JPS6396520A - Acoustic sensor - Google Patents

Abstract

PURPOSE:To make it unnecessary to provide a metallic lead wire on a detecting part, by measuring an intensity variation of reflected light beams which are reflected by a light reflecting part vibrated by sound and return to an optical fiber, and detecting a vibration of the light reflecting part. CONSTITUTION:Light beams which have been emitted from a light source 5 pass through an optical fiber and reach a directional coupler 4, and also, pass through the inside of an optical fiber 1 and emitted as parallel light beams from a focusing lens 2 being its end face. The emitted light beams are reflected in accordance with a shape of a light reflecting part 3, pass through the focusing lens 2 and returned to the inside of the optical fiber 1 again. On the contrary of the foregoing, light beams transmitted in the reverse direction in the optical fiber 1 are sent to a photodetecting part 7 side by the directional coupler 4. In the photodetecting part 7, an intensity of the reflected light beams are measured. The intensity of this reflected light beams are sent as an electric signal to a detecting circuit 6, compared with the intensity of the emitted light beams which have been sent from the light source 5, and a vibrating state of the light reflecting part 3 is detected.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an acoustic sensor.

[Prior Art] Conventionally, a so-called microphone has been used as an acoustic attenuator, and the microphone uses a piezoelectric type or
It is converted into an electrical signal using a conversion method such as an electric type or an electrostatic type.

[Problems to be solved by the invention] However, since the microphone detects and transmits the vibration of the diaphragm as an electrical signal as described above, the M
It has the disadvantage of being susceptible to interference such as magnetic induction. For this reason, there was a problem that it could not be used near high voltage equipment or the like.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and to provide a sensor that can detect sound without being affected by electromagnetic induction.

Means for Solving Problems] The acoustic sensor of the present invention includes a light reflecting section that vibrates due to the sound to be detected, and an optical fiber that emits light from an end face of the light reflecting section. Vibrations in the light reflecting section are detected by changes in the intensity of the reflected light that is reflected and returns to the optical fiber.

[Function] In the acoustic sensor of the present invention, the light from the end face of the optical fiber is emitted to the light reflecting part, and the intensity change of the reflected light that is reflected by the light reflecting part and returned to the optical fiber is measured. The vibration of the light reflecting section is detected. Since the vibration due to p2 is thus detected as an optical signal and transmitted as an optical signal, it is not affected by electromagnetic induction.

[Embodiment] FIG. 1 is a schematic diagram showing an embodiment of the present invention. A focusing lens 2 is provided at one end of the optical fiber 1, and the other end is joined to a directional coupler 4. A light source 5 and a light receiving section 7 are respectively connected to the directional coupler 4 via optical fibers. A detection circuit 6 is connected to the light source 5 iJ3 and the light receiving section 7 via a connection line.

A light reflecting section 3 is provided opposite the end surface of the focusing lens 2. The light reflecting section 3 vibrates due to the sound to be detected. Such a light reflecting portion can be formed, for example, by coating a reflective layer on the surface of a material conventionally used as a vibrating membrane for microbons. Alternatively, the vibrating membrane may be formed of a material that reflects light, such as metal, and this vibrating membrane may be used as the light reflecting portion.

Here, in order to explain the relationship between the vibration state of the light reflecting section and the intensity of the reflected light that is reflected by the light reflecting section and returns to the optical fiber, FIGS. 2 to 4 are shown. FIG. 2 shows a state in which the light reflecting section 3 is flat. In such a state J3, the light emitted from the converging lens 2, which is the end face of the optical fiber 1, becomes parallel light and enters the light reflecting section 3. Light reflecting part 3
are arranged substantially perpendicular to the direction of light incidence, so that the incident light is reflected in the opposite direction and returned to the optical fiber 1 through the converging lens 2. At this time, although some light 10 is lost, almost all of the light emitted from the focusing lens 2 is reflected and returned.

FIG. 3 shows a state in which the light reflecting section 3 has a concave shape with respect to the optical fiber 1. As shown in FIG. In this state, the parallel light emitted from the focusing lens 2 enters the light reflecting section 3 which has a concave shape.

The light reflecting section 3 reflects light according to the incident angle, but since the light reflecting section 3 has a concave shape, the incident parallel light is
J indicated by the arrow in FIG. 3: Reflected in the direction of divergence from the sea urchin. In this way, only a part of the light emitted from the focusing lens 2 passes through the focusing lens 2 again and returns to the optical fiber 1.
The intensity of the reflected light is weaker than when the light reflecting section 3 is flat as shown in FIG.

FIG. 4 shows a state in which the light reflecting section 3 has a convex shape with respect to the optical fiber 1. As shown in FIG. The parallel light emitted from the condenser lens 2 enters the light reflecting section 3 having a convex shape.

In the light reflecting section 3, light is reflected depending on the incident angle. Since the light reflecting section 3 has a convex shape, the reflected light diverges in the direction shown by the arrow in FIG. 4. In this way, only a portion of the light emitted from the focusing lens 2 is returned through the focusing lens 2 into the optical fiber 1. Therefore, even when the light reflecting section 3 has a convex shape, the intensity of the reflected light is weaker compared to a flat state as shown in FIG. 2, as in the case where the light reflecting section 3 has a concave shape.

As described above, the intensity of the reflected light returning to the optical fiber changes depending on the imaging state of the light reflecting section 3, so by measuring the change in the intensity of this reflected light, the vibration of the light reflecting section can be detected. can do.

To further explain this embodiment with reference to FIG. 1, the light emitted from the light source 5 passes through the optical fiber and reaches the directional coupler 4, and then passes through the optical fiber 1 and the converging lens 2, which is the end face of the optical fiber. is emitted as parallel light. The emitted light is reflected according to the shape of the light reflecting section 3 as described above, passes through the condenser lens 2, and is returned into the optical fiber 1. Contrary to the above, the light transmitted in the opposite direction within the optical fiber 1 is sent to the light receiving section 7 side by the directional coupler 4. The light receiving section 7 measures the intensity of the reflected light.

The intensity of this reflected light is sent as an electrical signal to the detection circuit 6, where it is compared with the intensity of the emitted light sent from the light [5], and the vibration state of the light reflecting section 3 is detected.

By performing such detection continuously or intermittently, changes in the vibration of the light reflecting section 3 are detected. In the above embodiments, the shape of the light reflecting portion deforms due to acoustic vibration,
In other words, the vibration of the light reflecting part is detected by measuring the intensity of the reflected light that changes due to a series of changes in the shape of the concave part, flat shape, and convex part.
A plane mirror may be attached to the vibrating membrane (), and the optical loss of the reflected light may be increased or decreased by changing the distance between the end face of the optical fiber and the plane mirror, thereby changing the intensity, and detecting the vibration of the light reflecting section. In such a case, if a focusing lens is not attached to the end face of the optical fiber and the light is emitted so as to diverge from its cross section, the difference in optical loss due to vibration can be further increased.

[Effects of the Invention] The 'fI acoustic sensor of the present invention detects the imaging of the light reflection part by measuring the intensity change of the reflected light that is reflected by the light reflection part that vibrates due to acoustics and returns to the optical fiber. There is. Therefore, since a metal lead wire is not required in the detection part, vibration can be detected without being affected by the electric fj1 induction. In addition, since the signal detected by the detection unit is transmitted as an optical signal, the transmission part is not affected by electromagnetic induction, etc., and can be transmitted over long distances within the allowable range of optical loss. It is possible.

As explained above, the acoustic sensor of the present invention is particularly effectively used for measuring sounds such as noise at locations where electromagnetic induction interference is common, such as in high-voltage equipment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing the optical path when the light reflecting section is flat. FIG. 3 is a diagram showing an optical path when the light reflecting portion has a concave shape with respect to the optical fiber. FIG. 4 is a diagram showing an optical path when the light reflecting portion has a convex shape with respect to the optical fiber. In the figure, 1 is an optical fiber, 2 is a focusing lens, 3 is a light reflection section, 4 is a directional coupler, 5 is a light source, 6 is a detection circuit,
7 shows the light receiving part.

Claims (3)

[Claims] (1) A light reflecting section that vibrates due to sound to be detected, and an optical fiber that emits light from an end face of the light reflecting section, and reflected light that is reflected by the light reflecting section and returns to the optical fiber. An acoustic sensor that detects vibrations of a light reflecting part based on changes in the intensity of the light. (2) The light reflecting section is configured by coating a reflective layer on the surface of a vibrating membrane.
An acoustic sensor according to claim 1. (3) The acoustic sensor according to claim 1, wherein the light reflecting section is constituted by a vibrating membrane made of a material that reflects light.