Acoustic wave orientation sensor module with polyhedral structure, array and acoustic wave orientation method

Abstract

The invention relates to a polyhedral structure sound wave orientation sensor module, an array and a sound wave orientation method in the technical field of sound wave detection. The sound wave directional sensor module comprises a sensor and a calculation unit. The sensor comprises a rigid backing and n piezoelectric sensing units. And the calculation unit is used for determining a primary direction surface and a secondary direction surface according to the signal amplitude of the sensor, calculating the amplitude ratio P of the primary direction surface and the secondary direction surface, inquiring the amplitude ratio-incident angle mapping database based on the P to obtain the azimuth angle theta of the sound wave on the primary direction surface, and calculating to obtain the sound wave direction based on the theta and the primary direction surface. According to the invention, through the innovative polyhedral integrated design, the sound wave direction discrimination function which can be completed by a sensor array originally is realized in a single compact device, the problem of direction fuzziness of a traditional single-unit sensor is solved from the physical principle, and in addition, through a two-step decoding algorithm which is tightly combined with the sensor structure, the sound wave direction discrimination function is realized. And an optimal closed loop from physical perception to information output is formed.

Description

Technical Field

[0001] This invention relates to the field of acoustic wave detection technology, and in particular to a polyhedral acoustic wave orientation sensor module, array, and acoustic wave orientation method. Background Technology

[0002] In the field of acoustic wave detection, such as pipeline leak location, equipment fault acoustic emission monitoring, and security sound source detection, determining the location of the sound source is a core requirement. Existing technologies, traditional single-unit sensors (such as circular piezoelectric elements), suffer from directional symmetry issues, making it impossible to distinguish between equally symmetrical directions when receiving sound waves. While using multiple circular piezoelectric elements to form a multi-unit array can solve the directional symmetry problem, it presents challenges such as large size, complex calibration, and high cost. Furthermore, existing acoustic wave detection localization algorithms (such as the microphone array-based MUSIC algorithm) are typically computationally complex and heavily reliant on the precise geometric model of the sensor array and the consistency of performance across channels. They are also sensitive to environmental noise and channel mismatch, making deployment difficult in practical engineering. Summary of the Invention

[0003] To address the directional symmetry problem inherent in traditional single-unit sensors, and the technical challenges of large size and complex calibration associated with multi-unit arrays, this invention provides a polyhedral acoustic wave orientation sensor module, array, and acoustic wave orientation method.

[0004] In a first aspect, the present invention provides a polyhedral structure acoustic wave orientation sensor module, comprising: a sensor and a computing unit. The sensor includes: a rigid backing and... n One piezoelectric sensing unit. The rigid backing is set to positive. n Prismatic structure, used as the mechanical framework of the sensor. n ≥3. n Each piezoelectric sensing unit is correspondingly attached to a rigid backing. n On each side, a device is used to receive sound waves and generate corresponding charge signals. The computing unit is used to first determine the charge signals based on the sound waves received. n The amplitude of each charge signal is used to determine the orientation of the piezoelectric sensing unit that produces the largest amplitude as the principal direction of sound wave incidence, and the signal amplitude of the principal direction surface is recorded. A main Next, the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane are compared. The orientation of the piezoelectric sensing unit with the larger amplitude is determined to be the secondary direction plane where the sound wave is incident, and the signal amplitude of the secondary direction plane is recorded. A second .calculate A main and A second amplitude ratio P .based on PThe azimuth angle of the sound wave on the principal direction plane is obtained by querying the "amplitude ratio - incident angle" mapping database. θ .based on θ The direction of the sound wave is calculated from the principal direction plane.

[0005] Secondly, this invention also proposes a polyhedral acoustic wave orientation sensor array, which includes at least two polyhedral acoustic wave orientation sensor modules as described in the first aspect. Cross-validation is performed using the detection results from multiple polyhedral acoustic wave orientation sensor modules to reduce noise contamination on individual sensor modules and obtain a more accurate acoustic wave direction.

[0006] Thirdly, the present invention also proposes a polyhedral structure acoustic wave orientation method, which uses the polyhedral structure acoustic wave orientation sensor module described in the first aspect for acoustic wave orientation. This acoustic wave orientation method includes: First according to n The amplitude of each charge signal is used to determine the orientation of the piezoelectric sensing unit that produces the largest amplitude as the principal direction of sound wave incidence, and the signal amplitude of the principal direction surface is recorded. A main Next, the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane are compared. The orientation of the piezoelectric sensing unit with the larger amplitude is determined to be the secondary direction plane where the sound wave is incident, and the signal amplitude of the secondary direction plane is recorded. A second .calculate A main and A second amplitude ratio P .based on P The azimuth angle of the sound wave on the principal direction plane is obtained by querying the "amplitude ratio - incident angle" mapping database. θ .based on θ The direction of the sound wave is calculated from the principal direction plane.

[0007] The beneficial effects of this invention are as follows: 1. This invention achieves the sound wave direction discrimination function, which originally required a sensor array, in a single compact device through an innovative polyhedral integrated design. It solves the problem of directional ambiguity in traditional single-unit sensors from a physical principle perspective. In addition, through a two-step decoding algorithm that is closely integrated with the sensor structure, an optimal closed loop from physical perception to information output is formed, resulting in high overall efficiency, good real-time performance, and controllable cost.

[0008] 2. This invention permanently fixes the spatial relationship between each piezoelectric sensing unit through an integrated rigid structure, overcoming the performance degradation problem caused by temperature drift and vibration in separate arrays, achieving "one-time calibration, long-term maintenance-free", avoiding the complex calibration problem of traditional multi-unit arrays, and is particularly suitable for harsh environments such as industrial and outdoor environments.

[0009] 3. This invention provides a novel sensor hardware and a complete signal processing chain and dedicated decoding method that are compatible with it, providing users with a ready-to-use directional detection module, which greatly reduces the technical integration threshold and secondary development costs. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of the overall structure of the sensor; Figure 2 This is a schematic diagram of the exploded structure of the sensor; Figure 3 This is a simulation diagram of the acoustic field response and directivity of a single sensor in existing technology; Figure 4 This is a simulation diagram of the acoustic field response and directivity of the hexagonal prism-shaped sensor in this invention; Figure 5 This is a flowchart of a two-step directional decoding method; Figure 6 This is a schematic diagram illustrating the principle of determining the direction of sound waves based on the azimuth angle on the principal direction plane. Figure 7 This is a schematic diagram of the experimental calibration mapping database when the sound source is in one of the locations. Figure 8 This is a schematic diagram of the experimental calibration mapping database when the sound source is in another location.

[0012] In the figure: rigid backing 1, regular prism 11, upper end cover 12, lower end cover 13, screw 14, piezoelectric sensing unit 2. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0016] This embodiment provides a polyhedral acoustic wave orientation sensor module, which includes: a sensor and a computing unit. Further, please refer to... Figure 1 and Figure 2 The sensor mainly consists of two parts: a rigid backing and a piezoelectric sensing unit. Each part will be described in detail below.

[0017] (1) Rigid backing.

[0018] The rigid backing serves as the mechanical framework and acoustic substrate of the entire sensor. Its core function is to provide a stable geometric structure, acoustic backing, and geometric coordinate system, defining a clear spatial orientation for the sensing units on each side and suppressing overall low-frequency resonant modes, resulting in a smoother sensor response within the operating frequency band. To this end, the rigid backing can be configured as a regular triangular prism, square prism, pentagonal prism, hexagonal prism, octagonal prism, or other geometric shapes with more than one prism facet. The fewer the facets, the simpler the sensor structure and subsequent positioning algorithm, and the better the reliability. Conversely, the more facets the rigid backing, the more complex the sensor structure and subsequent positioning algorithm, but the positioning accuracy increases significantly. In this embodiment, balancing reliability and positioning accuracy requirements, the rigid backing is configured as a regular hexagonal prism, naturally dividing the 360° horizontal space into six 60° sectors, providing a natural physical coordinate system for subsequent orientation decoding. Furthermore, the rigid backing can be made of high-rigidity, high-loss materials such as aluminum alloy, stainless steel, or engineering plastics. The rigid backing includes: a regular prism (hexagonal prism), an upper end cap, and a lower end cap. Screws are provided on both the upper and lower base surfaces of the hexagonal prism. The upper end cap is detachably screwed to the upper base surface of the hexagonal prism via the screws. The lower end cap is detachably screwed to the lower base surface of the hexagonal prism via the screws, thus forming a framework for confining and mounting the piezoelectric sensing unit.

[0019] (2) Piezoelectric sensing unit.

[0020] Please refer to this again. Figure 2 The number of piezoelectric sensing units is the same as the number of sides of the rigid backing, and they are respectively attached to the six sides of the rigid backing, meaning each side corresponds to an independent piezoelectric sensing unit. In this embodiment, the piezoelectric sensing unit is made of flexible piezoelectric material (such as polyvinylidene fluoride PVDF, polyvinylidene fluoride-trifluoroethylene PVDF-TrFE), and silver paste electrodes are prepared by printing or coating processes. The piezoelectric sensing unit is firmly bonded to the backing body with conductive epoxy resin, and the upper and lower end caps lock against the upper and lower edges of the piezoelectric sensing unit, making the piezoelectric sensing unit more stable and reducing deformation in other directions. When the piezoelectric sensing unit receives sound waves, it generates a corresponding charge signal and outputs it through leads. It should be noted that the piezoelectric sensing unit uses flexible piezoelectric material instead of traditional rigid piezoelectric ceramics, the purpose of which is to better fit the polyhedral curved surface and have better impact resistance and wider frequency response characteristics. The sound field response and directivity simulation of the sensor proposed in this invention and existing single sensors are performed, such as... Figure 3 and Figure 4 As shown, it can be clearly seen that the sensor in this invention can receive sound waves 360° without any angle limitations or directional issues.

[0021] like Figure 5 As shown, when in use, the sensor first transmits a signal omnidirectionally through an external sound source, and the reflected echo of the signal is received by the sensor. After the sensor acquires the charge signal about the reflected sound wave, the computing unit (not shown in the figure) is the key to decoding the direction information of the sound wave. It is designed as a multi-channel system that is highly coordinated with the above-mentioned sensor structure, and it mainly includes: signal processing circuit and MCU (microcontroller unit).

[0022] (1) Signal processing circuit.

[0023] In this embodiment, the signal processing circuit is used to preprocess and perform analog-to-digital conversion on the charge signal generated by the piezoelectric sensing unit. It includes six pre-charge amplifiers, a filter gain circuit, and an analog-to-digital converter. Because flexible piezoelectric materials exhibit high output impedance at low frequencies, the charge signal would be severely lost due to voltage division if a conventional voltage amplifier were used. Therefore, each piezoelectric sensing unit is equipped with an independent pre-charge amplifier. This pre-charge amplifier converts the charge signal from the piezoelectric sensing unit... Q Converted into a low-impedance voltage signal proportional to it. V out =- Q / C f ( C f(This refers to the feedback capacitor). This design allows for near-lossless charge collection, significantly improving the signal-to-noise ratio and system sensitivity, while accurately maintaining the relative amplitude relationship of each channel signal, which is the basis for subsequent direction determination. The output of this six-channel preamplifier enters a filter gain circuit for necessary bandpass filtering (removing noise outside the operating frequency band) and gain adjustment. The adjusted six voltage signals are then sent to an analog-to-digital converter with multi-channel synchronous sampling capability to convert them into digital signals. This synchronous sampling is crucial, ensuring that the phase relationship of the six signals is not distorted during digitization, thus preserving the minute time differences (or phase differences caused by structural asymmetry) of sound arrival at each surface.

[0024] (2) MCU.

[0025] The embedded MCU's built-in algorithm calculates the specific acoustic wave positioning direction based on the signal acquired by the piezoelectric sensing unit. This acoustic wave positioning employs a two-step direction decoding method, including the following steps: The MCU calculates in real time the amplitude characteristics (such as the root mean square value, RMS) of the six digital signals (i.e., the six charge signals output by the six piezoelectric sensing units) processed by the signal processing circuit. The channel with the largest amplitude is identified by amplitude comparison. The orientation of the piezoelectric sensing unit corresponding to this channel is the principal direction of the sound wave incident plane, thus quickly locking the 360° omnidirectional search of the sound wave into a sector of approximately 60°, achieving a coarse determination of the principal direction. Then, a precise angle determination is performed; after determining the principal direction plane, the signal amplitude of the principal direction plane is recorded. A main The system compares the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane, determines that the piezoelectric sensing unit with the larger amplitude is the orientation of the secondary direction plane where the sound wave is incident, and records the signal amplitude of the secondary direction plane. A second Then calculate A main and A second amplitude ratio P .according to P By querying a pre-stored "amplitude ratio-incident angle" mapping database in the MCU, the precise azimuth angle of the sound wave within a 60° sector of the main direction plane can be interpolated and calculated. θ Based on azimuth angle θ The direction of the sound wave is calculated from the principal direction plane. For example, the amplitude ratio is calculated. P If the value is 1.2, then the azimuth angle can be found by querying. θ It is 43°. Amplitude ratio P If the value is 1.5, then the azimuth angle can be found by querying. θ It is 35°. Amplitude ratio P If the value is 1.7, then the azimuth angle can be found by querying. θFor example, 26°, etc. It's worth mentioning that the rigid backing has been calibrated at the angles before use; the direction each side faces has been determined. Azimuth angle. θ This is equivalent to the deviation angle based on the main direction plane. For example... Figure 6 As shown, for example, after the angle calibration, the primary direction plane faces due south. At this point, a ray is drawn towards due south, with the center of the rigid backing as the origin. Based on the lateral position of the secondary direction plane relative to the primary direction plane, the ray is rotated by an azimuth angle towards the secondary direction plane. θ The direction of the sound wave can then be obtained. This "amplitude ratio-incident angle" mapping database is obtained through acoustic simulation (such as COMSOL simulation) or experimental calibration of the sensor, and it is deeply tied to the decoding method and hardware structure. Specifically, this embodiment provides an experimental calibration method for the "amplitude ratio-incident angle" mapping database and its calibration principle. Please refer to... Figure 7 The six piezoelectric sensing units are denoted as S1 to S6 in clockwise order. Assuming the positive x-axis is 0 degrees and clockwise is the positive direction, the sound source propagates from 0 degrees. Figure 7 The voltage values ​​of surfaces S1 to S6 can be seen. The voltage values ​​of S4 and S5 are basically the same and represent the maximum voltage; this is a special case where the exact direction can be confirmed when the incident angle is 0 degrees. Then refer to... Figure 8 Still taking the positive x-axis direction as 0 degrees and clockwise as the positive direction, the sound source propagates from 315 degrees, from... Figure 8 It can be seen that the voltage value of S4 is the maximum voltage, corresponding to the main direction plane. Based on the voltage ratios of adjacent planes S3 and S5 with S4, the secondary direction and the angle between the sound source and the main direction, i.e., the azimuth angle, can be determined. θ Similarly, for other incident sound sources, a "amplitude ratio - incident angle" mapping database can be established based on this simulation method.

[0026] In summary, the working principle of this invention follows the technical path of "spatial mechanical encoding → high-fidelity charge conversion → intelligent two-step decoding": 1. Encoding Stage: When a sound wave is incident from a certain direction in space, the regular hexagonal prism structure acts as a "space mechanical encoder." Due to the differences in the path of the sound wave reaching each surface, the differences in the incident angle, and the different constraints of the rigid backing on the vibration of each surface, the amount of charge generated by the six flexible piezoelectric sensing units will exhibit a specific distribution pattern that is uniquely related to the incident direction. This fundamentally "encodes" the directional information in the relative strength relationship of the charge signals in the six channels.

[0027] 2. Conversion and Extraction Stage: A six-channel pre-charge amplifier acts as the signal pre-processing circuit, converting the charge mode to the voltage mode with extremely low loss. The multi-channel synchronous ADC then digitizes this analog signal mode without distortion, providing raw data for subsequent processing.

[0028] 3. Decoding Stage: A dedicated algorithm embedded in the MCU acts as an "intelligent decision maker." First, it quickly locates the primary direction plane by "comparing sizes" (coarse judgment). Then, by determining the secondary direction plane and combining it with a pre-stored mapping database, it performs precise angle interpolation (fine judgment). The entire process is computationally efficient, requiring no complex matrix operations or spectral estimation, and achieves real-time, robust direction calculation on a low-power MCU.

[0029] In another embodiment, a polyhedral structure acoustic wave orientation method is also proposed, which uses the polyhedral structure acoustic wave orientation sensor module described in the above embodiment to perform acoustic wave orientation. The acoustic wave orientation direction includes: First according to n The amplitude of each charge signal is used to determine the orientation of the piezoelectric sensing unit that produces the largest amplitude as the principal direction of sound wave incidence, and the signal amplitude of the principal direction surface is recorded. A main Next, the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane are compared. The orientation of the piezoelectric sensing unit with the larger amplitude is determined to be the secondary direction plane where the sound wave is incident, and the signal amplitude of the secondary direction plane is recorded. A second .calculate A main and A second amplitude ratio P .based on P The azimuth angle of the sound wave on the principal direction plane is obtained by querying the "amplitude ratio - incident angle" mapping database. θ .based on θ The direction of the sound wave is calculated from the principal direction plane.

[0030] In another embodiment, a polyhedral acoustic wave orientation sensor array is proposed, comprising at least two polyhedral acoustic wave orientation sensor modules described in the above embodiments. Each sensor module in the array is capable of detecting the acoustic wave direction independently. By averaging the positioning results of all sensor modules, the resulting array can filter out noise contamination from individual sensor modules, yielding a more accurate acoustic wave direction.

[0031] In another embodiment, a computer-readable storage medium is also provided, which stores a computer program. When the computer program is executed by a processor, it implements the steps of the polyhedral structure acoustic wave direction-directing method described in the above embodiments. The computer-readable storage medium may include, but is not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0032] In another embodiment, a computer program product is also proposed, which includes computer instructions. These computer instructions are used to cause a computer to perform the steps of the polyhedral structure acoustic wave direction-oriented method described above. The computer program instructions may exist in a computer-readable medium in forms including, but not limited to, source files, executable files, and installation package files. Accordingly, the computer program instructions may be executed by a computer in ways including, but not limited to: the computer directly executing the instructions; the computer compiling the instructions and then executing the corresponding compiled program; the computer reading and executing the instructions; or the computer reading and installing the instructions and then executing the corresponding installed program.

[0033] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0034] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A polyhedral acoustic wave orientation sensor module, characterized in that, It includes: Sensors, including: Rigid backing, which is set to positive n Prismatic structure, used as the mechanical framework of the sensor; n ≥3; n Each piezoelectric sensing unit is correspondingly attached to a rigid backing. n On each side, it is used to receive sound waves and generate corresponding charge signals; The calculation unit is used to first determine the calculation unit based on the calculation unit. n The amplitude of each charge signal is used to determine the orientation of the piezoelectric sensing unit that produces the largest amplitude as the principal direction of sound wave incidence, and the signal amplitude of the principal direction surface is recorded. A main Next, the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane are compared. The orientation of the piezoelectric sensing unit with the larger amplitude is determined to be the secondary direction plane where the sound wave is incident, and the signal amplitude of the secondary direction plane is recorded. A second ;calculate A main and A second amplitude ratio P ;based on P The azimuth angle of the sound wave on the principal direction plane is obtained by querying the "amplitude ratio - incident angle" mapping database. θ ;based on θ The direction of the sound wave is calculated from the principal direction plane.

2. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, Rigid backing includes: A regular prism with a piezoelectric sensing unit connected to its side; The upper and lower end caps are detachably connected to the upper and lower bottom surfaces of the regular prism, respectively; and when the upper and lower end caps are locked, they abut against the edge of the piezoelectric sensing unit.

3. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, The rigid backing is made of aluminum alloy, stainless steel, or engineering plastics. The piezoelectric sensing unit uses a flexible piezoelectric material, which is bonded to the side of a rigid backing.

4. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, The computing unit includes: signal processing circuitry and an MCU; The signal processing circuit is used to preprocess and perform analog-to-digital conversion on the charge signal generated by the piezoelectric sensing unit; the MCU is used to identify the main direction plane based on the analog-to-digital converted charge signal and calculate the azimuth angle of the sound wave on the main direction plane. θ .

5. The polyhedral acoustic wave orientation sensor module according to claim 4, characterized in that, The signal processing circuit includes: n Each precharge amplifier is connected to a corresponding precharge amplifier. n The output of each piezoelectric sensing unit is used to convert charge signals into voltage signals. The filter gain circuit is used to perform bandpass filtering and gain adjustment on voltage signals; An analog-to-digital converter (ADC) is used to convert bandpass-filtered and gain-adjusted voltage signals into digital signals.

6. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, The "amplitude ratio-incident angle" mapping database is pre-stored in the computing unit; The "amplitude ratio - incident angle" mapping database is obtained by acoustic simulation or experimental calibration of the sensor.

7. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, The rigid backing is provided with a regular hexagonal prism structure, and each side of it is fitted with a piezoelectric sensing unit.

8. The polyhedral acoustic wave orientation sensor module according to claim 1, characterized in that, The rigid backing is calibrated at an angle before use so that each side of the rigid backing points to a specific angle.

9. A polyhedral acoustic wave orientation sensor array, characterized in that, It includes at least two polyhedral acoustic wave orientation sensor modules as described in any one of claims 1 to 8.

10. A method for directional acoustic waves through a polyhedral structure, characterized in that, It uses the polyhedral acoustic wave orientation sensor module as described in any one of claims 1 to 8 for acoustic wave orientation; Sound wave direction finding methods include: First according to n The amplitude of each charge signal is used to determine the orientation of the piezoelectric sensing unit that produces the largest amplitude as the principal direction of sound wave incidence, and the signal amplitude of the principal direction surface is recorded. A main Next, the charge signal amplitudes of two adjacent piezoelectric sensing units on the main direction plane are compared. The orientation of the piezoelectric sensing unit with the larger amplitude is determined to be the secondary direction plane where the sound wave is incident, and the signal amplitude of the secondary direction plane is recorded. A second ;calculate A main and A second amplitude ratio P ;based on P The azimuth angle of the sound wave on the principal direction plane is obtained by querying the "amplitude ratio - incident angle" mapping database. θ ;based on θ The direction of the sound wave is calculated from the principal direction plane.

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