JPH0476420B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power sensor used to detect or measure optical power or a wide range of electric power, and in particular relates to a power sensor used to detect or measure the power of light or a wide range of electric power, and in particular, it relates to a power sensor that is used to detect or measure the power of light or a wide range of electric power. Using waves (SAW: Surface Acoustic Wave)
This article relates to a power sensor that applies the temperature sensing function of a SAW delay line.

[Conventional technology]

Power sensors that detect electric power and optical power include photodiodes and phototransistors that utilize the photoelectric effect of semiconductors, as well as thermistors and thermocouples that convert input power into heat, and then convert the heat into resistance and heat. There are thermal sensors that detect changes in electromotive force.

These thermal sensors include a type in which the thermistor/thermocouple itself generates heat, and a type in which a heating element is provided nearby and the amount of heat generated from the heating element is detected by the thermistor/thermocouple. In addition, a SAW power sensor using a SAW delay line that belongs to this technology (Japanese Patent Application No. 14523/1983, filed by the same applicant)
by the same inventor).

This SAW power sensor is an application of the SAW temperature sensor, and its main component is a SAW delay line oscillator that includes a heating element and a surface acoustic wave delay line element.
By thermally distorting the state of the propagation path, the SAW propagation speed,
Alternatively, the specific oscillation frequency of the oscillation circuit is changed by causing a change in the SAW propagation path length, and the power received by the heating element is detected from the amount of change.

Furthermore, this SAW power sensor is small and lightweight.
It has the characteristics of high precision, easy manufacture of the SAW sensor section, and high reproducibility. In addition, since the signal is output as a frequency change that can be easily measured digitally, it has the feature of being able to be easily adapted to measurement and process control using a microcomputer.

[Problem that the invention seeks to solve]

The SAW delay line that constitutes the SAW power sensor described above has a structure in which a heating element is provided on a piezoelectric substrate. This heating element may be placed anywhere on the piezoelectric substrate, but considering the sensitivity of the power sensor, it should be placed between the transmitting interdigital electrode and the receiving interdigital electrode. , it is best to install it at a location where surface acoustic waves propagate.

However, when the end face of the heating element is provided parallel to the transmitting interdigital electrode, the surface acoustic wave (SAW) is reflected from the end face of the heating element and reaches the transmitting interdigital electrode in the same phase. It turns out. This causes ripples in the passband of the SAW delay line,
At the same time, group delay distortion also occurs. As a result, when an oscillator is configured to form a power sensor, the linearity of the sensor deteriorates.

In addition, when it is necessary to increase the resistance value of the heating element when adjusting the resistance value, the first
As shown in the figure and FIG. 2, the heating element 4 is elongated and has a pattern that is folded back on the propagation path of the surface acoustic wave. However, in this case, when the heating element is folded back perpendicularly to the propagation direction of the surface acoustic waves as shown in FIG. 2 was reflected in the same phase, causing ripples in the passband and group delay distortion. Furthermore, as shown in FIG. 2, when the heating element 4 is folded back in parallel to the propagation direction of the surface acoustic wave, the distribution of the heating element 4 becomes uneven on the propagation path of the surface acoustic wave. This results in a wave propagation velocity, making it difficult to construct an oscillator.

Furthermore, in addition to this, if the center frequency of the SAW delay line is increased and a SAW oscillator is configured to create a power sensor, when compared with a power sensor configured with a lower frequency SAW delay line, the Although the rate of change is the same, the amount of change is larger. Therefore, the resolution of the sensor is improved. However, as the frequency increases, electrical signals instead of surface acoustic waves begin to flow between the transmitting interdigital electrode 2 and the receiving interdigital electrode 3.
The SAW delay line no longer exhibits its original frequency characteristics.
To prevent this, it is necessary to provide a shield electrode between the transmitting interdigital electrode 2 and the receiving interdigital electrode 3. However, since the shield electrode has a heat capacity, the amount of heat generated in the heating element 4 is absorbed,
Problems such as a decrease in sensor sensitivity occurred.

As explained above, conventional SAW power sensors are installed without considering the shape of the heating element, and the influence of the heating element on the linearity of the sensor has not been considered. Furthermore, if the oscillation frequency is increased in order to improve the sensor resolution, a shield electrode is required, and the sensitivity of the sensor is reduced due to the heat capacity of the shield electrode.

This invention was made in view of the above-mentioned circumstances, and the shape of the heating element improves the linearity of the sensor, and the heating element itself has a shielding effect.
The purpose is to improve the resolution of the sensor by increasing the oscillation frequency without reducing the sensitivity of the sensor.

[Means for solving problems]

In this invention, a piezoelectric crystal with temperature characteristics is used as a substrate, and interdigital electrodes (referred to as IDT: Inter-Digital Transducer) for transmitting and receiving surface acoustic waves are provided on this substrate. It has a shape that blocks the path of the surface acoustic wave between the two interdigital electrodes that propagate, and does not cause reflection of the surface acoustic wave in the same phase to the transmitting interdigital electrode. SAW with heating elements distributed to generate heat evenly in the propagation direction
An oscillator is constructed with a delay line, and the input power is output as a change in the oscillation frequency of the oscillator.

In addition, when increasing the oscillation frequency to improve the resolution of the sensor in power measurement,
Place the heating element under measurement so that electrical signals do not flow directly between the transmitting interdigital electrode (hereinafter also referred to as the transmitting electrode) and the receiving interdigital electrode (hereinafter also referred to as the receiving electrode). The power input terminal (hot side) is folded back to the left and right, and current flows in two directions, left and right.The heating element divided into left and right sides is connected to the other power input terminal to be measured (ground side).
Connect to.

Using this method, the outermost part of the heating element divided into left and right sides is shorter in length from the ground side input terminal than the high potential side, so it can be made to have almost the same potential as the ground potential, and the shield It can have an effect.

〔Example〕

FIG. 3 shows a configuration diagram of an embodiment of the present invention.

A transmission interdigital electrode 2 for emitting surface acoustic waves (SAW) onto the surface of the piezoelectric substrate 1, and a SAW
In order to prevent the receiving interdigital electrode 3 for receiving and the surface acoustic waves emitted from the transmitting interdigital electrode 2 from being reflected to the transmitting interdigital electrode 2 in the same phase, A SAW delay line element is formed by providing a heating element 4 that is folded back obliquely to the propagation direction of the surface acoustic wave and converts power input from the outside into heat.

The electrode on one side of each interdigital electrode described above is
All are grounded, and interdigital electrodes for transmission 2
An amplifier 5 constituting a surface acoustic wave delay line oscillator is connected between the signal input side electrode of the receiving interdigital electrode 3 and the signal output side electrode of the receiving interdigital electrode 3. An electrical loop circuit is created by this amplifier 5, the transmitting interdigital electrode 2 and the receiving interdigital electrode 3,
Self-oscillation is generated with the center frequency of the surface acoustic wave delay line as the natural vibration. The surface acoustic wave generated in the transmitting interdigital electrode 2 due to this self-excited oscillation travels on the piezoelectric substrate 1, and a part of it is reflected by the heating element 4 and reaches the transmitting interdigital electrode 2. The waves are reflected again by the transmitting interdigital electrode 2, but since the phases are not aligned, ripples cannot be utilized in the passband of the surface acoustic wave and no group delay distortion occurs. The waves that are not reflected by the heating element 4 are received by the receiving interdigital electrode 3.

At this time, since the heating elements 4 are evenly distributed in the propagation direction of the surface acoustic waves, the surface acoustic waves received by the receiving interdigital electrode 3 have the same phase. When power is input to the heating element 4 provided on the piezoelectric substrate 1 to generate heat, the temperature of the piezoelectric substrate 1 rises.
The surface acoustic wave velocity of the SAW delay line changes.

Furthermore, the distance between the transmitting interdigital electrodes 2 and the receiving interdigital electrodes 3 changes due to thermal expansion,
The delay time of the SAW delay line changes.

In response to this change, the frequency of self-oscillation with the center frequency of the SAW delay line as its natural frequency changes.

If this vibration frequency (frequency) or its variation is detected by the frequency counter 6, the piezoelectric substrate 1
The amount of distortion, that is, the amount of power applied to the SAW delay line, can be detected.

Next, an embodiment will be described in which a heating element has a shielding effect in a power sensor that measures power using an input terminal.

In order to improve the resolution of a SAW power sensor, it is necessary to increase the natural frequency when configuring the oscillator.

This is because as the oscillation frequency of the power sensor increases, the amount of frequency change increases accordingly. However, when the oscillation frequency of the sensor is increased, a phenomenon occurs in which electrical signals are directly transmitted on the surface of the piezoelectric substrate from the transmitting interdigital electrode to the receiving interdigital electrode, and this tendency becomes more pronounced as the center frequency becomes higher. Therefore, the frequency selectivity of the SAW delay line is lost, and the oscillator cannot oscillate at the center frequency of the SAW delay line. To prevent this phenomenon, a shield electrode can be provided on the surface of the piezoelectric substrate, but since this SAW power sensor is a mechanism that detects input power by adding heat to the SAW propagation path, heat is generated due to the heat capacity of the shield electrode. The amount of heat generated by the body is absorbed, reducing the sensitivity of the sensor. Therefore, the heating element should have a shielding effect.

FIG. 4 shows an embodiment of a sensor equipped with a heating element having this shielding effect.

A transmitting interdigital electrode 2 and a receiving interdigital electrode 3 are provided on the surface of a piezoelectric substrate 1.

A heating element 4 is provided at a portion where surface acoustic waves propagate between these two interdigital electrodes. This heating element 4 is connected to an input electrode 7 for the power to be measured, is bent left and right to have the same length, and is connected to a ground electrode 8.

When the heating element is shaped like this, the outermost part of the left and right heating element, that is, the part adjacent to the transmitting interdigital electrode and the receiving interdigital electrode, has a short length from the grounding electrode, so the voltage is low. When added, the potential can be set to approximately the ground potential, making it possible to create a heating element that also has a shielding effect.

〔Effect of the invention〕

As explained above, the power sensor of the present invention
Reflection of the surface wave by the end face of the heating element on the SAW delay line The heating element is placed diagonally so that it does not occur in the same phase at the transmitting interdigital electrode.
Ripples in the passband of the SAW delay line and group delay distortion, which were problems with SAW power sensors, have been reduced.
The linearity of the sensor when configured as a SAW power sensor can be improved.

In addition, since the heating element has a structure that has a shielding effect, it is possible to omit the shield electrode that was previously required when increasing the oscillation frequency to improve sensitivity. It could have been prevented.

As described above, the SAW power sensor of the present invention is reliable, stable, and highly sensitive, and can be widely used industrially in place of conventional SAW power sensors.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the heating element folded back parallel to the transmitting interdigital electrode when adjusting the resistance value of the heating element. FIG. 2 is a diagram showing the heating element folded back perpendicularly to the transmitting interdigital electrode when adjusting the resistance value of the heating element. Figure 3 shows
FIG. 2 is a configuration diagram of an electric circuit of a power sensor of the present invention. Figure 4 shows a heating element with a shielding effect.
FIG. 3 is a diagram showing a SAW delay line. In the figure, 1 is a piezoelectric substrate, 2 is a transmitting interdigital electrode (transmitting electrode), 3 is a receiving interdigital electrode (receiving electrode), 4 is a heating element, 5 is an amplifier, and 6
is a frequency counter, 7 is an input electrode, and 8 is a ground electrode.

Claims (1)

[Claims] 1. A piezoelectric substrate, a transmitting electrode provided on the surface of the piezoelectric substrate for emitting surface acoustic waves,
a surface acoustic wave delay line element comprising a receiving electrode for receiving the surface acoustic waves emitted from the transmitting electrode; It blocks the path of surface acoustic waves and is evenly distributed over the entire wavefront of surface acoustic waves.
and a heating element that is provided on the piezoelectric substrate and has a pattern that generates reflected waves with out-of-phase toward the transmitting electrode, and that absorbs the power to be measured and generates heat; the surface acoustic wave delay line; a surface acoustic wave delay line oscillator including an element; and a counting means for counting the frequency or the amount of change in frequency of the surface acoustic wave delay line oscillator caused by heat generation of the heating element.
SAW power sensor. 2. The heating element according to claim 1, wherein the heating element has a pattern such that the side connected to the ground potential surrounds the other side.
SAW power sensor.