JPH0411810B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device used for measuring temperature in a living body, and more specifically, to a device equipped with a piezoelectric vibrator whose resonant frequency changes according to temperature changes. A small capsule without power supply is sent to the measurement target such as inside a living body,
The present invention relates to an in-vivo temperature measuring device that has a small capsule as a sensor that measures the temperature around the capsule by detecting the reverberation of the vibrator that occurs in response to excitation applied from outside the measurement object.

[Prior Art] Recently, it has been said that bacteria living in the intestinal tract, for example, have a great influence on the health conditions of humans and animals, and the occurrence of diseases. Bacteria research is considered to be one of the important issues.

By the way, when conducting this type of bacterial research, it is necessary to culture the collected bacteria in an environment similar to that of the intestines, so we need to know the specific environmental conditions such as temperature, pressure, pH, etc. This must be known in advance. In addition, knowing the environment at a specific site within a living body is not only important for knowing the growth conditions of intestinal bacteria as described above, but is also an element in diagnosing the health status of each living organism, which has individual differences. will also be beneficial.

Therefore, a medical telemeter that uses a radio capsule that has a built-in sensor and transmits information wirelessly has been considered as a device that can meet this purpose.

However, even with this method, the following difficulties have been pointed out. In other words, the radio capsule mentioned above has a restriction in its use that it must be swallowed by humans and animals and delivered into the body cavity, but since it requires a transmitter, it has no internal electronic circuits, batteries, etc. This poses a problem in that it is difficult to miniaturize due to dimensions and weight, which leads to unavoidable problems such as restricting the daily life of the living body to be measured and giving psychological stress during measurement.

Another problem has been pointed out that the battery capacity makes it unsuitable for long-term continuous use.

[Problems to be Solved by the Invention] In view of these various points, the present inventor has devised an object to utilize the reverberation effect of a crystal oscillator whose resonant frequency changes according to temperature changes, for the purpose of measuring temperature inside a living body. We have developed a small capsule-shaped information transmitter that does not require a special transmitter or battery.

[Means for Solving the Problems] The present invention provides an in-vivo temperature measuring device suitably used as such a telemeter,
It is characterized by a container that is covered with a chemical-resistant surface and formed in the shape of a capsule for in-vivo use, and is excited by an antenna and a high frequency transmitted through this antenna, and whose resonant frequency changes depending on the temperature. A small capsule as a sensor for measuring temperature inside a living body without a power supply, which is equipped with a crystal oscillator that changes accordingly, and a high frequency that is placed outside the living body and whose frequency changes stepwise above and below the resonant frequency of the crystal oscillator. A transmitter/receiver device comprising: a transmitter that sweeps pulses intermittently; and a receiver that receives a reverberant high-frequency signal (echo) that persists after the crystal resonator is excited. It's in the internal temperature measuring device.

Here, the above-mentioned container is covered with a chemical-resistant surface for measurement of in-vivo temperature, which is achieved by subjecting the container surface to a chemical-resistant treatment such as acid resistance or alkali resistance.

[Example] Embodiments of the present invention will be described below based on the drawings, but first, the principle of the present invention will be explained using a crystal resonator as an example. This crystal resonator generally has resonance characteristics. It is now known that an antenna is attached to a crystal oscillator, which is extremely sharp, has a Q value that indicates its resonance characteristics, reaches several million, has a stable frequency, and is known to have a large reverberation effect. If you use an oscilloscope to observe the state when the object is excited at its resonant frequency, the first
As shown in the figure, the crystal oscillator resonates during transmission (during time t), and the terminal voltage maintains damped oscillation when transmission is stopped, and its damping characteristic is expressed by the following equation.

X=Ae ^-Kt cos(ωt+α)...(1) k=ω/2Q...(2) Where, X: Amplitude A: Constant ω: Angular frequency in the damped vibration range Also, the damping time ΔT is ΔT=1/k. Therefore, if the Q value of a crystal resonator is 100,000 and the resonance frequency is 28 MHz, the decay time ΔT will be on the order of m _sec . Since a crystal resonator has the characteristic that its resonant frequency changes in proportion to the temperature (see Figure 2), by detecting the damped vibration (reverberation) and knowing its vibration frequency, the resonant frequency of the crystal resonator changes in proportion to the temperature. It is possible to know the temperature, in other words, the environmental temperature around the crystal resonator.

FIG. 3 shows an example of the structure of a sensor, which is a small capsule as an information transmitter, constructed when the above principle is applied to the present invention, and 1 is a second sensor.
A crystal resonator with the resonant frequency characteristics shown in the figure,
A loop antenna 2 is wound around a ferrite core 3, and both terminals thereof are connected to a counter electrode terminal P of the crystal resonator 1 to form a parallel circuit. Note that these are resin-molded, and a part of the crystal resonator 1 is projected outside the mold 4 in consideration of the time constant.

Furthermore, since the sensor configured as a small capsule in this example is used to measure the temperature inside the body cavity, the outer surface is coated with chemically resistant metal, taking into consideration the environment in which it will be used. A plating process was performed.

The sensor, which is a small capsule in this example, has a diameter of
It was installed in a capsule shape of about 10mm and 20mm in height.

Next, circuit No. 4 shows an example of a transmitting/receiving device used in combination with the sensor which is the small capsule.
To explain with reference to Figure A, in the same figure, T _X represents a transmitting section and R _X represents a receiving section. Reference numeral 5 designates a clock oscillator, and the clock pulses outputted from this are converted into clock signals of an appropriate period by a frequency divider 6.
CLK and added to counter 7. Here, the clock signal is repeatedly counted every i clock signal, and the digital/analog converter 8 converts the clock signal into 1, 2, ... n (V).
It becomes an analog control voltage signal that changes in steps between 1 and 2, is inputted to the voltage controlled variable frequency oscillator 9 via a level shift circuit, and is transmitted as a radio wave from an antenna 12 via a frequency multiplier 10 and a power amplifier 11.

where the frequency multiplier is 10 and the power amplifier is 1
1 is inputted with the branched output of the frequency divider and controls these operations on/off to control the pre-stage period t _A of the predetermined unit period T for each frequency.
(about several m _sec ), and the output is cut off during the subsequent period t _B (about several m _sec ). Therefore, what is transmitted from the antenna 12 is the period t _A1 , t _A2 , . . . of each consecutive unit period.
According to t _Ao , f _p +Δf, f _p +2Δf . . . f _p +nΔf are transmitted as a stepwise changing frequency signal VCO in sequence, and this is repeated every nT time as a whole.

Now, if we consider that the present invention uses a living body as the object of temperature measurement and uses the sensor which is a small capsule as exemplified as having the characteristics of FIGS. 2 and 3, a and b, 1 of the frequency
The change per step is 100Hz (corresponding to 0.1℃), and if the frequency of f _p is set to correspond to an arbitrary temperature (for example, 33℃), the crystal resonator 1 in the small capsule will be Reverberation is generated in accordance with the resonance characteristics during the period t _B of each unit period.

Next, referring to the receiving section, in the receiving section, the crystal oscillator performs a receiving operation every period t _B within each unit period T, as shown by R _X -ON in FIG.
As shown _{by T}
It has a controlled configuration.

In the circuit shown in Figure 4A, the reverberation level generated in the crystal oscillator when the transmission frequency is swept as f _p + Δf, f _p + 2 Δf...f _p + n Δf is determined by the fact that the above-mentioned transmission frequency is The value is highest when it matches the resonant frequency, and the value decreases as it moves away from the resonant frequency.Using this characteristic, the circuit is configured to detect the received frequency when the received power reaches its maximum level as the resonant frequency. has been done.

That is, the received reverberant frequency is
3. After passing through the mixer 15 connected to the high frequency amplifier 14 and the local oscillator 16, the intermediate frequency signal is filtered and amplified by the demodulator 17, and then level detected to obtain a DC detection output proportional to the reverberation level. There is.

This detected output is then compared with a constant reference voltage by a comparator 18. This comparator 18 outputs a pulse only when the detected output is greater than the reference voltage.

The output pulses of the comparator 18 will be explained using the timing chart shown in FIG. 4B.
- in the figure indicate waveforms in the circuit of Figure 4A. The output pulse (COMP PLS) obtained from the comparator 18 is input to a counter 20 and a latch driver 22 for controlling the amount of attenuation of the attenuator 13. The counter 20 increments the count only when the output pulse is input, that is, only when it is successfully received.
The amount of attenuation increases as shown in .

As the reverberation of the crystal oscillator approaches the resonant frequency, the receiving input level also gradually increases, so the receiving operation is performed through the attenuator 13, but after the transmitting frequency reaches the resonant frequency, the reverberation level decreases. As it continues to drop, reception becomes impossible.

Since the transmission frequency at this time indicates the maximum value of the reception level, that is, the resonant frequency of the crystal oscillator 4, the number of steps in the transmission frequency sweep from the initial stage of transmission to the maximum reception level is counted by the counter 2.
1 and display it.

The counter 21 is preset at 33°C and counts up by 0.1°C each time it is transmitted or received.
As the resonant frequency of the crystal oscillator approaches, a received pulse output is obtained from the comparator 18.
This is the latch driver 2 at the same time as the counter 20.
2 is also input. Every time this pulse is input to the latch driver 22, the contents of the counter 21 are transferred and stored in the latch driver 22, and the temperature is displayed on the display 23.

In other words, during the period when the transmission frequency reaches the resonant frequency from just before the resonant frequency of the crystal resonator, the displayed temperature is also updated by the pulse output from the comparator 18, and the latest contents of the counter 21 are displayed. When the frequency is exceeded, the reception level decreases and the pulse output is no longer output from the comparator 18, so the displayed temperature remains unchanged and the current temperature of the crystal resonator is displayed.

FIG. 5 shows a state in which a human swallows the small capsule as the sensor described above and measures the temperature inside the body cavity, and this is the same even in animals other than humans.

In the example shown in Fig. 5A, a loop-type antenna 31 (for example, wire diameter 2 mm) is connected in series to a variable capacitor 32 to obtain the maximum sensitivity, and the measurer measures while moving this antenna 31 as appropriate. I did it like that.

Furthermore, FIG. 5B shows a case where a semi-cylindrical spiral antenna 33 is used, which is more effective than the antenna shown in FIG. 5B in terms of antenna directivity.

FIG. 6 shows an example of changes over time in internal body temperature measured using the above-described temperature measuring device.

Next, another example of the structure of the transmitting/receiving device will be explained based on the circuit diagram of FIG. 7 and the time chart of outputs of each part shown in FIG. 8.

In the embodiment shown in Fig. 4A, the system is controlled and measured by detecting the presence or absence of a received signal output, whereas in the embodiment shown in Fig. 7, the presence or absence of a received signal is detected. , At the same time as the absence detection, the PLL circuit of the receiving section is phase-synchronized with the reverberation signal of the crystal oscillator, and the frequency of the VCO-2 in this PLL circuit 56 is directly counted by the counter 58, so that the frequency of the crystal oscillator, In other words, it measures temperature.

To explain this embodiment in detail below, a timing controller 42 to which input is applied to a clock oscillator 41 operates a counter 43, a digital/analog converter 44, and a voltage-controlled variable frequency oscillator 45, as shown in FIG. Similarly to the above example, a frequency signal VCO-1 (approximately 455 kHz in this example) which is swept so as to increase gradually every unit period T is output. And this frequency is switch SW-A,
The antenna 5 passes through the impact amplifier 46, the mixer 47 that receives the signal from the local oscillator 48, the bandpass filter 49, the switch SW-B, and the power amplifier 50.
1, and the transmission at this time is output in the first half period _tA of each unit period T, as shown in FIG.
It is designed to be cut off during the latter half period, and enters a receiving state within the latter half period, as shown by _tB in FIG. This transmission/cutoff control is performed by the timing controller 42 by turning on/off switch SW-B.

The above is the initial state of _the transmitter _T A is frequency signal VCO-2
This point will be discussed later.

_The receiving _{section R} The resulting reverberation is passed through a high-frequency amplifier 52, a mixer 53 that receives the same signal from the local oscillator 48 as that on the transmitting side, a bandpass filter 54, and an intermediate frequency amplifier 55, and the received frequency is input to a phase-locked loop (hereinafter referred to as a PLL circuit) 56. .

This PLL circuit 56 has a rube constant determined so that it locks in an extremely short time.
Also, in this initial state, the sample hold circuit 57
The input from the timing controller 42 is off.
Therefore, the phase detection output of the PLL circuit is passed through the terminal of the voltage controlled oscillator of the PLL circuit.
Input to VCO-IN.

And the oscillation frequency of the oscillator (VOC) 45
When VCO-1 matches the input frequency, that is, when the PLL circuit 56 is locked,
When a lock signal (LOCKSIG) is output and a stable lock state is reached where this signal is continuously applied a certain number of times, the timing controller 42 switches the switch SW-A to the VCO-2 side, and also switches the sample hold circuit 57. On/off at regular intervals
for a certain unit time (in this example, approximately
0.1 sec), the held voltage is applied to the terminal VCO-IN of the PLL circuit 56.

At this time, the timing controller 42
is the frequency signal VCO−2 output from the PLL circuit
is counted by the counter 58, and the latch/drive circuit 59 is operated based on this counted value.
A temperature corresponding to the detected resonance frequency is displayed on the display section 60. That is, the display at this time is the measured temperature.

When the PLL circuit 56 is unlocked, the switch SW-A is returned to the VCO-1 side.

In this manner, in this embodiment, in relation to the resonance characteristics of the crystal oscillator in the sensor, which is a small capsule sent into the living body, the frequency signal VCO-1 side is forms a loop, and as it approaches the resonant frequency, VCO−
The loop is switched to the second side to ensure accurate temperature measurements.

[Effects of the Invention] As described above, the in-vivo temperature measuring device according to the present invention consists of a sensor that is formed into a small capsule shape without a power source and has a crystal resonator therein, and is covered with a chemical-resistant surface. It is used internally,
By transmitting and receiving high frequencies with a transmitting/receiving device placed outside the living body, it is possible to accurately measure the temperature of a desired part of the living body.

In addition, the capsule-shaped sensor is a power-free type and requires only an antenna attached to a crystal oscillator, so it does not restrict the daily life of the living body being measured. This has the effect of making it possible to measure temperature without putting stress on the target area, etc., since the psychological stress can be reduced.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the resonant reverberation characteristics of a crystal resonator, Figure 2 is a diagram showing an example of the characteristics of a crystal resonator applied to the present invention, and Figure 3A is a diagram for explaining the resonant reverberation characteristics of a crystal resonator applied to the present invention. Figure 3 (b) is a circuit diagram showing the structure of a small capsule as a sensor; Figure 4 (a) is a circuit diagram showing an example of a transmitting/receiving device used in combination with a sensor that is a small capsule; Figure B is a time chart showing the output of each part of the circuit, Figures 5A and 5B are diagrams to explain the measurement status, and Figure 6 is a time chart showing the output of each part of the circuit.
7 is a diagram showing an example of the measurement results, FIG. 7 is a diagram showing another example of the transmitting/receiving device, and FIG. 8 is a time chart showing the outputs of each part of the circuit.

Claims (1)

[Scope of Claims] 1. A container covered with a chemically resistant surface and formed in the shape of a capsule for use in a living body is provided with an antenna and a radio frequency transmitted through the antenna, which is excited and has a resonant frequency. A small capsule is used as an unpowered in-vivo temperature measurement sensor that contains a crystal oscillator that changes depending on the temperature; A transmitter comprising a transmitter that intermittently sweeps a changing high-frequency pulse, and a receiver that receives a reverberant high-frequency signal (echo) that persists after the crystal resonator is excited.
An in-vivo temperature measuring device comprising: a receiving device;