A capacitance microphone for photoacoustic cell measurements

Abstract

The utility model discloses an embodiment provides a kind of condenser microphone for photoacoustic cell measurement, comprising: cylindrical shell, diaphragm connected to the front end of shell and the insulating sheet being set to the inside of shell, rear cavity is formed between diaphragm and insulating sheet;Uniform pressure hole is also provided on shell, and uniform pressure hole communicates rear cavity with outside.This technical scheme in which one uniform pressure hole is arranged on the side of condenser microphone, and spiral capillary is arranged in rear cavity by uniform pressure hole, so that the pressure balance of rear cavity and outside is realized, a unique side uniform pressure mode is realized, and the mode is very suitable for photoacoustic cell measurement.

Description

Technical Field

[0001] This utility model relates to the field of microphone technology, and more particularly to a capacitor microphone, and more specifically, a capacitor microphone for photoacoustic cell measurement. Background Technology

[0002] An electret microphone is a common type of acoustic-electric transducer, widely used in various acoustic measurement systems. The working principle of an electret microphone involves a small air gap between a polarized diaphragm (also called a vibrating diaphragm) and a back plate, forming a parallel-plate capacitor. When sound waves act on the diaphragm, they change the distance between the capacitor plates, causing a change in the capacitor's capacitance, thus generating an alternating voltage and a real-time changing electrical signal output. Inside the microphone, the cavity composed of an insulating sheet and a diaphragm is the rear cavity. The air in the rear cavity helps maintain the normal vibration of the microphone diaphragm. If the air volume in the rear cavity is too small, the resistance difference between the front and rear vibrations of the diaphragm will be too large, leading to signal overload.

[0003] Commercially available electret condenser microphones are generally divided into pressure field microphones and free field microphones. Free field microphones are typically used in open spaces, where the entire microphone is placed in the sound field for measurement. Pressure field microphones, on the other hand, are used to measure the sound pressure on the front surface of the diaphragm and are often used in enclosed spaces, such as measuring the sound pressure on a wall or inside a small cavity. Usually, only the diaphragm of the microphone is exposed to the sound field.

[0004] The rear cavity of a microphone contains a certain volume of gas. When the static pressure outside the microphone changes, if there is no vent to connect the rear cavity and the outside for pressure equalization, the resulting pressure imbalance can cause significant interference signals or cause the diaphragm to deviate from its normal operating position. Vents, also known as pressure equalization holes, are typically located at the rear of the microphone, hence the term rear pressure equalization. Pressure equalization is achieved through tiny air gaps in the internal structure. This design and manufacturing process is relatively inexpensive, making it the most common microphone pressure equalization structure on the market.

[0005] A photoacoustic cell is a common acoustic environment requiring pressure field microphone testing. It's a device that utilizes the photoacoustic effect to transmit information or detect media. The photoacoustic effect refers to the phenomenon where, as light propagates through a medium, the molecules in the medium absorb modulated light radiation energy of a specific wavelength and are excited, resulting in changes in temperature and density, which in turn alters the medium's pressure and generates sound wave vibrations on the microphone diaphragm surface. Photoacoustic cells are commonly used for the spectral detection of gases, determining their composition and concentration by detecting acoustic signals. A photoacoustic cell typically consists of a photoacoustic cavity with inlet / outlet ports and a connected measurement cavity. One end of the measurement cavity is the inlet, through which gas from the photoacoustic cavity enters the measurement cavity. The microphone is mounted at the other end of the measurement cavity, with only the diaphragm exposed. In existing technologies, post-equalizing microphones are commonly used for photovoltaic cell measurements.

[0006] In the process of realizing this utility model, the inventors discovered that the prior art has at least the following problems: when using a post-equalizing microphone to measure a photovoltaic cell, the measurement results are often inaccurate or even impossible to measure. Therefore, how to ensure the accuracy of the measurement results is a problem that needs to be solved. Utility Model Content

[0007] This utility model provides a capacitor microphone for photoacoustic cell measurement to ensure the accuracy of the measurement results.

[0008] To achieve the above objectives, this utility model provides a capacitor microphone for photoacoustic cell measurement, comprising: a cylindrical outer shell, a diaphragm connected to the front end of the outer shell, and an insulating sheet disposed inside the outer shell, wherein a rear cavity is formed between the diaphragm and the insulating sheet; the outer shell is also provided with an equalizing hole, which connects the rear cavity to the outside.

[0009] Furthermore, the capacitive microphone used for photoacoustic cell measurement also includes a capillary tube located inside the housing, with the fixed end of the capillary tube connected to the equalizing orifice.

[0010] Furthermore, the fixed end of the capillary is fitted inside the pressure equalization hole, and the portion of the capillary outside the fixed end is arranged around the rear cavity and attached to the inner wall of the outer shell.

[0011] Furthermore, the number of turns of the capillary tube within the rear cavity is ≤1.

[0012] Furthermore, the inner diameter of the capillary is 0.2 mm to 0.4 mm.

[0013] Furthermore, the capillary is made of aluminum.

[0014] Furthermore, the pressure equalization hole is parallel to the diaphragm and tangent to the inner wall of the outer shell.

[0015] Furthermore, the capacitor microphone used for photoacoustic cell measurement also includes an adapter ring, and the housing is provided with a connecting section for connecting the adapter ring; the connecting section is provided with a platform surface, the outer side of the equalizing hole is connected to the platform surface, and the platform surface is parallel to the axis of the housing.

[0016] Furthermore, the distance between the equalizing hole and the diaphragm is 4.8 mm to 5.3 mm.

[0017] Furthermore, a sealing ring is provided between the insulating sheet and the outer shell.

[0018] The above technical solution has the following beneficial effects:

[0019] In this technical solution, a pressure equalization hole is set on the side of the condenser microphone, and a spiral capillary is set in the rear cavity through the pressure equalization hole, thereby realizing the pressure equalization between the rear cavity and the outside, achieving a unique side pressure equalization method. This method effectively solves the problem of acoustic testing of microphones in closed cavities with rapid pressure changes, such as photoacoustic cells, and improves the measurement error caused by the pressure difference before and after the microphone in traditional rear pressure equalization microphones. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of a capacitor microphone for photoacoustic cell measurement according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram showing the location of the pressure equalization hole in an embodiment of this utility model;

[0023] Figure 3 This is a schematic diagram of the platform surface opening in an embodiment of this utility model;

[0024] Figure 4 This is a schematic diagram of the sealing ring installation position in an embodiment of this utility model;

[0025] Reference numerals: 1. Outer shell; 2. Insulating sheet; 3. Diaphragm; 5. Adapter ring; 6. Rear cavity; 7. Equalizing hole; 8. Capillary tube; 9. Sealing ring; 11. Connecting section; 12. Platform surface. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0027] First, the inventors discovered the cause of the aforementioned problem through research: the measuring cavity in the photoacoustic cell is very small, and because the gas composition, density, and pressure inside the photoacoustic cavity differ from air, using a pressure-equalizing microphone in the photoacoustic cell easily causes an imbalance in the static pressure before and after the diaphragm. When the pressure inside the measuring cavity of the photoacoustic cell increases, the diaphragm cannot vibrate normally, resulting in signal overload. Through multiple experiments, it was found that when the relative pressure rises to a high value, the microphone's output signal will experience overload, thus preventing the normal output of the measurement signal.

[0028] like Figure 1 As shown, to solve this problem, this utility model embodiment designs a condenser microphone for photoacoustic cell measurement. Its specific structure includes: a cylindrical outer shell 1, a diaphragm 3 connected to the front end of the outer shell 1, and an insulating sheet 2 disposed inside the outer shell 1. A rear cavity 6 is formed between the diaphragm 3 and the insulating sheet 2. A pressure equalization hole 7 is also provided on the outer shell 1, and the pressure equalization hole 7 connects the rear cavity 6 to the outside. That is, in this condenser microphone, a pressure equalization hole 7 is provided on the side (outer shell 1), which can be called a side-equalization type. The pressure equalization hole 7 is located closer to the diaphragm 3, thereby reducing the pressure difference between the front and rear, and solving the problem of large measurement errors when the microphone is used for acoustic testing in a closed cavity with rapidly changing pressure, such as a photoacoustic cell.

[0029] Furthermore, testing revealed several issues with relying solely on the equalizing holes 7 (including gaps between internal structures) on the outer casing 1 for pressure equalization. For example, if the equalizing holes 7 are too small, insufficient airflow will slow down the pressure equalization process, resulting in poor equalization. If the equalizing holes 7 are too large, low-frequency sound waves from the external sound field will enter the rear cavity 6 through the equalizing holes 7, causing a decrease in the microphone's low-frequency response and an increase in the low-frequency cutoff frequency. Therefore, this technical solution also incorporates a capillary tube 8 inside the condenser microphone. One end of the capillary tube 8 is connected to the equalizing holes 7, combining the capillary tube 8 and the equalizing holes 7 as a pressure equalization structure. This achieves increased airflow path length while maintaining a smaller diameter for the equalizing holes 7 and reducing the entry of low-frequency sound waves into the rear cavity 6, thus maintaining a faster pressure equalization speed inside the microphone and achieving better measurement accuracy.

[0030] Furthermore, to facilitate installation, the fixed end of the capillary tube 8 can be directly fitted into the pressure equalization hole 7. That is, during installation, the capillary tube 8 is directly inserted into the pressure equalization hole 7 from the outside and further extended into the rear cavity 6. After observing under a microscope that the capillary tube has wound to the required length within the rear cavity 6, the remaining tube exposed outside the outer shell 1 is cut off. Meanwhile, if... Figure 1 As shown, the capillary tube 8 entering the rear cavity 6 can be spiraled and attached to the inner wall of the outer shell 1 for easy arrangement.

[0031] Furthermore, to achieve better results, the inventors performed the following calculations: The frequency response curve of the microphone from 1Hz to 250Hz was measured in the low-frequency coupling cavity, and a stable sound field with consistent amplitude from 1Hz to 250Hz was output from the coupling cavity. Using 250Hz as a reference point, the frequency point with a frequency response 3dB lower than 250Hz was determined as the lower limit of the microphone's low-frequency range. This lower limit is related to the microphone's equalization time, which is determined by the size of the equalization orifice 7 and the length of the capillary tube 8. Through experiments, the length of the capillary tube 8 was ultimately determined to be approximately one turn (ideally close to one turn but not more than one turn), and the inner diameter of the capillary tube 8 was 0.2mm to 0.4mm. At this point, the lower limit of the microphone's frequency range was approximately between 1 and 3Hz.

[0032] Furthermore, the capillary tube 8 is preferably made of aluminum, as aluminum capillary tube 8 is easier to form into a spiral shape.

[0033] Furthermore, such as Figure 2 As shown, it is preferable to set the pressure equalization hole 7 parallel to the diaphragm 3 and to set the pressure equalization hole 7 tangent to the inner wall of the outer shell 1. At this time, the capillary tube 8 can be inserted more easily, and under the squeezing action of the inner wall arc surface, as the capillary tube 8 extends inward, it can automatically form a circle. Subsequently, the capillary tube 8 in the rear cavity can be fixed to the inner wall of the outer shell 1 by adhesive.

[0034] Furthermore, in this design, the side-equalizing microphone no longer uses a traditional microphone protective cover during operation, but instead uses an adapter ring 5, which is installed on the connecting section 11. Then, a platform surface 12 is machined into the connecting section 11 by milling or other methods, and the outer side of the equalizing hole 7 is connected to the platform surface 12 (see...). Figure 3 Furthermore, the platform surface 12 is parallel to the axis of the outer shell 1. In this case, the adapter ring 5 can be prevented from blocking the pressure equalization hole 7, so that the platform surface 12 with the pressure equalization hole 7 and the adapter ring 5 form a gap for gas flow.

[0035] Furthermore, after testing, in order to achieve better results, the position of the equalizing hole 7 can be limited so that the distance between it and the diaphragm 3 is kept between 4.8 mm and 5.3 mm.

[0036] Furthermore, such as Figure 4As shown, to ensure that the air pressure in the rear cavity 6 is equalized with the external atmospheric pressure only through the capillary tube 8 and the equalizing hole 7, and to prevent air leakage in the rear cavity 6 from causing attenuation of the microphone's low-frequency response, a sealing ring 9 (preferably a rubber O-ring) can be installed in the rear cavity 6 to enhance its sealing performance. The sealing ring 9 is installed between the insulating sheet 2 and the outer shell 1, and is fitted onto the bottom outer side of the insulating sheet 2.

[0037] The following detailed description of this technical solution is provided through a specific embodiment:

[0038] In this specific embodiment, the microphone's external dimensions conform to the 1 / 2-inch microphone specifications specified in the ICE 61094 standard. The main structure includes a housing 1, a diaphragm 3, a rear electrode plate, and an insulating sheet 2. A small hole (i.e., a pressure equalization hole 7, used to install a capillary tube 8 (or a sound guide tube) and as an inlet for the capillary tube 8 to connect with the external air pressure; the hole diameter matches the outer diameter of the capillary tube 8) is drilled from the outside of the housing 1 into the inside of the microphone until it connects to the rear cavity 6 and is tangent to the cross-sectional circle of the inner wall. The purpose of drilling in a tangential direction is to facilitate inserting a capillary tube 8 into the microphone from the pressure equalization hole 7, wrap it tightly around the inner wall of the housing 1, and then fix it with glue. The capillary tube 8 is made of aluminum and has a certain degree of plasticity. After wrapping around the inside, its end connects to the rear cavity 6 of the microphone.

[0039] The outer shell 1 is made of aluminum. Since the capillary tube 8 is installed on the side wall of the outer shell 1 between the insulating sheet 2 and the rear electrode plate, during assembly, the capillary tube 8 is inserted into the outer shell 1 through the pressure equalization hole 7. The capillary tube 8 is attached to the inner wall of the outer shell 1 using tools such as plastic rods. After being fixed with glue, the excess capillary tube 8 outside the outer shell 1 is cut off.

[0040] The capillary tube 8 has a diameter ≤ 0.6 mm and an inner diameter of 0.2 mm to 0.4 mm.

[0041] In the above detailed description, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0042] The disclosed embodiments have been described above to enable any person skilled in the art to implement or use this invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of this disclosure. Therefore, this disclosure is not limited to the embodiments given herein, but is consistent with the widest scope of the principles and novel features disclosed in this application.

[0043] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above description is only a specific embodiment of this utility model and is not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A capacitor microphone for photoacoustic cell measurement, characterized in that, include: A cylindrical outer shell (1), a diaphragm (3) connected to the front end of the outer shell (1), and an insulating sheet (2) disposed inside the outer shell (1) form a rear cavity (6) between the diaphragm (3) and the insulating sheet (2); a pressure equalization hole (7) is also provided on the outer shell (1), and the pressure equalization hole (7) connects the rear cavity (6) to the outside.

2. The capacitor microphone for photoacoustic cell measurement as described in claim 1, characterized in that, It also includes a capillary tube (8) located inside the outer casing (1), the fixed end of which is connected to the pressure equalization hole (7).

3. The capacitor microphone for photoacoustic cell measurement as described in claim 2, characterized in that, The fixed end of the capillary tube (8) is sleeved in the pressure equalization hole (7), and the part of the capillary tube (8) other than the fixed end is arranged around the rear cavity (6) and attached to the inner side wall of the outer shell (1).

4. The capacitor microphone for photoacoustic cell measurement as described in claim 3, characterized in that, The number of turns of the capillary tube (8) inside the rear cavity (6) is ≤1.

5. The capacitor microphone for photoacoustic cell measurement as described in claim 2, characterized in that, The inner diameter of the capillary (8) is 0.2 mm to 0.4 mm.

6. The capacitor microphone for photoacoustic cell measurement as described in claim 2, characterized in that, The capillary tube (8) is made of aluminum.

7. The capacitor microphone for photoacoustic cell measurement as described in claim 1, characterized in that, The pressure equalization hole (7) is parallel to the diaphragm (3), and the pressure equalization hole (7) is tangent to the inner wall of the outer shell (1).

8. The capacitor microphone for photoacoustic cell measurement as described in claim 1, characterized in that, It also includes an adapter ring (5), and the outer shell (1) is provided with a connecting section (11) for connecting the adapter ring (5); the connecting section (11) is provided with a platform surface (12), the outer side of the equalizing hole (7) is connected to the platform surface (12), and the platform surface (12) is parallel to the axis of the outer shell (1).

9. The capacitor microphone for photoacoustic cell measurement as described in claim 7, characterized in that, The distance between the equalizing hole (7) and the diaphragm (3) is 4.8 mm to 5.3 mm.

10. The capacitor microphone for photoacoustic cell measurement as described in claim 1, characterized in that, A sealing ring (9) is also provided between the insulating sheet (2) and the outer shell (1).

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