Broadband ultrasonic sensor

Abstract

A broadband ultrasonic sensor is characterized in that the ultrasonic sensor comprises a housing, one end of which is provided with a horn opening; the PCB is fixed in the shell, a front cavity is formed between one side of the PCB and the loudspeaker opening, and a rear cavity is formed in the shell on the other side of the PCB; the leading-out joint penetrates through the side wall of the shell and is positioned on one side of the rear cavity; and the piezoelectric ceramic element array is electrically connected with the leading-out joint, is positioned in the front cavity, is fixed with the PCB, and comprises a plurality of piezoelectric ceramic elements which are different in resonant frequency and are connected in series. A wide detection frequency band is obtained by designing piezoelectric vibrator structures which are connected in series and have different center frequencies, and meanwhile, the sensor keeps high detection sensitivity by designing a horn opening type sensor shell, a conical energy gathering device and a piezoelectric ceramic material component; when the partial discharge defect of the power equipment is monitored, defect signals with more frequencies can be captured, and the equipment fault detection rate is improved.

Description

Technical Field

[0001] The invention belongs to the field of ultrasonic sensors, and in particular relates to a broadband ultrasonic sensor. Background Art

[0002] Piezoelectric ultrasonic sensors can convert the vibration mechanical energy generated by the received ultrasonic waves into high-frequency electrical energy through the piezoelectric effect, thereby achieving measurement. Because noise in the ultrasonic range is rare in ordinary backgrounds, and ultrasonic waves are insensitive to ambient light, electromagnetic interference, dust or other factors, ultrasonic sensors have become one of the most important sensors widely used in the automotive industry, industrial monitoring and other fields. The most common application of ultrasonic sensors is underwater sonar, which uses ultrasonic propagation for navigation, detection and communication. In addition, piezoelectric ultrasonic sensors have been further developed for non-contact sensing in the air, namely the so-called air-coupled ultrasonic sensors. Due to this contactless characteristic, it has obvious advantages in monitoring unsafe high-voltage power equipment failures at close range. During the operation of high-voltage power equipment, early faults such as corona discharge, partial discharge, ablation discharge and spark discharge will occur due to defects or aging, and these discharges are usually accompanied by the generation of ultrasonic waves. Therefore, air-coupled ultrasonic sensors can safely monitor these discharges online and play an important role in the intelligence of equipment.

[0003] The inherent disadvantage of air-coupled ultrasonic sensors is that ultrasonic energy suffers huge energy losses when it is reflected and refracted across impedance-mismatched interfaces (such as air-solid interfaces). For example, the acoustic impedances of lead zirconate titanate (PZT) piezoelectric ceramics and air are approximately 3×107Rayl and 425Rayl, respectively, which results in large energy losses at the interface. By designing an appropriate focused resonant structure, ultrasonic waves can be focused at the center of the device, forming a higher energy density at that point, thereby achieving the highest amplitude vibration near the resonant frequency. However, this resonant structure is inherently accompanied by a narrow bandwidth feature, which loses information from other frequencies of ultrasonic sources that deviate from the resonant frequency. In order to improve the detection sensitivity of a specific fault or phenomenon, the resonant frequency of the sensor needs to be adjusted more accurately, but this often sacrifices its ability to respond to other frequency signals, thereby affecting the overall sensing accuracy; conversely, in order to expand the detection range, it may be necessary to relax the selectivity of the resonant frequency, but this will reduce the sensitivity to specific signals, so a trade-off between improving sensitivity and accuracy is required in actual design. At present, scholars mainly use acoustic matching design to compensate for this problem. The impedance of the gas-solid interface is tuned to an intermediate value through the matching layer to reduce energy loss and thus improve sensitivity. However, existing ultrasonic sensors still have the problem of small bandwidth and poor adaptability. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the existing ultrasonic sensor has small bandwidth and poor adaptability.

[0005] The purpose of the present invention is to adopt the following technical solutions to achieve:

[0006] A broadband ultrasonic sensor, characterized in that the ultrasonic sensor comprises:

[0007] a housing having a horn opening at one end;

[0008] A PCB board is fixed inside the housing, with one side of the PCB board and the speaker opening forming a front cavity, and the other side of the PCB board forming a rear cavity inside the housing;

[0009] A lead-out connector, which passes through the side wall of the shell and is located at one side of the rear cavity;

[0010] The piezoelectric ceramic element array is electrically connected to the lead-out connector, is located in the front cavity and is fixed to the PCB board, and includes a plurality of piezoelectric ceramic elements with different resonance frequencies and connected in series with each other.

[0011] Preferably, the shell includes an upper cover, a shell side wall and a shell bottom plate; the upper cover is fixed to one end of the shell side wall; the shell bottom plate is fixed to the other end of the shell side wall; the speaker opening is arranged on the upper cover; the shell bottom plate is provided with a through hole for installing the lead-out connector.

[0012] Preferably, the ultrasonic sensor further comprises: a waterproof and sound-permeable membrane fixed to the upper cover and sealing the speaker opening.

[0013] Preferably, the waterproof and sound-permeable membrane is a polytetrafluoroethylene membrane.

[0014] Preferably, the resonant frequency of the piezoelectric ceramic element is within a frequency band of 20k-60kHz.

[0015] Preferably, the shell is made of aluminum alloy.

[0016] Preferably, the piezoelectric ceramic element array includes four piezoelectric ceramic elements, and the center frequencies of the piezoelectric ceramic elements are 25 kHz, 30 kHz, 40 kHz, and 50 kHz, respectively.

[0017] Preferably, the piezoelectric ceramic element comprises: an element base connected to the PCB board, a piezoelectric ceramic arranged on the element base, a metal sheet fixed to the top of the piezoelectric ceramic, and an energy concentrator fixed to the top of the metal sheet.

[0018] Preferably, the piezoelectric ceramic comprises 0.025Sm-(1-x)PbMg 1 / 3 Nb 2 / 3 O 3 -xPbTiO 3 (0 <x<1)。

[0019] Preferably, the piezoelectric constant d of the piezoelectric ceramic is 33 It is 450-460pC / N.

[0020] Preferably, the metal sheet is welded to the piezoelectric ceramic using silver paste at low temperature.

[0021] Preferably, the material of the energy concentrator includes aluminum.

[0022] Preferably, the elementary base is bonded and fixed to the piezoelectric ceramic by a polysulfide synthetic rubber adhesive.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] A broadband ultrasonic sensor, characterized in that the ultrasonic sensor comprises: a shell, one end of which has a horn opening; a PCB board, which is fixed inside the shell, one side of which forms a front cavity with the horn opening, and the other side of which forms a rear cavity inside the shell; a lead-out connector, which passes through the side wall of the shell and is located on one side of the rear cavity; a piezoelectric ceramic element array, which is electrically connected to the lead-out connector, is located in the front cavity and is fixed to the PCB board, and includes a plurality of piezoelectric ceramic elements with different resonant frequencies and connected in series. The present invention obtains a wider detection frequency band by designing a piezoelectric vibrator structure with different center frequencies connected in series, and at the same time designs a horn opening type sensor housing, a conical energy concentrator and a piezoelectric ceramic material component so that the sensor maintains a high detection sensitivity, thereby obtaining a high-sensitivity broadband ultrasonic sensor based on structural design, which can capture defect signals of more frequencies when monitoring partial discharge defects of power equipment, thereby improving the equipment fault detection rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A three-dimensional structural cross-sectional view of a broadband ultrasonic sensor of the present invention;

[0026] Figure 2 For the present invention Figure 1 Structural cross-section of the middle upper cover;

[0027] Figure 3 For the present invention Figure 1 A top view of the side wall of the middle shell;

[0028] Figure 4 For the present invention Figure 1 Structural cross-section of the side wall of the middle shell;

[0029] Figure 5 For the present invention Figure 1 Top view of the bottom plate of the middle shell;

[0030] Figure 6 For the present invention Figure 1 Structural cross-section of the bottom plate of the middle shell;

[0031] Figure 7 For the present invention Figure 1 The circuit diagram of the voltage amplifier in the PCB board;

[0032] Figure 8 For the present invention Figure 1 The circuit diagram of the charge amplifier in the PCB board;

[0033] Fig. 9 For the present invention Figure 1 The low-pass filter circuit diagram in the PCB board;

[0034] Fig.10 This is the output waveform diagram of the ultrasonic sensor of the present invention under the excitation of the ultrasonic signal with a frequency of 25kHz;

[0035] Fig.11 This is the output waveform diagram of the ultrasonic sensor of the present invention under the excitation of the ultrasonic signal with a frequency of 30kHz;

[0036] Fig.12 This is the output waveform diagram of the ultrasonic sensor of the present invention under the excitation of the ultrasonic signal with a frequency of 40kHz;

[0037] Fig.13 This is the output waveform diagram of the ultrasonic sensor of the present invention under the excitation of the ultrasonic signal with a frequency of 50kHz;

[0038] Wherein: 1. Shell, 2. PCB board, 3. Lead connector, 4. Piezoelectric ceramic element array, 5. Waterproof sound-permeable membrane, 11. Upper cover, 12. Shell side wall, 13. Shell bottom plate, 10. Speaker opening, 100. Front cavity, 200. Rear cavity, 41. Piezoelectric ceramic element, 411. Element base, 412. Piezoelectric ceramic, 413. Metal sheet, 414. Energy concentrator, 111. Internal thread, 121. Ring structure, 122. Screw hole, 131. Through hole. DETAILED DESCRIPTION

[0039] The technical solution is further described below in conjunction with the accompanying drawings and specific embodiments to help understand the content of the present invention.

[0040] In this embodiment, four modules with continuous resonant frequencies in the range of 20 kHz to 60 kHz are connected in series and integrated into one sensor unit through structural design, so as to broaden the sensor detection frequency band and meet the sensitivity detection requirements.

[0041] like Figure 1 As shown, a broadband ultrasonic sensor is characterized in that the ultrasonic sensor comprises:

[0042] The housing 1 has a speaker opening 10 at one end;

[0043] A PCB board 2 is fixed inside the housing 1, with one side of the PCB board 2 and the speaker opening 10 forming a front cavity 100, and the other side of the PCB board 2 forming a rear cavity 200 inside the housing 1;

[0044] The lead-out connector 3 penetrates through the side wall of the housing 1 and is located at one side of the rear cavity 200;

[0045] The piezoelectric ceramic element array 4 is electrically connected to the lead-out connector 3 (not shown in the figure), is located in the front cavity 100 and fixed to the PCB board 2, and includes a plurality of piezoelectric ceramic elements 41 with different resonance frequencies and connected in series.

[0046] The housing 1 includes an upper cover 11, a housing side wall 12 and a housing bottom plate 13; the upper cover 11 is fixed to one end of the housing side wall 12; the housing bottom plate 13 is fixed to the other end of the housing side wall 12; Figure 2 As shown, the horn opening 10 is provided on the upper cover 11, and the upper cover 11 has an internal thread 111 for connecting to the housing side wall 12. Figure 3-4 As shown, the housing side wall 12 is a cylindrical part, and its upper end has an external thread ( Figure 4 Not shown, see Figure 1 ), the lower end of which has an internal thread for connecting to the housing bottom plate 13 ( Figure 4 Not shown, see Figure 1 ). The middle part of the ring structure 121 is used to install the PCB board 2, and the ring structure 121 is provided with four screw holes 122. Figure 5-6 As shown, the housing bottom plate 13 is provided with a through hole 131 for mounting the lead-out connector 3. The housing 1 is made of aluminum alloy.

[0047] like Figure 2 As shown, the ultrasonic sensor further comprises: a waterproof sound-permeable membrane 5 fixed to the upper cover 11 and closing the speaker opening 10. The waterproof sound-permeable membrane is a polytetrafluoroethylene membrane.

[0048] The resonance frequency of the piezoelectric ceramic element 41 is within the frequency band of 20k-60kHz. The piezoelectric ceramic element array comprises four piezoelectric ceramic elements connected in series, and the center frequencies of the piezoelectric ceramic elements are 25kHz, 30kHz, 40kHz and 50kHz respectively.

[0049] like Figure 1As shown in the figure, the piezoelectric ceramic element 41 includes: a base 411 connected to the PCB board 2, a piezoelectric ceramic 412 disposed on the base 411, a metal sheet 413 fixed to the top of the piezoelectric ceramic 412, and an energy concentrator 414 fixed to the top of the metal sheet 413. The metal sheet 413 is made of copper.

[0050] The piezoelectric ceramic 412 is made of 0.025Sm-(1-x)PbMg 1 / 3 Nb 2 / 3 O 3 -xPbTiO 3 (0 < x < 1). The piezoelectric constant d of the piezoelectric ceramic 412 33 is 450 - 460 pC / N.

[0051] The present invention designs a sensor housing of a horn opening type. Ultrasonic waves are gathered through the horn opening and then pass through a polytetrafluoroethylene waterproof and sound-permeable membrane, and then are transmitted to four series-connected piezoelectric ceramic elements through a bowl-shaped energy concentrator. The resonance frequencies of each piezoelectric ceramic element are different, so that the sensor has a relatively wide frequency band range. After the piezoelectric ceramic converts the ultrasonic signal into an electrical signal, the signal is output through a voltage amplifier, a charge amplifier and a low-pass filter integrated on the PCB board, thereby obtaining a broadband ultrasonic sensor with high sensitivity in the frequency band of 20k - 60kHz based on the structural design, providing a general and direct method for developing high-sensitivity and broadband high-performance air-coupled sensors.

[0052] The specific implementation process of the present invention includes the following contents:

[0053] The present invention can effectively improve the frequency band range of the ultrasonic sensor while maintaining high sensitivity through the following steps.

[0054] (1) Housing processing: Design the ultrasonic sensor housing as shown in Figure 2-6 the figure. The upper cover 11 is of a horn opening type to achieve ultrasonic convergence and improve the sensor sensitivity. The sensor housing is made of aluminum alloy, and the surface should be smooth, and the dimensional tolerances are all less than ±0.05mm. The housing consists of an upper cover 11, a housing side wall 12 and a housing bottom plate 13. The upper cover 11 and the housing side wall 12 and between the housing side wall 12 and the housing bottom plate 13 are connected by threads for easy assembly and sealing. A through hole 131 is opened in the middle of the housing bottom plate 13 to pass through the BNC connector to output an electrical signal.

[0055] (2) Piezoelectric ceramic testing: The piezoelectric ceramic formula used in the ultrasonic sensor of the present invention is 0.025Sm-(1-x)PbMg 1 / 3 Nb 2 / 3 O 3 -xPbTiO3 (0 < x < 1), its piezoelectric properties are tested before encapsulation. To ensure the performance consistency of the samples, ceramic samples with a piezoelectric constant d33 of 450 - 460 pC / N are screened.

[0056] (3) Low-temperature soldering of ceramics: Using a concentric circle tooling, a mixture of silver paste and diluent is controlled on the back of the copper metal sheet, and the piezoelectric ceramic is soldered at low temperature. It is pre-dried with a 70°C heat gun for 10 minutes and then placed in a constant-temperature oven at 70°C for 2 hours to dry.

[0057] (4) Fixing of the concentrator: Using the concentric circle tooling, the aluminum concentrator (conical resonance disk) is fixed to the other side of the copper metal sheet where the piezoelectric ceramic is soldered through an adhesive, keeping the plane of the concentrator bowl mouth parallel to the plane of the copper metal sheet.

[0058] (5) Wide-band design of the sensor: By adjusting the piezoelectric ceramic composition, size, and concentrator structure, piezoelectric composite vibrators with center frequencies of 25 kHz, 30 kHz, 40 kHz, and 50 kHz are obtained. The positive and negative electrodes of the piezoelectric material of each vibrator are connected in series in turn through thin wires, and a higher electro-acoustic conversion efficiency can be obtained compared with a single piezoelectric vibrator.

[0059] (6) Bonding of the piezoelectric composite vibrator and the base element: The composite vibrator and the base element are bonded together using a polysulfide synthetic rubber adhesive that is a semi-fluid milky liquid at room temperature. After bonding, the sample (semi-finished product) is placed at room temperature for at least 2 hours to allow the adhesive to absorb moisture and cure. There should be a certain bonding layer thickness to ensure the stability of the bonding. The bonding layer thickness is uniform, and the concentricity between the composite vibrator and the base element is greater than 95%.

[0060] (7) PCB board design: The PCB circuit integrates a voltage amplifier, a charge amplifier, and a low-pass filter. The designed circuit diagram is as Figure 7-9 shown. In the figure, XBP1 is a Bode plotter, which is connected to the input and output terminals respectively to detect the voltage waveform; XSC1 is an oscilloscope, which is used to measure the amplitude-frequency characteristic and phase-frequency characteristic of the circuit to detect the response of the circuit to signals of different frequencies; Ext Trig is the external trigger connection terminal.

[0061] (8) Fixing of the base element: Four base elements are assembled on the PCB board at equal intervals.

[0062] (9) Electrode soldering: The metal copper sheets connected to the positive and negative electrodes of the piezoelectric ceramic are soldered to the corresponding contacts on the PCB board. The soldering iron temperature is 450°C, and two leads are soldered to the positive and negative electrodes on the back of the PCB board. The other end is for connection to the adapter.

[0063] (10) Installation of the PCB board: Align the four prefabricated round holes on the edge of the PCB board with the four prefabricated round holes on the side wall of the sensor, and fix them with screws and nuts.

[0064] (11) Adapter assembly: Use tooling to fix the BNC connector, and use a spot welder to weld the PCB positive and negative leads to the BNC connector positive and negative. The welding time is 0.6s and the welding current is 14kA. The length of the remaining wire should be appropriate, generally 1.3 to 1.5 times the actual required length. Then assemble it into the sensor base plate housing and fix it with nuts.

[0065] (12) Sealing the connector: Use a hot melt glue stick of 1 cm long and 7 mm in diameter. After melting, pour it into the sensor base plate housing to seal the BNC thread and ensure water tightness.

[0066] (13) Waterproof and sound-permeable membrane sealing: A polytetrafluoroethylene (PTFE) microporous membrane is used as the waterproof and sound-permeable membrane for sealing the upper cover. The waterproof and sound-permeable membrane is a new type of polymer waterproof and dust-proof material with a microporous structure. Due to the special structure of the microporous membrane itself, the characteristic impedance is very close to that of air. In addition, the material itself has very little loss of sound energy, allowing most of the sound energy to pass through the film. According to the size of the circular hole on the upper cover of the sensor, a waterproof and sound-permeable membrane disc with a diameter of 22 mm is designed, and a 1 mm wide adhesive is attached to the edge. It is directly pasted on the inner side of the upper cover to complete the sealing of the upper cover.

[0067] (14) Overall packaging: The side wall of the sensor is fixed to the bottom plate by screwing, and the upper cover of the sensor housing is fixed to the side wall by screwing.

[0068] The inherent disadvantage of air-coupled ultrasonic sensors is that ultrasonic energy suffers huge energy losses when it is reflected and refracted through impedance-mismatched interfaces (such as air-solid interfaces). By designing an appropriate focused resonant structure, the ultrasonic wave can be focused at the center of the device, forming a higher energy density at that point, thereby achieving the highest amplitude vibration near the resonant frequency. However, this resonant structure is inherently accompanied by a narrow bandwidth characteristic, which loses information from other frequencies of the ultrasonic source that deviates from the resonant frequency. In order to improve the detection sensitivity of specific faults or phenomena, the resonant frequency of the sensor needs to be adjusted more accurately, but this often sacrifices its responsiveness to other frequency signals, thereby affecting the overall sensing accuracy; conversely, in order to expand the detection range, it may be necessary to relax the selectivity of the resonant frequency, but this will reduce the sensitivity to specific signals, so in actual design, a trade-off between improving sensitivity and accuracy is required. At present, scholars mainly use acoustic matching design to compensate for this problem. The impedance of the gas-solid interface is tuned to the intermediate value through the matching layer to reduce energy loss and thus improve sensitivity, but broadband ultrasonic detection is still not possible.

[0069] This solution obtains a relatively wide detection frequency band by designing a piezoelectric oscillator structure with different center frequencies in series. At the same time, a horn-opening sensor housing, a conical energy concentrator, and a piezoelectric ceramic material composition are designed to keep the sensor with a high detection sensitivity, so as to obtain a high-sensitivity wide-band ultrasonic sensor based on structural design. When monitoring the partial discharge defects of power equipment, more frequency defect signals can be captured, improving the equipment fault detection rate. This solution provides a new idea for optimizing the sensitivity and frequency band of the sensor, and has the advantages of simple operation, predictable results, and customization.

[0070] As Figure 10-13 shown, an ultrasonic sensor is prepared through the above solution. The output waveforms of the sensor are tested at four frequency points of 25 kHz, 30 kHz, 40 kHz, and 50 kHz. The preamplifier gain is 60 dB, the acquisition threshold is 40 dB, the sampling frequency is 5 MHz, and the acquisition depth is 1 k. After testing, the ultrasonic detector has 4 peak frequencies: when the ultrasonic signals with a sound pressure level of 33 dB and frequencies of 25 kHz, 30 kHz, 40 kHz, and 50 kHz are excited, the amplitude of the output waveforms of the ultrasonic sensor is about 6 mV. Obvious sine wave waveforms can be observed, and the frequencies are also consistent with the ultrasonic signals, indicating that the sensor proposed by the present invention can realize wide-band ultrasonic detection through structural design.

[0071] A high-sensitivity wide-band ultrasonic sensor based on structural design proposed by the present invention is used to detect the partial discharge ultrasonic signals of power equipment, and has the following characteristics:

[0072] (1) Piezoelectric ceramics with the formula of 0.025Sm-(1-x)PbMg 1 / 3 Nb 2 / 3 O 3 -xPbTiO 3 (0 < x < 1) are used as the core sensing material, and the piezoelectric coefficient is 450 - 460 pC / N.

[0073] (2) The horn-opening sensor housing and the conical energy concentrator are optimized and designed through simulation to improve the detection sensitivity of the sensor.

[0074] (3) Piezoelectric composite oscillators with different center frequencies are optimized and designed through simulation, and their positive and negative poles are connected in series, broadening the sensor detection frequency band to 20k - 60kHz, meeting the detection requirements of partial discharge of power equipment.

[0075] Figure 10-13 The brief explanations of Chinese and English abbreviations are as follows:

[0076] RIGOL: Abbreviation of the manufacturer name.

[0077] STOP: The stop refresh key of the oscilloscope.

[0078] Vpp: The abbreviation of "peak-to-peak voltage", usually called "peak-to-peak voltage" in Chinese.

[0079] CH1: Channel 1.

[0080] Time: time.

[0081] us: time unit, microseconds.

[0082] mV: voltage unit, millivolt.

[0083] Freq: frequency.

[0084] kHz: kilohertz, unit of frequency.

[0085] Other unexplained characters have common meanings of oscilloscopes and do not affect the technical content of the present invention.

[0086] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention.

Claims

1. A broadband ultrasonic sensor, characterized in that: The ultrasonic sensor comprises: a housing having a horn opening at one end; A PCB board is fixed inside the housing, with one side of the PCB board and the speaker opening forming a front cavity, and the other side of the PCB board forming a rear cavity inside the housing; A lead-out connector, which passes through the side wall of the shell and is located at one side of the rear cavity; The piezoelectric ceramic element array is electrically connected to the lead-out connector, is located in the front cavity and is fixed to the PCB board, and includes a plurality of piezoelectric ceramic elements with different resonance frequencies and connected in series with each other.

2. A broadband ultrasonic sensor as claimed in claim 1, characterized in that: The shell includes an upper cover, a shell side wall and a shell bottom plate; the upper cover is fixed to one end of the shell side wall; the shell bottom plate is fixed to the other end of the shell side wall; the speaker opening is arranged on the upper cover; the shell bottom plate is provided with a through hole for installing the lead-out connector.

3. A broadband ultrasonic sensor as claimed in claim 2, characterized in that: The ultrasonic sensor further includes a waterproof sound-permeable membrane fixed to the upper cover and sealing the speaker opening.

4. A broadband ultrasonic sensor as claimed in claim 3, characterized in that: The waterproof sound-permeable membrane is a polytetrafluoroethylene membrane.

5. A broadband ultrasonic sensor as claimed in claim 1, characterized in that: The resonance frequency of the piezoelectric ceramic element is within the frequency band of 20k-60kHz.

6. A broadband ultrasonic sensor as claimed in claim 1, characterized in that: The material of the shell includes aluminum alloy.

7. A broadband ultrasonic sensor as claimed in claim 1, characterized in that: The piezoelectric ceramic element array includes four piezoelectric ceramic elements, and the central frequencies of the piezoelectric ceramic elements are 25 kHz, 30 kHz, 40 kHz, and 50 kHz respectively.

8. A broadband ultrasonic sensor as claimed in claim 1, characterized in that: The piezoelectric ceramic element comprises: an element base connected to the PCB board, a piezoelectric ceramic arranged on the element base, a metal sheet fixed on the top of the piezoelectric ceramic, and an energy concentrator fixed on the top of the metal sheet.

9. A broadband ultrasonic sensor as claimed in claim 8, characterized in that: The piezoelectric ceramic includes 0.025Sm-(1-x)PbMg 1 / 3 Nb 2 / 3 O3-xPbTiO3(0 <x<1)。 10. The broadband ultrasonic sensor according to claim 8, characterized in that: The piezoelectric constant d of the piezoelectric ceramic 33 It is 450-460pC / N.

11. A broadband ultrasonic sensor as claimed in claim 8, characterized in that: The metal sheet is welded to the piezoelectric ceramic by using silver paste at low temperature.

12. A broadband ultrasonic sensor as claimed in claim 8, characterized in that: The material of the energy concentrator includes aluminum.

13. A broadband ultrasonic sensor as claimed in claim 8, characterized in that: The elementary base is bonded and fixed to the piezoelectric ceramic by a polysulfide synthetic rubber adhesive.

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