JPS61258126A - Saw power sensor - Google Patents

Abstract

PURPOSE:To reduce the deterioration of resolution and the variation of an oscillation frequency, which are caused by the variation of an external temperature, by constituting surface acoustic wave delay lines in the same structure on a piezoelectric substrate, and providing an oscillating circuit for measurement and reference so that a beat of two oscillating signals is outputted. CONSTITUTION:A power sensor is provided with transmitting use IDT electrodes (interdigital type electrodes) 2a, 2b for emitting an SAW (surface acoustic wave), which is provided on the same piezoelectric substrate 1, receiving use IDT electrodes 3a, 3b for receiving the SAW which is emitted from the respective IDT electrodes, and an SAW delay line 5 formed by heating elements 4a, 4b, which is provided on the respective SAW propagation paths. Also, this sensor is provided with amplifiers 6a, 6b for constituting an oscillating circuit, a power input terminal 7, an oscillation frequency adjusting input terminal 8, a mixer 9 for taking a beat of an oscillating signal of two oscillating circuits, and a detecting circuit 10 for fetching only an envelope of an output signal of this mixer. According to such constitution, a sensor which is scarcely influenced by a variation of an external temperature, and has a better linearity is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a power sensor used for rounding to detect or measure the power of light, electricity, etc. Wave (SAW: 5u
The present invention relates to a power sensor that applies the temperature sensing function of a SAW delay line using rface acoustic wave.

[Conventional technology]

Power sensors that detect the power of electric power and light include photodiodes and phototransistors that utilize the photoelectric effect of semiconductors, thermal sensors that output power from thermistors, and thermocouples.

There are two types of thermal sensors: one in which the thermistor or thermocouple itself generates heat, and the other in which a heating element is provided nearby and the amount of heat generated from the heating element is detected by the thermistor or thermocouple.

In addition, a SAW power sensor using a SAW delay line (% application 1452/1986) that belongs to this technology
No. 3, Japanese Patent Application No. 60-049289, filed by the same applicant and same inventor). These SAW power sensors apply SAW temperature sensors to SA including delay lines.
W delay line oscillator, SA in the excavation circuit of this oscillator
It is possible to thermally distort the state of the W propagation path and cause a change in the 5AWO propagation velocity or the SAW propagation path length9.
The specific oscillation frequency t of the oscillation circuit is changed, and the power received by the heating element is detected from the amount of change. Note that these SAW power sensors are small, light, and highly accurate, and have the characteristics that the SAW sensor section is easy to manufacture and has high reproducibility. In addition, since it outputs a signal as a frequency change that can be easily measured digitally, it has the feature of being immediately compatible with measurement and process control using a microcomputer.

[Problem that the invention seeks to solve]

SAW sensors are not limited to power sensors; most of them are SAW sensors.
A state in which a closed circuit that constitutes an AW oscillation circuit and is a typical device of this oscillation circuit, and that spontaneously emits energy or transforms the emitted energy of the object to be measured into other forms, oscillates steadily at its natural frequency. The 44A substrate used to make the 8-pole sensor has a temperature coefficient that is unique to the substrate, and when constructing a SAW power sensor, a material with a large temperature coefficient is used for the substrate to improve sensitivity. However, this causes the problem that the oscillator becomes sensitive to ambient temperature and the natural oscillation frequency of the oscillator fluctuates. In order to make the sensor more sensitive, it is necessary to simultaneously compensate for fluctuations in the oscillation frequency. Furthermore, in order to use the SAW sensor more practically, it is necessary to realize frequency control and zero adjustment of the output frequency.

Conventional SAW power sensors are constructed without considering compensation for ambient temperature, changes over time, etc., and do not have oscillation frequency control functions, such as a zero adjustment function when the input power is zero. Problems remained in terms of practical application.

[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 the nasal pressure are disposed on the substrate.

IDT is Inter Digital Transdu
2
An oscillator using a SAW delay line having a heating element that converts power input into heat between two electrodes, that is, a transmitting electrode and a receiving electrode, is provided, and this oscillator converts the input power into a change in frequency. Two output oscillators are prepared, the two structures are substantially the same or symmetrical (congruent), and the frequencies of both oscillators are mixed to detect the beat frequency. That is, in order to compensate for the temperature characteristics, a SAW delay line having two propagation paths is used, two oscillation circuits are configured for each delay line, and the output signals of the two oscillators are By detecting beats, it is possible to compensate for sensor fluctuations due to external temperature fluctuations. According to such a configuration, it is also possible to compensate for changes in the sensor over time.

On the other hand, power can also be supplied to the heating element installed in the delay line of the reference oscillation circuit, and this heating element is heated to change the oscillation frequency of the reference oscillation circuit, resulting in a reduction in the beat frequency. Adjustable.

[For production]

With the configuration described above, that is, the configuration in which two congruent structures are formed on the same substrate and the beat frequency is detected, the SAW power sensor of the present invention is less susceptible to external temperature fluctuations and has better linearity. Become a sensor. Moreover, changes over time caused by deterioration or deterioration of the delay lines and electrodes that constitute the SAW power sensor can be compensated for by using a differential system. Furthermore, adjustment of the output signal frequency and zero adjustment can be freely performed by inputting electric power to the heating element of the reference oscillation circuit.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of two ゛≠SAW delay lines used in the present invention. A transmitting IDT electrode 2 for emitting a message on one piezoelectric substrate 1
a, 2b, and receiving IDT electrodes for receiving the Loutai Lun i-han emitted from the respective transmitting IDTs: 3m, 3
In order to prevent the radio waves emitted from each transmitting IDT electrode from being reflected back to each transmitting IDT electrode in the same phase, the antenna is folded back diagonally to the propagation direction of the cloud. The system was set up as an external facility, and the structure was constructed using external human resources. As shown, the shapes of the two independent SAW delay lines are substantially congruent (identical or symmetrical) to each other.

FIG. 2 is a diagram showing the configuration of an embodiment of the present invention. Two transmitting IDT electrodes are provided on the same piezoelectric substrate, and
The SAW is equipped with two T-electrodes for receiving AIW signals emitted from each IDT electrode, and a heating element is installed in each -11 frame propagation path.
A delay line 5 (same as the one in FIG. 1), an amplifier 6a forming an oscillation circuit, an amplifier 6b forming an oscillation circuit, a power input terminal 7, an oscillation frequency adjustment input terminal 8, and two oscillation circuits. a mixer 9 for removing the beat of the oscillation signal;
Only the envelope of the output signal of this mixer is extracted and output. One electrode of all IDT electrodes and one end of the heating element are connected to ground potential. Further, the oscillation frequency adjustment input terminal is connected to the ground potential when no power is input. According to the above configuration, the oscillation circuit for translation measurement i
When the power to be measured is input, the SAW delay line's ! due to heat generation of the resistor due to the power! The propagation speed changes and the natural oscillation frequency of the oscillation circuit changes.

However, at the same time, it also responds sensitively to changes in external temperature.
This causes deterioration of sensor sensitivity. Since this change in external temperature has a similar effect on the delay line of the reference oscillation circuit, the natural oscillation frequency of the reference oscillation circuit also changes. Since this change is caused only by a change in external temperature, it can be used as a reference signal for compensating for temperature changes. Fluctuations in the SAW power sensor can be compensated for.

FIG. 3 shows an embodiment of the circuit in the sensor of the present invention. In order to suppress fluctuations in oscillation frequency due to fluctuations in power supply voltage, a constant voltage source was used for the measurement and reference oscillation circuits. Each oscillation circuit for measurement and reference uses a two-stage amplifier and SA.
It consists of a W delay line. In order to extract the signals of each oscillator, a one-stage transistor output buffer is provided individually. The mixer for the two oscillation signals is composed of a one-stage amplifier, and outputs a signal that is a mixture of the signals of the measurement and reference oscillation circuits.

FIG. 4 is a waveform showing the actual output signal from this circuit. (,) are the output signals of the measurement oscillation circuit, and (b) are the output signals of the reference oscillation circuit. These two signals are introduced into a mixer, which outputs a beat signal (c). When this output signal is output through a detection circuit, it becomes a signal with only a beat envelope as shown in (d).

FIG. 5 is a diagram showing the characteristics of a SAW power sensor constructed using the above circuit. The horizontal axis represents the power value of the signal under measurement, and the vertical axis represents the amount of change in the oscillation frequency of the beat signal with respect to this input. DC power was used as the signal to be measured. The oscillation frequency of the beat changes linearly with respect to the input power. The correlation coefficient of this straight line was r=0.99997.

As other embodiments, it is also practical to provide the heating elements 4a and 4b as black bodies that absorb light and generate heat, or to use only one of them as the black body and the other as an electric resistance heating element.

〔Effect of the invention〕

As described above, the SAW power sensor of the present invention has SAW delay lines arranged adjacently with the same structure on the same piezoelectric substrate, includes measurement and reference oscillation circuits, and generates two oscillation signals. In order to output a beat of
It is possible to reduce resolution degradation due to external temperature fluctuations, which is a problem with power sensors using W delay lines, and fluctuations in oscillation frequency caused by changes in SAW delay lines over time.

Furthermore, frequency control such as setting the output signal frequency and zero adjustment can be easily performed by inputting power to the heating element of the reference oscillation circuit, making the sensor highly practical.

As a result, the SAW power sensor of the present invention has stability, linearity, and high sensitivity. Furthermore, since the output signal is a controllable frequency signal, it can be easily adapted to a digital measurement system by shaping the waveform. It has high industrial value as it can be used directly.

[Brief explanation of the drawing]

FIG. 1 shows the entire configuration of the SAW power sensor of the present invention.
FIG. 3 is a diagram showing an example of a W delay line. FIG. 2 is a diagram showing an embodiment of the SAW power station of the present invention. FIG. 3 is a diagram showing an embodiment of the circuit of the SAW power sensor of the present invention. FIG. 4 is a diagram showing an output waveform of an embodiment of the SAW power sensor circuit of the present invention. FIG. 5 is a diagram showing power versus frequency variation in an embodiment of the SAW power sensor circuit of the present invention. In the figure, 1 is a piezoelectric substrate, 2a is a transmitting electrode, 2b
is a transmitting electrode, 3a is a receiving electrode, 3b is a receiving electrode,
4a is a heating element, 4b is a heating element, 5 is a SAW delay line, 6a
6b is an amplifier, 7 is a power input terminal, 8 is an oscillation frequency adjustment input terminal, 9 is a mixer, and 10 is a detection circuit. Patent applicant: Anritsu Electric Co., Ltd. Agent: Patent attorney: Ryuta Koike
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Claims (1)

[Claims] A piezoelectric substrate; a first heating element provided on the surface of the piezoelectric substrate and generating heat by absorbing a first power; and the piezoelectric substrate heated by the first heating element. a first transmitting electrode for emitting a first surface acoustic wave onto the surface of the first surface acoustic wave; and a first receiving electrode for receiving the emitted first surface acoustic wave. a surface acoustic wave delay line; a first oscillator including the first surface acoustic wave delay line; a second heating element provided on the surface of the piezoelectric substrate and generating heat by absorbing second power; a second transmitting electrode for emitting a second surface acoustic wave to the surface of the piezoelectric substrate heated by the second heating element; and a second transmitting electrode for receiving the emitted second surface acoustic wave. a second receiving electrode; a second surface acoustic wave delay line adjacent to and having a congruent shape with the first surface acoustic wave delay line; A SAW power sensor comprising: a second oscillator; a mixer that mixes the output signals of the first oscillator and the second oscillator and outputs a beat of a frequency corresponding to the power to be measured.