JPS61175531A - Saw power sensor - Google Patents

Abstract

PURPOSE:To facilitate digital measurement with a simplified mechanism, by providing an oscillator comprising a surface acoustic wave (SAW) delay line on a piezoelectric substrate to output a power inputted as variations in the frequency. CONSTITUTION:Interdigital transducers (IDT)2 and 3 for transmitting and receiving SAW and a heat generating body 4 are provided on the surface of a piezoelectric substrate 1 to form a SAW delay line element, to which an amplifier 5 is connected to construct a SAW transmitting circuit while it is connected to a frequency counter 6. Then, as power of light is inputted into the heat generating body 4 to generate heat, the temperature of the piezoelectric substrate 1 to change the delay time with a variation in the SAW propagation speed of the SAW delay line and the frequency of a self-oscillator with the center frequency of the SAW delay line as natural frequency. Detecting the frequency with a frequency counter 6 facilitates digital measurement of the magnitude of the power applied to the SAW delay line.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a power sensor used to detect or measure the power of light or a wide range of electric power, and particularly relates to a power sensor that is used to detect or measure the power of light, and in particular to a surface that propagates on the surface of a solid material. Acoustic wave (SAW: 5urfa
SA using ce Acoustic Wave)
This article relates to nine power sensors that apply the temperature-sensing function of the W device.

[Conventional technology]

Power sensors that detect electric power and light power include photodiodes and phototransistors that utilize the photoelectric effect of semiconductors, as well as thermistors and thermocouples that convert input power into a quantity of heat.
There is a thermal type sensor that converts the amount of heat into Ic, further converts the amount of heat into a resistance value and thermoelectromotive force, and detects the change. There are two types of thermal sensors: one in which the thermistor/thermocouple itself generates heat, and another in which a heating element is provided nearby and the amount of heat detected by the thermistor/thermocouple. An example of the description of the former thermocouple type power sensor is "Power detector for short millimeter wave band" (Ago Sugiura 2 Hiromichi Toda, Institute of Electronics and Communication Engineers Technical Research Report, VOL, 78. NO, 119 PAGE, 4)
5-51'78). This power sensor is a short millimeter wave band power detector in which a Bi-Sb thermocouple is formed on a polyimide substrate, and the thermocouple itself is used as a matching load.
It absorbs electricity and generates heat. These thermal type power sensors basically belong to temperature sensors, and are added with a function of converting electric power or optical power into heat quantity.

By the way, as an example of a method for detecting the entire temperature, SA
In a generator circuit using a W device, the state of the SAW propagation path is thermally distorted, and the SAW propagation path is propagated through the SAW propagation path5.
By changing the AWO propagation speed or propagation path length: changing the oscillation frequency specific to the oscillation circuit,
There is a SAW temperature sensor that detects the amount of heat received by the SAW device from the amount of change in frequency. This SAW temperature sensor is small, lightweight, highly accurate, and the SAW sensor part is easy to manufacture and has high reproducibility, so it is one of the sensors that are being put into practical use among the SAW sensors.

[Problem that the invention seeks to solve]

As mentioned above, thermistors, which are thermal power sensors,
A thermocouple converts input power into heat, and then changes the heat into resistance or thermoelectromotive force, and finally into voltage. Therefore, in order to make these conversions highly accurate, expensive differential amplifiers are required to accurately amplify the output voltage, and when performing measurements and system control using microcomputer technology, expensive A
/D converter was required. Under these circumstances, there is a strong need for a sensor that can output measured power as a frequency that can be digitally detected.

In addition, in terms of manufacturing, thermocouples require complicated processes such as evaporation, etching, and the need to make contacts with high precision using only two types of metals.

Furthermore, since it is difficult to vapor-deposit a thermistor material which is an oxide due to its low vapor pressure, a method has been adopted in which an oxidation treatment is performed after the metal of the thermistor material is vapor-deposited. Furthermore, the thermistor consists of multiple substances,
Moreover, a complicated process was required to correctly control the ratio of these components.

As explained above, conventional thermal power sensors are complicated to manufacture and the materials used are limited.
Problems remain in terms of cost, stability, reliability, and mass productivity.

Therefore, the present invention was made in view of the above circumstances, and its purpose is to construct an oscillation circuit using a SAW delay line that changes the delay time depending on the input power, and to simplify the mechanism. It is an object of the present invention to provide a power sensor that outputs an amount of change in frequency that is easy to manufacture and easy to measure digitally.

[Means for solving problems]

In this invention, a piezoelectric crystal having temperature characteristics is used as a substrate, and electrodes (also called interdigital electrodes or IDTs) for transmitting and receiving surface acoustic waves are disposed on the substrate.

IDT is Inter Digital Transdu
cer), two electrode holders through which the surface acoustic waves propagate, and a heating element that converts power input into heat between the transmitting electrode and the receiving electrode.
An oscillator using a W delay line is provided, and the oscillator outputs the input power as a frequency change amount.

〔Example〕

FIG. 1 shows a configuration diagram of an embodiment of the present invention. In this invention, as shown in the figure, 5AW is applied to the surface of the piezoelectric substrate 10.
Transmitting interdigital electrode (IDT) 2 for t-firing
and a reception interdigital electrode (ID) for receiving SAW.
T) 3 and a heating element 4 that converts input power into heat are provided to form a SAW delay line element. Note that the heating element may be placed in contact with or in close proximity to at least a portion of the piezoelectric substrate. One electrode of each IDT is all grounded, and a SAW is connected between the signal input side electrode of the transmitting IDT and the signal output side electrode of the receiving IDT.
An amplifier 5 constituting an oscillation circuit is connected. Then, an electrical closed loop circuit is formed by this amplifier and the transmitting and receiving IDTs 9, and self-oscillation is performed with the center frequency of the SAW delay line as the natural frequency. The SAW generated in the transmitting IDT due to this self-excited oscillation travels on the piezoelectric substrate and is received by the receiving IDT. When optical power is input to the heating element provided on the piezoelectric substrate to generate heat, the temperature of the piezoelectric substrate rises, the SAW propagation speed of the SAW delay line changes, and at the same time the distance between the IDTs increases due to thermal expansion. The delay time of the SAW delay line changes. Under this influence, the frequency of self-oscillation with the center frequency of the SAW delay line as its natural frequency changes. This frequency is the frequency color / 6
By detecting this, it is possible to detect the amount of strain on the surface of the piezoelectric substrate, that is, the amount of power applied to the SAW delay line.

Next, a means for improving the sensitivity of the SAW power sensor will be described. The piezoelectric substrate of the SAW delay line constituting the SAW power sensor has a large heat capacity. Therefore, it is possible to make the piezoelectric substrate thinner and thinner, but mechanical strength becomes a problem. To solve this problem, SAW of piezoelectric substrate
The back side of the propagation path may be etched to make the substrate thinner so that the transmitter and receiver IDTs are aligned vertically. An example of this is shown in FIG. The basic principle of this SAW power sensor is to change the SAW propagation state by applying thermal strain between the transmitting interdigital electrode IDT and the receiving interdigital electrode IDT, so the SAW propagation area can be made thinner. , reducing the heat capacity of the piezoelectric substrate. In addition to this, interdigital electrodes for transmission (more T) and interdigital electrodes for reception (IDT) are used.
) are arranged in the vertical direction of the piezoelectric substrate. The two improvements described above make it possible to improve not only the sensitivity but also the response speed.

Next, we will discuss the SAW power sensor that was actually prototyped. FIG. 3 shows a SAW delay line equipped with a heating resistor that constitutes an actually prototype SAW power sensor. This sensor is for power measurement, and uses a heating resistor 7 as a heating element, and electrodes 8 for power input are provided at both ends of the heating resistor. Figure 4 shows the experimental results.

In the figure, the vertical axis shows the amount of change in the oscillation frequency of the SAW power sensor, and the horizontal axis shows the power input to the heating resistor. results of the experiment,
It was found that in this SAW power sensor, the amount of change in oscillation frequency changes with good linearity with respect to input power. The correlation coefficient r was 0.99997.

〔Effect of the invention〕

As explained above, the SAW power sensor of the present invention is
Unlike conventional power sensors, which output the input power as a voltage, the sensor outputs the input power as a frequency change that can be easily measured digitally. For this reason, unlike power sensors using conventional voltage output types such as thermistors and thermocouples, simple waveform shaping does not require the use of expensive A/D converters during digital signal processing. Data can be processed using a combiator.

Since the power detection mechanism originally utilizes the temperature characteristics inherent in the piezoelectric substrate, it can be a highly reliable and highly sensitive power sensor. This point also has an advantageous effect in terms of manufacturing, such that the electrodes and the heating element can be formed using only two photomasks using photolithography technology, for example. This shows that it is possible to stably manufacture a power sensor and provide a reliable and inexpensive sensor.

Next, the application aspect will be explained. For example, a microwave band power sensor can be realized by forming a matched load on a piezoelectric substrate, absorbing microwaves to generate heat, and detecting the amount of change in frequency. In addition, in order to create an infrared sensor, which is a type of optical power sensor, an infrared absorber such as all black is provided on a piezoelectric substrate to absorb infrared rays, and the amount of change in frequency can be detected in the same way. good.

As described above, the power sensor of the present invention is a sensor that has a signal output method, reliability, stability, and a wide range of applications, and can be widely used in place of conventional power sensors. .

[Brief explanation of the drawing]

Fig. 1 shows the electric circuit configuration of the power sensor of the present invention, Fig. 2 shows an embodiment aimed at improving the sensitivity of the SAW power sensor, and Fig. 3 shows the actual prototype SAW power sensor. FIG. 4 is a diagram showing the SAW delay line that is constructed, and is a diagram showing the output results of an actually prototype SAW power centimeter. In the figure, 1 is a piezoelectric substrate, 2 is an interdigital electrode for transmission (ID
T), 3 is a receiving intersecting hole electrode (IDT). 4 is a heating element, 5 is an amplifier, and 6 is a frequency counter. 7 is a heating resistor, and 8 is an electrode. Patent Applicant Anritsu Electric Co., Ltd. Agent Patent Attorney Ryotabe Koike Once

Claims (2)

[Claims] (1) A piezoelectric substrate; A heating element that is provided on the surface of the piezoelectric substrate and generates heat by absorbing the power to be measured; A transmitter for emitting surface acoustic waves onto the surface of the piezoelectric substrate a SAW delay line oscillator including a surface acoustic wave delay line element having an electrode and a receiving electrode for receiving the surface acoustic wave; a frequency or a frequency of the SAW delay line oscillator generated by heat generation of the heating element; A SAW power sensor comprising a counting means for counting the amount of change in. (2) The SAW power sensor according to claim 1, wherein the heating element is arranged in contact with or in close proximity to at least a portion of the piezoelectric substrate.