Impedance demodulation based very low frequency vector hydrophone and measurement method thereof

Abstract

The application relates to a very low frequency vector hydrophone based on impedance demodulation and a measuring method thereof, which comprises at least one piezoelectric ceramic disc serving as a very low frequency sensing element, the piezoelectric ceramic disc is deformed under the action of a very low frequency sound wave, and the impedance of the piezoelectric ceramic disc changes with the sound pressure; a signal source is used for generating a high-frequency voltage pulse signal and directly applying the high-frequency voltage pulse signal to two ends of the piezoelectric ceramic disc; and a current detection unit is used for measuring a current pulse signal flowing through the piezoelectric ceramic disc under the excitation of each high-frequency voltage pulse. The application can solve the problems of signal attenuation caused by excessively large impedance, easy overload of a preamplifier and long recovery steady state time of a traditional very low frequency hydrophone.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic measurement technology, specifically relating to a very low frequency vector hydrophone based on impedance demodulation and its measurement method. Background Technology

[0002] Very low frequency (VLF) underwater acoustic wave measurement has important applications in predicting marine geological hazards and measuring marine engineering noise. Currently, VLF underwater sensors commonly use piezoelectric ceramics as sensing elements, achieving acoustic sensing through sound-vibration-capacitance (piezoelectric ceramic) discharge and reception.

[0003] However, when measuring very low frequency sound waves, the current signal generated by the piezoelectric ceramic capacitor during discharge is approximately direct current. Due to the capacitor's high impedance at low frequencies, the signal exhibits significant attenuation. To address this issue, existing technologies typically employ a high-resistance preamplifier for impedance matching. However, high-resistance preamplifiers have low charge discharge efficiency, are prone to overload, and when the signal excitation stops, the slow outflow of charge generates a continuous negative exponential low-frequency interference signal, prolonging the hydrophone's recovery time and introducing measurement uncertainty components.

[0004] Therefore, how to avoid signal attenuation and preamplifier overload in very low frequency acoustic wave measurement, and improve measurement efficiency and signal-to-noise ratio, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a very low frequency vector hydrophone based on impedance demodulation and its measurement method, so as to solve the problems of signal attenuation, preamplifier overload and long recovery time caused by excessive impedance in traditional very low frequency hydrophones.

[0006] The technical solution of this invention is to provide a very low frequency vector hydrophone based on impedance demodulation, comprising:

[0007] At least one piezoelectric ceramic disk is used as a very low frequency sensing element, wherein the piezoelectric ceramic disk deforms under the action of very low frequency sound waves and its impedance changes with the sound pressure.

[0008] A signal source is used to generate high-frequency voltage pulse signals and apply them directly to both ends of the piezoelectric ceramic disk;

[0009] A current detection unit is used to measure the current pulse signal flowing through the piezoelectric ceramic disk under each high-frequency voltage pulse excitation.

[0010] An impedance demodulation unit, connected to the current detection unit, is used to calculate the impedance value of the piezoelectric ceramic disk at the current moment based on the voltage value of the high-frequency voltage pulse and the measured current pulse signal.

[0011] The sound pressure calculation unit is used to convert the calculated impedance value into the corresponding sound pressure signal based on the pre-calibrated impedance-sound pressure relationship model.

[0012] The output terminal of the signal source is directly connected to both ends of the piezoelectric ceramic disk, and the output terminal of the piezoelectric ceramic disk is directly connected to the input terminal of the current detection unit, without any preamplifier or charge amplifier in between.

[0013] This invention overcomes the technical bias in the prior art that requires a preamplifier to amplify the output signal of the piezoelectric ceramic in order to improve the measurement signal-to-noise ratio. It uses a high-frequency signal to measure the impedance change of a set of parallel very low frequency sensing elements to achieve sound wave measurement. This design can effectively solve the problems of very low frequency signal attenuation and preamplifier charge release in traditional very low frequency hydrophones, thereby improving measurement efficiency.

[0014] Preferably, the very low frequency sensing element includes three piezoelectric ceramic disks, the bottom surfaces of the three piezoelectric ceramic disks being orthogonal to each other, so as to realize vector measurement of the direction of the very low frequency sound wave.

[0015] Preferably, the frequency of the high-frequency voltage pulse signal is selected such that the impedance of the piezoelectric ceramic disk is sensitive to sound pressure. Maximum frequency point Where Z is the impedance and p is the sound pressure.

[0016] Preferably, the impedance demodulation unit calculates the sound pressure signal according to the following formula:

[0017]

[0018] in, Let be the sound pressure signal that varies with time t. The amplitude of the excitation voltage pulse, The measured current pulse signal, The impedance of the piezoelectric ceramic disk is the maximum sensitivity to sound pressure.

[0019] The present invention also provides a measurement method for a very low frequency vector hydrophone based on impedance demodulation, comprising the following steps:

[0020] Step S1: Place at least one very low frequency sensing element composed of a piezoelectric ceramic disk in water;

[0021] Step S2: Use a signal source to directly excite the very low frequency sensing element with a high-frequency voltage pulse signal. The output end of the signal source is directly connected to both ends of the piezoelectric ceramic disk.

[0022] Step S3: Measure the current pulse signal corresponding to each excitation pulse. The output terminal of the piezoelectric ceramic disk is directly connected to the input terminal of the current detection unit.

[0023] Step S4: Calculate the impedance value of the very low frequency sensing element based on the excitation voltage and the measured current pulse signal.

[0024] Step S5: Based on the pre-calibrated impedance-sound pressure relationship model, convert the calculated impedance value into a sound pressure signal;

[0025] In this configuration, no preamplifier or charge amplifier is provided between the signal source and the piezoelectric ceramic disk, or between the piezoelectric ceramic disk and the current detection unit.

[0026] This invention utilizes very low frequency current noise to achieve vector measurement of very low frequency sound waves. By leveraging the relationship between the impedance of the sensing element and the sound pressure, it bypasses a series of problems caused by excessive impedance in direct measurement of very low frequencies using piezoelectric ceramics.

[0027] Furthermore, the very low frequency sensing element includes three piezoelectric ceramic disks with their bottom surfaces orthogonal to each other.

[0028] In step S2, the three piezoelectric ceramic disks are simultaneously excited;

[0029] In step S3, the current signal corresponding to each of the piezoelectric ceramic disks is recorded respectively;

[0030] In steps S4 and S5, the sound pressure signal in each direction is calculated to achieve vector measurement of very low frequency sound waves.

[0031] Furthermore, in step S2, the frequency of the high-frequency voltage pulse signal is pre-selected to make the impedance of the piezoelectric ceramic disk sensitive to sound pressure. Maximum frequency point .

[0032] Furthermore, in step S5, the sound pressure signal is calculated according to the following formula:

[0033]

[0034] in, The amplitude of the excitation voltage pulse, The measured current pulse signal.

[0035] Furthermore, in step 2, very low frequency sound pressure vector measurement is achieved by utilizing the flow noise difference among the three piezoelectric ceramic disks.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) The high-frequency impedance of the electric ceramic is low, the signal attenuation is small, and there is no problem of insufficient signal-to-noise ratio;

[0038] (2) This solution does not require a preamplifier and has no overload risk;

[0039] (3) Vector measurement can be achieved by connecting multiple very low frequency sensing elements in parallel. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of the very low frequency vector hydrophone sensing element of the present invention.

[0041] Figure 2 This is a schematic diagram illustrating the working principle of the piezoelectric ceramic disk of the present invention.

[0042] Figure 3 This is a schematic diagram illustrating the working principle of the very low frequency vector hydrophone based on impedance demodulation according to the present invention. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0044] This invention provides a very low frequency vector hydrophone based on impedance demodulation.

[0045] like Figure 1 As shown, the sensing element of the very low frequency (VLF) vector hydrophone consists of three piezoelectric ceramic disks. The normals of the bottom surfaces of the three piezoelectric ceramic disks are pairwise orthogonal (i.e., in the X, Y, and Z directions). When a VLF sound wave passes through, the disks with normals in the same direction as the sound wave will be impacted by the fluid, and the flow noise will be measured. By analyzing the flow noise measurement results of each disk, the direction of the sound wave can be determined, thus achieving vector measurement.

[0046] like Figure 2 As shown, the working process of a single piezoelectric ceramic disk is as follows: the impedance characteristics of the piezoelectric ceramic disk change under two states: normal (solid line) and increased pressure (dashed line).

[0047] Impedance analysis system was used to analyze different pressures. The impedance frequency response of piezoelectric ceramic discs and their cables and other accessories Perform measurements and select Let the frequency f0 at the maximum point be taken as the operating frequency, and let it be... During operation, a stable voltage pulse U with a suitable pulse interval and pulse width is selected to excite the piezoelectric ceramic disk, and the current pulse corresponding to each voltage pulse is measured. Impedance fluctuation measurement is achieved by demodulating the current signal I. Figure 3 As shown.

[0048] In this embodiment, the output end of the signal source is directly connected to both ends of the piezoelectric ceramic disk, and the output end of the piezoelectric ceramic disk is directly connected to the input end of the current detection unit, without any preamplifier or charge amplifier in between.

[0049] The measurement principle formula is:

[0050] (1)

[0051] In the formula, t is the time variable.

[0052] The measurement procedure in this embodiment is as follows:

[0053] (1) Place the very low frequency vector hydrophone to be tested based on impedance demodulation in water;

[0054] (2) Use a signal source to excite three sensing elements simultaneously, and record the current signal I(t) of each channel respectively;

[0055] (3) Calculate the sound pressure signal p(t) in each direction according to formula (1) and synthesize the sound wave vector information.

[0056] In this embodiment, no preamplifier or charge amplifier is installed inside the hydrophone, thus avoiding the problems of overload and long recovery time caused by high impedance matching in traditional solutions.

[0057] This invention utilizes very low frequency current noise to achieve vector measurement of very low frequency sound waves, avoiding the signal attenuation and preamplifier overload problems caused by the low-frequency high impedance characteristics of piezoelectric ceramics in traditional very low frequency hydrophones; it also utilizes the relationship between the impedance of the sensing element and the sound pressure to bypass a series of problems caused by excessive impedance in direct measurement of very low frequencies using piezoelectric ceramics.

[0058] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. All equivalent modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A very low frequency vector hydrophone based on impedance demodulation, characterized in that, include: At least one piezoelectric ceramic disk is used as a very low frequency sensing element, wherein the piezoelectric ceramic disk deforms under the action of very low frequency sound waves and its impedance changes with the sound pressure. A signal source is used to generate high-frequency voltage pulse signals and apply them directly to both ends of the piezoelectric ceramic disk; A current detection unit is used to measure the current pulse signal flowing through the piezoelectric ceramic disk under each high-frequency voltage pulse excitation; An impedance demodulation unit, connected to the current detection unit, is used to calculate the impedance value of the piezoelectric ceramic disk at the current moment based on the voltage value of the high-frequency voltage pulse and the measured current pulse signal. The sound pressure calculation unit is used to convert the calculated impedance value into the corresponding sound pressure signal according to the pre-calibrated impedance-sound pressure relationship model. The output terminal of the signal source is directly connected to both ends of the piezoelectric ceramic disk, and the output terminal of the piezoelectric ceramic disk is directly connected to the input terminal of the current detection unit, without any preamplifier or charge amplifier in between.

2. The very low frequency vector hydrophone based on impedance demodulation according to claim 1, characterized in that, The very low frequency sensing element includes three piezoelectric ceramic disks, the bottom surfaces of which are orthogonal to each other, so as to realize vector measurement of the direction of the very low frequency sound wave.

3. The very low frequency vector hydrophone based on impedance demodulation according to claim 1, characterized in that, The frequency of the high-frequency voltage pulse signal is selected such that the impedance of the piezoelectric ceramic disk is sensitive to sound pressure. Maximum frequency point Where Z is the impedance and p is the sound pressure.

4. The very low frequency vector hydrophone based on impedance demodulation according to claim 1, characterized in that, The impedance demodulation unit calculates the sound pressure signal according to the following formula: in, Let be the sound pressure signal that varies with time t. The amplitude of the excitation voltage pulse, The measured current pulse signal, The impedance of the piezoelectric ceramic disk is the maximum sensitivity to sound pressure.

5. A measurement method for a very low frequency vector hydrophone based on impedance demodulation, characterized in that, Includes the following steps: Step S1: Place at least one very low frequency sensing element composed of a piezoelectric ceramic disk in water; Step S2: Use a signal source to directly excite the very low frequency sensing element with a high-frequency voltage pulse signal. The output end of the signal source is directly connected to both ends of the piezoelectric ceramic disk. Step S3: Measure the current pulse signal corresponding to each excitation pulse. The output terminal of the piezoelectric ceramic disk is directly connected to the input terminal of the current detection unit. Step S4: Calculate the impedance value of the very low frequency sensing element based on the excitation voltage and the measured current pulse signal. Step S5: Based on the pre-calibrated impedance-sound pressure relationship model, convert the calculated impedance value into a sound pressure signal; In this configuration, no preamplifier or charge amplifier is provided between the signal source and the piezoelectric ceramic disk, or between the piezoelectric ceramic disk and the current detection unit.

6. The measurement method for a very low frequency vector hydrophone based on impedance demodulation according to claim 5, characterized in that, The very low frequency sensing element comprises three piezoelectric ceramic disks whose bottom surfaces are orthogonal to each other. In step S2, the three piezoelectric ceramic disks are simultaneously excited; In step S3, the current signal corresponding to each of the piezoelectric ceramic disks is recorded respectively; In steps S4 and S5, the sound pressure signal in each direction is calculated to achieve vector measurement of very low frequency sound waves.

7. The measurement method for a very low frequency vector hydrophone based on impedance demodulation according to claim 5, characterized in that, In step S2, the frequency of the high-frequency voltage pulse signal is pre-selected to make the impedance of the piezoelectric ceramic disk sensitive to sound pressure. Maximum frequency point .

8. The measurement method for a very low frequency vector hydrophone based on impedance demodulation according to claim 5, characterized in that, In step S5, the sound pressure signal is calculated according to the following formula: in, The amplitude of the excitation voltage pulse, The measured current pulse signal.

9. The measurement method for a very low frequency vector hydrophone based on impedance demodulation according to claim 6, characterized in that, In step 2, very low frequency sound pressure vector measurement is achieved by utilizing the flow noise difference among the three piezoelectric ceramic disks.

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