JP2011200262A - Vascular pulse wave measuring system and physical property characteristic measuring system using light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vascular pulse wave measuring apparatus capable of more accurate measurement.SOLUTION: The vascular pulse wave measuring system 10 includes: an optical probe 12 attached to a region of a blood vessel 8 suitable for acquiring the pulse wave of a subject 6; a pulsation waveform output part 30 connected to the optical probe 12 via an optical probe circuit 20 for outputting the pulsation waveform as temporal variation of frequency by using a phase shift method; and an arithmetic operation processing part 50. A floating median setting module 56 of the arithmetic operation part 50 has a function of amplifying the maximum amplitude so that the maximum amplitude of periodical frequency data is a predetermined ratio to the range of arithmetic operation, and setting the median of the maximum amplitude in a floating manner at the median of the range of arithmetic operation regardless of the absolute value.

Description

  The present invention relates to a vascular pulse wave measurement system and a physical property measurement system using light, and in particular, a vascular pulse wave measurement system that acquires a pulsation waveform of a blood vessel using a light emitting element and a light receiving element and performs vascular pulse wave measurement. The present invention relates to a physical property measurement system using light for measuring physical properties of an object using a light emitting element and a light receiving element.

  As a technique for evaluating the characteristics of a substance, a method using vibration is known. Patent Document 1 discloses a mechanism that converts a phase change into a frequency change in consideration of the fact that the phase change is larger than the change in the frequency of vibration, but the accuracy of the phase measurement technique is not necessarily high, although the difference in material properties is. Has been.

  This technology includes a vibrator that injects ultrasonic waves into a substance, a vibration detection sensor that detects a reflected wave from the substance, an amplifier having an input terminal connected to a signal output terminal of the vibration detection sensor, and an output terminal of the amplifier. When the phase difference occurs between the input waveform to the transducer and the output waveform from the vibration detection sensor, change the frequency to zero the phase difference. The phase shift circuit includes a phase shift circuit that shifts, and a frequency change amount detection unit that detects a frequency change amount for shifting the phase difference to zero.

  Here, in the frequency change amount detection means, the phase difference due to the difference in hardness is shifted to zero and converted into a frequency change amount. In this conversion, a reference transfer function indicating the relationship between the amplitude gain and phase of the reflected wave with respect to the frequency is obtained in advance and used.

  In the above description, ultrasonic vibration is used as vibration, but this can be vibration of an electric signal in an electric circuit. For example, a light-emitting element is driven by a driving signal to emit light, the light is detected by a light-receiving element, and a detection signal is fed back as a driving signal for the light-emitting element. Signal vibration can be used.

  That is, there is a signal delay due to the structure of the light emitting element between the drive signal of the light emitting element and the emitted optical signal. Similarly, the optical signal incident on the light receiving element and the detection signal output by the light receiving element There is also a signal delay due to the structure of the light receiving element. Therefore, when a feedback loop is formed by combining a light emitting element and a light receiving element, self-excited oscillation occurs so that the phase difference that is a delay between them is made zero. By providing the feedback loop with the phase shift circuit disclosed in Patent Document 1, the phase difference can be converted into a frequency difference.

  When the light emitted from the light emitting element is applied to the substance to be evaluated, the light reflected from the substance is received by the light receiving element, and the above feedback loop is formed, the frequency of the self-excited oscillation circuit is determined by the light receiving element and the light emitting element. It depends on the delay caused by the structure of the substance and the delay caused by the characteristics of the substance to be evaluated. Therefore, by providing a phase shift circuit in this feedback loop, converting the phase difference into a frequency difference, and observing the frequency difference, the material characteristics can be measured in a non-contact or non-invasive manner.

  For example, in Patent Document 2, as a blood pressure measurement device, a sensor unit that transmits infrared light into the body and receives a reflected wave in the body, and an electric signal based on the received reflected wave is fed back to the transmitting unit. A self-oscillation circuit that self-oscillates. The self-oscillation circuit changes the gain in response to a change in frequency and adjusts the phase difference between the input phase and the output phase to zero to promote feedback oscillation. It is described that the blood pressure is calculated based on the oscillation frequency of the self-excited oscillation circuit obtained in this way, including a gain change correction circuit.

JP-A-9-145691 Japanese Patent Laid-Open No. 2001-187032

  As described above, according to the technique of the phase shift method, the pulsation waveform of the blood vessel can be accurately obtained using the light emitting element and the light receiving element. However, a living body that measures the pulsation of a blood vessel, for example, a measurement subject, does not always maintain a stable state during measurement. The posture may change, such as moving the arm to which the light emitting element and the light receiving element are attached, and if the mounting state of the light emitting element and the light receiving element is incomplete, the mounting state changes during measurement. Sometimes.

  Therefore, the pulsation waveform gradually changes during the measurement, and it may occur that, for example, the measurement range or the calculation range is out of range. If the pulsation waveform deviates from the measurement range in this way, accurate blood vessel pulse wave measurement cannot be performed. In addition, obtaining a blood vessel pulsation waveform with high accuracy using a light emitting element and a light receiving element is equivalent to measuring physical properties using light. To detect a pulsation waveform with high accuracy, a light emitting element and a light receiving element are used. It is necessary to construct a physical property system using light for measuring the physical property of an object with high accuracy.

  An object of the present invention is to provide a blood vessel pulse wave measuring apparatus that enables more accurate measurement. Another object is to provide a physical property measurement system using light that can accurately characterize physical properties of an object.

  A blood vessel pulse wave measurement system according to the present invention includes an optical probe having a light emitting element that irradiates light to a blood vessel through the skin, a light receiving element that receives reflected light from the blood vessel through the skin, and an amplifier for the optical probe. And a phase shift circuit that changes the frequency to compensate for the phase difference to zero when a phase difference occurs between the input waveform to the light emitting element and the output waveform from the light receiving element. Based on the pulsation waveform data from the output unit that outputs the periodic time change data of the frequency with the phase difference compensated to zero by pulsation waveform data, the predetermined calculation upper limit value and the calculation lower limit value The calculation means for performing calculation related to blood vessel pulse wave measurement in the calculation range between, the pulsation waveform data output from the output unit is acquired for a predetermined period, the median value and the maximum amplitude value of the acquired period data Means to execute the data acquisition process for the required period and amplify the maximum amplitude value so that the acquired maximum amplitude value has a predetermined ratio to the calculation range, and the acquired median value is floating regardless of its absolute value Floating median value setting means for executing a floating median value setting process for converting the acquired pulsation waveform data to fit within the calculation range of the computing means, and pulsation waveform data from the output unit Fluctuates with time, every time the frequency data constituting the pulsation waveform data reaches the calculation upper limit value or the calculation lower limit value, the period data acquisition process is executed again, and based on the result, the floating median value setting process is executed again. Means for executing.

  In the vascular pulse wave measurement system according to the present invention, the filter processing means for performing low-pass filter arithmetic processing on the frequency data output from the output section and supplying it to the arithmetic means, and the frequency data output from the output section at the sampling timing It is preferable to include a display unit that acquires the data every time and sequentially processes the acquired data by a moving average method to display in real time as a smooth pulsation waveform.

  The vascular pulse wave measurement system according to the present invention preferably includes FV conversion means for converting frequency data output from the output section into voltage data and supplying the voltage data to the calculation means as digital data.

  Further, in the vascular pulse wave measurement system according to the present invention, the floating median value setting means sets a data width which is a difference between the maximum value and the minimum value of the digital data for a predetermined period supplied by the FV conversion means, It is preferable to perform data bit expansion so that the data width is between 2/3 and 1/3 of the calculation range of the calculation means.

  In the vascular pulse wave measurement system according to the present invention, it is preferable that the calculation means calculates the blood pressure based on a relationship obtained in advance for the pulsation waveform and the blood pressure.

  In addition, a physical property measurement system using light according to the present invention includes a light emission driving circuit that drives under a predetermined driving condition for a light emitting element that irradiates an object with incident light, and an object corresponding to the incident light. A light receiving element that receives the light of the light receiving output circuit that outputs an output electric signal under a predetermined output condition, and is connected in series with an amplifier between the output terminal of the light receiving element and the input terminal of the light emitting element, Light receiving element delay time between light emitting element driving electric signal and irradiation light signal determined in advance by device characteristics of light emitting element, and light receiving element between light receiving light signal and light receiving element output electric signal predetermined by device characteristic of light receiving element The electrical signal phase difference determined by the delay time and the object delay time between the irradiated light signal and the received light signal caused by the physical property of the object is changed by changing the frequency. A phase shift circuit that shifts the phase difference to zero, and when no object is placed between the light emitting element and the light receiving element, the frequency at which the phase difference is compensated to zero by the phase shift circuit is set as the initial oscillation state frequency, and light emission When an object is placed between the element and the light receiving element, the frequency at which the phase difference is compensated to be zero by the phase shift circuit is defined as the object oscillation state frequency, and between the initial oscillation state frequency and the object oscillation state frequency. A physical property value output means for obtaining a physical property value of the object based on a change in frequency of the light, and the light emission drive circuit outputs an output electrical signal and an object oscillation state frequency under an initial oscillation state frequency of the light receiving output circuit. The driving conditions are set so that the irradiation light signal does not cause a signal saturation state with the output electric signal under the phase of the phase shift circuit, and the phase shift circuit has a predetermined frequency determined from the initial oscillation state frequency. Frequency separating the frequency width gain is characterized in that the operating center frequency becomes maximum.

  Further, in the physical property measurement system using light according to the present invention, the phase shift circuit may irradiate the irradiated light more than a predetermined frequency width when the physical property of the object is an optical reflectance property or an optical transmittance property. Preferably, the predetermined frequency width is set to be narrow in the case where the spectral characteristic is a spectral modulation characteristic modulated by an object.

  With at least one of the above-described configurations, the vascular pulse wave measurement system obtains pulsation waveform data of the blood vessel using the light emitting element and the light receiving element by the technique of the phase shift method, and performs calculations related to the vascular pulse wave measurement. At this time, the pulsation waveform data is acquired for a predetermined period, the median value and the maximum amplitude value of the acquired period data are obtained, and the maximum amplitude value is predetermined for the calculation range of the vascular pulse wave measurement calculation. The maximum amplitude value is amplified so as to be a ratio, and the median value is floatingly set to the median value of the calculation range regardless of the absolute value.

  Then, every time the pulsation waveform data fluctuates with time and the frequency data constituting the pulsation waveform data reaches the calculation upper limit value or the calculation lower limit value, data for the period is obtained again, and the maximum amplitude value is again obtained based on the data. The maximum amplitude value is amplified so as to have a predetermined ratio with respect to the calculation range of the blood vessel pulse wave measurement calculation, and the median value is floatingly set to the median value of the calculation range regardless of the absolute value. As a result, even if the pulsation waveform data fluctuates with time, the pulsation waveform data can be automatically stored in the calculation range, so that more accurate vascular pulse wave measurement can be performed.

  Further, in the vascular pulse wave measurement system, the low-pass filter arithmetic processing is performed on the frequency data output from the output unit and supplied to the calculation means, and the frequency data output from the output unit is acquired at each sampling timing, The acquired data is sequentially processed by the moving average method and displayed in real time as a smooth pulsation waveform. The low-pass filter processing calculation takes time, whereas the moving average calculation has a short calculation time. Therefore, by using the data after low-pass filter processing for blood vessel pulse wave measurement that requires accuracy, and using the results of the moving average method for real-time display, measurement results such as blood pressure can be obtained while viewing the pulsation waveform in real time. Can do.

  In the vascular pulse wave measurement system, the frequency data output from the output unit is converted into voltage data, and the voltage data is supplied as digital data to the calculation means. The conversion between frequency and voltage is called FV conversion, and by using a commercially available analog IC or the like, proven hardware can be used. Further, by converting the analog data into digital, digital processing can be performed for the subsequent calculation, and high-speed and high-precision arithmetic processing can be performed.

  In the vascular pulse wave measurement system, the data width, which is the difference between the maximum value and the minimum value of the digital data for a predetermined period supplied by the FV conversion means, is changed from 2/3 to 1 of the calculation range of the calculation means. Data bit expansion is performed so that the data width is between / 3. The data width is preferably ½. By doing so, it is possible to execute data processing using the calculation range as effectively as possible while providing a margin so as to be within the calculation range even if there is a temporal variation of data.

  In the vascular pulse wave measurement system, the blood pressure is calculated based on the relationship obtained in advance for the pulsation waveform and the blood pressure. Blood pressure measurement is generally performed by measuring the Korotkoff sound using a compression cuff. However, according to the method using a light emitting element and a light receiving element, a compression cuff is not required, and the examination load is reduced. Since the pulsation waveform obtained by using the light emitting element and the light receiving element is associated with the blood pressure obtained by using, for example, the compression cuff, the reliability of the measurement result is ensured.

  In addition, by at least one of the above-described configurations, the physical property measurement system can determine in advance the light-emitting element delay time between the light-emitting element driving electrical signal and the irradiation light signal determined in advance by the device characteristic of the light-emitting element and the device characteristic of the light-receiving element. About the phase difference of the electric signal determined by the light receiving element delay time between the light receiving light signal and the light receiving element output electric signal, and the object delay time between the irradiation light signal and the light receiving light signal generated by the physical property of the object A phase shift circuit that shifts the electric signal phase difference to zero by changing the frequency is used. Then, the physical properties of the object are measured based on the difference in frequency change between when the object is not disposed between the light emitting element and the light receiving element and when the object is disposed between the light emitting element and the light receiving element. To do. At that time, the drive condition of the light emission drive circuit is set so that the output electric signal of the light receiving output circuit does not become a signal saturation state. Thereby, the change in the phase of the output electric signal can be obtained with high accuracy.

  In addition, in the physical property measurement system, the phase shift circuit has a spectral characteristic of the irradiation light that depends on the object rather than a predetermined frequency width when the physical property of the object is an optical reflectance characteristic or an optical transmittance characteristic. A predetermined frequency width in the case of a spectrum modulation characteristic subjected to modulation is set narrow. The measurement of physical property using light is based on the phase difference of the electric signal determined by the object delay time between the irradiated light signal and the received light signal caused by the physical property of the object. Although the change is directly reflected in the phase difference, the change in the phase difference is often small because the spectrum modulation characteristic is detected as a change in reflectance or transmittance. Therefore, the operation center frequency of the phase shift circuit is brought close to the initial oscillation state frequency to increase the gain of the phase shift circuit. Thereby, the spectrum modulation characteristic can be measured with high accuracy.

It is a figure which shows the structure of the vascular pulse wave measurement system in embodiment which concerns on this invention. It is a figure explaining the structure of the optical probe in embodiment which concerns on this invention. In the embodiment according to the present invention, it is a diagram for explaining the configuration of the optical probe circuit and a pulsation waveform output unit. In embodiment which concerns on this invention, it is a figure explaining the measurement principle of the substance characteristic using light. It is a figure explaining the effect | action of a phase shift circuit. 5 is a flowchart illustrating a procedure for measuring a blood vessel pulse wave in the embodiment according to the present invention. In an embodiment concerning the present invention, it is a figure explaining a situation of floating median value setting. In embodiment which concerns on this invention, it is a figure which compares and shows the pulsation waveform obtained using light, and the pressure waveform by an open blood method. In embodiment which concerns on this invention, it is a figure which shows the example of the relationship between the frequency data obtained using light, and blood pressure. In embodiment which concerns on this invention, it is a figure which converts into a blood pressure waveform and shows the pulsation waveform obtained using light. In embodiment which concerns on this invention, it is a figure which shows a mode that a pulsation waveform changes with time and exceeds a calculation range. In embodiment which concerns on this invention, it is a figure which shows the mode of the pulsation waveform after performing a floating median value setting process. In embodiment which concerns on this invention, it is a figure explaining a mode that a pulsation waveform is processed by the moving average method. In embodiment which concerns on this invention, it is a figure explaining the structure of the physical-property characteristic measurement system which uses light. In embodiment which concerns on this invention, it is a figure explaining the construction | assembly procedure of the physical-property characteristic measurement system which uses light. In embodiment which concerns on this invention, it is a figure explaining the mode of the wavelength selection of a light emitting element and a light receiving element. In an embodiment concerning the present invention, it is a figure explaining light reflection type physical property measurement as an arrangement method of an initial oscillation state. In the embodiment according to the present invention, the arrangement method in the initial oscillation state is a diagram for explaining the measurement of light transmission physical properties. In an embodiment concerning the present invention, it is a figure explaining a condition setting method of a light emission drive circuit and a light reception output circuit. In embodiment which concerns on this invention, it is a figure explaining the example which light emission illumination intensity is appropriate and can detect a phase difference detection accurately. In embodiment which concerns on this invention, it is a figure explaining the example which light emission illumination intensity is inappropriate and a phase difference detection cannot be measured accurately. In embodiment which concerns on this invention, it is a figure explaining the mode of the setting of the operation center frequency of a phase shift circuit. In embodiment which concerns on this invention, it is a figure explaining the spectrum of irradiated light being modulated by the target object.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the pulse wave of a human blood vessel will be described as a measurement target. However, any pulse wave of a blood vessel of a living body may be used, and a non-human animal or the like can be targeted. In the following, measurement of pulse, maximum blood pressure, and minimum blood pressure will be described as blood vessel pulse wave measurement. However, any other measurement may be used as long as measurement is performed using a blood vessel pulsation waveform. For example, an amount corresponding to the blood flow amount may be measured from the integrated value of the pulsating waveform, and a measurement for evaluating the flexibility of the blood vessel may be performed from the differential value of the pulsating waveform. The materials, shapes, and dimensions described below are merely examples, and these contents can be changed as appropriate according to the purpose of use.

  Below, the same code | symbol is attached | subjected to the same element in all the drawings, and the overlapping description is abbreviate | omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a diagram illustrating the configuration of a vascular pulse wave measurement system 10. Although not a component of the blood vessel pulse wave measurement system 10, a measurement subject 6 who measures blood pressure and a blood vessel 8 that actually measures blood pressure are shown in FIG.

  The vascular pulse wave measurement system 10 emits light instead of a conventional compression cuff method for measuring Korotkoff sounds or a blood pressure method in which a pressure sensor is inserted into an artery to directly measure the pressure in the blood vessel. This is a system having a function of acquiring a pulsation waveform of a blood vessel 8 by using an optical probe 12 having an element and a light receiving element and measuring a pulse wave.

  The blood vessel pulse wave measurement system 10 emits light by driving an optical probe 12 attached to a site suitable for acquiring the pulsation of the blood vessel 8 of the subject 6 and a light emitting element constituting the optical probe 12. An optical probe circuit 20 for detecting reflected light by the light receiving element, a pulsation waveform output unit 30 connected to the optical probe circuit and outputting a pulsation waveform as a time change of the frequency by using a phase shift method; An FV converter 40 for converting frequency data into voltage data, an A / D converter 42 for converting analog data of the FV converter 40 into digital data, and an operation for processing the digital data and outputting vascular pulse wave data The processing unit 50 and a display unit 60 that displays the output of the arithmetic processing unit 50 are included.

  FIG. 2 is a diagram illustrating the configuration of the optical probe 12. The optical probe 12 has a light-emitting element 14 and a light-receiving element 16 attached to a circuit board 18 in an appropriate holding part 13. The holding unit 13 includes a circuit board 18 and is a member that protrudes and arranges the light emitting unit of the light emitting element 14 and the light detecting unit of the light receiving element 16 on the surface. For example, the holding unit 13 is formed by molding an appropriate plastic material. be able to.

  The light emitting element 14 and the light receiving element 16 are preferably arranged close to each other, but a structural device such as a light shielding wall is provided so that light from the light emitting element 14 does not directly enter the light receiving element 16. It is preferable to do. Alternatively, lenses may be provided on the light emitting element 14 and the light receiving element 16 to enhance directivity. In the example of FIG. 2, one light emitting element 14 and one light receiving element 16 are provided, but a plurality of light emitting elements and a plurality of light receiving elements may be provided. Further, the light receiving element may be arranged so as to be surrounded by a plurality of light emitting elements.

  The optical probe 12 is attached to a site suitable for detecting the pulsation of the blood vessel 8 of the measurement subject 6 with an appropriate band, tape, or the like not shown. Although FIG. 1 shows a state in which the optical probe 12 is attached to the radial artery portion of the wrist, other than this, the brachial artery portion corresponding to the inside of the elbow portion of the arm, the fingertip, the vicinity of the heart, etc. The optical probe 12 can be attached to this part.

  As the light emitting element 14, a light emission diode (LED) can be used. Here, an infrared LED of type TLN103A manufactured by Toshiba is used. This infrared LED is an LED using GaAs as a substrate, and has a capacitance value of 30 pF with a reverse bias voltage of 0 V and a frequency of 1 MHz. The forward voltage when the forward current is 10 mA is 1.00 V to 1.30 V. When the forward current is 20 mA, the radiation power is 2.5 mW, the emitted light intensity is 1 mW / cm 2, and the light has a standard characteristic of emitting light having a peak emission wavelength of 940 nm. The maximum distance to the light receiving element when combined with the light receiving element is about 5 mm for DC operation and about 30 mm for pulse driving.

  As the light receiving element 16, a photodiode or a phototransistor can be used. Here, a TPS603A two-terminal phototransistor manufactured by Toshiba is used. This phototransistor has a standard characteristic of outputting a photocurrent of 20 μA with a peak detection wavelength of 720 nm by irradiating the base with light of 0.1 mW / cm 2 when the collector-emitter voltage is 3V. . The load resistance is 1 kΩ, the Vcc voltage is 10 V, the collector current is 1 mA, and the rising switching time is 9 μs and the falling switching time is 10 μs.

  FIG. 3 is a diagram illustrating the configuration of the optical probe circuit 20 and the pulsation waveform output unit 30. The optical probe circuit 20 includes a drive circuit for the light emitting element 14 and a detection circuit for the light receiving element 16. The pulsation waveform output unit 30 is a feedback circuit that feeds back an output signal of the light receiving element 16 as an input signal of the light emitting element 14.

  As a driving circuit for the light emitting element 14, a configuration in which the light emitting element 14 and the driving transistor 24 are connected in series between Vcc and the ground, and a base that is a control terminal of the driving transistor 24 is used as a predetermined bias condition is used. In this configuration, when the input signal to the base of the drive transistor 24 becomes High, the drive transistor 24 is turned on and a drive current flows through the light emitting element 14. As a result, the light emitting element 14 emits light, and the light is emitted toward the blood vessel 8 through the skin.

  As a detection circuit for the light receiving element 16, a configuration in which a load resistor 22, a diode, and the light receiving element 16 are connected in series between Vcc and -Vcc is used. In this configuration, a standard photocurrent is generated in the light receiving element 16 when the light receiving element 16 receives the reflected light from the blood vessel irradiated by the light of the light emitting element 14 through the skin. The magnitude of the photocurrent is output as a voltage corresponding to the magnitude of the current flowing through the load resistor 22.

  The pulsation waveform output unit 30 is a feedback circuit provided between an input terminal that receives a voltage signal output from the detection circuit of the light receiving element 16 and an output terminal that outputs a voltage signal input to the drive circuit of the light emitting element 14. And has a function of outputting the time variation of the frequency in the feedback circuit to the F / V converter 40 as pulsation waveform data.

  In the pulsation waveform output unit 30, an amplifier 32 and a phase shift circuit 34 are arranged in series between an input terminal and an output terminal. That is, the input side of the amplifier 32 is connected to the input terminal on the light receiving element 16 side via a DC cut capacitor, the input side of the phase shift circuit 34 is connected to the output side of the amplifier 32, and the output side of the phase shift circuit 34 emits light. It is connected to the output terminal on the element 14 side.

  The phase shift circuit 34 is a circuit having a function of changing the frequency and compensating for the phase difference to zero when a phase difference occurs between the input waveform to the light emitting element 14 and the output waveform from the light receiving element 16. is there.

  FIG. 4 is a diagram for explaining the operation of the phase shift circuit 34 when light is used. The phase shift circuit in Patent Document 1 is a case where ultrasonic vibration is used. At that time, the frequency of the ultrasonic vibration is changed and the waveform between the input waveform to the ultrasonic transducer and the output waveform from the ultrasonic vibration detection element is changed. Set the phase difference of to zero. On the other hand, when light is used, when the wavelength of light is not changed, the voltage signal output from the light receiving element 16 is fed back to form a feedback loop as the voltage signal input to the light emitting element 14. In addition, the frequency of oscillation of the voltage signal in the feedback loop is changed.

  In FIG. 4, when a voltage signal is input to the light emitting element 14, light is emitted, but the optical signal is delayed in time from the input voltage signal. This delay is caused by a capacitive component or the like as the structure of the light emitting element 14. That is, in the light emitting element 14, the emitted light signal as the output signal is delayed with respect to the voltage signal as the input signal, and a phase difference is generated in that sense. In FIG. 4, the delay is indicated by a time delay Δtd1.

  When the light emitting element 14 and the light receiving element 16 are disposed in close contact, the light emitted from the light emitting element 14 is received by the light receiving element 16 as it is. In the case of the specification of the light emitting element 14 described above, the distance between the light emitting element 14 and the light receiving element 16 can be up to 30 mm, but the amount of light received by the light receiving element 16 decreases as the distance increases. . In any case, when the light emitting element 14 and the light receiving element 16 are disposed at an appropriate distance, the light receiving element 16 can receive light from the light emitting element 14.

  When the light receiving element 16 receives light, a voltage signal is generated according to the intensity of the light. The voltage signal is delayed in time from the received optical signal. This delay is caused by a capacitance component or the like as the structure of the light receiving element 16, and is indicated as a rising switching speed and a falling switching speed in the above specifications. That is, in the light receiving element 16, the voltage signal as the output signal is delayed with respect to the optical signal as the input signal, and a phase difference is generated in that sense. In FIG. 4, the delay is indicated by a time delay Δtd2.

  Therefore, when the light emitting element 14 and the light receiving element 16 are combined, a voltage signal is input to the light emitting element 14, and light is emitted from there with a phase difference. The light receiving element 16 receives the light, and the phase difference is obtained therefrom. Therefore, a voltage signal is output. Thus, there is a time delay between the drive voltage signal of the light emitting element 14 and the detection voltage signal of the light receiving element, and a phase difference is caused in that sense. In the example of FIG. 4, a time delay of Δtd1 + Δtd2 occurs.

  Here, it is considered that the detection voltage signal of the light receiving element 16 is fed back to the light emitting element 14 as a drive voltage signal using an appropriate amplifier 32. In this case, a voltage signal oscillates in the feedback loop at a frequency at which the sum of the delay time in the light emitting element 14 and the delay time in the light receiving element 16 is exactly 180 degrees in phase difference. For example, if Δtd1 + Δtd2 that is the sum of delay times is 2.5 μs, self-oscillation occurs in the feedback loop at a frequency of 200 kHz with one period of 5 μs.

  The above example is a case where there is only a space between the light emitting element 14 and the light receiving element 16, but light from the light emitting element 14 is radiated to the measurement object, and reflected light from the measurement object is received as the light receiving element 16. Is received, a time delay is generated between the incident light and the reflected light based on the material property of the measurement object. In that sense, a phase difference occurs between the incident light and the reflected light. In FIG. 4, the blood vessel 8 is shown as the measurement object, and the delay is shown as the time delay ΔTd between the light emitted to the blood vessel 8 and the reflected light.

  In this way, when light is emitted from the light emitting element 14 to the blood vessel 8 and the light receiving element 16 receives reflected light from the blood vessel 8, it is assumed that there is no influence of light directly incident on the light receiving element 16 from the light emitting element 14. The self-excited oscillation in the feedback loop reflects the material characteristics of the blood vessel 8.

  That is, in the example of FIG. 4, the voltage signal is output in the feedback loop at a frequency at which the sum of the delay time Δtd1 in the light emitting element 14, the delay time Δtd2 in the light receiving element 16, and ΔTd is exactly 180 degrees in phase difference. Oscillates. In the above example, if Δtd1 + Δtd2 + ΔTd, which is the sum of delay times, is 2.55 μs, for example, self-oscillation occurs in the feedback loop at a frequency of 196 kHz with a period of 5.1 μs. When there is no blood vessel 8, since it oscillated at a frequency of 200 kHz, the material characteristic of the blood vessel 8 can be determined from the difference in oscillation frequency.

  In this way, even if the amplifier 32 is provided in the feedback loop, self-oscillation occurs, and the material characteristics of the blood vessel 8 can be determined from the change in the self-oscillation frequency that changes by including the blood vessel 8 in the feedback loop. It becomes possible to judge.

  Although related to the characteristics of the light-emitting element 14 and the light-receiving element 16, the change in the self-oscillation frequency when the blood vessel 8 is included in the feedback loop is often very small. On the other hand, since the change in phase is relatively large, it is preferable to detect a phase difference that is a change in phase. However, precise measurement of the phase difference is more difficult than precise measurement of the frequency.

  As described above, when a phase difference occurs between the input waveform to the light emitting element 14 and the output waveform from the light receiving element 16, the phase shift circuit 34 changes the frequency to compensate the phase difference to zero. This is a circuit having a function. In other words, the circuit has a function of converting a change in phase into a change in frequency. What is characteristic is that a conversion rate for converting a phase difference into a frequency difference can be arbitrarily set.

  FIG. 5 is a transfer characteristic curve diagram in which the horizontal axis represents frequency and the vertical axis represents gain and phase. In FIG. 5, the characteristic line Gf is a gain-frequency characteristic line of the phase shift circuit 34, and the characteristic line θf is a phase-frequency characteristic line of the phase shift circuit 34. Characteristic lines G1 and G2 are gain-frequency characteristic lines of a self-excited oscillation circuit that does not include the phase shift circuit 34.

  As described above, the transfer characteristic curve diagram of the phase shift circuit 34 shows a kind of band-pass filter characteristic. The phase shift circuit 34 having such transfer characteristics can be configured by combining a plurality of resistance elements and a plurality of capacitance elements. Further, as the digital calculation, a plurality of integral calculation elements and a plurality of differential calculation elements can be combined.

  The operation of the phase shift circuit 34 will be described with reference to FIG. Assuming that a phase difference of Δθ is generated between the input waveform of the light emitting element 14 and the output waveform of the light receiving element 16 corresponding to the change in the state of the blood vessel 8, the phase shift circuit 34 is on the characteristic line θf. Thus, the operating point is moved by Δθ and the phase difference is made zero. At that time, the gain-frequency characteristic line of the self-excited oscillation circuit not including the phase shift circuit 34 changes from G1 to G2. This change becomes a frequency change Δf on the characteristic line Gf of the phase shift circuit 34.

  Thus, when a phase difference Δθ occurs between the input waveform to the light emitting element 14 and the output waveform from the light receiving element 16, the function of changing the frequency by Δf and compensating for the phase difference to zero is a phase shift. The circuit 34 has. The magnitude of Δf corresponding to the change in Δθ is determined by the setting of the characteristic line θf and the characteristic line Gf. That is, this size can be set appropriately by designing the transfer characteristics of the phase shift circuit 34. As a result, the phase change can be converted into a frequency change of an appropriate magnitude.

  This change in frequency reflects the material characteristics of the blood vessel 8. When the blood vessel 8 pulsates, the frequency changes according to the change in the pulsation. Therefore, a periodic change in frequency can be used as the pulsation waveform data of the blood vessel 8.

  Returning to FIG. 1 again, the pulsation waveform output unit 30 outputs the periodic time change data of the frequency whose phase difference is compensated to zero by the phase shift circuit 34 as described above, as pulsation data of the blood vessel 8, and FV This is supplied to the conversion unit 40.

  The FV conversion unit 40 is a circuit having a function of converting frequency data output from the pulsation waveform output unit 30 into voltage data. As the FV conversion unit 40, a commercially available IC having an appropriate FV conversion function can be used. For example, in the above example, when the self-oscillation frequency is 100 kHz to 200 kHz, an FV conversion IC having a specification in which the frequency range is about 1 kHz to 500 kHz and the voltage range is about 0 V to 5 V can be used.

  For example, when the frequency change is 110 kHz to 120 kHz using the FV conversion IC having the above specifications, the FV conversion characteristic is a linear characteristic, and this frequency change is converted as a voltage change of about 10 mV.

  The A / D converter 42 is a circuit having a function of converting the analog output of the FV converter 40 into digital data. As the A / D conversion unit 42, a commercially available A / D conversion IC or the like that can convert the number of digital bits suitable for the calculation range in the calculation processing unit 50 can be used. Appropriate converted digital data that is in the calculation range is supplied to the calculation processing unit 50.

  The arithmetic processing unit 50 is an arithmetic processing device having a function of processing frequency change data supplied as digital data and outputting it as vascular pulse wave measurement data. The arithmetic processing unit 50 can be configured by a computer suitable for arithmetic processing.

  The arithmetic processing unit 50 has several functions for blood vessel pulse wave measurement calculation. The vascular pulse wave measurement calculation module 52 has a function of performing calculation related to vascular pulse wave measurement within a calculation range between a predetermined calculation upper limit value and a calculation lower limit value based on the pulsation waveform data. The blood vessel pulse wave measurement calculation includes calculation of the pulse rate, calculation of the maximum blood pressure, and calculation of the minimum blood pressure.

  Further, the frequency data acquisition module 54 acquires pulsation waveform data, and if necessary, acquires data for a predetermined period, and performs period data acquisition processing for obtaining the median value and maximum amplitude value of the acquired data for the period. Has the function to execute. Further, the floating median value setting processing module 56 amplifies the maximum amplitude value so that the acquired maximum amplitude value becomes a predetermined ratio with respect to the calculation range, and the acquired median value is floated regardless of its absolute value. It has a function of setting the median value of the calculation range and converting the acquired pulsation waveform data so as to be within the calculation range of the calculation means. Further, the noise removal processing module 58 performs low-pass filter arithmetic processing on the frequency data and supplies it to the arithmetic means, acquires frequency data at every sampling timing, and sequentially processes the acquired data by the moving average method. And has a function to make a smooth pulsating waveform.

  Such a function can be realized by executing software, and specifically, can be realized by executing a blood vessel pulse wave measurement program. Some of these functions may be realized by hardware.

  The display unit 60 shown in FIG. 1 is a device that displays the calculation result of the calculation processing unit 50. In FIG. 1, the pulsation waveform display 62 after the low-pass filter processing, the pulsation waveform display 64 after the moving average method processing, and the display of the pulse rate, the maximum blood pressure Pmax, and the minimum blood pressure Pmin as the vascular pulse wave measurement value display 66 are shown. ing. An appropriate display, printer, or the like can be used as the display unit 60.

  The operation of the vascular pulse wave measurement system 10 having such a configuration will be described with reference to the flowchart of FIG. 6 and the diagrams of FIGS.

  FIG. 6 is a flowchart showing the procedure of blood vessel pulse wave measurement. Each procedure corresponds to each processing procedure of the blood vessel pulse wave measurement program. In order to perform blood vessel pulse wave measurement, the optical probe 12 is attached to an appropriate part corresponding to the blood vessel 8 of the person 6 to be measured, and the power of each electric circuit from the optical probe circuit 20 to the display unit 60 is turned on. Perform initialization as Then, in the arithmetic processing unit 50, a blood vessel pulse wave measurement program is launched.

  Then, pulsation waveform data is acquired for five cycles (S10). This step is executed by the function of the frequency data acquisition module 54 of the arithmetic processing unit 50. Specifically, the periodic frequency data output from the pulsation waveform output unit 30 is acquired for five periods. Since the pulsation waveform has periodicity according to the pulse period which is the period of pulsation of the blood vessel 8, the period corresponding to five periods is five pulses. Note that the five periods are exemplary, and may be other than five periods, or in some cases, one period.

  For example, as described above, when the frequency change due to the pulsation of the blood vessel 8 is 110 kHz to 120 kHz, the maximum amplitude value of the voltage change after FV conversion is about 10 mV even for five cycles. Since the voltage range of the FV converter is 5V, the maximum amplitude value of this voltage change is only 10/5000 of the voltage range.

  Since the data of the FV conversion unit 40 is digitally converted by the A / D conversion unit 42 and supplied to the calculation processing unit 50, the calculation processing unit 50 assumes the width of the voltage range of the FV conversion unit 40 as the calculation range, Is set. In the above example, when the voltage range of the FV conversion unit 40 is 0V to 5V, if the arithmetic processing unit 50 performs arithmetic processing with 16-bit data, A / Data conversion is performed in the D converter 42.

  Therefore, when the frequency change due to the pulsation of the blood vessel 8 is converted into a voltage change as in the above example, if the maximum amplitude value is approximately 10 mV, only 1/500 of the calculation range is used for the calculation. Therefore, a process of amplifying the 10 mV so as to be within the calculation range is performed.

  That is, the median value and the maximum amplitude value are calculated using the acquired pulsation waveform data for five cycles (S12). In the above example, the median value is 5 mV, and the maximum amplitude value is 10 mV. Actually, since digital conversion is performed, both the median value and the maximum amplitude value are represented by 16-bit data. However, since analog data is easier to understand in the explanation, in the following, analog data will be used. explain.

  Next, the maximum amplitude value is set to ½ of the calculation range (S14). In the above example, 10 mV is expanded to 5 V / 2. That is, the 10 mV data is expanded to 2500 mV.

  Then, the median is floatingly set to the median of the calculation range regardless of the absolute value (S16). In the above example, 5 mV is set to 2.5V. Steps S12, S14, and S16 are executed by the function of the floating median value setting processing module 56 of the arithmetic processing unit 50.

  This is schematically shown in FIG. FIG. 7 shows two diagrams with time on the horizontal axis and voltage on the vertical axis. The figure on the left shows the pulsation waveform for five cycles after FV conversion. In the above example, the maximum amplitude value is 10 mV and the median value is 5 mV. However, the median value is schematically biased to approximately 2 V, and the maximum amplitude value is also exaggerated. The right figure shows the pulsation waveform after the floating median value setting process. In both the left and right figures, the vertical axis is the full range of 5 V, and this range is the calculation range.

  In order to make it easier to compare the left and right diagrams in FIG. 7, the enlargement of the maximum amplitude value and the movement of the median value are indicated by arrows. Thus, in the floating median value setting process, the median value of the pulsation waveform is always moved to 2.5 V, which is the median value of the calculation range, regardless of the actual value. The maximum amplitude value is also expanded to 2.5 V, which is 1/2 of 5 V that is the calculation range, regardless of the actual value. In this way, the calculation range is used effectively in the subsequent calculations.

  The reason why the maximum amplitude value is set to ½ of the calculation range is that the pulsation waveform may fluctuate with time as will be described later. In the example of FIG. 7, since the data is in the range of 0V to 5V of the calculation range until the upper limit value of the pulsation waveform is increased by 1.25V or the lower limit value of the pulsation waveform is decreased by 1.25V, the calculation is continued. can do.

  Thus, the reason why the maximum amplitude value is set to 1/2 of the calculation range is to use the calculation range as effectively as possible while providing a margin so that it can be within the calculation range even if there are temporal fluctuations in the data. Therefore, the setting may be other than 1/2. For example, an appropriate value can be used in the range of 1/3 to 2/3.

  Returning to FIG. 6 again, once the center value and the maximum amplitude width of the actual frequency data are adjusted so that the calculation range can be used effectively in the subsequent calculation, the pulse wave measurement calculation is completed. Data collection. That is, sampling acquisition of pulsation waveform data is performed (S18). Sampling is preferably performed with sufficient fineness against changes in the pulsation waveform. For example, frequency data can be acquired every 5 ms.

  FIG. 8 is a diagram showing a comparison between sampling data of a pulsation waveform and data of pressure fluctuations in a blood vessel by an open blood method. The horizontal axis of FIG. 8 is time, and the upper diagram is obtained by converting the frequency data obtained by the configuration of FIG. 1 into voltage data using the light emitting element 14 and the light receiving element 16, and the vertical axis is voltage. The lower diagram is data obtained by separately inserting a pressure sensor into the blood vessel 8 and actually obtaining the temporal change of the pressure in the blood vessel, and the vertical axis is the pressure.

  As shown in FIG. 8, the data obtained by the configuration of FIG. 1 looks in good agreement with the actual intravascular pressure. Therefore, if the correlation between the periodic pulsation waveform data obtained by the configuration of FIG. 1 and the blood pressure data obtained by the open blood method or the like is obtained in advance, the periodic pulsation waveform data obtained by the configuration of FIG. Blood pressure can be obtained from

  FIG. 9 is an example showing a correlation between pulsation waveform data and blood pressure. Here, the horizontal axis represents frequency data obtained with the configuration of FIG. 1, and the vertical axis represents the blood pressure value obtained by the open blood method. The straight lines indicated as Q1 and Q2 are lines indicating the correlations between the two subjects. Since the correlation between the pulsation waveform data and the blood pressure value is different for each person to be measured in this way, it is necessary to obtain the correlation for each person to be measured in advance. In addition, even if the subject is the same, the correlation between the pulsation waveform and blood pressure value may differ between the resting state and the exercise state. It is necessary to keep.

  The correlation between the pulsation waveform and the blood pressure value obtained in FIG. 1 can be stored in an appropriate storage device in association with each measurement subject and each measurement condition. FIG. 10 is a diagram illustrating an example in which the pulsation waveform data of FIG. 1 is converted into blood pressure data using the correlation stored in such a manner. Here, the horizontal axis represents time, and the vertical axis represents the converted blood pressure value. When blood pressure data is converted in this way, vascular pulse wave measurements such as the pulse rate, the maximum blood pressure Pmax, and the minimum blood pressure Pmin can be performed based on the conversion.

  When the pulsation waveform data sampling is performed, the calculation of the vascular pulse wave measurement can be performed using the correlation between the frequency data and the blood pressure value as described above, but the pulsation waveform data may vary with time. FIG. 11 is a diagram showing such a case. Here, the horizontal axis represents time, and the vertical axis represents the voltage value after FV conversion. The full scale of the vertical axis is 5 V as described in FIG. In this way, with the passage of time, although the data amplitude values are substantially the same, the data center point gradually changes and eventually exceeds the full scale of the vertical axis.

  As described above, one of the causes that the pulsation waveform varies with time is that the optical probe 12 is not sufficiently attached, and the relative positional relationship between the optical probe 12 and the blood vessel 8 changes with time. Therefore, it is preferable that the optical probe 12 is firmly fixed so as not to be displaced from the measurement site of the person to be measured 6. As another cause, the posture state of the measurement subject may change with time. In any case, in order to collect the pulsation waveform accurately, it is necessary to amplify the pulsation waveform appropriately in order to use the calculation range effectively, so if the center point of the pulsation waveform moves, it will be out of the calculation range. Can occur.

  Therefore, returning to FIG. 6 again, it is determined whether or not the data is within the calculation range in the sampling acquisition of the pulsation waveform data (S20). Specifically, it is determined whether or not the voltage data after FV conversion is in the range of 0V to 5V corresponding to the calculation range. If the determination is negative, the process returns to S10 again, the setting of the maximum amplitude value of the pulsation waveform and the setting of the center value are restored, and pulsation waveform data for five cycles is acquired based on the raw data after the FV conversion. . Then, the processes of S12, S14, and S16, that is, the floating center value setting process is performed again.

  In this way, it is determined whether or not the acquired pulsation waveform data is within the calculation range, and when it exceeds the calculation range, the floating center value setting process is performed again, and the center value of the pulsation waveform is set to the center value of the calculation range. Return to. In many cases, the maximum amplitude value hardly changes, but if necessary, the maximum amplitude value is reset to ½ of the calculation range. FIG. 12 is a diagram showing a state of the pulsation waveform when the floating center value setting process is performed so that the pulsation waveform data is within the calculation range in this way. The horizontal axis is time, and the vertical axis is the voltage after FV conversion.

  Returning to FIG. 6 again, if the determination in step S20 is affirmative, the flow proceeds to the blood vessel pulse wave measurement calculation using the acquired pulsation waveform data, but before that, noise removal processing is performed on the pulsation waveform data. As the noise removal processing, low-pass filter processing for removing high-frequency noise is performed (S22).

  The pass frequency band of the low pass filter is preferably the frequency band in the pulsation waveform output unit 30. In the above example, it is preferable to set a band of 200 kHz or less as a pass frequency band and to remove frequency data higher than that as noise. For the pulsation waveform data subjected to the filter processing, the correlation described in FIG. 9 is read from the storage device and applied, and vascular pulse wave measurement such as blood pressure measurement (S24) is performed.

  The filtering process may take a calculation time and may exceed the sampling time of the pulsation waveform, and is not suitable for observing the pulsation waveform in real time. On the other hand, in the pulsation waveform after FV conversion, noise is often superimposed and is not suitable for observation.

  Therefore, moving average processing is performed on the pulsation waveform data so that the pulsation waveform can be observed in real time (S26). This process is performed in parallel with the filter process of S22. In moving average method, when sampling data is acquired at a certain time, the average of several previous sampling data is obtained, the average value is used as the data at that time, and the sampling should be averaged at each sampling time. It moves data. According to this method, sudden abnormal data can be rounded, and there is a kind of noise removal effect.

  FIG. 13 is a diagram illustrating a state in which a smooth pulsation waveform is generated from the raw data after the FV conversion by using the moving average method. In the upper diagram, the horizontal axis represents time, the vertical axis represents the voltage value a after FV conversion, and changes in voltage data at each sampling time are shown.

  In the lower diagram, the horizontal axis is time, and the origin position is aligned with the upper diagram. The vertical axis represents the moving average value b of data at each sampling time in the upper stage. The moving average value was assumed for five data. In this case, if the raw data at the sampling time i is ai, the moving average value bi at the sampling time i can be calculated by b = (ai−4 + ai−3 + ai−2 + ai−1 + ai). That is, since the moving average value bi can be calculated as soon as the sampling data ai is acquired, real-time processing is possible. Note that the number of data used for the moving average need not be five.

  When a smooth pulsation waveform is obtained by the moving average method, the pulsation waveform is displayed on the display unit 60 in real time (S28). Thus, as shown in FIG. 1, the display unit 60 displays the pulsation waveform by the moving average method in real time, and the blood vessel about the pulsation waveform through the filter operation for each calculation cycle is slightly delayed. The pulse, maximum blood pressure, and minimum blood pressure are displayed as the pulse wave measurement results. The above procedure is repeated until a series of measurements is completed (S30).

  In the above, the pulsation waveform of the blood vessel is obtained using light. Thus, obtaining a pulsation waveform of a blood vessel accurately using a light emitting element and a light receiving element is equivalent to measuring physical property using light, but in order to detect a pulsating waveform with high precision, a light emitting element and a light receiving element are used. Therefore, it is necessary to accurately construct a physical property system using light for measuring the physical property of an object. Below, the structure of the physical property system which uses the light for measuring the physical property of a target object accurately is demonstrated. The following description is also a method for constructing a material property measurement system for light.

  FIG. 14 is a diagram illustrating the configuration of a material property measurement system 100 that uses light. In the following description, a material property measurement system using light is simply referred to as a material property measurement system unless otherwise specified. In the material property measurement system 100, a light emitting element 14, a light receiving element 16, an amplifier 32, and a phase shift circuit 34 are connected in a loop. Here, an object to be measured is disposed between the light emitting element 14 and the light receiving element 16, light is irradiated from the light emitting element 14 to the object, and reflected light from the object is received by the light receiving element. This content is the same as in FIG. 4, and when measuring the characteristics of a substance using light, the voltage signal output from the light receiving element 16 is fed back instead of detecting the change in the wavelength of the light. Thus, when a feedback loop is formed as a voltage signal input to the light emitting element 14, a change in the frequency of vibration of the voltage signal in the feedback loop is detected.

  In FIG. 14, when a voltage signal is input to the light emitting element 14, light is emitted, but the optical signal is delayed in time from the input voltage signal. This delay is caused by a capacitive component or the like as the structure of the light emitting element 14. That is, in the light emitting element 14, the emitted light signal as the output signal is delayed with respect to the voltage signal as the input signal, and a phase difference is generated in that sense. In FIG. 4, the delay is indicated by a time delay Δtd1.

  When the light emitting element 14 and the light receiving element 16 are disposed in close contact, the light emitted from the light emitting element 14 is received by the light receiving element 16 as it is. In the case of the specification of the light emitting element 14 described above, the distance between the light emitting element 14 and the light receiving element 16 can be up to 30 mm, but the amount of light received by the light receiving element 16 decreases as the distance increases. . In any case, when the light emitting element 14 and the light receiving element 16 are disposed at an appropriate distance, the light receiving element 16 can receive light from the light emitting element 14.

  When the light receiving element 16 receives light, a voltage signal is generated according to the intensity of the light. The voltage signal is delayed in time from the received optical signal. This delay is caused by a capacitance component or the like as the structure of the light receiving element 16, and is indicated as a rising switching speed and a falling switching speed in the above specifications. That is, in the light receiving element 16, the voltage signal as the output signal is delayed with respect to the optical signal as the input signal, and a phase difference is generated in that sense. In FIG. 4, the delay is indicated by a time delay Δtd2.

  Therefore, when the light emitting element 14 and the light receiving element 16 are combined, a voltage signal is input to the light emitting element 14, and light is emitted from there with a phase difference. The light receiving element 16 receives the light, and the phase difference is obtained therefrom. Therefore, a voltage signal is output. Thus, there is a time delay between the drive voltage signal of the light emitting element 14 and the detection voltage signal of the light receiving element, and a phase difference is caused in that sense. In the example of FIG. 4, a time delay of Δtd1 + Δtd2 occurs.

  Here, it is considered that the detection voltage signal of the light receiving element 16 is fed back to the light emitting element 14 as a drive voltage signal using an appropriate amplifier 32. In this case, a voltage signal oscillates in the feedback loop at a frequency at which the sum of the delay time in the light emitting element 14 and the delay time in the light receiving element 16 is exactly 180 degrees in phase difference. For example, if Δtd1 + Δtd2 that is the sum of delay times is 2.5 μs, self-oscillation occurs in the feedback loop at a frequency of 200 kHz with one period of 5 μs.

  The above example is a case where there is only a space between the light emitting element 14 and the light receiving element 16, but light from the light emitting element 14 is radiated to the measurement object, and reflected light from the measurement object is received as the light receiving element 16. Is received, a time delay is generated between the incident light and the reflected light based on the material property of the measurement object. In that sense, a phase difference occurs between the incident light and the reflected light. In FIG. 14, the blood vessel 8 is shown as the measurement object, and the delay is shown as the time delay ΔTd between the light emitted to the blood vessel 8 and the reflected light.

  Now, assuming that the measurement object is a blood vessel 8, when the light receiving element 16 receives the reflected light from the light emitting element 14 from the light emitting element 14, the light directly incident on the light receiving element 16 from the light emitting element 14 is received. As no influence, the self-excited oscillation in the feedback loop reflects the material characteristics of the blood vessel 8.

  That is, in the example of FIG. 14, the voltage signal is output in the feedback loop at a frequency at which the sum of the delay time Δtd1 in the light emitting element 14, the delay time Δtd2 in the light receiving element 16, and ΔTd is exactly 180 degrees in phase difference. Oscillates. In the above example, if Δtd1 + Δtd2 + ΔTd, which is the sum of delay times, is 2.55 μs, for example, self-oscillation occurs in the feedback loop at a frequency of 196 kHz with a period of 5.1 μs. When there is no blood vessel 8, since it oscillated at a frequency of 200 kHz, the material characteristic of the blood vessel 8 can be determined from the difference in oscillation frequency.

  As described above, when light enters the measurement object and the light is reflected from the object, a delay time ΔTd occurs between the incident light signal and the reflected light signal according to the physical properties of the measurement object. This delay time ΔTd is often caused by the difference in the amplitude of the optical signal rather than the optical signal itself being delayed by hitting the object. That is, there is almost no significant difference between the rising and falling characteristics of the reflected light depending on the object, and therefore the pulse width of the optical signal when the amplitude of the reflected light signal is small is the light when the amplitude of the reflected light signal is large. It becomes shorter than the pulse width of the signal. This is because the difference in the pulse width of the optical signal is observed as a delay time or a phase difference.

  For this reason, when the reflectance of the material is large and small, the pulse width of the former optical signal is longer and therefore ΔTd is smaller. Further, comparing the material having a large transmittance with a material having a small transmittance, the pulse width of the former optical signal is longer, and therefore ΔTd is smaller.

  As described above, the delay time ΔTd differs depending on the optical reflectance characteristics and the optical transmittance characteristics of the target substance. In addition to this, when the irradiation light is applied to the target object, the wavelength − The spectral characteristic which is the amplitude characteristic is modulated, and as a result, the magnitude of the reflected light may change. That is, since the incident light is modulated, the amount of light received by the light receiving element changes, thereby changing the pulse width of the optical signal and changing the time delay ΔTd.

  Therefore, when measuring the material properties of an object using light, there are two types based on the difference in optical reflectance or optical transmittance of the object and on the basis of the spectral modulation characteristics of the irradiation light applied to the object. There will be. Since the latter will eventually be detected by the change in the amount of received light, generally speaking, the change in the amount of received light that changes according to the physical properties of the object is defined as the time delay ΔTd, and the magnitude of the corresponding phase difference is set. It is converted into a frequency deviation by a phase shift circuit and measured as a material property.

  Thus, the principle of measuring the material property of an object using light is to measure the change in the amount of received light that changes depending on the physical properties of the object. The reason why the phase shift circuit is used is that the delay time ΔTd caused by the change in the amount of received light can be used as a phase difference, and the phase difference can be converted into a frequency change, which can greatly improve the measurement accuracy.

  As described above, the components of the change in the amount of received light include those based on the difference in optical reflectance or optical transmittance of the object and those based on the spectral modulation characteristics of the irradiation light applied to the object. As actual physical properties of the object, both components are often superimposed. In general, the difference in optical reflectance or optical transmittance of an object greatly affects the change in the amount of received light, whereas the spectral modulation characteristics of irradiated light hitting the object The base thing has little influence on the change of the amount of received light. In the following, first, a configuration of a material property measurement system capable of accurately measuring a difference in optical reflectance or optical transmittance of an object will be described, and then a material property measurement system capable of accurately measuring a difference in spectrum modulation property will be described. The configuration will be described.

  FIG. 15 is a diagram for explaining the construction procedure of the physical property measurement system 100. First, the wavelength of the light emitting element 14 and the wavelength of the light receiving element 16 are selected so as to be suitable for measurement of an object (S100). For example, each wavelength can be matched to the color of the object. As an example, when the blood color is related to the pulsation waveform of the blood vessel, the peak emission wavelength of the light emitting element 14 can be set to 940 nm, and the peak detection wavelength of the light receiving element 16 can be set to 720 nm. Moreover, when it is related to the spectral characteristics of glucose, such as a blood glucose level, the peak emission wavelength can be 1300 nm and the peak detection wavelength of the light receiving element 16 can be 1550 nm.

FIG. 16 is a diagram for explaining how the actual amount of light received by the light receiving element 16 depends on the light emitting characteristics of the light emitting element 14 and the light receiving characteristics of the light receiving element 16. Here, the horizontal axis indicates the wavelength, the vertical axis indicates the light intensity, and the wavelength-light intensity characteristic 102 of the light emitting element 14 having the peak emission wavelength λ ₁ and the wavelength-light intensity characteristic 104 of the light receiving element 16 having the peak detection wavelength λ ₂ are obtained. Each is shown. The light reception amount region 106 is where the wavelength-light emission intensity characteristic 102 and the wavelength-light reception intensity characteristic 104 overlap. The larger the area of the received light amount region 106, the larger the amount of light received by the light receiving element 16.

  Here, it is assumed that the light emitted from the light emitting element 14 only changes its amplitude and does not change the frequency even if it hits the object, so the light emitting element is considered without considering the object. Only the 14 wavelength-light emission intensity characteristics 102 and the wavelength-light reception intensity characteristic 104 of the light receiving element 16 are examined. When the object is actually irradiated with light from the light emitting element 14, the amplitude of the wavelength-light emission intensity characteristic 102 of the light emitting element 14 decreases. Therefore, by replacing the wavelength-light emission intensity characteristic 102 of the light-emitting element 14 in FIG. 16 with the wavelength-reflection intensity characteristic, the received light amount region 106 can be examined more accurately.

As described above, the wavelength of the light emitting element 14 and the wavelength of the light receiving element 16 are selected based on the color, spectral characteristics, etc. of the object as described above, so that the area of the received light amount region 106 is appropriately widened. In addition, it is preferable to superimpose the respective wavelength-light intensity characteristics. When you want to take wide detection wavelength width is to reduce the difference between the wavelength lambda ₁ of the light emitting element 14 and the wavelength lambda ₂ of the light-receiving element 16, on the contrary, when it is desired to narrow the detection wavelength width is the wavelength of the light emitting element 14 lambda It is preferable to increase the difference between ₁ and the wavelength λ ₂ of the light receiving element 16.

  Returning to FIG. 15 again, after the wavelength selection of the light emitting element 14 and the light receiving element 16 is performed, the initial oscillation state arrangement is set (S102). As described above, when the light emitting element 14, the light receiving element 16, the amplifier 32, and the phase shift circuit 34 are connected in a loop shape, even if there is no measurement object between the light emitting element 14 and the light receiving element 16, When light from the light emitting element 14 enters the light receiving element 16 appropriately, an electric signal is oscillated. If the oscillation that occurs in the absence of the object is called an initial oscillation state, this initial oscillation state is due to the delay time Δtd1 in the light emitting element 14 and the delay time Δtd2 in the light receiving element 16 as described above. is there. However, if the light emitting element 14 and the light receiving element 16 are not properly disposed, the oscillation becomes unstable, depending on the case, the oscillation is attenuated, and finally the oscillation is stopped.

  In order to properly maintain the initial oscillation state, it is necessary to appropriately superimpose the light emission directivity characteristic of the light emitting element 14 and the light detection directivity characteristic of the light receiving element 16. The arrangement relationship between the light emitting element 14 and the light receiving element 16 is, for example, convenient when the light emitting element 14 and the light receiving element 16 face each other when the optical transmittance characteristic of the object is used. When using the reflectance characteristic, it is convenient to arrange the light emitting element 14 and the light receiving element 16 on a single substrate.

FIG. 17 shows an example in which the light emitting element 14 and the light receiving element 16 are arranged facing each other so as to be convenient for using the optical transmittance characteristic of the object. Here, the optical axis that is the light emission center axis of the light emitting element 14 and the optical axis that is the light reception center axis of the light receiving element 16 are preferably aligned as the coaxial center axis 110. At this time, the emitted light from the light emitting element 14 can be appropriately received as the received light amount corresponding to the received light amount region described in FIG. As the distance L ₁ between the light emitting element 14 and the light receiving element 16 becomes longer, the distance from the light source in the light emission directivity characteristic becomes longer. ₁ ) ^Decreases in proportion to ^-3 . Therefore, L ₁ should be narrowed to such an extent that an object can be inserted therebetween.

FIG. 18 shows an example in which the light emitting element 14 and the light receiving element 16 are arranged on a single substrate so as to be convenient for using the optical transmittance characteristics of the object. Here, the light emission directivity characteristic 114 of the light emitting element 14 and the light reception directivity characteristic 116 of the light receiving element 16 are shown. By arranging the target object in a portion where these two directivity characteristics overlap, the light irradiated from the light emitting element 14 hits the target object, and the light reflected thereby can be received by the light receiving element 16. In that sense, a portion where these two directivity characteristics overlap can be referred to as a light receiving area 118. The position of the light receivable region 118 is determined by the light emission directivity characteristic 114 of the light emitting element 14, the light reception directivity characteristic 116 of the light receiving element 16, and the distance L ₂ between the light emitting element 14 and the light receiving element 16. The distance L ₂ between the substrate and the object is determined. As L ₂ becomes longer, the distance from the light source in the light emission directional characteristic becomes longer, so the amount of light received by the light receiving element 16 from the light emitting element 14 decreases almost in proportion to (L ₃ ) ⁻³ . Therefore, L ₃ is an object and the light emitting element 14, as the degree or not the light receiving element 16 are in contact, it is preferable as small as possible.

  Returning to FIG. 15 again, when an arrangement suitable for maintaining the initial oscillation state is set, the conditions of the light emission drive circuit and the light reception output circuit are set (S104). As described above, the physical property of an object is measured using light because the amount of received light varies depending on the physical property of the object as a difference in time delay ΔTd. Therefore, it is necessary to make a difference between the amount of received light in the initial oscillation state and the amount of received light when the object is disposed between the light emitting element 14 and the light receiving element 16. In other words, it is difficult for the output electric signal of the light receiving output circuit to be saturated. For example, if the light emitted from the light emitting element 14 is too strong and the amount of light received in the initial oscillation state is the same as the amount of light received when the object is placed between the light emitting element 14 and the light receiving element 16, it is difficult. . Therefore, irradiation in which no signal saturation occurs between the output electric signal under the initial oscillation state of the light receiving output circuit and the output electric signal when the object is disposed between the light emitting element 14 and the light receiving element 16. Driving conditions are set so as to be an optical signal.

  FIG. 19 is a diagram illustrating a state of the light emission drive circuit and the light reception output circuit. As a light emission driving circuit for the light emitting element 14, a light emitting element 14, a driving transistor 24, and a resistance element 27 are connected in series between + Vcc and ground, and a base that is a control terminal of the driving transistor 24 is connected to + Vcc and ground. A configuration is used in which the connection is made between the connection points of two resistance elements 25 and 26 connected in series. Here, by setting the values of the resistance elements 25, 26, and 27, the light emission intensity that is the magnitude of the irradiation light signal of the light emitting element 14 is determined. As the light receiving output circuit, a configuration in which the load resistor 22, the diode 23, and the light receiving element 16 are connected in series between + Vcc and -Vcc is used. The load resistor 22 is for converting the current of the light receiving element 16 into a voltage.

  Since the characteristics of the light emitting element 14 and the light receiving element 16 are set in S100, an object is arranged between the output electric signal under the initial oscillation state of the light receiving output circuit and the light emitting element 14 and the light receiving element 16. In order to obtain an irradiation light signal that does not cause a signal saturation state with the output electric signal at that time, the values of the resistance elements 25, 26, and 27 are appropriately set while observing the output electric signal of the light receiving output circuit. Will change.

20 and 21 are diagrams schematically illustrating the relationship between the amplitude of the irradiation light signal, the amplitude of the light reception signal, and the pulse width of the light reception signal. FIG. 20 shows a case where the light emission illuminance, which is the magnitude of the amplitude of the irradiation light signal 122, is appropriate. With respect to the respective light reception signals 124 for three different objects, the pulse widths T ₁ , T ₂ , T of the respective light reception signals. _Three differences can be clearly distinguished. Since the difference between the pulse widths T ₁ , T ₂ , T ₃ corresponds to the difference in the time delay ΔTd, in the case of FIG. 20, the difference in the time delay ΔTd due to the difference in the object, that is, the phase difference can be appropriately distinguished and detected. .

On the other hand, FIG. 21 shows a case where the light emission illuminance, which is the magnitude of the amplitude of the irradiation light signal 122, is inappropriately large, and the amplitudes of the respective light reception signals 124 for three different objects are close to saturation. Thus, the difference between the pulse widths T ₄ , T ₅ , and T ₆ of the respective light receiving signals can hardly be distinguished. Since the difference between the pulse widths T ₄ , T ₅ , and T ₆ corresponds to the difference in the time delay ΔTd, in the case of FIG. 21, the difference in the time delay ΔTd due to the difference in the object, that is, the phase difference is hardly distinguished. . The drive conditions of the light emission drive circuit described with reference to FIG. 19 are appropriately changed while experimentally changing the values of the resistance elements 25, 26, and 27 so as to be the example of FIG. It is necessary to set. Note that adjustment of the load resistor 22 of the light receiving output circuit is also effective in some cases.

  Returning to FIG. 15 again, when the condition setting of the light emission drive circuit and the light reception output circuit is completed, the operation center frequency of the phase shift circuit 34 is set (S106). As described above, the oscillation frequency in the initial oscillation state is based on the delay time Δtd1 in the light emitting element 14 and the delay time Δtd2 in the light receiving element 16 as described above. This frequency can be called the initial oscillation normal frequency. Here, when an object is disposed between the light emitting element 14 and the light receiving element 16, oscillation occurs based on the time delay ΔTd due to the physical properties of the object, the above Δtd1, and Δtd2. The oscillation frequency at this time can be called an object oscillation state frequency. In the physical property measurement system 100 using the phase shift circuit 34, the difference between the initial oscillation state frequency and the object oscillation state frequency is used.

  Therefore, the operation center frequency of the phase shift circuit 34 can be set based on the initial oscillation state frequency or the object oscillation state frequency. However, since the object oscillation state frequency cannot be determined from the beginning, the initial oscillation state frequency is set. It is preferable to set based on the frequency. Therefore, here, the operation center frequency of the phase shift circuit 34 is set based on the initial oscillation state frequency.

  FIG. 22 is a diagram for explaining how the operation center frequency of the phase shift circuit 34 is set. FIG. 22 is a gain / phase characteristic diagram 130 in which the horizontal axis represents frequency and the vertical axis represents gain and phase. Here, the gain characteristic 132 with respect to the frequency of the phase shift circuit 34 is a symmetrical so-called band-pass filter characteristic having a peak. The phase characteristic with respect to the frequency of the phase shift circuit 34 is a characteristic of phase inversion at the peak of the gain characteristic. The operation center frequency of the phase shift circuit 34 is a frequency at which this gain characteristic peaks. The gain characteristic and the phase characteristic of the phase shift circuit 34 can be variously set by changing the element constants constituting the phase shift circuit 34.

  In FIG. 22, the gain characteristic 136 is a characteristic when the light emitting element 14, the light receiving element 16, and the amplifier 32 are connected in a loop shape except for the phase shift circuit 34. That is, the gain characteristic of the phase shift circuit 34 is removed from the overall gain characteristic when the light emitting element 14, the light receiving element 16, the amplifier 32, and the phase shift circuit 34 in the initial oscillation state are connected in a loop. is there. Therefore, when the light emitting element 14, the light receiving element 16, the amplifier 32, and the phase shift circuit 34 in the initial oscillation state are connected in a loop, the oscillation state of the entire loop is the gain characteristic 136 and the phase shift circuit 34. This is indicated by an operating point 138 where the gain characteristics 132 intersect. That is, the frequency at the operating point 138 becomes the initial oscillation state frequency.

  As shown in FIG. 22, the operation center frequency of the phase shift circuit 34 is set at a predetermined frequency width separated from the initial oscillation state frequency. In the example of FIG. 22, the frequency of the operating point 138 is the initial oscillation state frequency, but a frequency higher than this by an appropriate frequency is the operating center frequency at which the peak is maximum in the gain characteristic 132 of the phase shift circuit 34. . The element constants constituting the phase shift circuit 34 are set so that the operation center frequency is obtained. Since the state of the operation center frequency of the phase shift circuit 34 is the resonance state of the phase shift circuit 34, in order to maintain the initial oscillation state stably, the difference between the initial oscillation state frequency and the operation center frequency of the phase shift circuit 34. It is desirable to take a large frequency width. Accordingly, the gain at the operating point 138 is lowered, and this must be taken into consideration.

  Returning to FIG. 15 again, when the setting of the operation center frequency of the phase shift circuit 34 is completed, the operation condition setting for the physical property measurement system 100 is completed (S108). Under this condition, the physical property measurement of the object is measured. Is performed (S110). Specifically, an object is arranged between the light emitting element 14 and the light receiving element 16, and the object oscillation state frequency, which is the oscillation frequency at that time, is detected, compared with the initial oscillation state frequency, and between them Frequency change is required. Then, the physical property value of the object is obtained using the conversion relationship of the frequency change-physical property value obtained separately from experiments or the like.

Up to now, the configuration of the material property measuring system 100 that can accurately measure the difference in optical reflectance or optical transmittance of the object has been described. Next, the configuration that can accurately measure the difference in spectral modulation property will be described. . FIG. 23 is a diagram illustrating the case of an object in which spectrum modulation characteristics occur. FIG. 23 is a diagram corresponding to FIG. 16, but here, the wavelength-luminescence intensity characteristic 102 of the light-emitting element 14 having the peak emission wavelength λ ₁ is irradiated to the object, whereby the wavelength-reflection light intensity characteristic is obtained. 103 is shown to modulate. By changing in this way, the received light amount region 107 changes from the case of FIG. Based on the change in the received light amount region, the spectral modulation characteristic of the object can be measured.

  Since the change in the light reception amount region 106 in FIG. 16 and the light reception amount region 107 in FIG. 23 is not so large, the time delay ΔTd due to this change is not so large. Therefore, the frequency change between the initial oscillation state frequency and the object oscillation state frequency is not so large. Therefore, in order to enlarge and measure this frequency change, the operation frequency of the phase shift circuit 34 is set so as to increase the gain. That is, the predetermined frequency width when the spectral characteristic of the irradiated light is modulated by the target is larger than the predetermined frequency width when the physical property of the target is the optical reflectance characteristic or the optical transmittance characteristic. Set the frequency width narrower.

  Referring to FIG. 22, in the case of the spectrum modulation characteristic, the characteristic when the light emitting element 14, the light receiving element 16, and the amplifier 32 are connected in a loop shape, excluding the phase shift circuit 34, is the gain characteristic 140. To do. The operation center frequency of the phase shift circuit 34 is set so that the operating point 142 has a large gain / frequency gradient of the gain characteristic of the phase shift circuit 34. Specifically, the frequency width between the frequency of the operating point 142 and the operating center frequency at which the gain of the phase shift circuit 34 reaches a peak is the frequency of the operating point 138 and the operating center frequency of the phase shift circuit 34. It is set to be narrower than the frequency width in between.

  The blood vessel pulse wave measurement system according to the present invention can be used to measure the state of blood flow flowing through a blood vessel, such as blood pressure measurement, using a blood vessel pulsation waveform.

  6 person to be measured, 8 blood vessel, 10 blood vessel pulse wave measurement system, 12 optical probe, 13 holding part, 14 light emitting element, 16 light receiving element, 18 circuit board, 20 optical probe circuit, 22 load resistance, 23 diode , 24 drive transistor, 25, 26, 27 resistance element, 30 pulsation waveform output unit, 32 amplifier, 34 phase shift circuit, 40 FV conversion unit, 42 A / D conversion unit, 50 arithmetic processing unit, 52 vascular pulse wave measurement calculation Module, 54 Frequency data acquisition module, 56 Floating median value setting processing module, 58 Noise removal processing module, 60 Display unit, 62 Pulsation waveform display after low-pass filter processing, 64 Pulsation waveform display after moving average method processing, 66 Blood vessel Pulse wave measurement value display, 100 physical property measurement system, 102 emission intensity characteristic, 103 reflected light intensity characteristic, 04 Light reception intensity characteristic, 106, 107 Light reception amount area, 114 Light emission directivity characteristic, 116 Light reception directivity characteristic, 118 Light reception possible area, 122 Irradiation light signal, 124 Light reception signal, 130 in / phase characteristic diagram, 132, 136, 140 Gain characteristic 138, 142 operating points.

Claims (7)

An optical probe having a light emitting element that emits light to the blood vessel through the skin, and a light receiving element that receives the reflected light from the blood vessel through the skin;
Phase shift that is connected in series with the amplifier to the optical probe and compensates for the phase difference by changing the frequency to zero when there is a phase difference between the input waveform to the light emitting element and the output waveform from the light receiving element. Circuit,
An output unit that outputs periodic time change data of a frequency whose phase difference is compensated to zero by a phase shift circuit as pulsation waveform data;
Based on the pulsation waveform data from the output unit, calculation means for performing calculation related to blood vessel pulse wave measurement in a calculation range between a predetermined calculation upper limit value and a calculation lower limit value;
Means for acquiring pulsation waveform data output from the output unit for a predetermined period, and executing a period data acquisition process for obtaining a median value and a maximum amplitude value of the acquired period data;
The maximum amplitude value is amplified so that the acquired maximum amplitude value becomes a predetermined ratio with respect to the calculation range, and the acquired median value is floatingly set to the median value of the calculation range regardless of its absolute value. Floating median value setting means for performing floating median value setting processing for converting the pulsation waveform data to be within the calculation range of the calculation means;
Every time the pulsation waveform data from the output unit fluctuates with time and the frequency data constituting the pulsation waveform data reaches the calculation upper limit value or the calculation lower limit value, the data acquisition process for the period is executed again, and based on the result Means for executing the floating median value setting process again;
A blood vessel pulse wave measurement system comprising: 1. The blood vessel pulse wave measurement system according to 1,
Filter processing means for performing low-pass filter arithmetic processing on the frequency data output from the output unit and supplying the low-pass filter arithmetic processing;
Display means for acquiring frequency data output from the output unit at each sampling timing, sequentially processing the acquired data by a moving average method, and displaying in real time as a smooth pulsation waveform;
A blood vessel pulse wave measurement system comprising: 1. The blood vessel pulse wave measurement system according to 1,
A blood vessel pulse wave measurement system comprising: FV conversion means for converting frequency data output from an output section into voltage data and supplying the voltage data as digital data to a calculation means. In the blood vessel pulse wave measurement system according to 3,
The floating median value setting means sets the data width, which is the difference between the maximum value and the minimum value of digital data for a predetermined period supplied by the FV conversion means, from 2/3 to 1/3 of the calculation range of the calculation means. A blood vessel pulse wave measurement system, wherein data bits are expanded so that the data width is between. 1. The blood vessel pulse wave measurement system according to 1,
The blood vessel pulse wave measurement system, wherein the calculation means calculates the blood pressure based on a relationship obtained in advance for the pulsation waveform and the blood pressure. For a light emitting element that irradiates an object with incident light, a light emission driving circuit that is driven under a predetermined driving condition;
About a light receiving element that receives light from an object corresponding to incident light, a light receiving output circuit that outputs an output electric signal under a predetermined output condition;
A light emitting element delay time between the light emitting element driving electrical signal and the irradiation light signal, which is connected in series with the amplifier between the output terminal of the light receiving element and the input terminal of the light emitting element, and is determined in advance by the device characteristics of the light emitting element, The light receiving element delay time between the light receiving light signal and the light receiving element output electrical signal determined in advance by the device characteristics of the element, and the object delay time between the irradiation light signal and the light receiving light signal generated by the physical property of the object A phase shift circuit that shifts the electrical signal phase difference to zero by changing the frequency for the determined electrical signal phase difference,
When no object is placed between the light emitting element and the light receiving element, the frequency at which the phase difference is compensated to zero by the phase shift circuit is set as the initial oscillation state frequency, and the object is placed between the light emitting element and the light receiving element. Sometimes, the frequency at which the phase difference is compensated to zero by the phase shift circuit is the object oscillation state frequency, and the physical property value of the object is calculated based on the frequency change between the initial oscillation state frequency and the object oscillation state frequency. Desired physical property value output means;
With
The light emission drive circuit
The drive conditions are set so that the irradiation light signal does not cause signal saturation between the output electrical signal under the initial oscillation state frequency of the light receiving output circuit and the output electrical signal under the object oscillation state frequency. ,
The phase shift circuit
A physical property characteristic measuring system using light, characterized in that a frequency separating a predetermined predetermined frequency width from an initial oscillation state frequency is set as an operation center frequency at which a gain is maximized. In the physical property measurement system using light according to claim 6,
The phase shift circuit
Predetermined frequency width when the spectral characteristic of the irradiated light is modulated by the object rather than the predetermined frequency width when the physical property of the object is an optical reflectance characteristic or an optical transmittance characteristic A physical property measurement system using light, characterized in that the angle is set narrow.

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