Rectangular-section frustoconical front cover plate and longitudinal piezoelectric ultrasonic transducer

Abstract

The utility model relates to a kind of rectangular section frustum front cover plate and longitudinal piezoelectric ultrasonic transducer;Wherein front cover plate is rectangular section frustum structure, its taper angle α range is 30 °-40 °, side length L range is 13mm-17mm, preferably 35 ° and 15mm.The front cover plate is coaxially sequentially provided with cover top, cover waist and cover bottom from connecting end to radiation end, and cover bottom size is greater than cover top.Through optimizing the above-mentioned geometric parameter, the emission voltage response (TVR) of transducer under specific working frequency (63kHz) is effectively improved.The front cover plate and piezoelectric crystal stack, rear cover plate etc.are pre-tightening assembled by screw and washer.Experimental test shows that the transducer resonance frequency using the front cover plate is consistent with design value, and TVR is significantly higher than traditional structure, while keeping simple structure, effectively improves emission performance, applicable to underwater acoustic communication, detection and sonar system.

Description

Technical Field

[0001] This utility model relates to the technical field of transducer components, and in particular to a rectangular cross-section frustum front cover plate and a longitudinal piezoelectric ultrasonic transducer. Background Technology

[0002] Underwater acoustic transducers are core components for converting electrical energy into acoustic energy and are widely used in underwater communication, detection, navigation, and sonar systems. Among them, the longitudinal composite rod (Tonpilz) piezoelectric transducer has become one of the mainstream underwater acoustic transmitting devices due to its compact structure, high efficiency, and ease of arraying. This type of transducer typically consists of a piezoelectric ceramic stack, a rear mass block, and a front cover plate. The front cover plate serves as the acoustic radiation surface and also undertakes the crucial functions of impedance matching and amplitude amplification; its performance directly determines the final transmission efficiency of the transducer.

[0003] The core metric for evaluating the performance of a transmitting transducer is the transmit voltage response (TVR), which reflects the sound pressure level generated by the transducer in the far field under a unit driving voltage. To improve TVR, the front cover is traditionally designed with a cylindrical or simple exponential profile. However, these traditional structures have gradually revealed their inherent limitations in practice: First, their bandwidth is typically narrow, making it difficult to maintain a high response over a wide frequency range; second, the TVR curve often exhibits significant fluctuations within the operating frequency band, especially near the desired operating frequency (e.g., 63 kHz), where the response gain is limited, making it difficult to output maximum acoustic power at a fixed frequency; furthermore, the simple geometry also limits its amplitude amplification capability and impedance matching effect with the load medium.

[0004] To overcome the aforementioned problems, existing technologies have proposed several improvement schemes. For example, complex structures such as cavities, perforations, or phonon crystals are introduced to excite bending vibration modes, utilizing longitudinal-bending coupled vibration to broaden the operating bandwidth. However, while these methods increase bandwidth, they often introduce problems such as structural complexity, increased manufacturing difficulty, reduced reliability, and increased manufacturing costs. More importantly, for many specific applications such as active sonar and ultrasonic processing, the transducer's operating frequency is relatively fixed. The primary goal is not to pursue a wide bandwidth, but to obtain the highest transmit voltage response at a specific frequency (e.g., 63 kHz) to improve the effective range and signal-to-noise ratio. Under such requirements, the aforementioned complex designs aimed at broadening bandwidth are not the optimal solution and may even reduce the peak response at the target frequency due to energy dispersion.

[0005] Therefore, while maintaining a simple overall transducer structure and avoiding the introduction of additional matching layers or complex internal structures, how to effectively improve the transmit voltage response at a specific operating frequency by optimizing the basic geometric parameters of the front cover (such as cross-sectional shape, cone angle, and radiating surface dimensions) has become a research direction of significant engineering value. In existing technologies, there is a lack of systematic research and clear design guidance on how key parameters such as the cone angle and side length of the front cover synergistically affect TVR after changing from a traditional circular cross-section to a rectangular cross-section. Therefore, a novel front cover design that is simple in structure, easy to manufacture, and can significantly improve transmit performance at a specific frequency is needed. Summary of the Invention

[0006] To solve the above-mentioned technical problems, this utility model provides a rectangular cross-section frustum front cover plate. The front cover plate has an overall frustum-shaped structure. The front cover plate is characterized by having a rectangular radial end face with a cone angle α ranging from 30° to 40° and a side length L ranging from 13mm to 17mm. The front cover plate is provided with a top, a waist, and a bottom coaxially arranged from its connection end with the piezoelectric crystal stack to the radial end, wherein the outer dimensions of the bottom cross-section are larger than those of the top cross-section.

[0007] In one embodiment of this utility model, the cone angle α is 35° and the side length L is 15mm.

[0008] In one embodiment of this utility model, the waist of the cover is conical, and its outer diameter gradually increases from top to bottom.

[0009] In one embodiment of this utility model, the upper end of the cover is provided with a mounting hole for accommodating the prestressed screw along the axial direction.

[0010] In one embodiment of this utility model, one end of the front cover plate and some transducer components, such as piezoelectric crystal stack, electrode sheet and rear cover plate, are pre-tightened together by screws and washers passing through the mounting hole.

[0011] In one embodiment of the present invention, and in an assembly, a prestressed screw applies an axial preload to the piezoelectric crystal stack, and the washer is disposed between the head of the screw and the rear cover plate or the front cover plate.

[0012] In one embodiment of this utility model, the washer is an elastic washer, used to provide uniform clamping force and prevent loosening during the pre-tightening process.

[0013] In one embodiment of this utility model, the electrode sheet is disposed at both ends of the piezoelectric crystal stack or between the crystal wafers, and is connected to an external circuit through a wire.

[0014] This invention also provides a longitudinal piezoelectric ultrasonic transducer, comprising the front cover plate described in any one of the claims; and the transducer operates at a frequency of 63kHz, with a transmission voltage response of not less than 138dB.

[0015] Compared with the prior art, the above-mentioned technical solution of this utility model has the following advantages: The front cover plate solution of this utility model, by optimizing it into a rectangular cross-section frustum with a specific cone angle (35°) and side length (15mm), significantly improves the transmission voltage response at a working frequency of 63kHz, without requiring a complex structure or additional matching layer. This design is simple and robust, easy to process and manufacture, and has stable and reliable performance, effectively improving the sound source level and operating distance of the underwater acoustic communication and detection system. Attached Figure Description

[0016] To make the content of this utility model easier to understand, the present utility model will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0017] Figure 1 This is the existing electromechanical equivalent circuit diagram of the transducer; Figure 2 This is a schematic diagram of an existing transducer structure; Figure 3 This is the three-dimensional finite element geometric model of the transducer described in this utility model; Figure 4 This invention provides underwater frequency domain analysis curves (including admittance curves and transmit voltage response). Figure 5 These are the underwater admittance curves of the transducer under different side lengths in this invention. Figure 6 These are the transducer emission voltage response curves for different side lengths in this invention. Figure 7 These are the underwater admittance curves of the transducer at different cone angles in this invention; Figure 8 This invention relates to the transducer's emission voltage response at different cone angles. Figure 9 This is a schematic diagram of the experimental test in this utility model; Figure 10 This is the transducer test emission response curve of this utility model; Figure 11 This is a schematic diagram of a transducer with an irregular front cover plate in this utility model; Figure 12 These are the simulation and test emission response curves of the transducer in this utility model.

[0018] As shown in the figure, 1. wafer; 2. electrode plate; 3. connector plate; 4. front cover plate; 5. rear cover plate; 6. screw; 7. washer. Detailed Implementation

[0019] like Figure 1 and Figure 2 As shown, based on the electromechanical analogy principle, the distributed parameter equivalent network of the passive unit is first constructed using the wave equation and boundary conditions; then, relying on the four-terminal network theory, the passive units are cascaded into a T-type four-terminal network; finally, the piezoelectric ceramic active branch is coupled to form a complete six-terminal electromechanical equivalent model (Figure 1). The transducer input impedance expression can be rigorously derived from this equivalent network, and setting the imaginary part of the impedance to zero yields its resonant frequency analytical equation.

[0020] in , , , , , , , , ; The radiator head has a radius of 10mm, a cone height of 5mm, and a column height of 3mm; the ceramic plate has an outer diameter of 10mm, an inner diameter of 5mm, and a thickness of 3mm; the rear cover plate has a diameter of 11mm and a height of 12mm. The calculated resonant frequency is 63kHz. A detailed schematic diagram of the transducer structure is shown below. Figure 2 As shown. Example 1

[0021] Further, see Figure 11 This embodiment provides a rectangular cross-section frustum front cover plate. The overall configuration of the front cover plate 4 is a rectangular cross-section frustum, that is, its radiating end face (the surface that radiates sound waves into the water) is rectangular, rather than a traditional circle.

[0022] The front cover plate 4, from its connection end with the piezoelectric crystal stack 1 to the radiation end, is coaxially provided with a top cover, a waist cover, and a bottom cover (for ease of description, the front cover plate structure is divided into these three functional segments). The top cover is used to connect the piezoelectric crystal stack 1, the waist cover is a transitional conical segment, and the bottom cover is the final acoustic radiation surface. The cross-sectional dimensions of the bottom cover are significantly larger than those of the top cover to achieve impedance matching and amplitude amplification.

[0023] The key innovation of this invention lies in the optimization of two key geometric parameters of the front cover plate 4: the cone angle (α) and the side length (L). Through theoretical calculations, finite element simulation (FEA), and experimental verification, it was determined that when the cone angle (α) of the current cover plate is in the range of 30° to 40° and the side length (L) of the radiating end face is in the range of 13mm to 17mm, the transmit voltage response (TVR) of the transducer near the target operating frequency of 63kHz is significantly improved.

[0024] Specific simulation modeling: Since the equivalent circuit analytical formula is only applicable to conical cover plates, and the actual array layout often simplifies the radiating end face to a rectangle to meet requirements, the finite element method is further introduced to perform full-wave numerical calculation of the transducer transmit voltage response (TVR) in order to improve prediction accuracy. Taking a rectangular radiating head with a width of 15 mm and a cone angle of 36.31° as the benchmark model, the system scans the dual-parameter space of side length and cone angle to quantify the influence of structural perturbations on TVR.

[0025] The actual longitudinal piezoelectric transducer consists of multiple components, including a radiating head, piezoelectric crystal stack, prestressed screw, electrode plates, epoxy resin, acoustic layer, and shell. To balance accuracy and efficiency, the critical energy transfer path is retained during FEA modeling, and only 1 / 4 of the periodic domain is taken using structural symmetry. Figure 3 shows the corresponding three-dimensional geometry: red—radiating head, yellow—piezoelectric crystal stack, blue—rear cover plate, green—prestressed bolt, purple—electrode plates; the remaining auxiliary components are coupled to the adjacent main body in an equivalent density-elastic constant manner to achieve efficient and accurate frequency response calculation.

[0026] Furthermore, specific modal and response analyses are conducted: extracting the transducer's characteristic frequencies and mapping them to corresponding mode shapes allows for a direct understanding of its acoustic radiation mechanism. During calculations, only the solid-liquid coupling interface is retained, while the water-area elements are hidden to eliminate fluid domain morphology interference and highlight the solid vibration modes, thereby clearly tracing the radiator displacement distribution and energy spillover path under each resonance order.

[0027] Next, the transducer's transmit voltage response in water is calculated and analyzed. During the analysis, the frequency range is set to 50–80 kHz, the scan frequency step is 1 kHz, and the mesh size is one-sixth of the wavelength in water. The calculated admittance curve and transmit voltage response curve are shown below. Figure 4 As shown.

[0028] Depend on Figure 4 It is known that the resonant frequency of the transducer in water is 63kHz, and the maximum response is 138dB.

[0029] To investigate the influence of the front cover plate's side length and taper on the emission voltage response, the admittance and emission voltage response in water for transducers with front cover plate side lengths of 10mm, 12mm, 14mm, 16mm, 18mm, and 20mm were calculated, as well as the admittance and emission voltage response in water for transducers with a side length of 15mm and taper angles of 65°, 60°, 55°, 50°, 45°, 40°, 35°, 30°, 25°, 20°, 15°, 10°, and 5°. The calculation results are as follows: Figure 5 , 6 As shown in 7 and 8.

[0030] Depend on Figure 5 It is known that as the side length of the front cover increases, the resonant frequency and the peak conductance decrease monotonically in sync. Figure 6Further, it is shown that the resonant emitter voltage response (TVR) also weakens with increasing side length. However, when the side length is >16 mm, both the conductance and TVR show a second-order increase in the 70–80 kHz frequency band. This is attributed to the dominance of the bending mode induced by the increased plate size, and the longitudinal-bending coupling causing the intervention of an additional resonant branch, resulting in a redistribution of high-frequency energy. Depend on Figure 7 It is known that as the cone angle decreases, the admittance of the transducer first decreases and then increases, while the resonant frequency continuously increases; from Figure 8 It is known that as the cone angle decreases, the transducer's emission voltage response first decreases and then increases, and the emission voltage response changes slowly when the cone angle varies between 65°~45° and 15°~5°.

[0031] Based on theoretical calculations, six transducers of different sizes were designed and fabricated for experimental verification, with front cover side lengths of 15mm and 16mm, and cone angles of 80°, 75°, 53.69°, and 35°. Since the transducers operate underwater, radiating sound waves into the water in an array, cork and polyurethane were required during actual fabrication to achieve watertightness and sound absorption, decoupling, and vibration isolation.

[0032] The main transducer testing items include underwater admittance curves, transmit voltage response, and directivity. The instruments used include an impedance analyzer, signal generator, filter, oscilloscope, and hydrophone. The transducer is installed and placed three meters underwater in an anechoic tank, ensuring that the hydrophone and transducer are on the same horizontal plane and that the far-field conditions for transducer measurement are met. A schematic diagram of the underwater testing is shown below. Figure 9 As shown.

[0033] The transducer emitter voltage response obtained from the experiment is as follows: Figure 10 As shown. To facilitate comparison between experiments and simulations, one size (35°) is selected as an example, and the transmit voltage response obtained from simulation calculations and experimental tests is placed on the same graph, as shown. Figure 12 As shown.

[0034] Depend on Figure 10 It is known that as the cone angle decreases, the launch response first decreases and then increases; as the side length of the front cover plate increases, the launch response decreases. The experimental results show the same trend as the simulation results, verifying the reliability of the simulation calculation.

[0035] Simulation calculations and experimental measurements confirm that, without considering transducer bandwidth, appropriately reducing the cone angle and side length of the front cover plate can improve the transducer's transmit voltage response. However, the experimental measurements involved directivity measurements, and there were certain errors in assembly and measurement during the manufacturing process, leading to theoretical values ​​calculated in the simulation being lower than the experimental values.

[0036] In summary, in one embodiment, the cone angle (α) is 35°, and the side length (L) of the radiating end face is 15mm. Under this parameter combination, FEA simulation calculations show... Figure 4 , Figure 8 The transducer achieves a peak emission voltage response of over 138 dB in water (reference value 1 V / μPa @ 1 m), demonstrating excellent acoustic emission performance. Example 2

[0037] This embodiment provides a complete longitudinal piezoelectric ultrasonic transducer, which includes the front cover plate 4 described in Embodiment 1.

[0038] This transducer employs a classic Tonpilz (sandwich) structure, and its components include: Piezoelectric crystal stack 1: Composed of multiple PZT piezoelectric ceramic rings stacked together, it is the driving source of the transducer.

[0039] Electrode 2: Located at both ends of the piezoelectric crystal stack 1, used to introduce driving electrical signals.

[0040] Front cover plate 4: It adopts a rectangular cross-section frustum structure with a cone angle of 35° and a side length of 15mm as described in Example 1. The material can be lightweight and high-strength metals such as aluminum alloy or titanium alloy.

[0041] Rear cover plate 5: As the rear mass block, it is usually made of steel or tungsten-based high-density material to form a front-to-rear mass ratio and ensure unidirectional radiation of energy.

[0042] The prestressed screw is replaced by screw 6, which functions to tighten the aforementioned components by applying axial preload, preventing the piezoelectric ceramic from being damaged by tension during vibration. In this embodiment, this function is achieved by screw 6.

[0043] Washer 7: Located between the head of screw 6 and rear cover plate 5, preferably an elastic washer, to ensure uniform distribution of preload and prevent loosening of components.

[0044] Connector 3: Used for soldering wires to lead the electrical signal from the external cable to electrode 2.

[0045] The transducer is assembled as follows: The piezoelectric crystal stack 1 and electrode plate 2 are placed sequentially between the front cover plate 4 and the rear cover plate 5. Then, screws 6 are passed sequentially through the washer 7, the through hole in the center of the rear cover plate 5, the inner hole of the piezoelectric crystal stack 1, and the electrode plate 2, finally screwed into the specially prepared mounting hole at the top of the front cover plate 4. By tightening the screws 6, the necessary axial prestress is applied to the entire stacked structure, thereby forming a robust and efficient vibration system.

[0046] In summary, this front cover design, by shaping the front cover into a rectangular cross-section frustum with a specific cone angle (30°-40°, preferably 35°) and side length (13mm-17mm, preferably 15mm), effectively improves the transmission voltage response of the longitudinal piezoelectric transducer at a specific operating frequency (63kHz) without introducing complex structures or increasing manufacturing costs. This provides a simple, practical, and efficient optimization solution for the design of high-performance underwater acoustic transducers.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A rectangular cross-section frustum front cover plate, wherein the front cover plate (4) is integrally frustum shaped, characterized in that: The radiating end face of the front cover plate (4) is rectangular, with a cone angle α ranging from 30° to 40° and a side length L ranging from 13mm to 17mm. The front cover plate (4) is provided with a top cover, a waist cover, and a bottom cover in sequence from the end connected to the piezoelectric crystal stack to the radiating end. The outer dimensions of the bottom cover cross-section are larger than those of the top cover cross-section.

2. The front cover plate according to claim 1, characterized in that: The cone angle α is 35° and the side length L is 15mm.

3. The front cover plate according to claim 1, characterized in that: The waist of the cap is conical, and its outer diameter gradually increases from top to bottom.

4. The front cover plate according to claim 1, characterized in that: The top of the cover has a mounting hole along the axial direction for accommodating the prestressed screw.

5. The front cover plate according to claim 1, characterized in that: The front cover plate (4) is pre-tightly assembled with some transducer components, such as the piezoelectric crystal stack (1), electrode sheet (2), and rear cover plate (5) by screws (6) and washers (7) through the mounting holes.

6. The front cover plate according to claim 5, characterized in that: Furthermore, in the assembly, the prestressed screw applies an axial preload to the piezoelectric crystal stack (1), and the washer (7) is disposed between the head of the screw (6) and the rear cover plate (5) or the front cover plate (4).

7. The front cover plate according to claim 6, characterized in that: The washer (7) is an elastic washer used to provide uniform clamping force and prevent loosening during the pre-tightening process.

8. The front cover plate according to claim 5, characterized in that: The electrode sheet (2) is disposed at both ends of the piezoelectric crystal stack (1) or between the crystal wafers, and is connected to an external circuit through a wire.

9. A longitudinal piezoelectric ultrasonic transducer, characterized in that, It includes a front cover plate (4) as described in any one of claims 1 to 8; and the transducer operates at a frequency of 63 kHz and has a transmit voltage response of not less than 138 dB.

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