An apparatus and method for measuring the density of states of a sound field

Abstract

The application discloses a device and a method for measuring the local density of states of a sound field, and the measuring device comprises a sound source, a square waveguide, a MEMS silicon microphone and an acoustic vector sensor; one end of the square waveguide is connected with the sound source, and the other end is embedded with the MEMS silicon microphone and the acoustic vector sensor which are attached to the inner wall of the square waveguide. By measuring the particle velocity of the end surface of the waveguide, the volume flow rate of the waveguide into the measured structure can be obtained, and the local density of states of the measured structure can be calculated by combining the sound pressure obtained by the MEMS silicon microphone. The application overcomes the difficulty that the volume flow rate of the sound source in a narrow area cannot be accurately measured by using the vector detection technology, realizes the experimental measurement of the local density of states of the sound field, can be applied to the characterization of acoustic structural materials, and provides guidance for the design of acoustic radiation structures.

Description

Technical Field

[0001] This invention relates to an apparatus and method for measuring local state density, and more specifically to an apparatus and method for measuring the local state density of a sound field. Background Technology

[0002] The density of states (DOS) refers to the number of modes per unit volume and per unit frequency range, specifically the ratio of the number of states with energies between E and E+ΔE per unit volume to the energy difference ΔE. It characterizes the density of states within a given energy range. The spatial distribution of the density of states is often non-uniform. To describe this non-uniform distribution in real space, the concept of local density of states (LDOS) is introduced. LDOS is defined as the number of modes per unit frequency range at a specific spatial point. Compared to the density of states, LDOS provides more detailed information and can reflect the spatial distribution of eigenstates to a certain extent.

[0003] Local density of states (MDS) is an important physical quantity that plays a crucial role in research on radiation rate modulation, material property characterization, and wave-matter interactions. In the field of micro-nano photonics, the manipulation of photon MDS has been a popular research direction. Various nanophotonic structures have been proposed to enhance MDS, playing significant roles in single-photon sources, nanolasers, and the strong interaction between light and matter. In acoustics, in 2018, Maryamlandi et al. at the University of Mississippi discovered that the sound source radiation rate is proportional to the sound field MDS using a spatially folded structure, revealing that the enhancement of sound radiation efficiency originates from the increase in MDS at the sound source. Although significant progress has been made in acoustic artificial microstructure materials in recent years, research on acoustic MDS remains relatively limited, and experimental methods for directly measuring the MDS of a sound field are still lacking.

[0004] The local density of states of a sound field is directly related to the Green's function. To characterize the local density of states, it is necessary to know both the intensity information of the sound source and the sound pressure information at the source, which is still quite difficult in experiments. Summary of the Invention

[0005] Objective of the invention: The present invention aims to provide an apparatus capable of accurately measuring the local density of states of a sound field; another objective of the present invention is to provide a method for measuring the local density of states of a sound field using the aforementioned apparatus.

[0006] Technical Solution: The device for measuring the local density of states of a sound field according to the present invention includes a sound source, a square waveguide, a MEMS silicon microphone, and an acoustic vector sensor; one end of the square waveguide is connected to the sound source, and the other end is embedded with the MEMS silicon microphone and the acoustic vector sensor, which are attached to its inner wall. The size of the sound source and the acoustic vector sensor, as well as the cross-sectional size of the square waveguide, are less than one-tenth of the wavelength. The sound inlet of the MEMS silicon microphone and the hot wire of the acoustic vector sensor are flush with the inner wall of the square waveguide. The sound pressure and sound particle velocity at the end face of the square waveguide are obtained through the MEMS silicon microphone and the acoustic vector sensor, respectively, thereby obtaining the local density of states of the measured structure at the excitation frequency of the sound source. Specifically:

[0007] The local density of states near the sound source is calculated from the imaginary part of the Green's function. Where ω is the excitation angular frequency of the sound source, and These are the detection location and the sound source location, respectively. Where c0 is the speed of sound, and the Green's function at the sound source is determined by the intensity of the sound source and the sound pressure at that point: , where p s ρ represents the sound pressure at the source. air For air density, u s and S s These represent the surface velocity and surface area of ​​the sound source, respectively. The local density of states of the measured structure at the corresponding frequency at the waveguide end face is obtained from the sound pressure and particle velocity at the square waveguide end face. .

[0008] A method for measuring the local state density of a sound field using the aforementioned apparatus includes the following steps:

[0009] (1) Make a square hole in the structure under test, so that the structure under test is connected to one end of the square waveguide through the square hole, and the sound wave enters the structure under test through the waveguide;

[0010] (2) Select a set of frequencies near the resonant frequency of the structure under test as the excitation of the sound source;

[0011] (3) Insert the square waveguide into the structure under test, and obtain the sound pressure and sound particle velocity at the end face of the square waveguide by the MEMS silicon microphone and the acoustic vector sensor, respectively.

[0012] (4) Calculate the local density of states near the sound source based on the imaginary part of the Green's function. Combine the sound pressure and sound particle velocity at the end face of the square waveguide described in step (3) to obtain the local density of states of the structure under test at the corresponding frequency at the end face of the waveguide.

[0013] Furthermore, a square barrel sleeve is provided around the square hole of the structure under test for inserting the local density of states measurement device.

[0014] Furthermore, in step (4), the measurement environment should be kept open during measurement to avoid obstacles scattering sound waves and causing inaccurate measurement results.

[0015] Furthermore, in step (4), in order to prevent the sound energy from escaping, an external force should be used to ensure that the local density of states measuring device is fully in contact with the structure being measured throughout the measurement process.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) It overcomes the problem of not being able to accurately measure the volume flow rate of the sound source in a narrow area and realizes the measurement of the local density of states of the sound field for the first time; (2) It integrates the measurement of sound pressure and particle velocity into one device, simplifying the steps of measuring the local density of states of the sound field; (3) By using the developed local density of states of the sound field measurement technology, it is possible to measure the distribution of the sound field state and apply it to the characterization of acoustic artificial structure materials and the design of acoustic radiation structures. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the sound field local state density measuring device of the present invention;

[0018] Figure 2 This is a schematic diagram of the structure for measuring the local state density of the sound field in a Helmholtz resonator using the device described in this invention;

[0019] Figure 3 This is a schematic diagram of the Helmholtz resonator of the structure under test;

[0020] Figure 4 The sound field local state density map is obtained by measuring the Helmholtz resonator using the device described in this invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] like Figure 1 As shown in the figure, the following are labeled: 1. Sound source, 2. Square waveguide, 3. MEMS silicon microphone, 4. Acoustic vector sensor, 5. Helmholtz resonant cavity, 51. Square hole, 52. Sleeve.

[0023] The device for measuring the local state density of a sound field according to the present invention includes a sound source 1, a square waveguide 2, a MEMS silicon microphone 3, and an acoustic vector sensor 4. The sound source 1 is a Knowles CI-22955-000 Knowles moving iron unit. The square waveguide 2 has dimensions of 15 × 10 × 14 mm. 3 It is manufactured using a photopolymerization printing method. The square waveguide 2 has an opening size of 7.18 × 4.1 mm at one end. 2(Same size as the longitudinal section of the sound source), gradually extending to another size of 10 × 14 mm. 2 The port is [port number missing]. The MEMS silicon microphone 3 is model SPH0641LU4H. The acoustic vector sensor 4 is the acoustic vector sensor disclosed in patent publication number CN 209247158 U.

[0024] like Figure 1 As shown, the sound source 1 is inserted into the small port of the square waveguide 2, thus confining the sound source within the square waveguide 2. The MEMS silicon microphone 3 and the acoustic vector sensor 4 are respectively embedded in the large port of the square waveguide 2, so that the surfaces of the MEMS silicon microphone 3 and the acoustic vector sensor 4 are flush with the inner wall.

[0025] like Figure 2 As shown, the structure selected for testing in this embodiment is a Helmholtz resonant cavity 5, with cavity dimensions of 60 × 60 × 60 mm. 3 Its opening size is π × 18 2 × 5mm 3 Its wall thickness is 4mm.

[0026] like Figure 3 As shown, a cavity with the same dimensions (10 × 14 mm) as the large port of the square waveguide 2 needs to be opened in the Helmholtz resonator 5 of the structure under test. 2 The square opening 51 requires a square sleeve 52 outside the square hole 51, with a through hole size of 10 × 14 mm. 2 The local density of states measuring device is inserted into the Helmholtz resonant cavity. To prevent acoustic energy from escaping from the contact point between the local density of states measuring device and the structure under test, a gasket should be added at the contact point to seal the entire acoustic channel. At the same time, external force should be used to ensure that the local density of states measuring device and the structure under test are in full contact.

[0027] The measurement method based on the above-mentioned sound field local state density measurement device specifically includes the following steps:

[0028] (1) The Helmholtz resonator needs to have a port size identical to the large port size of the square waveguide in the sound field local density of states measurement device (10 × 14 mm). 2 The square hole 51 allows the sound wave to enter the structure under test through the square waveguide;

[0029] (2) A square sleeve 52 needs to be set around the square hole 51 of the Helmholtz resonant cavity so that the sound field local state density measuring device can be inserted into the structure under test.

[0030] (3) Select a set of frequencies around 694Hz resonant frequency of the Helmholtz resonator: 670~720Hz, with a frequency interval of 2Hz, as the excitation of the sound source. The sound source signal is transmitted from the host to the sound source through the power amplifier.

[0031] (4) Insert the local state density measurement device into the structure under test, and use the NI9234 signal acquisition card to collect the sound pressure and sound particle velocity at the end face of the MEMS silicon microphone and acoustic vector sensor respectively at the square waveguide end face.

[0032] (5) Calculate the local density of states near the sound source using the imaginary part of the Green's function: , and These are the detection location and the sound source location, respectively. (where c0 is the speed of sound), the Green's function at the sound source is determined by the intensity of the sound source and the sound pressure at that point: , where p s ρ represents the sound pressure at the source. air For air density, u s and S s These are the surface vibration velocity and surface area of ​​the sound source, respectively. Combining the sound pressure and sound particle vibration velocity at the square waveguide end face obtained in step (4), the local density of states of the measured structure at the waveguide end face at the corresponding frequency can be obtained. .

[0033] The measurement results are as follows Figure 4 As shown, the local density of states of the Helmholtz resonator at a resonant frequency of 694 Hz is 19.65 Hz. -1 m -3 .

[0034] Therefore, the method for measuring the local state density of a sound field described in this invention is the first to achieve experimental measurement of the local state density of a sound field, and can be applied to sound wave modulation and the design of novel acoustic devices.

Claims

1. A device for measuring the local state density of a sound field, characterized in that, The measuring device includes a sound source (1), a square waveguide (2), a MEMS silicon microphone (3), and an acoustic vector sensor (4); One end of the square waveguide (2) is connected to the sound source (1), and the other end is embedded with a MEMS silicon microphone (3) and an acoustic vector sensor (4) that are attached to its inner wall. The size of the sound source (1) and the acoustic vector sensor (4), as well as the cross-sectional size of the square waveguide (2), are less than one-tenth of the wavelength. The sound inlet of the MEMS silicon microphone (3) and the hot wire of the acoustic vector sensor (4) are flush with the inner wall of the square waveguide (2). The sound pressure and sound particle velocity at the end face of the square waveguide (2) are obtained through the MEMS silicon microphone (3) and the acoustic vector sensor (4), respectively, thereby obtaining the local density of states of the structure under test at the excitation frequency of the sound source. Specifically: The local density of states near the sound source is calculated from the imaginary part of the Green's function. Where ω is the excitation angular frequency of the sound source, and These are the detection location and the sound source location, respectively. Where c0 is the speed of sound, and the Green's function at the sound source is determined by the intensity of the sound source and the sound pressure at that point: , where p s ρ represents the sound pressure at the source. air For air density, u s and S s These represent the surface velocity and surface area of ​​the sound source, respectively. The local density of states of the measured structure at the corresponding frequency at the waveguide end face is obtained from the sound pressure and particle velocity at the square waveguide end face. .

2. The apparatus for measuring the local state density of a sound field according to claim 1, characterized in that, The sound source (1) is composed of a moving iron unit.

3. A method for measuring the local state density of a sound field using the apparatus described in any one of claims 1-2, characterized in that, Includes the following steps: (1) Make a square hole in the structure under test, so that the structure under test is connected to one end of the square waveguide (2) through the square hole, and the sound wave enters the structure under test through the waveguide; (2) Select a set of frequencies near the resonant frequency of the structure under test as the excitation of the sound source; (3) Insert the square waveguide (2) into the structure under test, and obtain the sound pressure and sound particle velocity at the end face of the square waveguide (2) by the MEMS silicon microphone (3) and the acoustic vector sensor (4); (4) Calculate the local density of states near the sound source based on the imaginary part of the Green's function. Combine the sound pressure and sound particle velocity at the end face of the square waveguide (2) described in step (3) to obtain the local density of states of the structure under test at the corresponding frequency at the end face of the waveguide.

4. The method for measuring the local state density of a sound field according to claim 3, characterized in that, A square barrel sleeve is also provided around the square hole of the structure under test for the insertion of the local density of states measurement device.

5. The method for measuring the local state density of a sound field according to claim 3, characterized in that, The environment during the measurement was kept open.

6. The method for measuring the local state density of a sound field according to claim 3, characterized in that, The contact surface between the square waveguide (2) and the structure under test is provided with a silicone pad to prevent gaps from forming on the contact surface and causing acoustic energy to escape.

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