Research on the Characteristics of High-Performance Textured Ceramic Materials and Their Application in Composite Rod Transducers

Abstract

Recently, textured piezoelectric ceramics have become a hot topic in the field of piezoelectric materials. Due to their high cost-effectiveness, textured ceramics are expected to be the material of choice for the next generation of acoustic transducers. In this study, we investigated the coercive field (E_c), piezoelectric constant (d₃₃), and dielectric constant (ε₃₃) of textured PIN-PSN-PT ceramics under different torques, in response to the demand for the development of composite rod transducer technology for transmitting and receiving. Based on the obtained data, a wideband composite rod transducer was designed and fabricated using textured PIN-PSN-PT ceramics with high performance. Compared with conventional PZT piezoelectric ceramic transducers of the same size, the wideband composite rod transducer made with textured ceramics extends the frequency band to a lower frequency of 6.5 kHz, improves the emission performance by 2 dB, and enhances the reception performance by 2 dB. Compared with conventional PZT piezoelectric ceramics in the same frequency band, the acoustic performance is comparable, but there is a volume reduction of 59.23% and a weight reduction of 49.7%, solving the technical bottleneck of developing composite rod transducers that are miniaturized and lightweight. The research results of this study have important reference value for the engineering application of textured ceramic materials in acoustic transducers.

1. Introduction

To meet the application requirements of acoustic detection technology, it is necessary to move the development of shared composite rod transducers for transmission and reception towards low frequency, wide frequency band, high acoustic performance, small size, and light weight in order to improve the detection and environmental adaptability of sonar equipment [1,2,3,4,5,6,7,8,9,10,11,12,13,14].

At present, due to the low piezoelectric coefficient (d₃₃~290 pC/N) and electromechanical coupling factor (k₃₃~68%) of PZT-4 and its modified piezoelectric ceramics, their use as driving elements can no longer meet the technological development needs of composite rod transducers for transmission and reception. There is an urgent need to find high-performance (d₃₃ and k₃₃) piezoelectric materials to solve this problem [1,15].

Textured ceramics are made by arranging their grains in a specific direction through a specific process to achieve optimal performance. It is precisely because of the preferred orientation of grains that the performance of textured piezoelectric ceramics is usually higher than that of traditional ceramics (such as PZT-4). Recently, due to their crystal-like properties (d₃₃~1000 pC/N and k₃₃~0.9), ceramic-like cost, and high composition homogeneity, textured ceramics have become one of the main research focuses in the field of piezoelectric materials [16,17,18,19,20,21,22,23,24]. Compared with PZT-4 and its modified piezoelectric ceramics, textured ceramics have significant advantages in terms of piezoelectric constant, frequency constant, electromechanical coupling coefficient, etc., which can achieve the miniaturization of composite rod transducers for transmission and reception, expand the frequency bandwidth, and improve transmission and reception performance. Their mechanical properties, consistency, and stability are comparable to PZT-4 and its modified piezoelectric ceramics; therefore, they attracted widespread attention in the academic community. In addition, textured ceramics with high piezoelectric constant and electromechanical coupling factors will also be beneficial for the development of a medical 2D matrix array transducer and intravascular ultrasound.

This study combined the development process and application conditions of a composite rod transducer for transmitting and receiving, and investigated the variation laws of the coercive field, frequency constant, dielectric constant, and piezoelectric constant of textured ceramic materials related to the power tolerance, acoustic performance, and usage environment of composite rod transducers in a clamped state. In designing and manufacturing miniaturized wideband high-performance composite rod transducers, a solid foundation is laid for the promotion and application of high-performance textured piezoelectric materials in the field of underwater acoustic sonar.

2. Research on the Characteristics of High Performance Textured Ceramic Materials

A composite rod transducer is an acoustic transducer with a prestressed screw, and piezoelectric material is used as its driving element in a clamped state. To understand the material properties of textured ceramics in a clamped state, the variation laws of the coercive field (E_c), piezoelectric constant (d₃₃), dielectric constant (ε₃₃), and frequency constant (N_f) of textured ceramics under torques of 0, 3, 5, 7, and 9 N·m were studied. Here, textured 19Pb(In_1/2Nb_1/2)O₃-44.5Pb(Sc_1/2Nb_1/2)O₃-36.5PbTiO₃ (PIN-PSN-PT) ceramics were prepared using the template grain growth method with BaTiO₃ template seeds. The detailed preparation method can be found in Reference [24].

2.1. Coercive Field Characteristics

The coercive field of textured ceramics is the core element that affects the maximum sound source level of composite rod transducers, and the relationship between the two is shown in Equations (1) and (2). This study investigated the frequency and clamping force characteristics of the coercive field in textured ceramics. Through experimental testing, the variation in the coercive field with frequency was obtained, and the results are shown in Figure 1 and Figure 2, while the torques are shown in Figure 3 and Figure 4.

$$Sv{L}_{\max }=TVR+20\ast \log (V_{\max })$$

(1)

$$V_{\max }=E_c\ast t$$

(2)

• $Sv{L}_{\max }$—maximum sound source level of composite rod transducer;
• $TVR$—voltage frequency response sent by composite rod transducer;
• $V_{\max }$—maximum voltage a composite rod transducer with piezoelectric crystal stack can load;
• $E_c$ (kV/cm)—coercive field of piezoelectric materials;
• $t$—thickness of piezoelectric element.

Figure 1 shows the frequency dependence of the P-E loops for the textured PIN-PSN-PT ceramic. The P-E hysteresis loops were measured using the ferroelectric testing system (TF Analyzer 2000E, aix-ACCT, Aachen, Germany). The sample size of the textured PIN-PSN-PT ceramics was 5 × 5 × 0.2 mm³. Five textured PIN-PSN-PT samples were used for measurement, and the E_c and P_r values are shown in Figure 2. With an increase in frequency, the P-E loops of the textured sample become “shorter” and “broader”. As shown in Figure 1 and Figure 2, as the frequency increases from 1 to 2000 Hz, the coercive field increases from 6.9 kV/cm to 9.3 kV/cm, and the residual polarization intensity decreases from 29 μC/cm² to 24 μC/cm².

Piezoelectric materials also work under clamping force, and it is necessary to study the electrical behavior of piezoelectric materials in this condition. In this study, we applied torque to these piezoelectric materials based on the actual situation of transducer manufacturing. Figure 3a shows the image of the fixture; using a digital torque wrench can apply torque to the sample. Thus, we can measure the P-E loops, d₃₃ value, impedance, and dielectric constant using this fixture by connecting it to the ferroelectric testing system, the quasi-static d₃₃-meter (ZJ-4A, Institute of Acoustics, Beijing, China), the impedance analyzer (HP4294A, Agilent, Santa Clara, CA, USA), and the LCR meter (E4980A, Agilent, Santa Clara, CA, USA), respectively. Figure 3b shows an image of the PZT-4 and textured PIN-PSN-PT ceramics with an outer diameter of 17 mm, an inner diameter of 10 mm, and a height of 4 mm (D17*d10*t4 mm³).

Figure 4 and Figure 5 show the P-E hysteresis loops and the data of the coercive field of textured PIN-PSN-PT ceramics under torques of 0 to 9 N·m. As the torques increased from 0 to 9 N·m, the coercive field decreased from 6.8 kV/cm to 6.05 kV/cm; a decrease of 11%. The residual polarization intensity decreased from 28.12 μC/cm² to 22.7 μC/cm²; a decrease of 19%. Referring to the trend shown in Figure 2, when the pre-torque of the composite rod transducer is less than 9 N·m and the frequency f ≥ 10 kHz, the estimated coercive field is greater than 9 kV/cm. Actually, the piezoelectric ceramics work at a torque of approximately 9 N·m and a frequency greater than 10 kHz in the composite rod transducers. Thus, the behavior of the piezoelectric ceramic element under corresponding service conditions will provide important data for the design of transducers.

2.2. Piezoelectric Constant Characteristic

The piezoelectric constant (d₃₃) is a core element that affects the emission and reception performance of composite rod transducers. This study investigated the piezoelectric constant characteristics of textured ceramics under different torques. The results obtained through experimental testing and comparison with conventional PZT-4 piezoelectric materials are shown in Figure 6.

The torque dependence of the piezoelectric constant for textured ceramic and PZT-4 is shown in Figure 6. It can be seen that when the torque increases from 0 to 9 N·m, the piezoelectric constant of the textured ceramic and PZT-4 increases from 1020 to 1342 pC/N and 290 to 345 pC/N, showing an increase of 31% and 19%, respectively. Because of the large longitudinal elastic coefficient ($S_{33}^E\ge 40\times {10}^{-12}$ m²/N) [25], textured ceramics exhibit “soft” characteristics. Thus, textured ceramics are more sensitive to torque along the longitudinal direction. By contrast, PZT-4 conventional ceramics have a low longitudinal elastic coefficient ($S_{33}^E\le 16\times {10}^{-12}$ m²/N), exhibiting “hard” characteristics. Thus, PZT-4 conventional ceramics are almost unaffected by torque and are relatively stable. The piezoelectric constant of textured ceramics is more than three times that of PZT-4 conventional ceramics. Generally, the emission and reception performance of transducers is positively correlated with the piezoelectric constant of the materials. Thus, the use of textured ceramics with a high piezoelectric constant as driving elements for composite rod transducers can significantly improve their emission and reception performance.

2.3. Dielectric Constant Characteristic

The dielectric constant (ε₃₃) is an important factor affecting the capacitance, operating current, and receiving sensitivity of composite rod transducers. This study investigated the dielectric constant characteristics of textured ceramics under different torques. The results obtained through experimental testing and comparison with conventional PZT-4 piezoelectric materials are shown in Figure 7.

From Figure 7, it can be seen that when the torque increases from 0 to 9 N·m, the dielectric constant of the textured ceramic and PZT-4 increases from 2258 to 3001 and 1310 to 1468, showing an increase of 32% and 12%, respectively. PZT-4 conventional ceramics are almost unaffected by torque and relatively stable. The dielectric constant of textured ceramics is more than twice that of PZT-4 conventional ceramics. When designing composite rod transducers using textured ceramics as driving elements, it is necessary to fully consider the changes in dynamic capacitance and operating current under different torques.

2.4. Impedance-Frequency Characteristic

The frequency constant (product of resonant frequency and corresponding size of piezoelectric materials) is an important factor affecting the volume and weight of composite rod transducers. The magnitude of torque can also adjust the frequency of transducers. Thus, this study investigated the impedance characteristics of textured ceramics under different torques and compared them with conventional PZT-4 piezoelectric materials through experimental testing. The results are shown in Figure 8 and Figure 9.

From Figure 8 and Figure 9, it can be seen that the textured ceramics exhibit excellent low-frequency characteristics at the same size (D17*d10*t4.5 mm³). When the torque increases from 0 to 1 N·m, the resonant frequency of the two piezoelectric devices significantly decreases, which is caused by the auxiliary structural fixture. When the torque increases from 1 N·m to 9 N·m, the resonant frequency increases, with that of the textured ceramics increasing from 23.46 kHz to 28.40 kHz, an increase of 20%, while that of the PZT-4 ceramics increases from 30.94 kHz to 35.94 kHz, an increase of 16%. When the torque of the textured ceramic test piece is 7 N·m, the impedance change amplitude at the resonant frequency is large, which requires special attention when designing composite rod transducers. Due to their low frequency constant (compared with PZT-4), textured ceramics as driving elements are an effective way to achieve miniaturization and lightweighting of composite rod transducers.

3. Theoretical Design of Wideband Composite Rod Transducer

Based on the above research results, the theoretical design of textured ceramic composite rod transducers for transmission and reception was carried out by using Comsol 6.2 software. The detail parameters, such as density ρ, flexibility constant $S_{33}^E$, piezoelectric strain constant d₃₃, electromechanical coupling coefficient k₃₃, elastic constant $C_{ij}^E$, piezoelectric stress constant $e_{ij}$, and relative dielectric constant ${\epsilon }_{ij}^S/{\epsilon }_0$, were measured based on the IEEE Standard on Piezoelectricity. Details of the method can be found in Ref. [25]. All the parameters of the textured PIN-PSN-PT and PZT-4 used in the finite element simulation are given in

Table 1. The parameters of textured PIN-PSN-PT ceramic and PZT-4.

	ρ (kg/m3)	${\mathit{S}}_{33}^{\mathit{E}}$ (10−12 m2/N)	d33 (pC/N)	k33
Textured ceramics	7700	55.3	1050	0.90
PZT-4	7600	15.5	289	0.70

,

Table 2. The elastic constant of textured PIN-PSN-PT ceramic and PZT-4.

${\mathit{C}}_{\mathit{i}\mathit{j}}^{\mathit{E}}$ (1010 N/m2)	${\mathit{C}}_{11}^{\mathit{E}}$	${\mathit{C}}_{12}^{\mathit{E}}$	${\mathit{C}}_{13}^{\mathit{E}}$	${\mathit{C}}_{33}^{\mathit{E}}$	${\mathit{C}}_{44}^{\mathit{E}}$	${\mathit{C}}_{66}^{\mathit{E}}$
Textured ceramics	15.35	12.03	10.35	9.64	5.72	1.66
PZT-4	13.9	7.78	7.43	11.5	2.56	3.06

,

Table 3. The piezoelectric stress constant of textured ceramic and PZT-4.

${\mathit{e}}_{\mathit{i}\mathit{j}}$ (C/m2)	${\mathit{e}}_{15}$	${\mathit{e}}_{31}$	${\mathit{e}}_{33}$
Textured ceramics	7.9	−3.78	15.7
PZT-4	10	−10.76	37.32

and

Table 4. The relative dielectric constant of textured ceramic and PZT-4.

	${\mathit{\epsilon }}_{11}^{\mathit{S}}/{\mathit{\epsilon }}_0$	${\mathit{\epsilon }}_{22}^{\mathit{S}}/{\mathit{\epsilon }}_0$	${\mathit{\epsilon }}_{33}^{\mathit{S}}/{\mathit{\epsilon }}_0$
Textured ceramics	1207	1207	415
PZT-4	730	730	635

. These PZT-4 ceramics and corresponding data were obtained from Yu Hai Electronic Ceramics Co., Ltd., Zibo, China.

A finite element model was established, as shown in Figure 10, to simulate the acoustic performance of the transducer, which was compared with transducers of the same size and frequency band. Based on the detail parameters, three types of transducers were designed. Among them, two types of transducers use PZT-4 ceramics (with dimensions of D17*d10*t4.5 mm³ and D19*d12*t6 mm³) and one uses textured ceramics (with dimensions of D17*d10*t4.5 mm³). The transducer using PZT-4 ceramics with dimensions of D17*d10*t4.5 mm³ is the same size PZT-4 transducer (same size as the transducer with textured ceramic), and the transducer using PZT-4 ceramics with dimensions of D19*d12*t6 mm³ has the same frequency band PZT-4 transducer (same frequency band as the textured ceramic transducer). These results are shown in Figure 11 and Figure 12.

The theoretical calculation results indicate that the textured ceramic composite rod transducer has good emission performance, reception performance, and wideband characteristics. Compared with the PZT-4 transducer with the same frequency band, the acoustic performance of the textured ceramic transducer is comparable, but it is smaller in size and mass (PZT-4: D19*d12*6 mm³, textured PIN-PSN-PT ceramic: D17*d12*4.5 mm³, the density of the two materials is the same). Compared with PZT-4 transducers of the same size, both the transmission and reception performance have been improved, and the low-frequency advantage is very obvious. Under the condition of unchanged operating frequency band and acoustic performance, using textured ceramics as driving elements can achieve the goal of achieving the miniaturization and light weight of composite rod transducers.

4. Manufacturing and Comparative Analysis of Three Broadband Composite Rod Transducers

Based on the theoretical design results, a wideband textured ceramic transducer was developed with a pre-torque of 5 N·m. The actual product is shown in Figure 13. The emission and reception performance tests were conducted in a soundproof water tank, and the test results are shown in Figure 14 and Figure 15, respectively.

From Figure 14 and Figure 15, it can be seen that the theoretical calculation results of the wideband textured ceramic composite rod transducer are in good agreement with the measured results, verifying the effectiveness of the theoretical calculation results. The frequency bandwidth exceeds one octave band, and within the frequency range of 18.5 kHz to 38.5 kHz, the transmission voltage response is greater than 135 dB with fluctuations of less than 6 dB. In the frequency band of 19 kHz to 42.5 kHz, the receiving sensitivity is −180 dB with fluctuations of less than 6 dB. According to theoretical calculations, applying a peak-to-peak voltage of 2000 V (V_P-P) at both ends of the transducer can achieve an emission sound source level of over 192 dB.

At the same time, wideband PZT-4 piezoelectric ceramic composite rod transducers of the same size and frequency band were developed. The comparative analysis results of the three transducers are shown in Figure 16 and Figure 17 and

Table 5. Comparison of performance parameters of three transducers.

Type	Volume (mm3)	Weight (g)	−6 dB Transmission Frequency Band (Hz)	Maximum Transmission Voltage Frequency Response (dB)	−6 dB Receiving Frequency Band (Hz)	Maximum Receiving Sensitivity (dB)
Textured ceramics	20,827.1	73.3	18.5 kHz~38.5 kHz	140.6	19 kHz ~42.5 kHz	−174.2
Same size PZT-4 transducer	19,193.6	67.2	25 kHz ~ 52 kHz	138.7	27 kHz ~ 53 kHz	−176.5
Same frequency band PZT-4 transducer	51,083.1	145.7	15.5 kHz~33.5 kHz	139.3	17 kHz ~42.5 kHz	−172.8

.

The research results show that compared with the composite rod transducers using the PZT-4 ceramic of the same size with textured ceramic, the wideband textured ceramic composite rod transducer extends the frequency band to a lower frequency of 6.5 kHz, with significant low-frequency advantages. The emission and reception performance are both improved by 2 dB, and higher than that of the published work (~132.5 dB) [26], and the volume and weight are comparable with the same size PZT-4 transducer. Compared with composite rod transducers using PZT-4 ceramics with a size of D19*d12*t6 mm³, the acoustic performance is comparable, but the volume is reduced by 59.23% and the weight is reduced by 49.7%, showing significant advantages in miniaturization and lightweighting.

5. Discussion

To meet the demand for miniaturization and lightweighting of composite rod transducers, we designed and fabricated composite rod transducers using textured PIN-PSN-PT ceramics with high piezoelectric performance. We studied the material characteristics of high-performance textured ceramic materials such as coercive field, piezoelectric constant, dielectric constant, and frequency constant under torque. The piezoelectric coefficient of textured PIN-PSN-PT ceramic (1050 pC/N) is three times that of PZT-4 ceramic (290 pC/N), enabling the miniaturization and lightweighting of composite rod transducers. The external field properties and full matrix data will be beneficial for the simulation design of this composite rod transducer and other piezoelectric devices. Based on the obtained data, we fabricated three types of composite rod transducers (textured ceramic transducer, same frequency band PZT-4 transducer, and same size PZT-4 transducer). Compared with the composite rod transducer using PZT-4 piezoelectric ceramic and being of the same size, the operating frequency of textured ceramic is wider and lower, and the transmitting voltage response increased by 2 dB. Compared with a PZT-4 piezoelectric ceramic composite rod transducer of the same frequency band, the volume and weight were reduced by 59.23% and 49.7%, respectively. It can be foreseen that the use of textured ceramics can reduce the size of array elements and increase the number of array elements, thereby achieving dense array layout in a medical 2D matrix array transducer.

Thus, the research results indicate that using textured ceramics as driving elements can develop miniaturized and lightweight high-performance wideband transceiver-shared composite rod transducers, achieve a high-density array layout, and solve the bottleneck of the development of transceiver-shared composite rod transducer technology. Furthermore, the experience of miniaturization and lightweighting of underwater transducers can be applied to a medical device, especially intravascular ultrasound transducers.