JPS60122303A - Strain gauge - Google Patents

Abstract

PURPOSE:To attain size reduction and simplification of a sending circuit system, and to obtain the convenience of use by sticking a surface acoustic wave element which is formed by providing a comb-shaped electrode on a piezoelectric substrate on a metallic film formed on a body to be inspected, and connecting a transmitting circuit. CONSTITUTION:The surface acoustic wave (SAW) element 2 is stuck on the metallic film 1 formed on the body to be formed. The element 2 is formed by providing the comb-shaped electrode 4 on the surface of the piezoelectric substrate 3, and a surface wave generated on the surface of the substrate 3 with a signal inputted from an input terminal 5 is reflected successively by the comb- shaped electrode 4 to obtain an accompanying high-frequency output at an output terminal 6. The SAW element 2 is covered with a metallic can 10 with the buffer material 9 of the SAW element between; and a small-sized battery 11 as a power source and the transmitting circuit 12 which sends out the output of the element 2 are provided in the can, and an FM antenna 13 is provided externally. Consequently, the size reduction and simplification of the sending circuit are attained and the convenience of use is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain meter using a surface acoustic wave device (hereinafter abbreviated as SAW device).

Conventionally, various strain meters have been known, but generally several
Not only does it require a power source of about Hz, but the output is weak, so it is necessary to run shield wires around it.

The present invention aims to reduce the size of the SAW element by using the SAW element, and is structured so that the transmitting circuit system can be simplified. Also, the built-in battery allows it to operate for a long time, and the solar battery allows it to operate only when the electromotive force is generated. The purpose is to provide a strain meter that is easy to operate and use.

In the strain meter of the present invention, comb-shaped electrodes are installed on the surface of a piezoelectric substrate, and surface waves generated on the piezoelectric substrate by input signals to the electrodes are sequentially reflected by the comb-shaped electrodes, and the accompanying high frequency waves are generated. This surface acoustic wave element is attached to a metal film thin enough to cause distortion along with the test subject, and This is characterized in that a transmitting circuit using the surface acoustic wave element as a transmitting element is connected to the surface acoustic wave element.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In the strain meter shown in Figure 1, l is a thin metal film that adheres to the test object, and is generally 0. It has a thickness of about 01 to 0.1 mm, and is formed so as to be strained together with the test object to which it is adhered. As shown in FIG. 2, the SAW element 2 firmly attached to the metal film 1 generates a surface wave by installing a comb-shaped electrode 4 on the surface of a piezoelectric substrate 3, and has an input terminal 5. A surface wave generated on the surface of the piezoelectric substrate 3 due to a signal input from the piezoelectric substrate 3 propagates left and right, but is sequentially reflected by a large number of comb-shaped electrodes, and a corresponding high-frequency output is delivered to the output terminal 8. At this time, when the pitch of the comb-shaped electrodes 4 matches the half wavelength λ/2 of the surface wave, the wave is almost completely reflected,
Almost all output is output to output terminal 6. This SAW element is configured to have a transmitting frequency in the F'M broadcast wave band by using it as a transmitting element for the carrier frequency of the telemeter.

When a strain due to an external force is applied to such a SAW element 2 in a direction perpendicular to the comb-shaped electrodes 4 (in the direction of arrow A), the pitch changes accordingly, so that the series resonant frequency, parallel resonant frequency, The transmission frequency changes as the transmission characteristics change, so that the SAW element 2 can be operated as a strain sensor.

In the strain meter shown in FIG. 1, the SAW element 2 is covered with a metal surface 1o placed around a metal film 1 with a buffer material 8 made of silicon rubber or the like interposed therebetween, and a small battery is housed inside the metal surface 1o as a power source. A transmitting circuit 12 for transmitting the output of the SAW element 2 described in 11 and -G is provided, and the metal surface 1 thereof is provided.
FM antenna terminal 13 for bipedal transmission is exposed to the outside. The metal surface 1o also has the function of shielding the SAW element 2 and the like to reduce external influences.

The above power source includes a built-in battery 1 as shown in Figure 1.
1 can be used, but it is also possible to supply power from outside, and as shown in Figure 3, an appropriate number of solar cells 15 can be used.
．． +5. The power supply board 18 with... pasted thereon may be fixed on the metal surface 10 and irradiated with a strong light source, or a ferrite core with a wire wound inward to the metal may be installed to eliminate the electromagnetic field applied from the outside. It is also possible to generate electric power by In FIG. 3, reference numeral 17 indicates a direction mark indicating the direction of strain sensitivity.

In Figure 4, an external electromagnetic field 22 is applied to a ferrite core 21 with a winding as described above, but it is used not as a driving power source but to control the transmission of measurement data in a strain meter. This is an example of the circuit configuration in the case of . That is, the signal current induced in the winding by the external signal electromagnetic field 22 causes the MOS type FET to
23 is operated, thereby controlling on/off transmission of measurement data by the built-in battery 24.

Therefore, there is no waste in using the built-in battery 24, and it can be used for a long period of time. In the figure, 25 indicates a SAW element, and 26 indicates an oscillation circuit.

Further, FIG. 5 shows a specific example of the above-mentioned transmitting circuit 26, in which the SAW element is connected to the SAW element by an extremely simple configuration mainly consisting of one transistor 27, a mercury battery 28, a switch 29 that can be operated from the outside, etc. Transmission can be performed using SAW element 25 as a transmitting element of a carrier frequency, and by applying a stress corresponding to the strain of the subject to the SAW element 25, the transmitting frequency changes, so that the receiving device Data regarding body strain can be received.

FIGS. 6 and 7 show examples of how the strain meter is used. When discontinuously measuring strain by installing strain gauges at multiple locations on the rotating body 30 as shown in FIG. 6, the strain gauge 31 shown in FIG. Only the solar cells 32 in the meter are arranged and fixed on the surface of the rotating body 30 by a power supply plate 33, and a powerful light source 34 is arranged near the rotating body 30 so as to emit light to these solar cells. The light source 34 may sequentially emit light to the solar cells 32 that come to a position opposite the light source 34 as the light source 30 rotates. As a result, an electromotive force is generated only in the solar cell emitted from the light source 34, and an output is generated only in the strain meter 31 to which the solar cell is connected. When each strain gauge 31 is operated continuously, the solar cell 32 of each strain gauge may be configured to be operated by surrounding illumination light.

In addition, when measuring the strain discontinuously at multiple locations in a large structure 40 as shown in FIG. 7, the strain gauges 41 shown in FIG. It is also possible to emit light using a projector brought along while traveling and to measure the output of the strain meter 41.

Note that when the number of strain meters used at the same time is small, data from each strain meter can be identified and received by transmitting data with different transmission frequencies.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a strain meter according to the present invention, FIG. 2 is an enlarged configuration diagram of a SAW element, FIG. 3 is a perspective view of another embodiment of the present invention, and FIGS. 4 and 5 6 is a circuit configuration diagram of the strain meter and oscillation circuit of the present invention, and FIGS. 6 and 7 are explanatory diagrams showing usage examples of the strain meter. 1.Metal film, 2.25.Fist SAW element, 3φ.Piezoelectric substrate, 4.-comb-shaped electrode, 5..input terminal, 6..
Output terminal, 12.2Ei oscillation circuit, 31.41...distortion meter. Figure 4

Claims (1)

[Claims] 16 Comb-shaped electrodes are installed on the surface of the piezoelectric substrate, so that the surface waves generated on the piezoelectric substrate by the input signal to the electrodes are sequentially reflected by the comb-shaped electrodes, and the accompanying high-frequency output is obtained from the output terminal. This surface acoustic wave element is attached to a test object and attached to a metal film thin enough to cause distortion along with the test object, and the surface acoustic wave element is used as a transmitting element. A strain meter characterized by having a transmitting circuit connected thereto.