JPS63236928A - Acoustic sensor - Google Patents

Abstract

PURPOSE:To miniaturize an acoustic sensor by using a core having a fine groove for maintaining the high-airtightness space formed of a diaphragm and an optical fiber at atmospheric pressure. CONSTITUTION:The optical fiber 12 is inserted fixedly into the core constituted by inserting a pipe 4 fixedly and integrally into the through hole 3 of a pipe 1 so that a groove 5 formed in the cylindrical surface of the pipe 4 perpendicularly to the circumference and a groove 2 formed in the end surface of the pipe 1 whose internal diameter is larger than the external diameter of the pipe 4 from the center of the pipe 1 to the outer periphery form a continuous groove. The end surface of the fiber 12 on the side of the pipe 4 is polished and a spacer 7 is inserted and fixed to the pipe 4. The diaphragm of a diaphragm unit 8 is projected by the projection part of the spacer 7 to secure optical flatness and the grooves 5 and 2 form the continuous groove. Thus, the core having the fine groove is used to miniaturize the sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an acoustic sensor that converts physical conditions such as pressure and vibration into optical signals.

BACKGROUND OF THE INVENTION In recent years, optical sensors have been applied to many equipment systems for measurement, monitoring, and inspection purposes.

As for the conventional technology, for example, Amaba et al. "Optical Fiber Globe Microphone" Transactions of the Institute of Electronics Engineers (Vol. J64)
-C42PF 137-1431981/2).

An example of the conventional acoustic sensor mentioned above will be described below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of a conventional acoustic sensor. In FIG. 4, 9 is a laser, and 1o is an isolator that blocks light returning to the laser 9. 26 is frame 2
2, the optical fiber 12 and the core 2
They are in opposing positions via 8. 23 is beam sprit;
It splits the light at the same time. A photoelectric detector 24 converts the branched light from the beam splitter 23 into electricity. 25 is a filter, and 17 is an output terminal.

A indicates incident light, C indicates reflected light, and B indicates a physical state from the outside, which in this case is pressure.

The operation of the acoustic sensor configured as described above will be described below.

First, light from the laser 9 is guided to the optical fiber 12 via the isolator 10. Furthermore, the beam splitter 23
becomes the incident light A. Incident light A enters the optical fiber 12
The optical fiber 12 is guided by a reflective film surface formed on one end of the optical fiber 12.
The reflected light C is repeatedly reflected and interfered with the reflecting film surface formed on the mica vibrating film 26 which is located in an opposing position. The reflected light C is split by a beam splitter 23 and sent to a photoelectric converter 2
4, it is converted into an electrical signal. Further, the signal is detected as an output signal at the output terminal 17 via the filter 26. Next, the conversion principle will be explained. FIG. 6 is a schematic diagram showing the configuration of the converter section.

The incident light A is guided from the reflective film with a reflectance of 40% formed on the end face of the optical fiber part 12 to the reflective film surface with a reflectance of 40% of the vibrating membrane 26 at a refraction angle of X, and a part of the light is transmitted. , a part of the light is reflected and returns to the end face of the light 7 eye/kube 2 again. A portion of the returned light becomes reflected light C and propagates through the optical fiber to become an optical signal, and a portion is reflected and guided to the reflective surface of the vibrating membrane 26 again. Hereinafter, the above-mentioned optical signal, which is repeatedly reflected and interfered between the vibrating membrane 26 and the optical fiber 2, is determined by the intensity reflection coefficient, which is the ratio of the intensity of the incident light A to the intensity of the reflected light C. The intensity of incident light A is 1.1 reflected light C
The intensity reflection coefficient can be expressed as the following equation.

Here, δ==4 T ” n□ ' d ' CLJS body) /λd=do+Δd r: Amplitude reflection coefficient of the optical fiber end and vibrating membrane n0: Refractive index of air do: Distance between the optical fiber end and the vibrating membrane Δd Displacement of the two-vibration membrane X: Refraction angle λ from the end of the optical fiber to the air: Incident wavelength.The reflectance generally used is the square of this amplitude reflection coefficient.

Now, the incident wavelength λ is 1.3 μm, the amplitude reflection coefficient of the vibrating membrane 26 made of mica with a dielectric multilayer coating of 16.0 μm thick, and the amplitude of the optical fiber section 12 similarly coated with a dielectric multilayer film. If the reflection coefficients are the same and do is set optimally, the intensity reflection coefficient will change depending on the value of d from the first equation. In other words, it can be seen that it changes depending on the displacement Δd of the vibrating membrane 2e due to the external pressure B.

Further, a sectional view of the fixed state of the core 28 and the optical fiber 12 in FIG. 4 is shown in FIG. As shown in FIG. 6, the optical fiber 12 is inserted and fixed into the core 28, and the end face of the optical fiber 12 is polished. The core 28 is provided with a hole 27. This is middle child 2
The linearity of the vibrating membrane 26 due to the expansion of the air in the closed chamber formed by the vibrating membrane 26 and the vibrating membrane 26 is improved, and at the same time, the stability is also improved. Here, as described above, since mica is used for the vibrating membrane 2e, the amount of displacement of the vibrating membrane 2e with respect to pressure is small. In other words, the sensitivity becomes lower and the S-/N becomes worse. Therefore, the vibrating membrane 26 is a polymer film (simply referred to as a film) that has a ratio of about 1/4 of the ratio of mica to mica.
It is common to use However, in order to ensure the optical flatness of the film, a push-up mechanism is required to hold the film under tension and ensure flatness. Therefore, the outer diameter of the vibrating membrane 26 becomes large, and in order to achieve miniaturization, the peripheral area of the end face of the optical fiber 12 must be reduced, and the hole 27 cannot be provided.

Problems to be Solved by the Invention However, in order to achieve compact size and high sensitivity with the above configuration, a vibrating membrane tensioning mechanism is required, the core and frame also become large, and the shape of the sensor is inevitably changed. also becomes larger. Therefore, it was impossible to measure and inspect in a narrow space. moreover,
There were problems with the shape, such as disturbing the sound field and airflow during measurements and inspections.

Therefore, it is desired to develop an acoustic sensor that is small and highly stable.

In view of the above problems, the present invention provides a compact acoustic sensor.

Means for Solving the Problems In order to solve the above problems, the acoustic sensor of the present invention includes a groove of the first pipe that is perpendicular to the circumference of the first pipe and formed on a cylindrical surface; The first pipe is connected to the first pipe so that the groove formed in the end surface of the second pipe, which has an inner diameter larger than the outer diameter of the first pipe, is continuous from the center of the end surface toward the outer periphery. An optical fiber is inserted and fixed into the core integrated into the second pipe, and a pipe-shaped spacer that is longer than the uninserted part of the first pipe is inserted and fixed into the first pipe of the core. The structure is such that the vibrating membrane pushed up and held under tension by the spacer and the end face of the first pipe face each other in a positional relationship.

Function: With the above-described configuration, the present invention allows fine grooves to be provided in the core, making it possible to reduce the size and obtain acoustic information in a narrow space.

Embodiment An acoustic sensor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing the configuration of an acoustic sensor according to the present invention.

In the M1 diagram, the groove 5 is perpendicular to the circumference of the first pipe 4 and is formed on the cylindrical surface, and the outer circumference from the center of the end surface of the second pipe 1 having an inner diameter larger than the outer diameter of the first pipe 4. The first pipe 4 is inserted into the through hole 3 of the second pipe 1 so that the groove 2 formed on the end face becomes a continuous groove. 12 and fix it. Here, the grooves were created by electrical discharge machining. The end surface of the inserted optical fiber 12 on the first pipe side is polished, and the spacer 7 is inserted and fixed into the first pipe 4. The fixing method here is YA
G laser welding and soldering were used. The end face of the polished optical fiber 12 is coated with a dielectric multilayer film 40.
% reflective film is formed.

The vibrating membrane of the vibrating membrane unit 8 is a polyimide film having a thickness of 7.6 μm, and is held in a frame 22 shown in FIG. This polyimide film has a heat resistance of about 400℃, 3
It is possible to form a hard coating that requires heat resistance of 00'C to 350'C. As described above, a multilayer dielectric film is coated here. The reflectance at this time is 4
I set it to 0%. The reflectance is not necessarily 4 depending on the use and purpose.
It does not need to be 0%. Naturally, the back side of the polyimide film coated with a reflective film is coated with a non-reflective hard coating. The reflective film of the vibrating film of the vibrating film unit 8 and the reflective film of the optical fiber 12 are fixed in a position facing each other, thereby forming a resonant system.

FIG. 2 is a cross-sectional view of the converting section of the acoustic sensor configured as described above. In FIG. 2, the diaphragm of the diaphragm unit 8 is pushed up by the protrusion of the spacer 7 to ensure optical flatness, and the diaphragm of the diaphragm unit 8 is pushed up by the protrusion of the spacer 7 to ensure optical flatness. 2 is a continuous groove. The metal materials for each part are 32% nickel, 4% cobalt, and 6% iron.
A 4% low expansion alloy was used.

FIG. 3 shows the overall configuration of an acoustic sensor device using the acoustic sensor configured as described above. In FIG. 3, 9 is a laser, 10 is an isolator, and 20 is a lens for collimating or condensing light. Reference numeral 11 denotes an optical splitter which splits the light into two equal parts, and is also called an optical fiber coupler. Reference numeral 12 denotes an optical fiber, and a reflective film is formed on one end surface. Reference numeral 13 denotes a vibrating membrane, and a reflective film is formed on the surface facing the reflective film surface of the optical fiber 12.

A photodiode 14 converts the light branched by the optical splitter 11 into an electrical signal, which is amplified by an amplifier 15. 16 is a filter, and 17 is an output terminal. 1
8 is a temperature control circuit for controlling the temperature of the laser 9, and 19 is a drive circuit for the laser 9.

In addition, laser 9. Isolator 10. optical fiber 12,
Output terminal 17. The frame 22 is the same as the conventional example. This frame 2
2 and the vibrating membrane 13 form a vibrating membrane unit 8.

Regarding the acoustic sensor configured as above, the following is the third section.
The operation will be explained using figures. In FIG. 3, light from a laser 9 is converted into parallel light by a lens 2o and coupled to an optical splitter 11 via an isolator 10. This isolator 10 prevents light from returning to the laser 9. Two stages are used here. The light from the optical splitter 11 propagates through the optical fiber 12 and becomes incident light A. The incident light A undergoes repeated reflection interference between the reflective film applied to the end face of the fiber 12 and the reflective film applied to the vibrating membrane 13, and becomes reflected light C. The reflected light C propagates through the optical fiber 12 again, is split by the optical splitter 11, and converted into an electrical signal by the photodiode 14,
Amplifier 15. The signal is guided to an output terminal 17 via a filter 16. Here, the temperature control circuit 18 controls instability of the oscillation wavelength of the laser 9 due to temperature changes. 19
is a constant current drive circuit for driving the laser 9.

Note that the operating principle is the same as the conventional example. In this way, according to this embodiment, by using the core 21 in which the grooves provided in each of the two parts are integrated so as to form a continuous groove, the core 21 can be
Since the sensor 1 itself can be made smaller, the entire sensor can also be made smaller.

As described above, according to this embodiment, the highly airtight space formed by the diaphragm 13 and the optical fiber 12 is miniaturized by using the core 21 having fine grooves that maintain the same pressure as the atmosphere. can be achieved.

Effects of the Invention As described above, the present invention uses a core having fine grooves, so it is possible to realize a small size. Therefore, measurement.

Accurate information can be obtained without disturbing the atmosphere or conditions being inspected, making it possible to perform measurements in narrow spaces that were previously impossible. Furthermore, a vibrating membrane tensioning mechanism for maintaining optical flatness can be provided, resulting in a sensor with stable quality.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing the configuration of an acoustic sensor according to an embodiment of the present invention, FIG. 2 is a sectional view of the converter, and FIG. 3 is a block diagram of an acoustic sensor device using the acoustic sensor. Figure 4 is a block diagram showing the configuration of a conventional acoustic sensor, and Figure 6 is a block diagram showing the configuration of a conventional acoustic sensor.
The figure is a schematic diagram showing the configuration of the converter, and FIG. 6 is a sectional view of the converter. 1...Second pipe, 2...Groove of second pipe, 4...First pipe, 6...
・First pipe groove, 9... Laser, 12...
...Optical fiber, 13... Vibration membrane, 21.
... Core, 22 ... Frame, 27 ...
・Hole, 28... Core, A... Incident light,
B...Pressure, C...Reflected light. Name of agent: Patent attorney Toshio Nakao and one other person f=
-%211r(Ige 2-・-v v Groove 3-・-V Me'!''! 1 ordinary da--#fri7ζ17゛S...-〆l v calculation 7-'Suther cho e-1 hardening 2 pieces

Claims (1)

[Claims] The groove of the first pipe is perpendicular to the circumference of the first pipe and formed on the cylindrical surface, and the second pipe has an inner diameter larger than the outer diameter of the first pipe. The optical fiber is inserted and fixed into the core integrated with the first pipe and the second pipe so that the groove of the second pipe formed on the end surface becomes a continuous groove. A pipe-shaped spacer that is longer than the uninserted part of the first pipe is inserted and fixed into the first pipe, and the vibration membrane is pushed up and held under tension by the spacer and the end face of the first pipe. What is claimed is: 1. An acoustic sensor characterized in that the acoustic sensor is configured such that the two are in a positional relationship facing each other.