A device and method for diffusing and radiating ultrasonic waves into the air.

Abstract

A device and method for diffusing ultrasonic waves into the air include an ultrasonic generator, an ultrasonic transducer, and a coupling fixture. The coupling fixture is hemispherical in shape with pine cone-scale-like radiating blades on its surface. The ultrasonic transducer consists of a piezoelectric ceramic, a back cover plate, and bolts. The back cover plate secures the piezoelectric ceramic to the bottom surface of the coupling fixture using bolts. The piezoelectric ceramic has electrodes electrically connected to the ultrasonic generator. The ultrasonic generator drives the piezoelectric ceramic to vibrate perpendicular to the bottom plate, exciting elastic waves in the coupling fixture. The coupling fixture then converts these elastic waves into airborne sound waves. This invention utilizes the piezoelectric ceramic to generate elastic waves within the coupling fixture and diffuses ultrasonic waves into the air through the radiating blades, improving coupling efficiency and widening the radiation range, allowing ultrasonic interference signals to diffuse more evenly into the target room.

Description

Technical Field

[0001] This invention relates to the field of anti-eavesdropping and anti-recording technology, and in particular to a device and method for diffusing and radiating ultrasonic waves into the air. Background Technology

[0002] With the continuous development of electronic information technology, eavesdropping and recording technologies are constantly being upgraded, seriously endangering personal privacy, national economic order, and even national security. Therefore, voice information confidentiality technology is receiving increasing attention. Existing recording jammers emit ultrasonic waves into the recording equipment and utilize the nonlinear effect of the MEMS microphone in the recording equipment on ultrasonic waves to generate audible frequency electrical signals in the internal circuit of the recording equipment, thereby polluting the recorded audio. For example, reference [1] utilizes the nonlinearity of the microphone on ultrasonic signals and simultaneously inputs 40kHz and 50kHz ultrasonic signals to generate a 10kHz signal in the recording equipment.

[0003] In practical applications, since the location of the recording device cannot be known, it is usually necessary to achieve effective coverage of the interfering ultrasonic waves throughout the entire space. However, the existing ultrasonic transducers are very directional, and the ultrasonic signal intensity will be attenuated by 25 to 30 dB in the direction of the non-main lobe. This will greatly reduce the interference performance of the recording jamming device in the direction of the non-main lobe. In addition, the ultrasonic transducers and ultrasonic transducer arrays used in the existing technology have zero directionality, which makes blind spots that cannot be interfered with appear in some areas. To address the above problems, reference [2] uses an ultrasonic transducer array to form a bracelet and uses the speaker's body movements to compensate for the blind spots of the recording jammer itself. However, this jamming device is relatively large and conspicuous, and cannot meet the concealment and disguise requirements of the recording jammer in sensitive situations.

[0004] The references are listed below:

[0005] [1]Roy,N.,Hassanieh,H.,&Roy Choudhury,R.(2017,June).Backdoor:Makingmicrophones hear inaudible sounds.In Proceedings of the 15th AnnualInternational Conference on Mobile Systems,Applications,and Services(pp.2-14).

[0006] [2]Chen,Y.,Li,H.,Nagels,S.,Li,Z.,Lopes,P.,Zhao,BY,&

[0007] Zheng, H. (2019). Understanding the effectiveness of ultrasonic microphone jammer. arXiv preprint arXiv:1904.08490. Summary of the Invention

[0008] To overcome the above problems, the present invention provides a device and a realization method for diffusing and radiating ultrasonic waves into the air.

[0009] The first aspect of the present invention provides a device for diffusing and radiating ultrasonic waves into the air, including an ultrasonic generator, an ultrasonic transducer, and a coupling tooling; the coupling tooling is integrally hemispherical, and the coupling tooling includes a hemisphere and a plurality of radiation blades in the shape of pinecone scales, and the plurality of radiation blades in the shape of pinecone scales are arranged on the surface of the hemisphere; an installation hole is provided on the bottom surface of the hemisphere, and an ultrasonic transducer is provided in the installation hole; the ultrasonic transducer includes a piezoelectric ceramic and a rear cover plate, the piezoelectric ceramic is arranged in the installation hole, and the rear cover plate fixes the piezoelectric ceramic to the bottom surface of the coupling tooling through bolts; the piezoelectric ceramic has an electrode electrically connected to the ultrasonic generator, and the ultrasonic generator drives the piezoelectric ceramic to generate vibrations perpendicular to the bottom surface of the hemisphere, exciting elastic waves of the coupling tooling, and the coupling tooling converts the elastic waves into air sound waves.

[0010] Further, the radius D of the coupling tooling satisfies D > λ , ,

[0015] ,

[0010] , , s ,

[0014] , s , , p ,

[0013] , p , ,

[0012] , ,

[0011] , ,

[0016] , where λ p [[ID=IS]]is the wavelength corresponding to the compression wave in the hemisphere material at 30 kHz.

[0011] Further, the width W of the radiation blade satisfies W < 2λ s , where λ s is the wavelength corresponding to the shear wave in the hemisphere material at 40 kHz, and the length L of the radiation blade satisfies W < L < D, and D is the radius of the coupling tooling.

[0012] Further, the contact point between the piezoelectric ceramic and the coupling tooling is located at the center of the spherical coupling tooling.

[0013] Further, the piezoelectric ceramic is a longitudinally vibrating piezoelectric ceramic stack and is excited in the direction perpendicular to the plane of the coupling tooling.

[0014] Further, the piezoelectric ceramic is bonded to the rear cover plate and the coupling tooling through epoxy resin.

[0015] Further, the ultrasonic generator includes a signal generator and a power amplifier, the signal generator is electrically connected to the power amplifier, and the positive and negative electrodes of the output end of the power amplifier are connected to the electrodes of the ultrasonic transducer.

[0016] Furthermore, while the piezoelectric ceramic undergoes longitudinal deformation, an excitation perpendicular to the bottom surface of the hemisphere is applied to the surface of the coupling fixture, generating compression waves, shear waves, and surface waves inside the coupling fixture; among which the compression waves and shear waves are spherical waves, and the surface waves are cylindrical waves, and the three modes of waves propagate outward from the center of the hemisphere as the origin.

[0017] Furthermore, the main lobe of the compression wave, in a direction perpendicular to the hemispherical plane of the coupling fixture, causes the top surface of the hemisphere to vibrate radially and radiate sound waves; the main lobe of the shear wave, in a direction with a pitch angle of 60°, causes the radiating blades to vibrate laterally, thereby radiating sound waves; the surface wave is concentrated on the hemispherical surface of the coupling fixture, driving the radiating blades corresponding to a pitch angle of 90° to vibrate laterally, thereby radiating sound waves.

[0018] A second aspect of the present invention provides a method for an apparatus for diffusing and radiating ultrasonic waves into the air, comprising the following steps:

[0019] Step 1: Adjust the output impedance of the ultrasonic generator to match the impedance of the piezoelectric ceramic electrical terminals;

[0020] Step 2: The ultrasonic generator generates a voltage signal and feeds it to the two ends of the piezoelectric ceramic electrode, causing it to undergo longitudinal deformation;

[0021] Step 3: Excite the piezoelectric ceramic coupling fixture to generate compression waves, shear waves and surface waves inside it. The compression waves and shear waves are spherical waves, and the surface waves are cylindrical waves. The waves of the three modes propagate outward from the center of the hemisphere.

[0022] Step 4: Allow the elastic wave to propagate to the surface of the coupling fixture, causing the air on the fixture surface to vibrate and radiate ultrasonic waves into the air. Among them, the compression wave causes the hemispherical surface to vibrate in the radial direction, while the shear wave and surface wave drive the scale-like radiation blades to produce transverse vibration.

[0023] The beneficial effects of this invention are:

[0024] (1) The present invention provides a pine cone scale-shaped radiation rod on the surface of the coupled radiation fixture. The piezoelectric ceramic excites the surface of the fixture to generate elastic waves dominated by shear waves and surface waves. The shear waves and surface waves drive the radiation rod to vibrate laterally, which improves the radiation efficiency of shear waves and surface waves and expands the coverage of ultrasonic radiation.

[0025] (2) The present invention designs the main body of the pine cone-shaped coupling radiation fixture as a hemispherical shape, so that when the elastic wave reaches the boundary of the fixture body, the wavefront is parallel to the boundary, which ensures the consistency of the phase of the ultrasonic interference signal when it radiates in all directions, reduces the distortion of the ultrasonic interference signal, and ensures the effect of ultrasonic interference recording.

[0026] (3) The wide-directional ultrasonic radiation device proposed in this invention has a novel and beautiful appearance, which is not easy to arouse suspicion. It can be deployed in sensitive places and can interfere with eavesdropping and recording activities without being noticed. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the ultrasonic transducer and coupling fixture involved in the embodiment.

[0028] Figure 2 This is a side sectional view of the ultrasonic transducer and coupling fixture.

[0029] Figure 3 This is a modular structure diagram of a device for diffusing and radiating ultrasonic waves into the air, as described in the embodiment.

[0030] Figure 4 The effect of 35kHz ultrasound on the recording of a Xiaomi phone.

[0031] Figure 5 The interference effect of 35kHz to 45kHz sweep frequency ultrasonic waves on recording on Apple mobile phones.

[0032] Figure 6 This is a flowchart illustrating a method for diffusing and radiating ultrasonic waves into the air, as described in the embodiment.

[0033] Figure 7 This is a connection diagram of the circuit parameter optimization steps involved in the embodiment;

[0034] Figure 8 This is a flowchart illustrating a method for diffusing and radiating ultrasonic waves into the air, as described in the embodiment.

[0035] The labels in the diagram are as follows: 101. Coupling fixture, 202. Piezoelectric ceramic, 203. Back cover plate, 204. Adjustable resistor. Detailed Implementation

[0036] The technical solution of this invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Example 1

[0040] like Figure 1-2 As shown, a device for radiating ultrasonic waves into the air includes an ultrasonic generator, an ultrasonic transducer, and a coupling fixture.

[0041] An ultrasonic generator is used to output powerful ultrasonic interference signals; it consists of a signal generator and a power amplifier, with the positive and negative electrodes at the output end connected to the electrodes of the ultrasonic transducer.

[0042] The ultrasonic transducer, driven by an ultrasonic generator, produces vibrations perpendicular to the mounting surface, which in turn excite the coupling fixture to vibrate. It is composed of stacked piezoelectric ceramics, tightly bonded to the coupling fixture with epoxy resin, and further secured with a rear cover plate and bolts. Figure 1 As shown.

[0043] A coupling fixture used to convert elastic waves into airborne sound waves; it is manufactured using 3D printing technology and is made of polystyrene; its main body is a solid hemisphere, such as... Figure 1 As shown; the radius of the solid hemisphere is 8cm; radial blades are machined on the surface of the solid hemisphere, and the dimensions of the radial blades are 65*55*5mm (length*width*thickness).

[0044] The piezoelectric ceramic has electrodes that are electrically connected to an ultrasonic generator. The ultrasonic generator drives the piezoelectric ceramic to generate vibrations perpendicular to the bottom surface of the hemisphere, which excites the elastic wave of the coupling fixture. The coupling fixture converts the elastic wave into an airborne sound wave.

[0045] Example 2

[0046] like Figure 3 As shown, this embodiment provides a device for diffusing and radiating ultrasonic waves into the air, including a voice perception module 301, a signal synthesis module 302, and a power amplification and ultrasonic wave transmission module 303, with the following specific functions:

[0047] Module 301, Speech Perception Module.

[0048] The energy of a voice signal changes over time, and the operating conditions can be divided into "speech signal presence" and "silence" based on the sound intensity level in the room. In the "speech signal presence" condition, preventing eavesdropping and recording can be achieved by making the energy of the ultrasonic jamming signal the same as and changing synchronously with the voice signal. This reduces the noise exposure generated by the ultrasonic jammer, minimizing potential harm to the human body while interfering with eavesdropping and recording. Furthermore, it reduces the standby power consumption of the device, making the ultrasonic jamming device easier to implement and use.

[0049] The speech perception module includes a microphone for the speech frequency band, an analog-to-digital (A / D) conversion circuit, and a sound intensity level calculation circuit. The microphone output signal x(t) first passes through a 100Hz to 3kHz bandpass analog filter, and then is converted into a digital signal x(n) by the A / D circuit. The sound intensity level calculation circuit divides x(n) into frames and estimates the sound intensity level of each frame. When the sound intensity level exceeds 20dB, an enable signal is used to start the power amplifier module.

[0050] Module 302, signal synthesis module.

[0051] Ultrasonic interference technology mainly relies on specific excitation signals to interfere with recordings. The principles used can be summarized into three types: first, using the nonlinear response of the microphone to the ultrasonic signal to contaminate the recorded audio; second, using the aliasing phenomenon caused by the limited sampling frequency during A / D conversion to contaminate the recorded audio; and third, using the high-intensity signal generated by ultrasonic waves in the circuit to make the circuit unable to work properly. Therefore, it is necessary to use specific modules to generate ultrasonic interference signals.

[0052] Figure 4 The demonstration shows the recording interference effect of an Apple phone under a 35kHz to 45kHz sweep frequency signal, and the interference result of the e303 ultrasonic signal in the audible frequency band caused by the aliasing effect. Figure 4 The results show that Apple phones exhibit aliasing under ultrasonic signals, which is the second type of interference.

[0053] Figure 5 The demonstration shows the recording interference effect of a Xiaomi phone under the action of a 35kHz ultrasonic signal. e301 is the start time of the ultrasonic signal, and e302 is the stop time of the ultrasonic signal. Figure 5The results show that the ultrasonic signal interfered with the microphone circuit of the Xiaomi phone, causing the A / D conversion module to malfunction, which is the third type of interference.

[0054] In this embodiment, the ultrasonic interference signal consists of 5 independent DDS signal generators, 5 random signal generators, 5 sets of registers, 1 adder, and a digital-to-analog (D / A) conversion module. The reference frequencies of the 5 DDS signal generators correspond to 5 preferred excitation modes, denoted as f1(0), f2(0), f3(0), f4(0), and f5(0), respectively. Each random signal generator generates a random number r(n) in each clock cycle, ranging from (-1, 1). The input frequency of the DDS signal generator is updated once in each clock cycle. i (n) = f(n-1) + 100*r(n), i = 1, 2, 3, 4 or 5; the adder accumulates the signals generated by the 5 DDS signal generators and outputs them through the D / A module; wherein, the clock period is 10ms; the preferred excitation mode is obtained by measuring the frequency response of the ultrasonic transducer, and the corresponding frequency is between 30kHz and 40kHz. In this embodiment, five frequencies of 31kHz, 32kHz, 33kHz, 34kHz and 35kHz are used as reference frequencies.

[0055] Module 303, Power Amplification and Ultrasonic Transmission Module.

[0056] This process converts ultrasonic interference electrical signals into ultrasonic interference sound waves of a certain intensity. This step requires impedance matching between the circuit ports and efficient coupling between the elastic wave and the airborne sound wave.

[0057] In this embodiment, the power amplification and ultrasonic transmitting module consists of a power amplifier circuit, an ultrasonic transducer, and a coupling fixture. The power amplifier circuit has a gain of 23dB, a maximum driving voltage of 150V, and an output impedance of 300Ω. The ultrasonic transducer is constructed from a piezoelectric ceramic stack, with the piezoelectric ceramics polarized along the stacking direction and operating at a frequency of 40kHz. The coupling fixture is 3D printed from PA66 plastic (polyhexamethylene adipamide), and its main body is a solid hemisphere. Figure 1 As shown; the radius of the solid hemisphere is 9cm; radiating blades are machined on the surface of the solid hemisphere, and the dimensions of the radiating blades are 65*55*5mm (length*width*thickness); the ultrasonic transducer is glued to the coupling fixture with epoxy resin and further fixed by the rear cover plate and screws; the rear cover plate has wire through holes, through which the electrode connection wires of the ultrasonic transducer are led out; the ultrasonic transducer is electrically connected to the power amplifier.

[0058] Example 3

[0059] like Figure 6As shown, this embodiment provides a method for diffusing and radiating ultrasonic waves into the air, which can be achieved through four steps: electrical port impedance matching 401, electrical and vibration energy conversion 402, elastic wave excitation 403, and elastic wave and sound wave energy conversion 404. Details are as follows:

[0060] Step 401, electrical port impedance matching.

[0061] Used to ensure the proper functioning of parts of the system circuitry. For example... Figure 7 As shown, an adjustable resistor is connected in series with the ultrasonic transducer and then connected to the output of the signal generator. Oscilloscope channel 1 is connected in parallel with the transducer, and oscilloscope channel 2 is connected in parallel with the signal generator. A 33kHz sinusoidal signal is used for excitation. The adjustable resistor is adjusted so that the signals of channel 1 and channel 2 are in phase, thus achieving impedance matching.

[0062] Step 402, conversion of electrical and vibrational energy.

[0063] Used to convert electrical energy into mechanical energy; the ultrasonic generator generates a voltage signal that is fed to the two ends of the piezoelectric ceramic electrode, causing it to undergo longitudinal deformation.

[0064] Step 403, elastic wave excitation.

[0065] This device is used to excite elastic waves on the mounting surface of the coupling fixture. Simultaneously, the piezoelectric ceramic undergoes longitudinal deformation, applying an excitation perpendicular to the mounting surface to the coupling fixture, generating compression waves, shear waves, and surface waves within the fixture. The compression and shear waves are spherical waves, while the surface waves are cylindrical waves. All three wave modes propagate outwards from the center of the hemisphere. The piezoelectric ceramic is bonded to the coupling fixture with epoxy resin and further secured with a back cover and screws.

[0066] Step 404: Energy conversion between elastic waves and sound waves.

[0067] This is used to convert the energy of elastic waves into the energy of airborne sound waves, thereby achieving the diffusion and radiation of ultrasonic interference signals. Elastic waves propagate to the surface of the coupling fixture, causing the air on the fixture surface to vibrate and radiate ultrasonic waves into the air. The main lobe of the compression wave, in the direction perpendicular to the hemispherical plane, causes the top surface of the hemisphere to vibrate radially, radiating sound waves. The main lobe of the shear wave, in the direction with a pitch angle of 60° (assuming the direction perpendicular to the hemispherical surface is 0°), causes the radiating blades to vibrate laterally, thus radiating sound waves. Surface waves concentrate on the hemispherical surface, driving the radiating blades corresponding to a pitch angle of 90° to vibrate laterally, thus radiating sound waves.

[0068] In this embodiment, step 404 fully utilizes the energy of compression waves, shear waves, and surface waves to radiate sound waves, thereby improving the coupling efficiency of elastic waves and sound waves. In addition, step 403 excites elastic waves on the surface of the hemispherical coupling fixture, maintaining the original wavefront shape of the elastic waves, reducing the reflection of elastic waves, and making the phase of the radiated sound field controllable.

[0069] Example 4

[0070] like Figure 8 As shown, this embodiment provides a method for diffusing and radiating ultrasonic waves into the air, which can be achieved through three steps: interference device deployment optimization 501, interference signal optimization 502, and circuit parameter optimization 503. The specific steps are as follows:

[0071] Step 501: Optimize the deployment of interference devices.

[0072] The primary application scenarios for eavesdropping and recording jammers are indoors, where the walls and ceilings are padded, and furniture such as tables and chairs is present, creating a complex sound field. In areas far from the speaker and walls, sound waves arrive randomly, meeting the conditions for a reverberant sound field. However, actual eavesdropping and recording devices are often placed under tables, on the floor, or near chairs—places too close to sound reflectors to fully meet the reverberant sound field requirements. For ultrasonic signals, the sound field is even more complex. To ensure that the ultrasonic jamming signal covers all sensitive areas, the placement of the ultrasonic jamming device needs to be optimized.

[0073] In the optimization step of the interference device deployment, a high-fidelity ultrasonic loudspeaker is used as the sound source, and multiple microphones are used to collect sound pressure signals at sensitive locations. The equivalent reverberation time and transfer function of the room under ultrasonic excitation are estimated by the interrupted sound source method. Preferably, the excitation signal is a random noise signal after bandpass filtering from 25kHz to 40kHz. The room volume should not exceed 150m². 3 The reverberation time in the room at frequencies below 5000Hz should not exceed 1 second; otherwise, measures must be taken to reduce the reverberation time in the speech frequency band to ensure speech intelligibility. When the equivalent reverberation time of the ultrasonic signal is less than 0.1s or the transfer function amplitude is less than -10dB, the sound source position must be adjusted or an additional sound source must be added for compensation.

[0074] Step 502, interference signal optimization.

[0075] The coupling fixture under ultrasonic excitation exhibits a rich variety of vibration modes. Each vibration mode has a different radiation efficiency, which causes the amplitude of the ultrasonic waves radiated by the interfering device to vary significantly with the frequency of the excitation signal. To ensure that the ultrasonic interference signal can be effectively radiated, it is necessary to avoid frequency bands with low radiation efficiency of the coupling fixture and identify several vibration modes with high radiation efficiency as preferred excitation modes. The frequencies corresponding to these preferred excitation modes should be accurately measured, and the interference signal should be optimized based on this measurement.

[0076] The interference signal optimization step is performed in an anechoic chamber. A band-limited ultrasonic signal is used for excitation, and the transducer unit's response is measured using a microphone capable of acquiring ultrasonic signals. Ten angles are uniformly selected within a pitch range of 0° to 90°, and measurements are taken at a distance of 20cm from the transducer unit. The transfer function curves corresponding to each angle are calculated and summed to obtain the summed frequency spectrum. The five frequency points with the highest frequency spectrum amplitude are selected as the preferred excitation frequencies, denoted from low to high as f1, f2, f3, f4, and f5, respectively, and their corresponding modes are the preferred excitation modes. The ultrasonic transducer unit consists of piezoelectric ceramics and coupling fixtures. The band-limited ultrasonic signal is a random noise signal with a bandpass filter from 25kHz to 40kHz.

[0077] Step 503, circuit parameter optimization.

[0078] Due to impedance mismatch, the excitation signal undergoes significant attenuation at both the excitation signal source and the ultrasonic transducer, resulting in a significant reduction in the amplitude of the actual radiated sound wave. Therefore, circuit parameter optimization is necessary, particularly matching the output impedance of the excitation signal source with the input impedance of the ultrasonic transducer. Furthermore, due to the electro-mechanical-acoustic coupling of the interferometer, adjusting the output impedance of the excitation signal source will affect the resonant frequencies corresponding to each mode. Therefore, after impedance matching, the optimal excitation frequency needs to be measured again.

[0079] The connection diagram for the circuit parameter optimization steps is as follows: Figure 7 As shown, an adjustable resistor is connected in series with the ultrasonic transducer and then connected to the output of the signal generator. Oscilloscope channel 1 is connected in parallel with the transducer, and oscilloscope channel 2 is connected in parallel with the signal generator. A sinusoidal signal with frequency f3 is used as the excitation signal. The adjustable resistor is adjusted so that the signals from channel 1 and channel 2 are in phase, achieving impedance matching. After impedance matching, the frequencies f1, f2, f3, f4, and f5 corresponding to the preferred excitation mode need to be remeasured.

[0080] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A device for radiating ultrasonic waves into the air, characterized in that: The device includes an ultrasonic generator, an ultrasonic transducer, and a coupling fixture. The coupling fixture is hemispherical in shape and includes a hemisphere and multiple pine cone-shaped radiating blades. The multiple pine cone-shaped radiating blades are disposed on the surface of the hemisphere. The bottom surface of the hemisphere has mounting holes, and the ultrasonic transducer is disposed in the mounting holes. The ultrasonic transducer includes a piezoelectric ceramic and a back cover plate. The piezoelectric ceramic is disposed in the mounting holes, and the back cover plate is used to fix the piezoelectric ceramic to the bottom surface of the coupling fixture by bolts. The piezoelectric ceramic has electrodes that are electrically connected to the ultrasonic generator. The ultrasonic generator drives the piezoelectric ceramic to generate vibrations perpendicular to the bottom surface of the hemisphere, which excites elastic waves in the coupling fixture. The coupling fixture converts the elastic waves into airborne sound waves.

2. The device for diffusing and radiating ultrasonic waves into the air as described in claim 1, characterized in that: The radius D of the coupling fixture satisfies D>λ p , where λ p This represents the wavelength of a compression wave in a hemispherical material at 30 kHz.

3. The device for diffusing and radiating ultrasonic waves into the air as described in claim 1, characterized in that: The width W of the radiation blade satisfies W < 2λ s , where λ s is the wavelength corresponding to the shear wave in the 40 kHz hemispherical material, and the length L of the radiation blade satisfies W < L < D, where D is the radius of the coupling tooling.

4. The device for diffusing and radiating ultrasonic waves into the air as described in claim 1, characterized in that: The contact point between the piezoelectric ceramic and the coupling fixture is located at the center of the hemispherical coupling fixture.

5. The device for diffusing and radiating ultrasonic waves into the air as described in claim 4, characterized in that: The piezoelectric ceramic is a longitudinally vibrating piezoelectric ceramic stack, which is excited in a direction perpendicular to the plane of the coupling tooling.

6. The device for diffusing and radiating ultrasonic waves into the air as described in claim 4, characterized in that: The piezoelectric ceramic is bonded to the rear cover plate and coupling tooling with epoxy resin.

7. The device for diffusing and radiating ultrasonic waves into the air as described in claim 1, characterized in that: The ultrasonic generator includes a signal generator and a power amplifier. The signal generator and the power amplifier are electrically connected, and the positive and negative electrodes of the output terminal of the power amplifier are connected to the electrodes of the ultrasonic transducer.

8. The device for diffusing and radiating ultrasonic waves into the air as described in claim 1, characterized in that: While the piezoelectric ceramic undergoes longitudinal deformation, it applies an excitation perpendicular to the bottom surface of the hemisphere to the surface of the coupling fixture, generating compression waves, shear waves, and surface waves inside the coupling fixture; among them, the compression waves and shear waves are spherical waves, and the surface waves are cylindrical waves, and the waves of the three modes propagate outward from the center of the hemisphere as the origin.

9. The device for diffusing and radiating ultrasonic waves into the air as described in claim 8, characterized in that: The main lobe of the compression wave, in a direction perpendicular to the hemispherical plane of the coupling fixture, causes the top surface of the hemisphere to vibrate radially and radiate sound waves; the main lobe of the shear wave, in a direction with a pitch angle of 60°, causes the radiating blades to vibrate laterally, thereby radiating sound waves; the surface wave is concentrated on the hemispherical surface of the coupling fixture, driving the radiating blades corresponding to a pitch angle of 90° to vibrate laterally, thereby radiating sound waves.

10. A method for a device for diffusing and radiating ultrasonic waves into air as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Adjust the output impedance of the ultrasonic generator to match the impedance of the piezoelectric ceramic electrical terminals; Step 2: The ultrasonic generator generates a voltage signal and feeds it to the two ends of the piezoelectric ceramic electrode, causing it to undergo longitudinal deformation; Step 3: Excite the piezoelectric ceramic coupling fixture to generate compression waves, shear waves and surface waves inside it. The compression waves and shear waves are spherical waves, and the surface waves are cylindrical waves. The waves of the three modes propagate outward from the center of the hemisphere. Step 4: Allow the elastic wave to propagate to the surface of the coupling fixture, causing the air on the fixture surface to vibrate. Ultrasonic waves radiate into the air, with compression waves causing the hemispherical surface to vibrate radially. Shear waves and surface waves drive the scale-like radial blades to produce transverse vibrations.

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