A device for detecting acoustic signals based on laser transverse displacement and a method thereof

Abstract

The application relates to a laser transverse displacement-based sound signal detection device and a method thereof. The method comprises the following steps: step 1, designing and building an optical path, collimating the optical path, and debugging a four-quadrant detector and a NI acquisition board card; step 2, obtaining a test result by using the principle of laser transverse displacement-based sound signal detection; step 3, explaining the feasibility and superiority of laser transverse displacement-based sound signal detection in extracting the characteristics of a target sound source by deducing the relationship between the displacement of a diaphragm and the sound pressure of a sound source; step 4, analyzing the relationship between the displacement of the diaphragm and the vibration of a sound source from the theoretical perspective of the diaphragm; step 5, performing optimization analysis on the diaphragm; and step 6, obtaining an image of the relationship between the displacement of the diaphragm and the sound source. The method can accurately detect sound signals based on laser transverse displacement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microphones, and particularly relates to a device for detecting acoustic signals based on laser transverse displacement and a method thereof. BACKGROUND

[0002] Laser beam displacement measurement technology is an important branch of optical precision measurement. It is mainly applied to atomic force microscopes, optical tweezers, space free communication, precise guidance, and gravitational wave detection. With the increasing demand for precise measurement, target identification, and spot position measurement in multiple application scenarios, the existing electronic microphone measurement method cannot meet the application scenarios of non-contact, high action distance, and strong concealment.

[0003] At present, the methods for measuring the vibration characteristics of the surface of an object can be divided into contact measurement and non-contact measurement. The contact measurement mainly installs an acceleration sensor on the surface of the measured object. The traditional contact measurement uses an electronic microphone to transmit and detect acoustic signals. However, in some special environments, it is necessary to avoid electromagnetic interference, improve the conversion efficiency, and realize non-contact measurement by using acousto-optic conversion. Sound wave is a material wave, which is essentially a form of particle vibration, stress, pressure, etc. in an elastic medium (solid, liquid, gas). In non-contact measurement, light beams are mainly used to carry the vibration information of particles. In particular, the use of infrared light detection can improve the detection concealment and anti-interference. In the field of acoustics, the generation mechanism, propagation form, and detection method of sound waves are related. The detection, accurate identification, and positioning of sound waves require the use of the propagation law of sound waves in elastic media. Sound belongs to a micro-pressure dynamic signal, and it can be measured by monitoring the frequency or sound pressure. At present, the environment brings difficulties to the acoustic property identification of the target. Moreover, the optical path of the detection system is redundant, the installation is relatively complex, and the detection accuracy is limited.

[0004] The above research status shows that the existing methods for measuring the vibration characteristics of the surface of an object have the following two shortcomings:

[0005] The contact measurement limits the distance between the measurement equipment and the measured object, introduces electromagnetic interference, the optical path of the non-contact measurement detection system is redundant, the installation is relatively complex, and the detection accuracy is limited.

[0006] In summary, we believe that in the conversion method, the acousto-optic conversion of the microphone and the method of reflecting and modulating the acoustic signal of the optical path are one of the ways to improve the accuracy of target detection and conversion efficiency. Therefore, the present application provides a device for detecting acoustic signals based on laser transverse displacement, which can realize target detection of weak acoustic signals based on the transverse displacement of the light beam by using the vibration characteristics of laser echoes, and realize real-time measurement of optoelectronic target feature identification with strong concealment. SUMMARY

[0007] The purpose of the present application is to provide a laser transverse displacement-based sound signal detection device and method to overcome the shortcomings of the prior art.

[0008] The technical scheme adopted by the present application is: a laser transverse displacement-based sound signal detection device, comprising a laser, a first high-reflection mirror, a second high-reflection mirror, a focusing lens, a wave plate, a beam splitter, an optical power meter, a third high-reflection mirror, a focusing lens, a gold-plated large diaphragm, a four-quadrant detector, a PC display, an NI acquisition board, a signal source, a loudspeaker, and an oscilloscope; the 1064nm fiber laser is placed on a platform, and the optical coupling head carried thereby is fixed; the first high-reflection mirror is placed in the same direction as the laser light output on a straight line, and the angle between the placement angle and the optical path direction is 45 degrees; the position of the light is at the center of the first high-reflection mirror; the second high-reflection mirror is placed at a distance of 20cm from the first high-reflection mirror 2 reflection light path, so that the light path is 45 degrees incident to the second high-reflection mirror; the position of the light is at the center of the second high-reflection mirror; the focusing lens, the wave plate, the beam splitter, and the third high-reflection mirror are placed in the reflection light path direction of the second high-reflection mirror in turn; the optical power meter is placed perpendicular to the optical path direction at the optical center of the beam splitter; the third high-reflection mirror is placed behind the beam splitter, and the third high-reflection mirror and the front end of the optical path on this path are at an angle of 45 degrees; the focusing lens and the gold-plated large diaphragm are installed in the light path direction after the third high-reflection mirror; the gold-plated large diaphragm is at an angle of 45 degrees with the front end of the optical path; the four-quadrant detector is installed in the light path direction after the reflection of the gold-plated large diaphragm, and three BNC cables are used to connect the outputs of the x, y, and sum of the four-quadrant detector 11 to the input ports of the oscilloscope; the BNC line is used to output the x channel of the four-quadrant detector 11 to the acquisition port of the NI board; the NI board is connected with the PC display; the paper cone of the loudspeaker is placed towards the gold-plated large diaphragm, so that the centers of the two are on a straight line; the BNC line is used to connect the CH1 output port of the signal source;

[0009] The method for detecting sound signals using the laser transverse displacement-based sound signal detection device of the present application comprises the following steps:

[0010] Step 1: the light from the laser passes through the first high-reflection mirror and the second high-reflection mirror for light path collimation, and then is focused by the focusing lens; the wave plate and the beam splitter are used for beam splitting; one beam is used to monitor the stability of the optical power of the optical power meter, and the other beam is reflected by the third high-reflection mirror, focused by the focusing lens, and then hits the center of the gold-plated large diaphragm; the signal source is used to output single-frequency information or sweep-frequency information to drive the loudspeaker to make the gold-plated large diaphragm surface vibrate, so that the reflection surface carries the information of the vibration source due to forced vibration;

[0011] Step 2: Collimate and focus the Gaussian beam of the laser, adjust the left and right and pitch of the first high reflector and the second high reflector in the system, observe the changes of the three input channels corresponding to the x, y, sum of the four-quadrant detector on the oscilloscope, adjust the x, y channels to be not abrupt, and the sum is the photocurrent size when the light is all on the photosensitive surface of the detector, at this time the light is all on the photosensitive surface of the four-quadrant detector, the adjustment process first blocks the laser with the cursor of the oscilloscope to mark the original position of x, y, then observes the position of x, y restored to the cursor position when the light is not blocked, and the sum is the photocurrent size when the light is all on the photosensitive surface of the detector;

[0012] Step 3: The reflected light of the gold-plated large diaphragm carries the information of the sound source, the reflected light is received and collected by the four-quadrant detector and converted into an electrical signal, at the same time the x channel output of the four-quadrant detector is output to the NI board card through the BNC cable, and the collected data is displayed on the PC connected with the NI board card;

[0013] Step 4: When a beam of light is incident at an angle of 45 degrees, the gold-plated large diaphragm is forced to vibrate, causing the transverse position of the light beam to change, at a certain moment the displacement of the gold-plated large diaphragm in the direction perpendicular to its surface is z, the four-quadrant detector can convert the transverse displacement of the light beam through photoelectric conversion, and the vibration displacement of the gold-plated large diaphragm is equal to the transverse displacement of the light beam;

[0014] Step 5: Explain the relationship between the transverse displacement of the light beam and the vibration displacement z of the gold-plated large diaphragm, Q is the absolute value of the noise power spectrum at the peak point of the collected single frequency signal displayed on the PC display of the NI board card, the absolute value of the noise power spectrum reflects the information of the transverse displacement of the light beam, d=q*(10 j*Q / 20 -1) is the formula of the vibration displacement z of the gold-plated large diaphragm, q, j are determined values after the basic framework of the measurement system is determined, and d can be obtained by bringing Q into the formula;

[0015] Step 6: The loudspeaker generating a single frequency signal is a sound source, the sound pressure generated by the vibration of the loudspeaker is proportional to the driving voltage input by the signal source, p=k*U, where p is the sound pressure of the loudspeaker, U is the driving voltage of the loudspeaker, and k is the gain of the sound source; according to the method of step 4, Figure 4 fitting the line type, the calculated d is approximately proportional to the driving voltage of the loudspeaker, and the displacement z of the gold-plated large diaphragm is approximately proportional to the driving voltage of the sound source loudspeaker, that is, the displacement z of the gold-plated large diaphragm is approximately proportional to the sound pressure of the sound source loudspeaker. Thus the acoustic amplitude characteristics of the target can be obtained;

[0016] Step 7: the principle of vibration of the gold-plated large diaphragm, forced vibration is to use the sound source to act on the system to maintain the vibration of the system, wherein the driving force frequency is the frequency corresponding to the sound source, the natural frequency is the frequency of the vibration of the system when it is not affected by external force, and the natural frequency is the inherent property of the system; the vibration equation of any point on the diaphragm surface is as follows:

[0017] The vibration equation of the particle is:

[0018]

[0019] It can be concluded that as long as the time of sound source driving is long enough, the vibration frequency is equal to the driving force frequency, and the steady state can be reached

[0020] The steady-state vibration equation is:

[0021] (2)

[0022] Amplitude does not change with time, the vibration frequency of the gold-plated large diaphragm is the frequency of the loudspeaker, and the vibration frequency of the gold-plated large diaphragm can modulate light. The frequency at the position with the highest noise power spectrum can restore the frequency information of the sound source;

[0023] Step 8: theory of diaphragm for optimizing gold-plated large diaphragm of reflecting surface

[0024] Diaphragm natural frequency pre-tightening force formula:

[0025]

[0026] Wherein 2.405 is derived according to the root of the first type of Bessel function, T is the in-plane force per unit thickness and pre-tension, h is the thickness of the diaphragm, p is the density of the diaphragm material, h p is the mass per unit area, and R is the radius of the diaphragm;

[0027] Diameter and thickness are the factors that determine the natural frequency. For a complete diaphragm, the thickness h and the radius R are used for analysis; both determine the fundamental frequency f and the central deformation y(p) of the diaphragm; in general, according to (4), the central deformation y(p) is related to the response sensitivity, and the sensitivity is represented by S d ;

[0028]

[0029] Wherein μ, E, f n , h, R represent Poisson's ratio, Young's modulus, natural frequency, diaphragm thickness, diaphragm radius. y(p) is the central deformation of the circular diaphragm, f and p are the frequency and sound pressure of the sound wave, and ζ is the damping ratio of the diaphragm vibration;

[0030] The frequency f and the central displacement y(p) are multiplied to get

[0031]

[0032] wherein a and b are equivalent coefficients influenced by the elastic modulus, the Poisson's ratio and the density of the diaphragm material; at a certain frequency f, according to formula (5), the values of R and h causing the proper deformation y(p) of the center are found, which is equivalent to finding the proper ratio of R / h;

[0033] Compared with the prior art, the present application has the following advantages:

[0034] (1) The present application is aimed at the photoelectric information data collected by the four-quadrant in the actual scene, and carries the signal of the laser echo. The vibration information of the reflecting surface can be extracted from the detection of the sound signal based on the laser transverse displacement, so as to extract the vibration spectrum of the sound source. According to the difference of the vibration spectrum, the target sound source can be identified.

[0035] (2) The present application proposes a narrow-band fiber laser of infrared light 1064nm as a light source. The infrared light has extremely strong concealment. The method is improved, and will be widely applied in the fields of battlefield command, precise guidance, battlefield reconnaissance and the like. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Fig. 1 is a schematic diagram of the optical path of a device for detecting sound signals based on laser transverse displacement according to the present application;

[0037] Figure 2 Fig. 2 is a schematic diagram of the photosensitive surface of the four-quadrant detector in step 3 of embodiment 1 of the present application;

[0038] Figure 3 Fig. 3 is the single-frequency data of 2740Hz (the highest peak frequency) collected by the data acquisition board card in embodiment 1 of the present application;

[0039] Figure 4 Fig. 4 is the relationship between the diaphragm displacement and the driving voltage of the sound source in step 8 of embodiment 1 of the present application. DETAILED DESCRIPTION

[0040] As Figures 1 to 4The device for detecting acoustic signals based on laser transverse displacement of the embodiment comprises a laser 1, a first high-reflection mirror 2, a second high-reflection mirror 3, a focusing lens 4, a wave plate 5, a beam splitter 6, an optical power meter 7, a third high-reflection mirror 8, a focusing lens 9, a gold-plated large diaphragm 10, a four-quadrant detector 11, a PC display 12, an NI acquisition board 13, a signal source 14, a loudspeaker 15, and an oscilloscope 16.

[0041] The method for detecting acoustic signals using the device for detecting acoustic signals based on laser transverse displacement is as follows:

[0042] Step 1: The light from the laser 1 is collimated through the first high-reflection mirror 2 and the second high-reflection mirror 3, focused by the focusing lens 4, split by the wave plate 5 and the beam splitter 6, one of which is used to monitor the stability of the optical power by the optical power meter 7, and the other of which is reflected by the third high-reflection mirror 8, focused by the focusing lens 9, and then hits the center of the gold-plated large diaphragm 10; the signal source 14 outputs single-frequency information or sweep-frequency information to drive the loudspeaker 15 to make the gold-plated large diaphragm 10 vibrate, so that the reflection surface carries the information of the vibration source due to forced vibration.

[0043] Step 2: Collimate and focus the Gaussian beam of the laser 1 out, adjust the left and right and pitch of the first high reflector 2 and the second high reflector 3 in the system, observe the changes of the corresponding three input channels of the four-quadrant detector 11x, y, sum on the oscilloscope, adjust the x, y channels to be not abrupt, and the sum is the photocurrent size of the light hitting the photosensitive surface of the detector, at this time the light hits the photosensitive surface of the four-quadrant detector 11, adjust the process first block the laser with the cursor of the oscilloscope 16 to mark the original position of x, y, then observe the position of x, y when the light is not blocked, and the sum is the photocurrent size of the light hitting the photosensitive surface of the detector;

[0044] Step 3: The reflected light from the gold-plated large diaphragm 10 carries the information of the sound source, the reflected light is received and collected by the four-quadrant detector 11 and converted into an electrical signal, at the same time the x channel output of the four-quadrant detector 11 is output to the NI board card 13 through the BNC cable, and the result is displayed on the PC display 12 connected with the NI board card 13 to observe the collected data;

[0045] Step 4: When a beam of light is incident at an angle of 45 degrees, the gold-plated large diaphragm 10 is forced to vibrate, causing the transverse position of the light beam to change in space, at a certain moment the displacement of the gold-plated large diaphragm 10 in the direction perpendicular to its surface is z, the four-quadrant detector 11 can convert the transverse displacement of the light beam through photoelectric conversion, and the vibration displacement of the gold-plated large diaphragm 10 is equal to the transverse displacement of the light beam;

[0046] Step 5: Explain the relationship between the transverse displacement of the light beam and the vibration displacement z of the gold-plated large diaphragm 10, Q is the absolute value of the noise power spectrum at the peak point of the collected single frequency signal displayed on the PC display 12 of the NI board card 13, the absolute value of the noise power spectrum reflects the information of the transverse displacement of the light beam, d = q * (10 j*Q / 20 -1) is the formula of the vibration displacement z of the gold-plated large diaphragm 10, q, j is a determined value after the basic framework of the measurement system is determined, and d can be obtained by bringing Q into the formula;

[0047] Step 6: The horn 15 generating a single frequency signal is a sound source, the sound pressure generated by the vibration of the horn 15 is proportional to its driving voltage input from the signal source 14, p = k * U, where p is the sound pressure of the horn, U is the driving voltage of the horn, and k is the gain of the sound source; according to the method described in step 4, the line type is fitted, and the calculated d is approximately proportional to the driving voltage of the horn 15, so that the displacement z of the gold-plated large diaphragm 10 is approximately proportional to the driving voltage of the sound source horn 15, that is, the displacement z of the gold-plated large diaphragm (10) is approximately proportional to the sound pressure of the sound source horn 15. Thus the acoustic amplitude characteristics of the target can be obtained; Figure 4

[0048] ​Step 7: the principle of vibration of the gold-plated large diaphragm 10, forced vibration is to use the sound source to act on the system to maintain the vibration of the system, wherein the driving force frequency is the frequency corresponding to the sound source, the natural frequency is the frequency of the vibration of the system when it is not affected by external force, and the natural frequency is the inherent property of the system; the vibration equation of any point on the diaphragm surface is as follows:

[0049] The vibration equation of the particle is:

[0050]

[0051] It can be concluded that as long as the time of sound source driving is long enough, the vibration frequency is equal to the driving force frequency, and the steady state can be reached.

[0052] The steady-state vibration equation is:

[0053] (2)

[0054] Amplitude does not change with time, the vibration frequency of the gold-plated large diaphragm 10 is the frequency of the loudspeaker 15, and the vibration frequency of the gold-plated large diaphragm 10 can modulate light. The frequency at the position with the highest noise power spectrum can restore the frequency information of the sound source;

[0055] Step 8: theory of diaphragm for optimizing gold-plated large diaphragm 10

[0056] Diaphragm natural frequency pre-tightening force formula:

[0057]

[0058] Wherein 2.405 is derived according to the root of the first type of Bessel function, T is the in-plane force per unit thickness and pre-tension, h is the thickness of the diaphragm, p is the density of the diaphragm material, h p is the mass per unit area, and R is the radius of the diaphragm;

[0059] Diameter and thickness are the factors that determine the natural frequency, and thickness h and radius R are used to analyze; both determine the fundamental frequency f and the center deformation y(p) of the diaphragm; in general, according to (4), the center deformation y(p) is related to the response sensitivity, and the sensitivity is represented by S d ;

[0060]

[0061] Wherein μ, E, f n , h, R represent Poisson's ratio, Young's modulus, natural frequency, diaphragm thickness, diaphragm radius. y(p) is the center deformation of the circular diaphragm, f and p are the frequency and sound pressure of the sound wave, and ζ is the damping ratio of the diaphragm vibration;

[0062] The frequency f and the center displacement y(p) are multiplied to get

[0063]

[0064] where a and β are equivalent coefficients influenced by the elastic modulus, the Poisson's ratio and the density of the membrane material; at a certain frequency f, the values of R and h that induce a suitable deformation y(p) of the center are searched according to equation (5), which corresponds to finding a suitable ratio of R / h.

Claims

1. A method for detecting acoustic signals based on a laser lateral displacement detection acoustic signal device, characterized in that: A laser-based transverse displacement detection acoustic signal device includes a laser (1), a first high-reflection mirror (2), a second high-reflection mirror (3), a focusing lens (4), a waveplate (5), a beam splitter (6), an optical power meter (7), a third high-reflection mirror (8), a focusing lens (9), a gold-plated large diaphragm (10), a four-quadrant detector (11), a PC-side display (12), an NI acquisition board (13), a signal source (14), a speaker (15), and an oscilloscope (16). A 1064nm fiber laser (1) is placed on the platform, and... The optical coupling head is fixed, and a first high-reflection mirror (2) is placed on a straight line in the same direction as the light emitted from the laser (1). The placement angle is 45 degrees to the light path direction, and the light position is at the center of the first high-reflection mirror (2). A second high-reflection mirror (3) is placed 20 cm away from the first high-reflection mirror (2), so that the light path is incident on the second high-reflection mirror (3) at a 45-degree angle, and the light position is at the center of the second high-reflection mirror (3). A focusing lens (4), a waveplate (5), and a beam splitter (6) are placed sequentially in the direction of the reflected light path of the second high-reflection mirror (3). The third high-reflection mirror (8) is placed at the optical center of the beam splitter (6) in a direction perpendicular to the optical path. The third high-reflection mirror (8) is placed behind the beam splitter (6). The third high-reflection mirror (8) is at a 45-degree angle to the optical path at the front end of this path. A focusing lens (9) and a gold-plated large diaphragm (10) are installed in the optical path direction after the third high-reflection mirror (8). The gold-plated large diaphragm (10) is at a 45-degree angle to the optical path at the front end. The four-quadrant detector (11) is installed on the optical path after the gold-plated large diaphragm (10). In the direction of the emitted light path, the x, y, and sum outputs of the quadrant detector (11) are connected to the input port of the oscilloscope (16) using three BNC cables. Then, the x channel output of the quadrant detector (11) is connected to the acquisition port of the NI acquisition board (13) via BNC cables. The NI acquisition board (13) is connected to the PC display (12). The paper cone of the speaker (15) is placed facing the gold-plated large diaphragm so that the centers of the two are on a straight line. It is connected to the CH1 output port of the signal source (14) using BNC cables. The method for detecting acoustic signals based on a laser lateral displacement detection acoustic signal device includes the following steps: Step 1: The light emitted from the laser (1) is collimated by the first high-reflection mirror (2) and the second high-reflection mirror (3), and then focused by the focusing lens (4). The beam is split by the waveplate (5) and the beam splitter (6). One beam is fed into the optical power meter (7) to monitor the stability of the optical power. The other beam is reflected by the third high-reflection mirror (8), focused by the focusing lens (9), and then hits the center of the gold-plated large diaphragm (10). The signal source (14) outputs single-frequency information or sweep frequency information to drive the speaker (15) to make the surface of the gold-plated large diaphragm (10) vibrate, so that the information of the vibration source is carried on the reflective surface due to forced vibration. Step 2: Collimate and focus the Gaussian beam from the laser (1), adjust the left and right and the pitch of the first high-reflection mirror (2) and the second high-reflection mirror (3) in the system, and observe the changes of the three input channels corresponding to x, y, and sum of the four-quadrant detector (11) on the oscilloscope. Adjust the x and y channels so that they do not change abruptly. sum is the photocurrent when all the light hits the photosensitive surface of the detector. At this time, all the light hits the photosensitive surface of the four-quadrant detector (11). In the adjustment process, first block the laser and mark the original position of x and y with the cursor of the oscilloscope (16). Then observe that when the light is not blocked, x and y return to the position of the cursor. sum is displayed on the oscilloscope (16) as its optical power. sum is the photocurrent when all the light hits the photosensitive surface of the detector. Step 3: The light reflected by the gold-plated large diaphragm (10) carries the information of the sound source. The reflected light is received and collected by the quadrant detector (11) and converted into an electrical signal. At the same time, the x channel of the quadrant detector (11) is output to the acquisition channel of the NI acquisition board (13) using a BNC cable, and the results are displayed on the PC monitor (12) connected to the NI acquisition board (13) to observe the acquired data. Step 4: When a beam of light is incident at a 45-degree angle, the gold-plated large diaphragm (10) is forced to vibrate, causing the beam to change its lateral position in space. At a certain moment, the displacement of the gold-plated large diaphragm (10) in the vibration direction perpendicular to its surface is z. The four-quadrant detector (11) converts the lateral displacement of the beam into a photoelectric value. The vibration displacement of the gold-plated large diaphragm (10) is z, which is equal to the lateral displacement of the beam. Step 5: Explain the relationship between the lateral displacement of the beam and the vibration displacement z of the gold-plated large diaphragm (10). Q is the absolute value of the noise power spectrum at the peak point of the single-frequency signal acquired by the NI acquisition board (13) and displayed on the PC monitor (12). The absolute value of the noise power spectrum reflects the information of the lateral displacement of the beam. For the gold-plated large diaphragm (10), the vibration displacement z formula is given. q and j are fixed values ​​after the basic framework of the measurement system is determined. Substituting Q into the formula, d can be calculated. Step 6: The horn (15) that generates a single-frequency signal is the sound source. The sound pressure generated by the vibration of the horn (15) is proportional to the driving voltage input from the signal source (14), p=k*U, where p is the sound pressure of the horn, U is the driving voltage of the horn, and k is the gain of the sound source. According to the method described in Step 4, based on the fitted line shape, the calculated d is approximately proportional to the driving voltage of the horn (15), and the displacement z of the gold-plated large diaphragm (10) is approximately proportional to the driving voltage of the sound source horn (15), that is, the displacement z of the gold-plated large diaphragm (10) is approximately proportional to the sound pressure of the sound source horn (15). Thus, the acoustic amplitude characteristics of the target can be obtained. Step 7: Vibration principle of the gold-plated large diaphragm (10): Forced vibration is achieved by using a periodic external force to maintain the system's vibration. The driving force frequency is the frequency corresponding to the driving force, and the natural frequency is the frequency of vibration when the system is not subjected to external force. The natural frequency is an inherent property of the system. The vibration equation at any point on the diaphragm surface is as follows: The vibration equation of a particle: (1) It is concluded that as long as the sound source drives for a long enough time, the vibration frequency will equal the driving force frequency, and a steady state will be achieved. Steady-state vibration equation: (2) amplitude The vibration frequency of the gold-plated large diaphragm (10) is the same as the frequency of the speaker (15) as it does not change over time. The vibration frequency of the gold-plated large diaphragm (10) modulates the light, and the frequency at the highest position of the noise power spectrum is read to restore the frequency information of the sound source. Step 8: The theory of diaphragms, used to optimize gold-plated large diaphragms on reflective surfaces (10) Formula for preload at diaphragm natural frequency: (3) 2.405 is derived from the root of the first kind of Bessel function. T is called the in-plane force and pretension per unit thickness, h is the thickness of the film, ρ is the density of the diaphragm material, hρ is the mass per unit area, and R is the diaphragm radius. Diameter and thickness are factors that determine the natural frequency. At a certain resonant frequency, the smaller the diameter and the thinner the diaphragm, the greater the deformation of the diaphragm. For a complete diaphragm, two geometric parameters, thickness h and radius R, are used for analysis; both determine the fundamental frequency f and the central deformation y(p) of the diaphragm. Generally, according to (4), the larger the central deformation y(p), the higher the response sensitivity. The sensitivity is determined by... express; (4) in E, h and R represent Poisson's ratio, Young's modulus, natural frequency, diaphragm thickness, and diaphragm radius, respectively; y(p) is the center deformation of the circular diaphragm; f and p are the frequency and sound pressure of the sound wave; and ζ is the damping ratio of the diaphragm vibration. Multiplying the frequency f and the center displacement y(p) yields... (5) Where α and β are equivalent coefficients affected by the elastic modulus, Poisson's ratio and density of the diaphragm material; at a certain frequency f, according to equation (5), the R and h values ​​that cause the maximum deformation y(p) at the center are found, which is equivalent to finding a suitable ratio of R / h.

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