Overview of Fine-Scale Piezoelectric Ceramic/Polymer Composite Processing

In the past two decades, piezoelectric ceramic/polymer composites with different connectivities have been developed for transducer applications such as hydrophones, biomedical imaging, nondestructive testing, and air imaging. Recently, much attention has been given to fine-scale piezoelectric ceramic/polymer composites. These composites allow higher operating frequencies, and thus increased resolution, in medical imaging transducers. In this review, methods for processing fine-scale piezoelectric ceramic/polymer composites are discussed. The current capabilities, strengths, and weaknesses of each method are compared. The importance of spatial scale in composite performance is also reviewed. Several of the processing methods have demonstrated composites with fine-scale ceramic phases (<50 μm), and others have potential to form composites with a ceramic scale of under 20 μm.     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

Transparent lead lanthanum zirconate titanate (PLZT) ceramic fibers for high-frequency ultrasonic transducer applications

This paper presents fabrication of transparent lanthanum zirconate titanate (PLZT) fibers using extrusion technique. The diameter of the sintered PLZT fiber is about 400-μm, and the fibers exhibit very good transparency. Measured dielectric constant, remnant polarization and coercive field of PLZT fiber were found to be 2340, 22.5-μC/cm², and 9.8-kV/cm, respectively. The transparent piezoelectric materials may exhibit great potential for Photoacoustic (PA) imaging and hybrid intravascular imaging combining OCT and ultrasound imaging by using the transparent fiber as the path of light propagation and ultrasonic transducer material. In our study, these transparent PLZT fibers were designed to fabricate two types of high-frequency ultrasonic transducers: small aperture single PLZT fiber/epoxy composite and large aperture 1–3 PLZT fiber/epoxy composite ultrasonic transducers. Besides, a 20-μm tungsten wire phantom and the cornea of the porcine eye were also imaged with the 1–3 PLZT fiber/epoxy composite ultrasonic transducer to demonstrate its imaging capability.     

Processing of Piezocomposites by Fused Deposition Technique

Piezoelectric ceramic/polymer composites were made by a fused deposition (FD) technique, which is a solid-freeform fabrication (or layered manufacturing) technique where three-dimensional (3-D) objects are built layer by layer from a computer-aided design (CAD) file on a computer-controlled fixtureless platform. Indirect and direct FD methods were used to fabricate lead zirconate titanate (PZT)/polymer composites. For the indirect method, a CAD file for the negative image of the final part was created. A polymer mold was made via FD using a thermoplastic filament, and composite formation was completed via a lost mold technique. In the direct FD method, a thermoplastic polymeric filament that was filled with 50–55 vol% of PZT powder was used to form a positive image of the desired structure. Three-dimensional honeycomb ("3-D honeycomb") composites and "ladder" composites with 3-3 connectivity, which were formed via the FD technique, showed excellent electromechanical properties for transducer applications. In addition, the FD technique showed the ability to form composites with controlled phase periodicity, various volume fractions, and a variety of microstructures and macrostructures that are not possible with traditional composite-forming techniques.     

Directional properties of ordered 3‐3 piezocomposites fabricated by sacrificial template

Fabrication of piezoelectric composites with 3‐3 connectivity and their properties have attracted attention due to the application of these composites in acoustic transducers, medical imaging, and nondestructive testing. In this research, directional piezoelectric‐polymer composites with 3‐3 connectivity are prepared by a relatively simple fabrication process of dipping an ordered polymeric template (mesh) into lead zirconate titanate suspension followed by drying, pyrolysis, and sintering. The resulting porous ordered structures of lead zirconate titanate‐5A ranging from 18 to 32 vol% ceramic were subjected to polymer injection to form composites to be cut and polarized in different directions. In the composites, the effects of (i) polarization direction and (ii) active piezoelectric phase content on the dielectric and piezoelectric properties were investigated. The results showed that the dielectric constant and the piezoelectric properties are significantly dependent on the direction in composites of directional structure. In these composites, dielectric constant values were found to be higher in the direction parallel to ceramic ligaments. Moreover, the highest values for piezoelectric charge and voltage coefficient and figure of merit were found in the direction 45° to ceramic ligaments. In all composites, both dielectric constant and piezoelectric property values were proportional to the active piezoelectric phase content.     

Design,fabrication and properties of 1–3 piezoelectric ceramic composites with varied piezoelectric phase distribution

Here the 1–3 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were designed. The dielectric, piezoelectric and electromechanical properties of the composites were studied. The results indicate that the composite with varied distribution of piezoelectric ceramic has large relative permittivity, piezoelectric strain constant and electromechanical coupling coefficient at the thickness vibration mode. The composites with varied distribution of matrix phase have larger piezoelectric voltage constant, smaller mechanical quality factor and acoustic impedance value than those with varied distribution of piezoelectric ceramic phase. The electromechanical coupling property of the composites at the planar vibration mode shows obvious dependence on matrix phase distribution. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with specific surface vibration amplitude.     

0-3型水泥基压电机敏复合材料的制备和性能

智能结构体系正逐渐被引入土木工程领域，它对于解决土木工程结构的安全性、耐久性、灵活性以及自适应性课题提供了更强的支持，在智能结构中较为突出的问题是机敏材料与母体结构材料的相容性，由于土木工程中主要结构材料－－混凝土的特性，在其它智能结构中具有良好相容性的机敏材料，在混凝土智能结构中有可能存在相容性问题，针对这 一情况，提出以水泥基材料作为压电机敏复合材料的基体，期望解决机敏材料与混凝土结构材料之间的相容性问题，研究结果显示：0－3型水泥基压电机敏复合材料在制备上是可行的，而形成的0－3型水泥基压电机敏复合材料内部结构均匀，压电性能优于同条件下聚合物基压电复合材料的性能，而极化电压却大大降低，在性能上满足了作为机敏材料在智能结构中的使用条件。     

Piezoelectric Multilayer Ceramic/Polymer Composite Transducer with 2–2 Connectivity

A multilayer piezoelectric ceramic/polymer composite with 2–2 connectivity was fabricated by thermoplastic green machining after co-extrusion. The multilayer ceramic body was composed of piezoelectrically active lead zirconate titanate (PZN)–lead zinc niobate (PZN)-lead zirconate titanate (PZT) layers and electrically conducting PZN–PZT/Ag layers. After co-extruding the thermoplastic body, which consisted of five piezoelectric layers interspersed with four conducting layers, it was computer numeric-controlled machined to create periodic channels within it. Following binder burnout and sintering, an 18 vol% array of 190 μm thin PZT slabs with a channel size of 880 μm was fabricated. The channels were filled with epoxy in order to fabricate a PZN–PZT/epoxy composite with 2–2 connectivity. The piezoelectric coefficient (effective d ₃₃) and hydrostatic figure of merit ( d _h× g _h) of the PZN–PZT/epoxy composite were 1200 pC/N and 20 130 × 10⁻¹⁵ m²/N, respectively. These excellent piezoelectric characteristics as well as the relatively simple fabrication procedure will contribute in widening the application range of the piezoelectric transducers.     

Electromechanical coupling coefficient and acoustic impedance of 1-1-3 piezoelectric composites

1-1-3 piezoelectric composites consisting of a PZT-5H ceramic, an epoxy resin matrix and a silicone rubber filler were prepared using a modified 'slice and fill' method. The effect of the ceramic volume percentage on the properties of the composite was analyzed both through experiments and simulations. By adopting the 1-1-3 structure, the electromechanical coupling coefficient of the piezoelectric composites could be increased to 0.69, and the acoustic impedance reduced to 6.81. The experimental results further showed that the variation of the ceramic volume percentage had no effect on the electromechanical coupling coefficient of the composites, but only affected the acoustic impedance. The presented piezoelectric composites can be used to design high-performance transducer.     

Development of a multifrequency ultrasonic transducer using PZT/polymer 1-3 composite

In a number of clinical examinations using ultrasound, it is advantageous to be able to examine a patient at different frequencies. Low frequency is used to obtain images with adequate penetration and high frequency is used to obtain images with fine resolution. In this paper the feasibility of constructing a multiple-frequency transducer using piezoelectric composite is examined. The transducer is comprised of piezoelectric ceramic rods embedded in a polymer matrix. By selecting the appropriate thickness and width of ceramic rod, the transducer assembly can be made to resonate at a number of frequencies as predicted by the mode coupling theory. One of the resonance frequencies is determined by the width of the ceramic rod; other resonance frequencies are determined by the width-to-thickness ratio of the ceramic rods. A number of multiple-frequency transducers were constructed and the results correlate well with the theoretical prediction.     

Bismuth sodium titanate based lead-free ultrasonic transducer for microelectronics wirebonding applications

Bismuth sodium titanate based lead-free piezoelectric ceramic 0.885(Bi_1/2Na_1/2)TiO₃–0.05(Bi_1/2K_1/2)TiO₃–0.015(Bi_1/2Li_1/2)TiO₃–0.05BaTiO₃ (BNKLBT-1.5) rings (OD = 12.7mm, ID = 5.1 mm and 2.3 mm thick) were fabricated and characterized. Four ceramic rings were sandwiched between front and back metal plates to form a pre-stressed piezoelectric sandwich transducer and used as the driving element of an ultrasonic wirebonding transducer and the performance of the transducer was evaluated. The BNKLBT-1.5 transducer, when fitted with titanium front and back plates, was found to have axial vibration comparable to that of PZT transducer thus showing that BNKLBT-1.5 has the potential to be used in fabricating lead-free ultrasonic wirebonding transducers.     

Composite Polymers Transducers for Ultrasonic and Biological Applications

Ferrite polymer transducer and copolyesters are being used for ultrasonic generation to be used in technology and in biological applications like orthodontic treatment. The objectives of this study were to introduce a new piezoelectric composite polymers and to evaluate and compare their electric and mechanical properties with the widely used other materials. The resonance and antiresonance frequencies were measured for the materials in the radial mode. It is noticed that the resonance frequency decreased with increasing CoZn ferrite concentrations in polymers. The electromechanical coupling factor was determined to be of value 0.8 which is the highest value of the piezoelectric materials. It is very difficult to produce ceramic transducers in large sizes because they are fragile, thus the composite transducer could be an alternative. The ultrasonic wave velocity of the composite polymer is higher than that of other polymers and piezoelectric ceramics making them more attractive for many applications than ceramics. The Young's modulus of the composite polymer increased with increasing ferrite concentrations.     

Fabrication and Characterization of the Piezoelectric Ceramic–Polymer Composites

The modified sol–gel method was used to synthesize lead zirconate titanate nanoparticles, and the lead zirconate titanate nanoparticles and polyvinylidene fluoride were used to prepare piezoelectric nano‐ceramic–polymer composites with 0–3 connectivity type. The composites were successfully prepared by cold‐pressing and curing‐molding methods. X‐ray diffraction and scanning electron microscopy were adopted to characterize the microstructure of the obtained lead zirconate titanate nanoparticles and composites. The normal vibration modes of the lead zirconate titanate nanoparticles were investigated by Fourier transform infrared spectroscopy. The dielectric and piezoelectric properties of the composites were analyzed in detail with respect to different volume fractions of the lead zirconate titanate nanoparticles. It demonstrated that the values of d₃₃ and ε increased with the increase in the content of lead zirconate titanate. The results here pointed to potential and simple methods to fabricate the lead zirconate titanate nanoparticles and the piezoelectric ceramic–polymer composites for piezoelectric applications.     

Processing of 1-3 Piezoelectric Ceramic/Polymer Composites

Several methods of forming fine-scale 1–3 piezoelectric ceramic/polymer composites for possible transducer applications were demonstrated. These methods include tape casting, honeycomb dicing, and ceramic fiber weaving. In the tape casting technique, laminated structures were formed using thin PZT tapes. The tapes were stacked, with spacers separating the layers, and the stack embedded in polymer. Dicing the stack resulted in a composite with 1–3 connectivity. The thin tape technique can be used to develop composites with ceramic or polymer volume fraction gradients and multifunctional ceramics. Dicing of PZT honeycombs yields 1–3 composites with uniquely shaped rods. Shapes included +, T, and L. In the ceramic fiber weaving technique, green PZT fibers were woven through a PZT honeycomb support structure. The structure was fired to sinter the PZT fibers, and embedded with polymer to yield 1–3 composites. All 1–3 composites showed high and uniform piezoelectric coefficients across the electroded area.     

Piezoelectrically Assisted Ultrafiltration

Abstract

We have demonstrated the feasibility of using piezoelectrically assisted ultrafiltration to reduce membrane fouling and enhance the flux through ultrafiltration membranes. A preliminary economic evaluation, accounting for the power consumption of the piezoelectric driver and the extent of permeate flow rate enhancement, has also shown that piezoelectrically assisted ultrafiltration is cost effective and economically competitive in comparison with traditional separation processes.

Piezoelectric transducers, such as a piezoelectric lead zirconate titanate (PZT) disc or a piezoelectric horn, driven by moderate power, significantly enhance the permeate flux on fouled membranes, presumably because they promote local turbulence. Several experiments were conducted on polysulfone and regenerated cellulose UF membranes fouled during filtration of model feed solutions. Solutions of poly(ethylene glycol) and of high-molecular weight dextran were used as models. We found that we could significantly increase the permeate flux by periodically driving the piezoelectric transducer, horn or PZT disc, by application of moderate power over short periods of time, from 20 to 90 seconds. Enhancements as high as a factor of 8 were recorded within a few seconds, and enhanced permeate fluxes were maintained over a prolonged period (up to 3 hours). The prolonged flux enhancement makes it feasible to drive the piezoelectric transducer intermittently, thereby reducing the power consumption of the piezoelectric driver.

As piezoelectric drivers of sonically assisted ultrafiltration, PZT disc transducers are preferred over the piezoelectric horn because of their small size and ease of adaptability to ultrafiltration test cells. The horn transmits sonic energy to the UF membrane through a titanium element driven by a separate piezoelectric transducer, but a piezoelectric ceramic disc transmits energy directly to the UF membrane. Moreover, because piezoelectric ceramic elements can be fabricated in several configurations, they are potentially feasible for piezoelectrically driven ultrafiltration spiral-wound membrane modules.     

Computational analysis on cymbal transducer

Finite Element Analysis in collaboration with experimental studies was conducted to investigate the effects of dimensional parameters on the performance of the cymbal transducer. ANSYS 5.5 FEM code was used for computational analysis. Cymbal transducers were fabricated with steel and brass endcap materials and piezoelectric ceramic, PZT-5A, as driving elements. Admittance spectrum was measured by using HP4194A Impedance/Gain phase analyzer. Displacement and generative force characteristics of the transducers were tested by using a LVDT sensor. Experimental and calculated results matched quite well. Device diameter and cavity diameter has strong effect on cymbal transducer characteristic. Adjusting the dimensional parameters can extend potential application areas of cymbal transducer.     

Characterization and evaluation of piezoelectric composite bimorphs for in-situ acoustic emission sensors

Mixed connectivity composites consisting of a ferroelectric ceramic powder of calcium modified lead titanate dispersed in a polymer matrix have been fabricated into piezoelectric bimorph sensors. The piezoelectric, dielectric and electromechanical coupling coefficients of these sensors have been measured and a full characterization of the electromechanical properties are reported. The suitability of these bimorph transducers as in-situ acoustic emission sensors, embedded into glass-epoxy laminate plate like structures, has been investigated. A comparison of the performance of these sensors to those of previously investigated monomorph sensors fabricated from the same material has been made.     

压电陶瓷/聚氨酯智能阻尼复合材料的制备与表征

以热塑性聚氨酯弹性体为基材,压电陶瓷粉和导电石墨为功能相,制备了压电陶瓷/聚氨酯智能阻尼复合材料,并对其结构性能进行表征分析。结果表明,压电陶瓷粉添加质量份为20和40时,能得到具有较好分散性的压电陶瓷/聚氨酯智能阻尼复合材料;当压电陶瓷粉添加质量份为40时,tgδ峰值达到最大,说明制得的复合材料具有良好的阻尼性能;相对介电常数随着压电陶瓷粉添加量的增加而增加,当压电陶瓷粉质量份为40时,相对介电常数为15.06。热性能测定结果表明,加入压电陶瓷粉后,复合材料的软化点明显提高。     

热压法制备压电陶瓷／聚合物复合材料及性能研究

采用热压法分别制备了PZT／PVDF,PT／PVDF O-3型压电复合材料,所得材料具有较高的压电常数和良好的可柔性加工性能。并分析了无机压电陶瓷种类、含量对复合材料介电性能和压电性能的影响。     

Robocast Pb(Zr0.95Ti0.05)O3 Ceramic Monoliths and Composites

Robocasting, which is a computer-controlled slurry-deposition technique, was used to fabricate ceramic monoliths and composites of chemically prepared Pb(Zr_0.95Ti_0.05)O₃ ceramics. The densities and electrical properties of the robocast samples were equivalent to those obtained for cold isostatically pressed parts formed under a pressure of 200 MPa. Three-layer robocast composites that consisted of alternating layers of different sintered densities—93.9%/96.1%/93.9%—were fabricated using different levels of organic pore-former additions. Modification from a single-material to a multiple-material deposition robocaster was essential for the fabrication of composites that could withstand repeated cycles of saturated polarization switching under fields of 30 kV/cm. Furthermore, these composites withstood a poled ferroelectric-to-antiferroelectric phase transformation that was induced by a hydrostatic pressure of 500 MPa, during which strain differences on the order of 0.8% occurred between the composite elements.