JPS6018100A - Microphone - Google Patents

Abstract

PURPOSE:To detect directly a density change of a propagation medium by using a means which irradiates a laser light into the propagation medium of sound waves and a laser light detecting means to stitute a microphone. CONSTITUTION:A laser beam delivered from a laser light emitting means 1 is divided into two pathes by beam splitter 3. The 1st beam 5 propagates through a solid medium 8; while the 2nd beam 6 propagates through a propagation medium 9 of sound waves. Both beams 5 and 6 are synthesized by a reflector 4 and a beam splitter 7, and the intensity of the synthetic beam is detected by a photodetecting means 2. A density change of the medium 9 is produced in response to the variation of sound pressure. This produces the variation of propagating speed of the beam 6 and then the variation of phase. Then the sound pressure is detected in the form of a change of intensity of the synthetic beam by having th e synthesization and interference between beams 5 and 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microphone that uses laser light as sound pressure detection means.

The mainstream of Seiko's microphones is a method that detects the displacement and velocity of the diaphragm due to sound pressure, such as condenser type and moving coil N. Methods for detecting changes are not common.

On the other hand, optical fiber hydrophones, which are currently in the development stage as underwater microphones, use the coherence of laser light to detect changes in the refractive index caused by distortion of the optical fiber caused by underwater sound pressure. It does not directly detect changes in the density of the sound wave propagation medium.

An object of the present invention is to provide a new microphone that detects the density change of the medium by directly shining a laser beam into the medium.

In the first embodiment of the present invention shown in FIG. . On the other hand, the second beam 6 propagates through the sound wave propagation member Ip. Both beams 5.6
are combined using a reflecting mirror 4 and a beam splitter 7, and the intensity thereof is detected by a light detection means 2. Both beams l, 5 and 6 undergo a constant phase delay while propagating in their respective propagation media 8 and 9, but within propagation medium 9, 1
) The density of the medium changes in response to sound pressure fluctuations caused by waves,
The propagation speed of the beam 6 varies. As a result, the beam 6 undergoes phase fluctuations corresponding to sound pressure fluctuations. Therefore, the sound pressure can be detected as a change in the intensity of the synthesized beat by combining and interfering with the beat 6 and the beam 5 propagating in the solid medium 8 which is not affected by sound pressure fluctuations.

FIG. 2 is a sectional view showing a modified example of one component of the ff1l embodiment of the present invention, and is a container used in place of the solid medium 8 in the first embodiment. This container 10 contains a fluid medium 1
2, and communicates with the outside through a small hole 11. Therefore, when used in the atmosphere, the fluid medium 12 is air and the small holes 11 make its pressure equal to atmospheric pressure. Further, the size of the small hole 11 is sufficiently small to prevent sound pressure fluctuations from being transmitted into the container 10. Both ends of the container 10 are made of a material with good light transmittance. If this container is used in place of the solid medium 8 in FIG. 1, both the beams 5 and 6 will propagate in the same medium, making it possible to cancel out the effects of pressure fluctuations, temperature changes, etc.

In the second embodiment of the present invention shown in FIG. 3, two beam splitters 3 are arranged in a row S12, and the space between them is placed within a sound wave propagation hole YltO. A portion 13 of the laser beam 1 emitted from the laser emitting means 1 passes through both beam splitters and directly reaches the light detecting means 2, but the rest.
-Repeating multiple reflections between the two beam splitters 3,
A portion 14 of it reaches the photodetecting means 2. The laser beams 1, 13 and 14 are caused by the propagation pressure 81 [
However, they are subjected to different phase fluctuations in response to sound pressure fluctuations within the medium 9. Therefore, the intensity of the light incident on the light detection means 2 changes in accordance with the sound pressure. By detecting this, the sound pressure within the medium 9 can be determined as Al11.

A third embodiment of the present invention shown in FIG. 4 has a servo mechanism 15 added to the first embodiment, and the position of a reflecting mirror 17 is controlled by this and an apparatus control means 16. That is, the servo mechanism 15 receives the output signal 1 of the photodetection means 2.
8 is used as an input signal, and a control signal 19 is sent to the position control means 16 so that the input signal is always constant, thereby controlling the iζ device of the reflecting mirror 17. With the above configuration, the sound pressure fluctuation in the medium i/'t 9 can be detected as a change in one row of -1-the reflector 17. Alternatively, if the linearity of the position control means 16 is good, the value jJf
lg may be regarded as a signal corresponding to sound pressure fluctuations.

The fourth embodiment of the present invention shown in FIG.
By adding t,4M 15 and position control means 16, the same functions as those of the first and third embodiments are provided. In this case, the position control means 16 controls the distance between the two beam splitters 3, and variations in this distance correspond to changes in sound pressure.

As mentioned above, since the present invention detects changes in the density of a medium by using the coherence of laser light, it can be used not only as a microphone but also as a density meter or a pressure gauge. I can do it.

Furthermore, the present invention enables non-contact measurement of sound pressure, thereby making it possible to reduce the occurrence of wind noise. It should be noted that each of the above-described embodiments is for explaining the present invention, and the scope of the present invention is not limited by the manner in which they are constructed.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention. Figure 2 shows the variation of the first embodiment! FIG. 3 is an example cross-sectional view. FIG. 3 shows a second embodiment. FIG. 4 shows a third embodiment. FIG. 5 shows a fourth embodiment. 1 is a laser emitting means. 2 is a light detection means. 3 and 7 are beam splinters. 4 is a reflective mirror. 5 and 6 are laser beams. 8 is a solid medium. 9 is a propagation medium of sound waves. 10 is a container. 11 is a small hole. 12 is a fluid medium. 13 and 14 are laser beams. 15 is a servo mechanism. 16 is a position control means. 1
7 is a reflective mirror. 18 is the output (1" No. 1. 19 is the control signal. Patent applicant: Mikiyasu Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] means for irradiating laser light into a sound wave propagation medium;
and means for detecting the laser beam at a certain distance KPM.