit under test 4 consisting of an inductance Ls and a capacitor C1, for example, and the frequency of the oscillator 20 is changed from fl to f2. The frequency at both ends of the coil/L/3 and the voltage of the voltmeter are the resonant frequency f of the circuit under test as shown in Figure @5.
The value of the voltmeter changes to a minimum value at o.

This is as mentioned above.

This occurs because the energy of the excavator 2 is absorbed by the resonant circuit to be measured whose impedance is lower than this, and the measurer adjusts the frequency of the oscillator 2 so that the deflection of the voltmeter needle is minimized. By doing so, the frequency at that point can be detected.

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

That is, the minimum voltage value at the above-mentioned dip point is the ratio of the resistance component to the actance of the resonant circuit under test, so-called Q (qual
ity factor), or it changes depending on the mutual inductance between the circuit and the antenna coil/I/3, etc., and since it is implemented every time, it is difficult to identify it uniquely, so it is said that measurement accuracy is lacking. There are nine defects.

(Objective of the Invention) The present invention has been made to solve the deficiencies of the conventional resonance frequency measurement method as described above, and is capable of uniquely detecting a resonance point regardless of measurement conditions. The purpose of this invention is to provide a method for detecting resonance frequency with extremely high measurement accuracy.

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

That is, by frequency-modulating the circuit under test with a required low frequency signal and applying a nine-carrier signal, and demodulating the amplitude distortion that the carrier signal receives at the resonant frequency of the circuit under test and its vicinity, It is configured to detect the resonance frequency.

(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 circuit to be measured in a non-contact manner as described above, and briefly explain the shortcomings of the conventional dip meter method.

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

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 through the entire 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 through the antenna coil and observing the energy absorption when it resonates, that is, by detecting the resonance point of the probe using the above-mentioned dip meter method, the internal temperature can be measured. 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, making it extremely difficult to detect the resonance point. It was necessary.

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 same figure, 5 is the crystal oscillator X and the antenna coil L3.
This in-vivo probe is composed of a voltage-controlled oscillator (VCO) 7 which performs FM or PM modulation using the output of a low-frequency oscillator 6 on an antenna coil L4 facing the probe as an in-vivo device. Along with applying the output.

An AM detection circuit 8 is added to the antenna coil L4, and its output is passed through an amplifier 9 to a synchronous detection circuit IO which uses the output of the low frequency excavator 6 as a synchronous signal, and its output is used to control the VCo 7. The structure is such that the oscillation frequency is controlled.

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

That is, Figure @2 is a waveform diagram showing the state of AM modulation distortion that the irradiated electromagnetic wave receives in the vicinity of the resonant frequency fO of the probe.

Now, the low frequency signal is 80Hz, and the frequency deviation is ±2KH.
z [If the magnetic wave frequency is variable from 19 MHz to 21 MHz and the resonant frequency t-fO of the glove is 20 MHz, the electromagnetic wave that has received the frequency f harmonization is imaged at a cycle of 80 Hz over ±2KH2K from its center frequency. do.

Therefore, the center frequency is located at three points on the resonance characteristic curve of the glove, including the resonance point fO1- and lower than it by Δf (a), the same point as efO (b), and a point higher than efO (c). The AM modulation distortion in each case exhibits a waveform as shown by the arrow in the figure.

That is, during the deviation frequency of the electromagnetic wave, the resonance point f of the probe
o, the deviation frequency is 2
Double the amount of AMi-like distortion occurs.

This double distortion has a phase difference of 1800 degrees above and below fo, and when the center frequency of the electromagnetic wave coincides with fo, the double distortion described above becomes a y sine wave, although it is shifted in terms of direct current.

This is because the electromagnetic energy is absorbed by the resonant circuit of the glove, and at this time, both ends of the coil L2 of the external device facing the probe receive AM modulation as shown in Figure 3(c) (dl (el). A waveform appears.

FIG. 3 shows the signal waveforms of each part of the block diagram shown in FIG. The signal waveform applied to the carp and A/L4 with electromagnetic waves, (cl(
d) and tel are respectively shown in FIG.
This is a waveform that occurs at both ends.

Furthermore, when the waveforms of these (cl (dl) (el) 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 FIG.

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 waveform demodulated in this way is synchronously detected in the synchronous detection circuit 6 as the reference for all the low frequency signals, and then the waveform is shaped to obtain each AM modulation signal as shown in FIG. It is configured to obtain nine rectangular waves in response to distortion, detect the duty ratio of the rectangular waves, and use the fact that the duty ratio at the resonance point fO of the probe is 1:1 to determine the frequency at that time. This is used to measure the total temperature inside the living body.

Further, by integrating the rectangular wave and converting it into a DC voltage, a DC voltage corresponding to the duty ratio described above is obtained, and this value corresponds one-to-one to each point on the resonance characteristic curve of the probe.

That is, the relative value of r f ' is 0.5V, and the lower side than fO is below O, SV, and the higher side is 0.5V or more.

Therefore, if the DC voltage sound mentioned above is used to control the frequency control voltage of the vCO, each of these blocks will form a closed loop, and the center frequency of the electromagnetic wave can be automatically adjusted to the resonance point fo of the probe. becomes.

In other words, if the closed loop is operated so that the aforementioned DC voltage becomes O, SV, or this DC voltage output t O, 5vt - reference voltage is input to the comparator and the difference becomes O, the servo control loop If the resonant point fO of the probe moves according to the temperature using this system, a conventional phase-locked loop (PLL) can be used.
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 K to extract phase information requires a high level signal. 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,
In PLL, the entire frequency variable range, for example 2MHzt
-While the stability of the lockie/lock within a very narrow phase range of full scale, e.g. several KHz, greatly influences the stability of the system, in the present invention, the above-mentioned frequency deviation, e.g. ±2 KHz, is the full scale. It is sufficient to extract twice the frequency of the modulated signal, for example 160 Hz, or to detect a waveform duty ratio of 1:1, and the lock range and full scale ratio described above become small.

It can be seen that the system is extremely easy to control compared to the conventional PLL.

It is clear that the above-mentioned embodiment is a specific example of the present invention, and that the present invention is not limited thereto, and 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 phase detection circuit with synchronous sound.

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 at a maximum/minimum value stationary point (stage M) e point) by replacing the change with a frequency change. It will be obvious that the present invention can be applied to the detection of stopping points of innovations, for example, or any stopping points of changes in current, voltage, or other physical changes.

As another example of the use of the present invention, for example, an element or a circuit whose resonance frequency changes depending on pressure is used as the probe, and the resonant frequency is detected using a device configured similarly to the block diagram shown in the above embodiment. Then, the pressure can be detected by the same method as described above, and this method is very effective.

Further, although the above example shows the case of detecting the dip point of the resonant circuit, the present invention is not limited to this, and it is also possible to detect the maximum point of a change in a physical quantity. In this case, by making the antenna coil of the external circuit and the AM detection circuit resonate in series and lowering their innovation dance, 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 constructed and functions as explained above, it can be used as a means for accurately detecting the frequency at a stationary point when a physical quantity changes with a stationary point in response to frequency fluctuation. Furthermore, it 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 when measuring the total temperature or pressure inside a living body.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are waveform diagrams for explaining the operation of each part of the block diagram shown in FIG. 1. 4 and 5 are both principle diagrams showing a conventional resonance frequency measuring method. l...Voltmeter, 2...-...
・Oscillator. 3...Antenna coil, 4...
...Circuit under test, 5...Probe, 6...River...Low frequency oscillator, 7...
・・・・・・Voltage controlled oscillation circuit (VCO), s
......AM detection circuit. 9...-...Amplifier, 10...-...
...Synchronous detection circuit 11...Duty ratio detection circuit. Patent applicant: Toyo Tsushinki Co., Ltd. Iff Tower 2c Kuzu 3 Figure

Claims (1)

[Claims] When detecting the frequency at a stopping point of an element or circuit, etc., where a change in physical quantity such as voltage, current or impedance has a stopping point in response to a change in frequency, a carrier wave signal that has been frequency-modulated by the required signal is used. When the center frequency of the carrier wave signal is changed while involving the element or circuit, the frequency at the stationary point is detected by extracting the characteristics of the carrier demodulated waveform at the stationary point. Detection method of resonant frequency.