A miniaturized MEMS capacitive composite isotropic vector hydrophone

Abstract

The present invention discloses a miniaturized MEMS capacitive composite isoscillator vector hydrophone, which belongs to the technical field of underwater acoustic signal detection. The hydrophone comprises a MEMS capacitive accelerometer, a fixed core, a vertical suspension rod, a piezoelectric ceramic ring, a sound-transmitting sealed shell, and a conical helical spring. The MEMS capacitive acceleration sensor is orthogonally installed in the fixed core. The vertical suspension rod runs through the entire fixed core. The piezoelectric ceramic ring is sleeved on the outside of the fixed core. The sound-transmitting sealed shell is covered on the outside of the piezoelectric ceramic ring through a potting process. The conical helical spring is connected to the vertical suspension rod, and the hydrophone is suspended on a fixed bracket for use. The present invention can reduce the volume of the hydrophone while being able to detect the sound pressure signal and the vibration velocity signal at the same position underwater, thereby improving the accuracy of signal detection, and has a simple structure, good consistency, and high reliability.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic signal detection, and in particular to a miniaturized MEMS capacitive composite isochronous vector hydrophone. Background Art

[0002] Traditional scalar hydrophones, also called acoustic pressure hydrophones, are generally made of materials such as piezoelectric ceramics. They have various shapes and sizes and are mostly used as standard hydrophones, but can only measure scalar parameters in the sound field.

[0003] The core sensing element inside the traditional isotropic vector hydrophone is a vibration sensor. The vibration sensors used in hydrophone processing at home and abroad are mostly acceleration or velocity sensors based on the piezoelectric principle. This traditional piezoelectric vector hydrophone is large in size and heavy in weight, requires complex processing circuits at the back end, and is limited by traditional processing technology, has poor consistency, and is not easy to be installed on multiple platforms. It can no longer meet the current development needs of miniaturization and multi-platformization of underwater acoustic detection.

[0004] With the development of micro-electromechanical technology, MEMS hydrophones, which combine semiconductor devices based on MEMS technology with traditional hydroacoustic fields, have the advantages of low noise, high sensitivity, good consistency, etc., and can be highly integrated with the back-end ASIC circuit, greatly reducing the size and weight of the hydrophone, reducing the impact on the original radiated sound field, and making the detection results more accurate. The current MEMS isochronous vector hydrophones are piezoresistive, piezoelectric and capacitive. Piezoresistive and piezoelectric hydrophones generally have low sensitivity, large thermal noise, and are easily affected by temperature. MEMS capacitive hydrophones have the advantages of high detection accuracy, high sensitivity and high stability, and can effectively widen the bandwidth in conjunction with a closed-loop feedback circuit.

[0005] The patent with publication number CN1776390A discloses a "capacitive isochronous vector hydrophone and its process". This vector hydrophone uses a silicon micro-accelerometer as a sensitive element, but does not have the ability to detect scalar sound pressure. The patent with publication number CN208795359U discloses a "two-dimensional isochronous vector hydrophone". Although this structure can realize the detection of composite information of sound pressure and vibration velocity, it has the following problems: 1) The vibration velocity sensing element and the sound pressure sensing element are arranged vertically, resulting in a large size. 2) The vibration velocity sensing element and the sound pressure sensing element are not concentric, and the sound field information cannot be accurately obtained. 3) The suspension structure is relatively complex and requires eight spring supports. Summary of the invention

[0006] In view of this, the present invention provides a miniaturized MEMS capacitive composite isotropic vector hydrophone. The hydrophone can detect the sound pressure signal and vibration velocity signal at the same position underwater, which not only improves the accuracy of signal detection, but also has a simple structure, good consistency, high reliability, and can meet the needs of underwater low-frequency detection.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A miniaturized MEMS capacitive composite isoscillator vector hydrophone comprises a hydrophone body and a suspension, wherein the hydrophone body comprises a piezoelectric ceramic ring and a sound-permeable sealed shell whose outer surface is covered with a filling; the piezoelectric ceramic ring is connected to the outside via a cable; the hydrophone body also comprises a fixed core and at least two MEMS capacitive accelerometers; the top and bottom of the piezoelectric ceramic ring are covered with a foam cover plate, the fixed core is located inside the piezoelectric ceramic ring, the MEMS capacitive accelerometers are vertically arranged on the side wall of the fixed core, and adjacent MEMS capacitive accelerometers are perpendicular to each other and the centers of the two are located at the same height; the MEMS capacitive accelerometer is connected to the outside via a cable that penetrates the foam cover plate and the sound-permeable sealed shell.

[0009] Furthermore, the hydrophone body also includes a vertical hanging rod, which passes through the sound-transmitting sealed shell, the foam cover plate and the fixed core, and both ends of the vertical hanging rod are exposed outside the sound-transmitting sealed shell; the ends of the vertical hanging rod are provided with through holes, and the through holes at both ends are in an orthogonal relationship.

[0010] Furthermore, the fixed core is a cylinder, and the vertical suspension rod passes through the center line of the cylinder; the MEMS capacitive accelerometer is embedded on the side wall of the cylinder.

[0011] Furthermore, the center line of the piezoelectric ceramic ring coincides with the center line of the fixed core.

[0012] Furthermore, there are four MEMS capacitive accelerometers, which are spaced apart and mirror-symmetrical.

[0013] Furthermore, the suspension includes two conical coil springs; the cone heads of the two conical coil springs are respectively connected to the upper and lower through holes of the vertical suspension rod.

[0014] Furthermore, the material of the sound-transmitting sealing shell is polyurethane or butyl rubber.

[0015] Furthermore, the hydrophone body is located at the geometric center of the suspension.

[0016] Further, the center of gravity of the body including the suspension coincides with its geometric center.

[0017] Furthermore, the vertical suspension rod and the conical coil spring are made of stainless steel, titanium alloy or nylon.

[0018] The beneficial effects of the above technical solution of the present invention are:

[0019] 1. The present invention places a MEMS capacitive accelerometer inside a piezoelectric ceramic ring, which not only reduces the size and volume of the hydrophone, but also can simultaneously measure scalar signals and vector signals at the same position underwater, thereby ensuring the integrity and accuracy of the acquisition of sound field information.

[0020] 2. The present invention uses a MEMS capacitive accelerometer as a vibration velocity pickup unit, which can amplify the signal at the source end, thereby avoiding attenuation of weak signals caused by long-distance transmission.

[0021] 3. The present invention effectively reduces the suspension size of the hydrophone by using the vertically suspended conical coil spring device, and has a simple structure, and can also avoid the interference of the horizontal suspension device on the horizontal sound field. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural explosion diagram of an embodiment of the present invention;

[0023] Figure 2 It is a main cross-sectional view of an embodiment of the present invention;

[0024] Figure 3 Schematic diagram of a conical helical spring suspended hydrophone according to an embodiment of the present invention;

[0025] In the figure: 11, fixed core, 12, 13, MEMS capacitive accelerometer, 14, horizontal bolt, 15, vertical suspension rod, 16, piezoelectric ceramic ring, 17, upper foam cover plate, 18, lower foam cover plate, 19, vertical bolt, 32, through hole, 33, upper conical coil spring, 34, lower conical coil spring. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] The theoretical basis of scalar signal detection is that when the piezoelectric ceramic ring acts in the sound field, it can receive the sound signal excitation from the water medium, forcing the piezoelectric material to produce forced vibration and deformation, inducing electric charge, thereby converting the vibration signal into an electrical signal output, realizing scalar detection of the sound signal.

[0028] The theoretical basis of vector signal detection is: if the geometric size of the acoustic rigid body is smaller than the wavelength, when it vibrates freely under the action of sound waves in water, the vibration velocity amplitude V of the rigid cylinder is equal to the vibration velocity amplitude V of the water particle at the geometric center of gravity of the cylinder in the sound field.0 The following relationship exists:

[0029]

[0030] Where: 0 — water medium density, —The average density of a rigid cylinder.

[0031] According to the above formula, when the average density of the rigid cylinder is Equal to the water medium density ρ 0 When the vibration velocity amplitude V is the same as the vibration velocity amplitude V of the acoustically rigid column 0 Similarly, the vibration velocity is picked up by the MEMS capacitive acceleration sensor inside the rigid column, and the vibration signal is converted into an electrical signal output, so that the vibration velocity of the water particle at the geometric center of gravity of the hydrophone in the sound field can be obtained.

[0032] In summary, combining the detection principles of scalar signals and vector signals, it can be seen that the recorded sound field information is accurate only when the sound pressure signal and the vibration velocity signal are obtained at the same position in the water medium. Therefore, the piezoelectric ceramic ring and the vibration sensor are required to be as close as possible.

[0033] A miniaturized MEMS capacitive composite isoscillator vector hydrophone comprises a main body and a suspension, wherein the main body comprises a piezoelectric ceramic ring and a sound-transmitting sealed shell whose outer surface is covered with filling; the piezoelectric ceramic ring is connected to the outside via a cable; the main body also comprises a fixed core, a foam cover plate and at least two MEMS capacitive accelerometers; the top and bottom of the piezoelectric ceramic ring are both covered with a foam cover plate, the fixed core is located inside the piezoelectric ceramic ring, the MEMS capacitive accelerometers are vertically arranged on the side wall of the fixed core, and adjacent MEMS capacitive accelerometers are perpendicular to each other and located at the same height; the MEMS capacitive accelerometer is connected to the outside via a cable that penetrates the foam cover plate and the sound-transmitting sealed shell.

[0034] Furthermore, the main body also includes a vertical hanging rod, which passes through the sound-transmitting sealed shell, the foam cover plate and the fixed core, and both ends of the vertical hanging rod are exposed outside the sound-transmitting sealed shell; the ends of the vertical hanging rod are provided with through holes 32, and the through holes at both ends are in an orthogonal relationship.

[0035] Furthermore, the fixed core is a cylinder, the vertical suspension rod passes through the center line of the cylinder; and the MEMS capacitive accelerometer is embedded in the side wall of the cylinder.

[0036] Furthermore, the center line of the piezoelectric ceramic ring coincides with the center line of the fixed core.

[0037] Furthermore, there are four MEMS capacitive accelerometers, which are spaced apart and mirror-symmetrical.

[0038] Furthermore, the suspension includes two conical coil springs; the cone heads of the two conical coil springs are respectively connected to the upper and lower through holes of the vertical suspension rod.

[0039] Furthermore, the material of the sound-transmitting sealing shell is polyurethane or butyl rubber.

[0040] Further, the main body is located at the geometric center of the suspension.

[0041] Further, the center of gravity of the body including the suspension coincides with its geometric center.

[0042] Furthermore, the vertical suspension rod and the conical coil spring are made of stainless steel, titanium alloy or nylon.

[0043] The following is a more specific embodiment:

[0044] like Figure 1 As shown, this embodiment includes a fixed core 11 , a MEMS capacitive accelerometer 12 , a MEMS capacitive accelerometer 13 , a vertical suspension rod 15 , a piezoelectric ceramic ring 16 , an upper foam cover plate 17 , and a lower foam cover plate 18 .

[0045] The two MEMS accelerometers are orthogonally fixed on the fixed core 11 by horizontal screws 14 and kept perpendicular to the horizontal plane; the vertical suspension rod 15 vertically passes through the center hole of the fixed core 11 and is fixed by screws; the piezoelectric ceramic ring is sleeved on the outside of the assembled fixed core 11, and the two remain coaxial; the upper foam cover plate 17 and the lower foam cover plate 18 are respectively installed at the upper and lower openings of the piezoelectric ceramic ring, and are fixed by vertical screws 19.

[0046] After the assembly is completed, the exterior of the structure needs to be potted to form a sealed shell. The cross-sectional view of the hydrophone body after potting is as follows: Figure 2 As shown, including according to Figure 1 The assembled structure, the sound-transmitting sealed shell and the vertical suspension rod 15 are completed. The sound-transmitting sealed shell is made of sound-transmitting polyurethane, which is integrally potted, heated and cured through a special mold. On the one hand, the sound-transmitting sealed shell ensures that the various parts of the composite isoscillating vector sensor can be sealed and insulated and isolated from water for normal operation; on the other hand, it can transmit the sound pressure signal and vibration signal in the water to the annular piezoelectric ceramic ring and the MEMS capacitive accelerometer respectively without attenuation.

[0047] After potting, the overall density of the hydrophone body is close to 1g / cm 3 , able to maintain zero buoyancy in water.

[0048] After potting, the hydrophone body is suspended on the fixed bracket by a spiral spring. Figure 3 Shown, including Figure 2 The encapsulated hydrophone body, vertical suspension rod, upper conical coil spring 33, and lower conical coil spring 34. The upper and lower conical coil springs are connected to the upper and lower through holes 32 of the vertical suspension structure of the hydrophone through the bottom hook, and are hung on the fixed bracket for use after being tightened.

[0049] The upper and lower through holes of the vertical suspension rod are arranged orthogonally, and after being connected with the conical spiral spring hook, the hydrophone can be prevented from rotating during use.

[0050] The elastic coefficients k of the upper and lower conical helical springs enable the hydrophone to be located at the center of gravity and geometric center of the fixed bracket when suspended in water, and to vibrate freely in the horizontal plane with sound waves in water.

[0051] Vector hydrophone performance evaluation:

[0052] Step 1) Directivity test.

[0053] According to the national vector hydrophone calibration specifications, the directivity test of the vector hydrophone is carried out. The test is carried out in a standing wave tube, the test frequency range is 20Hz~2kHz, the directivity is "8", and the depth of the concave point is ≥30dB, indicating good directivity.

[0054] Step 2) Sensitivity test.

[0055] According to the national vector hydrophone calibration specifications, the sensitivity test of the vector hydrophone is carried out. The test is carried out in a standing wave tube, the test frequency range is 20Hz~2kHz, the sensitivity curve increases linearly at +6dB per octave, and the sensitivity at 1kHz is ≥-163dB.

[0056] Although the principles of the present invention are described in detail above in conjunction with the preferred embodiments of the present invention, those skilled in the art should understand that the above embodiments are merely explanations of the exemplary implementations of the present invention, and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute limitations on the scope of the present invention, and any obvious changes such as equivalent transformations, simple replacements, etc. based on the technical solution of the present invention, without departing from the spirit and scope of the present invention, fall within the protection scope of the present invention.

Claims

1. A miniaturized MEMS capacitive composite isochronous vector hydrophone, comprising a hydrophone body and a suspension, wherein the hydrophone body comprises a piezoelectric ceramic ring (16) and a sound-transmitting sealed shell covered with a filling on the outer surface of the piezoelectric ceramic ring; the piezoelectric ceramic ring is connected to the outside through a cable; characterized in that: The hydrophone body also includes a fixed core (11) and at least two MEMS capacitive accelerometers (12); the top and bottom of the piezoelectric ceramic ring are covered with a foam cover plate, the fixed core is located inside the piezoelectric ceramic ring, the MEMS capacitive accelerometers are vertically arranged on the side wall of the fixed core, and adjacent MEMS capacitive accelerometers are perpendicular to each other and the centers of the two are located at the same height; the MEMS capacitive accelerometers are connected to the outside through a cable that penetrates the foam cover plate and the sound-transmitting sealed shell; the hydrophone body also includes a vertical suspension rod (15), the vertical suspension rod passes through the sound-transmitting sealed shell, the foam cover plate and the fixed core, and both ends of the vertical suspension rod are exposed to the sound-transmitting sealed shell. The outer surface of the sealed shell; the ends of the vertical suspension rod are provided with through holes, and the through holes (32) at both ends are orthogonal; the fixed core is a cylinder, and the vertical suspension rod passes through the center line of the cylinder; the MEMS capacitive accelerometer is embedded in the side wall of the cylinder; the center line of the piezoelectric ceramic ring coincides with the center line of the fixed core; there are four MEMS capacitive accelerometers, and the MEMS capacitive accelerometers arranged at intervals are mirror-symmetrical; the suspension includes two conical helical springs; the cone heads of the two conical helical springs are respectively connected to the upper and lower through holes of the vertical suspension rod; the material of the sound-transmitting sealed shell is polyurethane or butyl rubber; the hydrophone body is located at the geometric center of the suspension; The center of gravity of the body including the suspension coincides with its geometric center; The materials of the vertical suspension rod and the conical coil spring are stainless steel, titanium alloy or nylon.

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