Measurement method based on co-vibration type vector suspension microphone

Abstract

The invention belongs to the technical field of vector microphones, and particularly relates to a measurement method based on a co-vibration type vector suspension microphone, and the co-vibration type vector suspension microphone comprises a first ultrasonic transducer, a second ultrasonic transducer, a reflector, and a laser vibration meter. Positioning of the sensing element of the co-vibrating vector suspension microphone is completed by controlling radiation force distribution in a standing wave sound field, and stepless positioning can be achieved; the sensitivity of the co-vibration type vector suspension microphone is only related to the ratio of a fluid medium to a sensing element, so that a microphone group with good consistency can be easily obtained; the traceability path of the co-vibration type vector suspension microphone is simple, and the measurement uncertainty of primary calibration is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of vector microphones, and in particular relates to a measurement method based on a co-oscillation vector suspension microphone. Background Art

[0002] Microphones are the most important test equipment in the field of acoustics. All acoustic research and application development are based on the measurement data of microphones. Initially, microphones could only measure the sound pressure scalar. With the development of acoustic technology, the demand for measuring the particle velocity began to emerge. Now microphones can measure the particle velocity vector. In order to distinguish them from sound pressure scalar microphones, microphones that can measure the particle velocity vector are collectively called vector microphones.

[0003] The development of vector microphones can be classified into pressure difference vector microphones, resonance vector microphones and micro thermal flow vector microphones based on the sensing principle. The pressure difference vector microphone realizes vector measurement based on the spatial phase change of sound waves during sound propagation, and is mostly used in the field of air sound; the resonance vector microphone realizes vector measurement based on the principle of vibration velocity conduction, and is mostly used in the field of underwater sound; the micro thermal flow sensor uses the phenomenon of thermal-acoustic coupling to realize vector measurement by measuring the disturbance of the sound field on the thermal field.

[0004] There are still some unresolved problems in the development of microphones.

[0005] First, all microphones are currently hard-connected to the motion mechanism through the measurement fixture, and then the positioning or displacement of the microphone is achieved by controlling the motion mechanism. In the actual measurement process, the scattering of sound waves by the fixture will affect the measurement accuracy, and the vibration generated during the start and stop of the motion mechanism will also affect the measurement accuracy; secondly, the manufacturing of all microphones currently requires many processes, and there are many factors that affect the final sensitivity of the microphone, resulting in the only way to obtain a microphone group with good consistency is through selection. The higher the sensitivity consistency requirement, the greater the cost; finally, the traceability path of all microphone sensitivities is currently very complicated. Compared with other value sensors, the measurement uncertainty of the first-level calibration is higher, and it cannot be directly traced back to the basic quantity, which restricts the development of acoustic metrology technology. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention proposes the following technical solutions:

[0007] A measurement method based on a co-vibration vector suspension microphone, wherein the co-vibration vector suspension microphone comprises a first ultrasonic transducer, a second ultrasonic transducer, a reflector and a laser vibrometer;

[0008] The measuring method comprises the following steps:

[0009] S1, placing ultrasonic transducer 1 and ultrasonic transducer 2 at a distance apart with their radiation surfaces facing each other;

[0010] S2, simultaneously exciting ultrasonic transducer 1 and ultrasonic transducer 2 to form a standing wave sound field between the radiation surfaces;

[0011] S3, placing the reflector at the node of the standing wave sound field, so that the reflector is in a suspended static state under the action of the radiation force;

[0012] S4. When a sound wave passes through the location of the reflector, it causes the reflector to vibrate;

[0013] S5. measuring the vibration of the reflector using a laser vibrometer;

[0014] S6. Calculate the vibration velocity of the sound wave according to the sensitivity calculation formula and complete the measurement.

[0015] Furthermore, in step S2, ultrasonic transducer 1 and ultrasonic transducer 2 simultaneously excite sound waves of the same amplitude and phase, and the sound wave excited by ultrasonic transducer 1 is set to p 1 The ultrasonic transducer excites the sound wave set to p 2 , A is the amplitude of the sound wave, ω is the angular velocity, k is the wave number, k = ω / c, c is the speed of sound, H is the distance between the transducers, z is the height coordinate, and the height of the transducer radiation surface is z = 0,

[0016] At this time, p 1 and p 2 The sound pressure distribution p of the standing wave sound field formed after superposition is:

[0017] p=p 1 +p 2 =2Acos(kH / 2-kz)e j(ωt-kH / 2) (1)

[0018] The corresponding velocity field distribution u is:

[0019]

[0020] In the formula, ρ 0 is the medium density;

[0021] According to Gor'kov's ultrasonic standing wave theory, when the reflector is a small sphere with a radius of R, the acoustic radiation force F on the object is determined by the time-averaged potential U of the acoustic radiation:

[0022]

[0023] In the formula, is the mean square value of sound pressure, is the mean square value of vibration velocity;

[0024]

[0025] Let gravitational acceleration be g and the density of the ball be ρ s When the sound field radiation force F acting on the ball is equal to the gravity G, the reflector in step S3 remains suspended and stationary, and the suspension position z of the reflector is 0 for:

[0026]

[0027] In the formula, u 0 is the vibration amplitude, u 0 =2A / ρ 0 c, when Time 0 is a real number, the reflector can float, that is, the resultant force on the reflector is 0.

[0028] Furthermore, by changing the phase difference of the sound waves emitted by the two transducers, the distribution position of the standing wave sound field can be changed, thereby realizing the movement of the suspension position of the reflector ball.

[0029] Furthermore, in step S4, when the reflector in the hovering state is affected by a plane wave incident along the positive direction of the x-axis, P i is the incident wave field, p 0 is the incident wave amplitude,

[0030] The spherical coordinate system is constructed with the center O of the reflector as the origin, θ as the angular coordinate axis, and r as the radial coordinate axis. The spherical coordinate expansion of the incident plane wave is:

[0031]

[0032] In the formula, j n (x) is the nth-order Bessel function, P n (x) is the nth-order Legendre function. The reflector is approximately regarded as a rigid sphere. At this time, the scattered wave sound pressure P s for:

[0033]

[0034] In the formula, is the spherical Hankel function of the second kind; a n is an undetermined constant, which represents the corresponding n-order modal coefficient when the second-kind spherical wave of the scattered wave is expanded;

[0035] Assume that a rigid sphere oscillates slightly along the x-axis at the origin under the action of a plane wave field, and the vibration speed of the sphere is u s =u 0 e jωt, at this time, the reflector can be regarded as a swinging ball. According to the continuity condition of the normal particle velocity on the spherical surface, the sound pressure P in the sound field is obtained as:

[0036]

[0037] In the formula, x 0 = kR is the normalized beam size of the reflector, D n (x) and δ n (x) represent the amplitude and phase of the derivative function of the second kind of spherical Hankel function in the z-axis direction, which can be obtained by the following relationship:

[0038]

[0039] Assume that the incident plane wave field has a water particle velocity u at the center of the sphere. s =u 0 e jωt =(P / ρ 0 c)e jωt , then Newton's second law can be obtained:

[0040]

[0041] When kR<<1, formula (11) can be simplified to:

[0042]

[0043] k is the wave number, R is the radius of the reflector ball, u 0 is the vibration amplitude, ρ s is the density of the ball, ρ 0 is the medium density.

[0044] Furthermore, the expression of the sound pressure P in the standing wave sound field changing with the angle θ can be simplified as follows:

[0045]

[0046] In the formula,

[0047]

[0048] In the interval θ∈(-π, π), P(θ)=P(-θ). When the reflector is spherical, the components of the pressure on the spherical surface that are perpendicular to the propagation direction of the plane wave cancel each other out, making the vibration direction of the reflector consistent with the propagation direction of the plane wave. That is, when a plane wave passes by, it will not excite the reflector to vibrate in other directions.

[0049] Furthermore, in step S5, when a laser vibrometer is used to measure the vibration of the reflector, if the measuring direction of the laser vibrometer is θ 0= 0 and is parallel to the x-axis. The plane wave propagation direction θ′ = θ. Then the vibration velocity measured by the laser vibrometer is actually the component u of the vibration velocity of the reflector on the x-axis. x =u s cosθ.

[0050] Furthermore, in step S6, the velocity measurement sensitivity of the laser vibrometer is set to M u , the output voltage is U, then the sensitivity of the synchronous vector suspension microphone is M p The sensitivity calculation formula is:

[0051]

[0052] It can be concluded that the sensitivity of the co-resonance vector suspension microphone has vector characteristics.

[0053] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0054] The positioning of the sensor element of the co-vibration vector suspension microphone of the present invention is completed by controlling the distribution of radiation force in the standing wave sound field, and stepless positioning can be achieved; the sensitivity of the co-vibration vector suspension microphone is only related to the ratio of the fluid medium to the sensor element, and it is easy to obtain a microphone group with good consistency; the traceability path of the co-vibration vector suspension microphone is simple, which reduces the measurement uncertainty of the first-level calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a structural schematic diagram of the synchronous vector suspension microphone of the present invention;

[0056] Figure 2 It is a schematic diagram of the sensing principle of the synchronous vector suspension microphone of the present invention;

[0057] Figure 3 It is a schematic diagram of the sound field between ultrasonic transducer 1 and ultrasonic transducer 2 of the present invention;

[0058] Figure 4 Schematic diagram of the coordinate relationship between the reflector ball and the incident plane wave of the present invention;

[0059] Figure 5 It is a schematic diagram of the forces acting on two symmetrical points of the reflector sphere of the present invention. DETAILED DESCRIPTION

[0060] The following is a clear and complete description of the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Based on the embodiments, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] Combined with Figure 1-5 As shown, a measurement method based on a co-vibration vector suspension microphone, the co-vibration vector suspension microphone comprises an ultrasonic transducer 1, an ultrasonic transducer 2, a reflector and a laser vibrometer; wherein the ultrasonic transducer 1 and the ultrasonic transducer 2 are piston-type transmitting transducers;

[0062] The measuring method comprises the following steps:

[0063] S1, placing ultrasonic transducer 1 and ultrasonic transducer 2 at a distance apart with their radiation surfaces facing each other;

[0064] S2, simultaneously exciting ultrasonic transducer 1 and ultrasonic transducer 2 to form a standing wave sound field between the radiation surfaces;

[0065] S3, placing the reflector at the node of the standing wave sound field, so that the reflector is in a suspended static state under the action of the radiation force;

[0066] S4. When a sound wave passes through the location of the reflector, the reflector will vibrate due to the influence of the sound pressure gradient;

[0067] S5. measuring the vibration of the reflector using a laser vibrometer;

[0068] S6. Calculate the vibration velocity of the sound wave according to the sensitivity calculation formula and complete the measurement. That is, the laser vibrometer will measure the vibration component of the reflector in the vibration velocity direction to achieve vector measurement of the sound wave.

[0069] This measurement method mainly utilizes the radiation force in the standing wave sound field to suspend the light reflector, and then uses a laser vibrometer to measure the vibration of the reflector to measure the vibration velocity of the sound wave particle.

[0070] Specifically, in step S2, ultrasonic transducer 1 and ultrasonic transducer 2 simultaneously excite sound waves of the same amplitude and phase, and a standing wave field is generated between the transducers, as shown in the attached Figure 3 As shown, the sound wave excited by the ultrasonic transducer is set to p 1 The ultrasonic transducer excites the sound wave set to p 2 , A is the amplitude of the sound wave, ω is the angular velocity, k is the wave number, k = ω / c, c is the speed of sound, H is the distance between the transducers, z is the height coordinate, and the height of the transducer radiation surface is z = 0,

[0071] At this time, p 1 and p 2 The sound pressure distribution p of the standing wave sound field formed after superposition is:

[0072] p=p 1 +p 2 =2Acos(kH / 2-kz)e j(ωt-kH / 2) (1)

[0073] The corresponding velocity field distribution u is:

[0074]

[0075] In the formula, ρ 0 is the medium density;

[0076] According to Gor'kov's ultrasonic standing wave theory, when the reflector is a small sphere with a radius of R, the acoustic radiation force F on the object is determined by the time-averaged potential U of the acoustic radiation:

[0077]

[0078] In the formula, is the mean square value of sound pressure, is the mean square value of vibration velocity;

[0079]

[0080] Let gravitational acceleration be g and the density of the ball be ρ s When the sound field radiation force F acting on the ball is equal to the gravity G, the reflector in step S3 remains suspended and stationary, and the suspension position z of the reflector is 0 for:

[0081]

[0082] In the formula, u 0 is the vibration amplitude, u 0 =2A / ρ 0 c, when Time 0 is a real number, the reflector can float, that is, the resultant force on the reflector is 0.

[0083] Specifically, changing the phase difference of the sound waves emitted by the two transducers can change the distribution position of the standing wave sound field and realize the movement of the suspension position of the reflector ball, that is, the change of the reflector position can be achieved by changing the node position in the standing wave field.

[0084] Specifically, in step S4, when the reflector in the hovering state is affected by a plane wave incident along the positive direction of the x-axis, P i is the incident wave field, p 0 is the incident wave amplitude, as shown in the attached Figure 4 As shown,

[0085] The spherical coordinate system is constructed with the center O of the reflector as the origin, θ as the angular coordinate axis, and r as the radial coordinate axis. The spherical coordinate expansion of the incident plane wave is:

[0086]

[0087] In the formula, j n (x) is the nth-order Bessel function, P n (x) is the nth-order Legendre function. In air acoustics, the characteristic impedance of a solid is generally much greater than that of an air medium. Therefore, the reflector can be approximately regarded as a rigid body. At this time, the scattered wave sound pressure P s for:

[0088]

[0089] In the formula, is the spherical Hankel function of the second kind; a n is an undetermined constant, which represents the corresponding n-order modal coefficient when the second-kind spherical wave of the scattered wave is expanded;

[0090] Assume that a rigid sphere oscillates slightly along the x-axis at the origin under the action of a plane wave field, and the vibration speed of the sphere is u s =u 0 e jωt , at this time, the reflector can be regarded as a swinging ball. According to the continuity condition of the normal particle velocity on the spherical surface, the sound pressure P in the sound field is obtained as:

[0091]

[0092] In the formula, x 0 = kR is the normalized beam size of the reflector, D n (x) and δ n (x) represent the amplitude and phase of the derivative function of the second kind of spherical Hankel function in the z-axis direction, which can be obtained by the following relationship:

[0093]

[0094] Assume that the incident plane wave field has a water particle velocity u at the center of the sphere. s =u 0 e jωt =(P / ρ 0 c)e jωt , then Newton's second law can be obtained:

[0095]

[0096] When kR<<1, formula (11) can be simplified to:

[0097]

[0098] k is the wave number, R is the radius of the reflector ball, u 0 is the vibration amplitude, ρ s is the density of the ball, ρ 0 is the medium density.

[0099] Specifically, the expression of the sound pressure P in the standing wave sound field changing with the angle θ can be simplified as:

[0100]

[0101] In the formula,

[0102]

[0103] In the interval θ∈(-π,π), P(θ)=P(-θ). When the reflector is spherical, the components of the pressure on the spherical surface perpendicular to the propagation direction of the plane wave cancel each other out, making the vibration direction of the reflector consistent with the propagation direction of the plane wave. Figure 5 As shown, f 1 and f 2 is the plane wave force on two symmetrical points on the reflector, and F is f 1 and f 2 The direction of the resultant force is the same as the propagation direction of the plane wave, that is, when a plane wave passes by, it will not excite the reflector to vibrate in other directions.

[0104] Specifically, in step S5, when a laser vibrometer is used to measure the vibration of the reflector, if the measuring direction of the laser vibrometer is θ 0 = 0 and is parallel to the x-axis. The plane wave propagation direction θ′ = θ. Then the vibration velocity measured by the laser vibrometer is actually the component u of the vibration velocity of the reflector on the x-axis. x =u s cosθ.

[0105] Specifically, in step S6, the velocity measurement sensitivity of the laser vibrometer is set to M u , the output voltage is U, then the sensitivity of the synchronous vector suspension microphone is M p The sensitivity calculation formula is:

[0106]

Claims

1. A measurement method based on a co-vibration vector suspension microphone, characterized in that: The co-vibration vector suspension microphone comprises ultrasonic transducer 1, ultrasonic transducer 2, a reflector and a laser vibrometer; the measuring method comprises the following steps: S1, placing ultrasonic transducer 1 and ultrasonic transducer 2 at a distance apart with their radiation surfaces facing each other; S2, simultaneously exciting ultrasonic transducer 1 and ultrasonic transducer 2 to form a standing wave sound field between the radiation surfaces; S3, placing the reflector at the node of the standing wave sound field, so that the reflector is in a suspended static state under the action of the radiation force; S4. When a sound wave passes through the location of the reflector, it causes the reflector to vibrate; S5. measuring the vibration of the reflector using a laser vibrometer; S6. Calculate the vibration velocity of the sound wave according to the sensitivity calculation formula and complete the measurement.

2. The measurement method based on the co-vibration vector suspension microphone according to claim 1 is characterized in that: In step S2, ultrasonic transducer 1 and ultrasonic transducer 2 simultaneously excite sound waves of the same amplitude and phase, the sound wave excited by ultrasonic transducer 1 is set to p1, the sound wave excited by ultrasonic transducer 2 is set to p2, A is the amplitude of the sound wave, ω is the angular velocity, k is the wave number, k=ω / c, c is the speed of sound, H is the distance between transducers, z is the height coordinate, and the height of the transducer radiation surface is z=0, At this time, the sound pressure distribution p of the standing wave sound field formed by the superposition of p1 and p2 is: p=p1+p2=2Acos(kH / 2-kz)e j(ωt-kH / 2) (1) The corresponding velocity field distribution u is: Where ρ0 is the medium density; According to Gor'kov's ultrasonic standing wave theory, when the reflector is a small sphere with a radius of R, the acoustic radiation force F on the object is determined by the time-averaged potential U of the acoustic radiation: In the formula, is the mean square value of sound pressure, is the mean square value of vibration velocity; Let gravitational acceleration be g and the density of the ball be ρ s , when the sound field radiation force F acting on the ball is equal to the gravity G, the reflector in step S3 is kept suspended and stationary, and the suspension position z0 of the reflector is: In the formula, u0 is the vibration amplitude, u0=2A / ρ0c, when The reflector can float only when z0 is a real number, that is, the resultant force acting on the reflector is 0.

3. The measurement method based on the co-vibration vector suspension microphone according to claim 2 is characterized in that: Changing the phase difference of the sound waves emitted by the two transducers can change the distribution position of the standing wave sound field and realize the movement of the suspension position of the reflector ball.

4. The measurement method based on the co-vibration vector suspension microphone according to claim 2 is characterized in that: In step S4, when the reflector in the hovering state is affected by a plane wave incident along the positive direction of the x-axis, P i is the incident wave acoustic field, p0 is the incident wave amplitude, The spherical coordinate system is constructed with the center O of the reflector as the origin, θ as the angular coordinate axis, and r as the radial coordinate axis. The spherical coordinate expansion of the incident plane wave is: In the formula, j n (x) is the nth-order Bessel function, P n (x) is the nth-order Legendre function. The reflector is approximately regarded as a rigid sphere. At this time, the scattered wave sound pressure P s for: In the formula, is the spherical Hankel function of the second kind; a n is an undetermined constant, which represents the corresponding n-order modal coefficient when the second-kind spherical wave of the scattered wave is expanded; Assume that a rigid sphere oscillates slightly along the x-axis at the origin under the action of a plane wave field, and the vibration speed of the sphere is u s =u0e jωt , at this time, the reflector can be regarded as a swinging ball. According to the continuity condition of the normal particle velocity on the spherical surface, the sound pressure P in the sound field is obtained as: Where x0 = kR is the normalized beam size of the reflector, D n (x) and δ n (x) represent the amplitude and phase of the derivative function of the second kind of spherical Hankel function in the z-axis direction, which can be obtained by the following relationship: Assume that the incident plane wave field has a water particle velocity u at the center of the sphere. s =u0e jωt =(P / ρ0c)e jωt , then Newton's second law can be obtained: When kR<<1, formula (11) can be simplified to: k is the wave number, R is the radius of the reflector ball, u0 is the vibration amplitude, ρ s is the density of the ball, and ρ0 is the density of the medium.

5. The measurement method based on co-vibration vector suspension microphone according to claim 4 is characterized in that: The expression of the sound pressure P in the standing wave sound field changing with the angle θ can be simplified as follows: In the formula, In the interval θ∈(-π, π), P(θ)=P(-θ). When the reflector is spherical, the components of the pressure on the spherical surface that are perpendicular to the propagation direction of the plane wave cancel each other out, making the vibration direction of the reflector consistent with the propagation direction of the plane wave. That is, when a plane wave passes by, it will not excite the reflector to vibrate in other directions.

6. The measurement method based on the co-vibration vector suspension microphone according to claim 5 is characterized in that: In step S5, when the laser vibrometer is used to measure the vibration of the reflector, if the measuring direction of the laser vibrometer is θ0=0 and parallel to the x-axis, and the plane wave propagation direction θ′=θ, then the vibration velocity measured by the laser vibrometer is actually the component u of the vibration velocity of the reflector on the x-axis. x =u s cosθ.

7. The measurement method based on co-vibration vector suspension microphone according to claim 6 is characterized in that: In step S6, the velocity measurement sensitivity of the laser vibrometer is set to M u , the output voltage is U, then the sensitivity of the synchronous vector suspension microphone is M p The sensitivity calculation formula is: It can be concluded that the sensitivity of the co-resonance vector suspension microphone has vector characteristics.

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