A non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer

Abstract

This invention discloses a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer, belonging to the field of piezoelectric ultrasonic transducer technology. It includes an upper piezoelectric sheet, a lower piezoelectric sheet, an upper ground electrode, a lower ground electrode, a signal electrode, and a circumferential backing. By employing a non-uniform cross-section and non-uniform height irregular double-layer piezoelectric structure, the upper and lower piezoelectric sheets form differentiated equivalent acoustic impedances and structural stiffness, constructing two independent and precisely controllable vibration resonance modes. This allows the two resonance peaks to be closely aligned and spliced ​​together on the frequency axis, forming a continuous and flat broadband response platform, thus completely solving the core problem of narrow bandwidth in traditional single-layer and conventional double-layer transducers.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ultrasonic transducer technology, and in particular to a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer. Background Technology

[0002] Piezoelectric ultrasonic transducers achieve the conversion between acoustic and electrical energy through the piezoelectric effect and are widely used in medical ultrasound, non-destructive testing, and other fields. Transmit and receive bandwidths are their core performance indicators, directly determining detection accuracy and signal quality. Currently, mainstream broadband designs often employ single-layer piezoelectric crystal optimization or a double-layer piezoelectric stacked structure with equal cross-section, slightly expanding the bandwidth by simply adjusting the resonant peak position. However, this often results in a decrease in sensitivity accompanying the bandwidth increase.

[0003] The existing technology has the following defects: (1) Traditional single-layer transducers have only a single resonant mode and narrow bandwidth, which cannot meet the wideband detection requirements; (2) Existing double-layer transducers with equal cross-sections have the same cross-section of the upper and lower piezoelectric plates, making it difficult to control the resonant peak spacing, resulting in limited bandwidth improvement and difficulty in balancing bandwidth and sensitivity performance.

[0004] Therefore, in response to the above phenomenon, a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer is proposed to meet the needs of practical use. Summary of the Invention

[0005] This invention provides a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer, which solves the technical problems of limited bandwidth, unstable broadband response, and difficulty in balancing bandwidth and sensitivity in existing piezoelectric ultrasonic transducers.

[0006] To address the aforementioned technical problems, this invention provides a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer, comprising an upper piezoelectric element, a lower piezoelectric element, an upper ground electrode, a lower ground electrode, a signal electrode, and a circumferential backing. The upper ground electrode is disposed on the upper surface of the upper piezoelectric element, the signal electrode is disposed between the lower surface of the upper piezoelectric element and the upper surface of the lower piezoelectric element, and the lower ground electrode is disposed on the lower surface of the lower piezoelectric element. The upper and lower piezoelectric elements have different cross-sectional dimensions and different heights. The circumferential backing is disposed on the periphery of the lower piezoelectric element, the upper surface of the circumferential backing is in contact with the lower surface of the signal electrode, and the lower surface of the circumferential backing is flush with the lower surface of the lower ground electrode.

[0007] Preferably, the cross-sectional shape of the upper piezoelectric sheet and the lower piezoelectric sheet are both square, and the cross-sectional ratios of the two are different.

[0008] Preferably, the cross-sectional dimension of the upper piezoelectric sheet is not smaller than the cross-sectional dimension of the lower piezoelectric sheet.

[0009] Preferably, the ratio of the cross-sectional dimensions of the upper piezoelectric sheet to the lower piezoelectric sheet is 1:1 to 3:1.

[0010] Preferably, the ratio of the height of the upper piezoelectric sheet to the height of the lower piezoelectric sheet is 1:1 to 2:1.

[0011] Preferably, the total height of the upper piezoelectric sheet and the lower piezoelectric sheet stacked along the thickness direction is 0.1mm-4mm, which is suitable for the medium and high frequency range.

[0012] Preferably, the device further includes a matching layer and a backing layer, wherein the matching layer is disposed on the acoustic radiation surface of the upper piezoelectric sheet, and the backing layer is disposed below the lower piezoelectric sheet.

[0013] Preferably, the circumferential backing is integrally formed with the backing layer.

[0014] Preferably, the central axes of the upper piezoelectric sheet and the lower piezoelectric sheet coincide or are offset from each other.

[0015] Preferably, the signal electrode is completely attached to the lower surface of the upper piezoelectric sheet.

[0016] Compared with related technologies, the non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer provided by the present invention has the following beneficial effects:

[0017] This invention employs an irregularly shaped double-layer piezoelectric structure with non-uniform cross-section and non-uniform height, enabling the upper and lower piezoelectric sheets to form differentiated equivalent acoustic impedance and structural stiffness. This constructs two independent and precisely controllable vibration resonance modes, allowing the two resonance peaks to be closely aligned and spliced ​​together on the frequency axis, forming a continuous and flat broadband response platform. This completely solves the core problem of narrow bandwidth in traditional single-layer and conventional double-layer transducers.

[0018] This invention achieves optimal matching of the resonant peak spacing by limiting the cross-sectional ratio, height ratio, total thickness, coaxiality, and shape of the lower piezoelectric sheet. This can stably maintain the lowest sound pressure level in the wideband platform region above -6dB of the peak value. Ultimately, without sacrificing sensitivity, it achieves an ultra-wide -6dB transmit bandwidth of 780kHz~1140kHz, and increases the receive bandwidth percentage to 72.6%, which is far superior to single-layer and equal-section double-layer contrast structures.

[0019] This invention fills the stepped gap between the upper and lower piezoelectric sheets with a circumferential backing, and combines it with an integrally molded backing layer to effectively absorb stray vibrations, suppress sound energy leakage, and eliminate resonance interference. While significantly widening the bandwidth without sacrificing sensitivity, it ensures the stability of the transmitted sound pressure and the receiving sensitivity in the full frequency domain, taking into account both wideband performance and detection accuracy. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0021] Figure 2 A comparative schematic diagram of four different piezoelectric ultrasonic transducers;

[0022] Figure 3 A comparison curve of the transmission bandwidth of four different transducer structures;

[0023] Figure 4 The simulation curves show the ratio of the upper and lower sections of a non-uniform cross-section irregularly shaped transducer.

[0024] Figure 5 The image shows the vertical height ratio scanning curve of an irregularly shaped transducer with a non-uniform cross-section.

[0025] Figure 6 Pulse-echo response diagram of a single-layer piezoelectric transducer;

[0026] Figure 7 The pulse-echo response diagram of a double-layer piezoelectric transducer with uniform cross-section and thickness;

[0027] Figure 8 The pulse-echo response diagram of a double-layer piezoelectric transducer with uniform cross-section but non-uniform thickness;

[0028] Figure 9 Pulse-echo response diagram of a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer;

[0029] Figure 10 The simulation curves of the lower piezoelectric sheet at different offset positions are shown.

[0030] Figure 11 Simulation curves for different cross-sectional shapes of the lower piezoelectric sheet;

[0031] Figure 12 The graph shows a comparison of the transmission bandwidth of four different transducer structures when the total thickness is 0.1 mm.

[0032] Figure 13 The graph shows a comparison of the transmission bandwidth of four different transducer structures when the total thickness is 4 mm.

[0033] The labels in the diagram are: 1. Upper piezoelectric sheet; 2. Lower piezoelectric sheet; 3. Upper ground electrode; 4. Lower ground electrode; 5. Signal electrode; 6. Circumferential backing; 7. Matching layer; 8. Backing layer. Detailed Implementation

[0034] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] This embodiment proposes a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer. By adjusting the cross-sectional dimensions and thickness of the upper and lower piezoelectric sheets, the equivalent acoustic impedance and stiffness of the two piezoelectric sheets are made different, thereby bringing the resonance peaks of the two vibration modes closer together on the frequency axis, forming a broadband response plateau. This expands the bandwidth of the transducer without sacrificing sensitivity, while maintaining high sensitivity.

[0037] like Figure 1 As shown, the non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer of this embodiment includes an upper piezoelectric element 1, a lower piezoelectric element 2, an upper grounding electrode 3, a lower grounding electrode 4, a signal electrode 5, and a circumferential backing 6. The upper grounding electrode 3 is disposed on the upper surface of the upper piezoelectric element 1. The signal electrode 5 is disposed between the lower surface of the upper piezoelectric element 1 and the upper surface of the lower piezoelectric element 2. The lower grounding electrode 4 is disposed on the lower surface of the lower piezoelectric element 2. The upper piezoelectric element 1 and the lower piezoelectric element 2 have different cross-sectional dimensions, and the heights of the upper piezoelectric element 1 and the lower piezoelectric element 2 are different. The circumferential backing 6 is disposed on the periphery of the lower piezoelectric element 2. The upper surface of the circumferential backing 6 is in contact with the lower surface of the signal electrode 5, and the lower surface of the circumferential backing 6 is flush with the lower surface of the lower grounding electrode 4.

[0038] In this embodiment, the cross-sectional dimension of the upper piezoelectric sheet 1 is larger than that of the lower piezoelectric sheet 2. The ratio of the side lengths of the cross-sections of the upper piezoelectric sheet 1 and the lower piezoelectric sheet 2 in the corresponding direction is 1.5:1. This ratio is within the preferred range of 1:1 to 3:1, which maximizes the modal coupling effect of the two piezoelectric sheets while ensuring structural stability. The ratio of the height of the upper piezoelectric sheet 1 to the height of the lower piezoelectric sheet 2 is 1.4:1. This ratio is within the preferred range of 1:1 to 2:1, which allows for precise coupling of the resonant peaks of the two piezoelectric sheets, forming a continuous broadband response platform.

[0039] The total thickness of this structure is set between 0.1mm and 4mm, primarily suitable for mid-to-high frequency ultrasonic applications, balancing bandwidth, radiation efficiency, and structural strength. The total height of the upper piezoelectric sheet 1 and the lower piezoelectric sheet 2 stacked along the thickness direction is 3mm. This thickness is only an example thickness and can be adjusted according to actual needs to adapt to the conventional size requirements of high-frequency ultrasonic transducers. The cross-sectional shape of both the upper piezoelectric sheet 1 and the lower piezoelectric sheet 2 is square, ensuring the symmetry of the vibration modes and avoiding performance loss caused by asymmetrical vibration.

[0040] The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer of this embodiment also includes a matching layer 7 and a backing layer 8. The matching layer 7 is disposed on the acoustic radiation surface of the upper piezoelectric element 1 to achieve acoustic impedance matching between the piezoelectric vibrator and the load medium, thereby improving acoustic energy radiation efficiency. The backing layer 8 is disposed below the lower piezoelectric element 2 to absorb back-radiated acoustic energy, suppress stray vibrations, and improve the transducer's time-domain response characteristics. The circumferential backing 6 and the backing layer 8 are integrally formed, simplifying the transducer's assembly process while ensuring the acoustic continuity of the backing structure, further optimizing the transducer's performance in extending bandwidth without sacrificing sensitivity.

[0041] Figure 2 This is a comparative schematic diagram of four different piezoelectric ultrasonic transducers with the same total thickness. Figure 2 (a) is a single-layer piezoelectric transducer; Figure 2 (b) is a double-layer piezoelectric transducer with equal cross-section and thickness; Figure 2 (c) is a double-layer piezoelectric transducer with equal cross-section but not equal thickness; Figure 2 In the middle (d), there is a non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer in this embodiment.

[0042] Figure 2 In this embodiment, the piezoelectric transducer has a piezoelectric element height of 3mm and a length and width of 1.5mm. One end of this single-layer piezoelectric element is connected to voltage, and the other end is grounded. The double-layer piezoelectric transducer with equal cross-section and thickness has piezoelectric elements of 1.5mm height and 1.5mm length and width for both the upper and lower layers. The double-layer piezoelectric transducer with equal cross-section and unequal thickness has piezoelectric elements of 1.75mm and 1.25mm height, respectively, and both layers are 1.5mm long and wide. In this embodiment, the upper piezoelectric element 1 of the unequal cross-section double-layer broadband piezoelectric ultrasonic transducer has a length and width of 1.5mm and a height of 1.75mm, while the lower piezoelectric element 2 has a length and width of 1mm and a height of 1.25mm. Both the upper and lower piezoelectric elements are connected to voltage in the middle, and both ends of the piezoelectric elements are grounded.

[0043] In this embodiment, the empty space around the lower piezoelectric sheet 2 of the non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer is filled with a circumferential backing 6. This structure allows for the installation of more backing structures within the same overall volume, thereby optimizing the acoustic performance of the device.

[0044] Figure 3 The graph shows a comparison of the transmission bandwidth of four different transducer structures. The horizontal axis represents frequency, and the vertical axis represents the transmitted sound pressure level. The red curve in the graph represents the transmission response curve of the non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer described in this embodiment. Its -6dB transmission bandwidth can reach 780kHz-1140kHz, which is significantly higher than that of the other three transducer structures, demonstrating the advantage of the structure in this embodiment in improving transmission bandwidth.

[0045] Figure 4 The simulation curves for the cross-sectional ratio of the upper and lower piezoelectric elements in a non-uniform cross-section transducer are shown. This simulation, while keeping the length and width of the upper piezoelectric element 1 constant at 1.5 mm, adjusts the length and width of the lower piezoelectric element 2 to 0.5 mm, 1 mm, 1.5 mm, and 2 mm respectively, to test the impact of different cross-sectional dimensions on the transducer's bandwidth performance. The results show that the transducer's bandwidth performance is optimal when the length and width of the lower piezoelectric element 2 are 1 mm. When the difference in cross-sectional dimensions between the upper and lower piezoelectric elements is too large, the transducer's transmission bandwidth performance decreases significantly. Furthermore, simulations were conducted at 0.05 mm intervals for lower piezoelectric element length and width between 0.75 mm and 1.5 mm, revealing a preferred ratio range of 1.1:1 to 1.5:1, with 1.5:1 being optimal. In this case, the transducer's bandwidth performance is also optimal when the length and width of the lower piezoelectric element 2 are 1 mm.

[0046] Figure 5 The simulation, which shows the height ratio of a non-uniform cross-section irregularly shaped transducer, adjusted the thickness of the upper piezoelectric element 1 while maintaining a total transducer thickness of 3 mm. This experiment tested the impact of different height ratios on the transducer's bandwidth performance. The results show that the transducer achieves optimal bandwidth performance when the thickness of the upper piezoelectric element 1 is 1.75 mm. Furthermore, simulations at 0.05 mm intervals yielded an optimal range of 1.4:1 to 1.7:1, with the best range being 1.4:1. This means that the transducer achieves optimal bandwidth performance when the thickness of the upper piezoelectric element 1 is 1.75 mm.

[0047] Figures 6-9 The pulse echo response diagrams are all obtained under the same excitation voltage conditions.

[0048] Figure 6 The image shows the pulse-echo response of a single-layer piezoelectric transducer, with a receiving bandwidth percentage of 58.3%.

[0049] from Figures 6 to 7 That is, from a single-layer piezoelectric element to a double-layer piezoelectric element, the bandwidth increases while the sensitivity also increases. Figure 7 The image shows the pulse-echo response of a double-layer piezoelectric transducer with equal cross-section and thickness. The receiving bandwidth percentage of this structure is 64.2%.

[0050] from Figures 7 to 8 By using a conventional non-uniform thickness design, the bandwidth increases but the sensitivity decreases, which is in line with conventional principles. Figure 8 The image shows the pulse-echo response of a double-layer piezoelectric transducer with equal cross-section but not equal thickness. The receiving bandwidth percentage of this structure is 68.3%.

[0051] Figure 9This is the pulse-echo response diagram of the non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer in this embodiment. Its bandwidth increases again, but its sensitivity recovers, compared to... Figure 7 The structure achieves near-uniformity and expands bandwidth without sacrificing sensitivity. The receiving bandwidth percentage of this structure reaches 72.6%, which is significantly higher than the other three structures, demonstrating the advantage of this embodiment in improving receiving bandwidth.

[0052] Figure 10 The simulation curves show the lower piezoelectric element at different offset positions. Specifically, after determining the optimal cross-sectional side length ratio of 1.5:1 and the height ratio of 1.4:1, the optimal conditions were kept unchanged, and the position of the lower piezoelectric element was changed (to be at the axis center, i.e., the piezoelectric element is in the exact middle; to be flush with the side, i.e., it is at the very edge). The figures show that the lower piezoelectric element performs better the closer it is to the center, but this requires higher processing precision and is more difficult to manufacture. However, even at the very edge, the extended bandwidth can reach 770kHz-1110kHz, close to 95% of the optimal performance. Therefore, this transducer does not have strict requirements for the coaxiality of the upper and lower piezoelectric elements and is easy to manufacture.

[0053] Figure 11 The simulation curves show different cross-sectional shapes of the lower piezoelectric sheet, with the total thickness maintained at 3mm. The cuboid is an example in this embodiment, and the cylinder thickness follows the optimal thickness ratio. The optimal cross-sectional side length ratio is the ratio of the diagonal length of the cuboid cross-section to the cylinder diameter. The outer diameter of the circular tube is consistent with the selected cylinder, and the inner diameter is, for example, half the outer diameter. It can be seen that the effect of this application is applicable to various common types of transducers. The effects of the cuboid and cylinder are similar, while the circular tube type can achieve a transmission bandwidth range of 840kHz-1110kHz, reaching 75% of the effect of the cuboid. Among these, truncated pyramid or other types of transducers are less common, used only in certain research areas, and are difficult to polarize, and are not within the scope of selection.

[0054] Figure 12 and Figure 13 The figures show the effects when the total thickness is 0.1mm and 4mm, respectively. As can be seen from the figures, as long as the optimal parameters such as the cross-sectional side length ratio and thickness ratio are maintained, the bandwidth expansion effect and pattern are similar, further confirming that the advantages of this structure can be extended to different thicknesses, and are not limited to the range of 0.1mm to 4mm. The 0.1mm total thickness transducer has a 6dB bandwidth that can be extended to 23.3MHz-34.1MHz. The 4mm total thickness transducer has a 6dB bandwidth that can be extended to 580kHz-850kHz.

[0055] The working principle of this embodiment is as follows: when the thickness and cross-sectional area of ​​the upper and lower piezoelectric sheets are different, their equivalent acoustic impedance and stiffness will also be different, resulting in the separation of the two main vibration modes in frequency. If their resonant peaks are close enough on the frequency axis, a wideband response plateau will be formed, thereby extending the -6dB bandwidth without sacrificing sensitivity. Through reasonable structural design, the minimum value of this bandwidth region can be kept above -6dB of the maximum value, thus obtaining a continuous maximum range bandwidth while ensuring that the transducer has high sensitivity to meet the needs of practical applications.

Claims

1. A non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer, characterized in that: The device includes an upper piezoelectric sheet, a lower piezoelectric sheet, an upper ground electrode, a lower ground electrode, a signal electrode, and a circumferential backing. The upper ground electrode is disposed on the upper surface of the upper piezoelectric sheet, the signal electrode is disposed between the lower surface of the upper piezoelectric sheet and the upper surface of the lower piezoelectric sheet, and the lower ground electrode is disposed on the lower surface of the lower piezoelectric sheet. The upper and lower piezoelectric sheets have different cross-sectional dimensions and different heights. The circumferential backing is disposed on the periphery of the lower piezoelectric sheet, the upper surface of the circumferential backing is in contact with the lower surface of the signal electrode, and the lower surface of the circumferential backing is flush with the lower surface of the lower ground electrode.

2. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: Both the upper piezoelectric sheet and the lower piezoelectric sheet have square cross-sectional shapes, but their cross-sectional ratios are different.

3. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 2, characterized in that: The cross-sectional dimensions of the upper piezoelectric sheet are not less than the cross-sectional dimensions of the lower piezoelectric sheet.

4. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The ratio of the cross-sectional dimensions of the upper piezoelectric sheet to the lower piezoelectric sheet is 1:1 to 3:

1.

5. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The ratio of the height of the upper piezoelectric sheet to the height of the lower piezoelectric sheet is 1:1 to 2:

1.

6. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The total height of the upper piezoelectric sheet and the lower piezoelectric sheet stacked along the thickness direction is 0.1mm-4mm, which is suitable for the medium and high frequency range.

7. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: It also includes a matching layer and a backing layer, the matching layer being disposed on the acoustic radiation surface of the upper piezoelectric sheet, and the backing layer being disposed below the lower piezoelectric sheet.

8. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The circumferential backing is integrally formed with the backing layer.

9. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The central axes of the upper piezoelectric sheet and the lower piezoelectric sheet coincide or are offset from each other.

10. The non-uniform cross-section double-layer broadband piezoelectric ultrasonic transducer according to claim 1, characterized in that: The signal electrode is completely attached to the lower surface of the upper piezoelectric sheet.

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