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This paper discusses the fabrication and characterization of 3.5-MHz single-element transducers for therapeutic applications in which the active elements are made of hard lead-free BNT-based and hard commercial PZT (PZT-841) piezoceramics. Composition of (BiNa 0.88 K 0.08 Li 0.04 ) 0.5 (Ti 0.985 Mn 0.015 )O 3 (BNKLT88-1.5Mn) was used to develop lead-free piezoelectric ceramic. Mn-doped samples exhibited high mechanical quality factor ( ) of 970, thickness coupling coefficient ( ) of 0.48, a dielectric constant ( ) of 310 (at 1 kHz), depolarization temperature ( ) of 200 °C, and coercive field ( ) of 52.5 kV/cm. Two different unfocused single-element transducers using BNKLT88-1.5Mn and PZT-841 with the same center frequency of 3.5 MHz and similar aperture size of 10.7 and 10.5 mm were fabricated. Pulse-echo response, acoustic frequency spectrum, acoustic pressure field, and acoustic intensity field of transducers were characterized. The BNT-based transducer shows linear response up to the peak-to-peak voltage of 105 V in which the maximum rarefactional acoustic pressure of 1.1 MPa, and acoustic intensity of 43 W/cm 2 were achieved. Natural focal point of this transducer was at 60 mm from the surface of the transducer.

We have studied the effect of deposition parameters on the microstructure, crystallinity, and ferroelectric properties of 0.88(Bi(0.5)Na(0.5))TiO(3)-0.08(Bi(0.5)K(0.5))TiO(3)¿0.04BaTiO(3) thin films grown on SrRuO(3)-coated SrTiO(3) substrates by pulsed laser deposition. The parameters studied were the repetition rates, substrate temperatures, oxygen pressures, and laser energies. It was realized that the films prepared at 800°C, 10 Hz, 400 mtorr, and 1.2 Jcm(-2) exhibited the highest ferroelectric properties. The measured remanent polarization, dielectric constant at 1 kHz, and coercive field for this film were about 30 μCcm(-2), 645, and 85 kVcm(-1), respectively. Increasing the oxygen pressure during deposition from 200 to 400 mtorr improved the crystallinity, microstructure, dielectric constant, and polarization of the films. The leakage current and dielectric loss were suppressed at 400 mtorr because of the lower concentration of oxygen vacancies and disappearing pinholes and surface undulations in the film deposited at this pressure.

This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi(0.5)Na(0.5)TiO(3)-0.08Bi(0.5)K(0.5)TiO(3)- 0.04Bi(0.5)Li(0.5)TiO(3) was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d(33)) of 84 pC·N(-1). To make the transducer, the ceramic was sandwiched between an epoxy-tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer's design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a -6-dB bandwidth of 55% and an insertion loss of -32 dB; the -20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers.

Recent progress in lead-free piezoelectric ceramics and thin films with special emphasis on alkaline niobatebased and bismuth sodium titanate-based systems is reviewed concisely. Modifications of potassium sodium niobate (KNN) ceramics are presented and subsequent improvements in the electrical properties are summarized. Special attention is devoted to the phase diagram of the KNN system when a solid solution is formed with other perovskite niobates and titanates. Impact of A-site and B-site dopants on the electromechanical properties of KNN ceramics are distinguished in view of transition temperatures. It is shown that the addition of most A-site and B-site dopants reduces the transition temperatures and improves the piezoactivity at room temperature. This is attributed to the shift of polymorphic transition from tetragonal to orthorhombic phase in the vicinity of room temperature. In contrast, formation of a solid solution of KNN with 18 mol% AgNbO₃ revealed a significant enhancement of properties without a notable change in the transition temperatures. Also, a bismuth sodium titanate (BNT) composition is introduced with particular emphasis on its binary and ternary derivatives. Moderate piezoelectric properties reported at the morphotropic phase boundaries, formed in BNT-based solid solutions are also represented. Advances on thin films based on these two compositions are evaluated and challenges involved with development of stoichiometric thin films with low leakage current are discussed.

We present a new type of actuator named bilayer piezoelectric/electrostrictive dome unimorph (BIPEDU), fabricated by attaching a piezoelectric-electrostrictive monolithic bilayer composites (PE-MBLC) to a metal plate. Various ratios of piezoelectric/electrostrictive (P/E) volume percent were used to form PE-MBLC. It was found that d(33)(eff) and K(eff) in PE-MBLC follow the series 2-2 composite mixing rule. However, the measured results were slightly lower than those of the calculated values because of a large difference in dielectric displacement between piezoelectric and electrostrictive layers and because the electrostrictor acts as the resistor that impedes the domain switching in piezoelectric layer during poling. In addition, we have investigated the field-induced displacement in PE-MBLC and BIPEDU actuators. In comparison, the displacement of BIPEDU actuators was much higher than that of PE-MBLC actuators. This was attributed to the good quality of bonding between ceramic and metal, which contributed to the proper stress/force transfer, as well as the metal sheet, which acted as a flextentional structure for PE-MBLC to generate more axial displacement in BIPEDU actuators. The load dependence of displacement in BIPEDU was obtained. In addition, the BIPEDU showed high reliability during the displacement cyclic testing.

Recent progress in (K0.44, Na0.52, Li0.04)O3-based ceramics (KNN) with special emphasis on(K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 (KNN-LT-LS) is reviewed concisely. The base KNN and its compositional derivatives are analyzed in terms of dopant-property relationships, which are then extended to the ternary derivatives. The effects of processing conditions such as humidity, precursor purity, and oxygen partial pressure during sintering are elaborated on from a phenomenological perspective. It is also shown that the spontaneous polarization is sensitive to the processing route chosen for synthesis (mixed oxide versus perovskite routes). Special attention is devoted to the discussion of the morphotropic phase boundary (MPB) dilemma in the KNN-LT-LS system, where it is shown that the origin of high piezoelectric activity is actually due to a polymorphic transition at room temperature. It is shown that prototype transducers based on pure and 1 mol% Ba2+ doped KNN-LT-LS exhibit performance metrics comparable to those fabricated using PZT-5H. Overall, KNNLT- LS ceramics show great promise for lead-free applications, although issues such as temperature dependence of properties and strong sensitivity to processing conditions remain as the 2 major challenges.

We propose a new type of flextensional actuator comprised of an electromechanically active element which is a piezoelectric-electrostrictive monolithic bi-layer composite (PE-MBLC) capped by truncated thin brass sheets. The PE-MBLC contains equal amounts of 0.65[Pb(Mg(1/3)Nb(2/3))O(3)]-0.35PbTiO(3) and 0.9[Pb(Mg(1/3)Nb(2/3))O(3)]-0.1PbTiO(3) by volume, and is obtained by a co-sintering process. With applied E(max) = 10 kV/cm unipolar drive, the maximum axial displacement (u(33)) produced by the uncapped and capped PE-MBLC is 11 and 21 microm, respectively. The hysteresis in unipolar u(33) at 0.5 E(max) is 4.6% for the uncapped PE-MBLC, while that for the capped one is 11%. Under bipolar excitation, the maximum u(33) for uncapped is 11.6 microm at +E(max) and 6.6 microm at +E(max) with an asymmetry factor (zeta) of 1.75 for which u(33) < 0 for all E < 0. Under bipolar excitation, the maximum u(33) at +E(max) for the capped PE-MBLC is 19 microm while that for -E(max) is 8 microm with zeta = 2.4, for which u(33) > 0 at -E(max) but is smaller than the u(33) at +E(max). The origins of the observed asymmetry in u(33) are discussed in the context of symmetry superposition and deformation mechanics of the endcaps.

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K(0.44)Na(0.52)Li(0.04))(Nb(0.84)Ta(0.10)S(0.06)b)O(3) powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and k(t) of 0.50, the KNN-LT-LS composition may be a good candidate for high frequency transducer applications. PZT fibers with 25 microm diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged k(t) = 0.64 and d(33) = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 ohm and higher thickness coupling coefficient of the ceramic transducer.

Lead-based piezoelectric ceramics are suitable materials for noninvasive applications of ultrasound in medicine. However, the embedded therapeutic and diagnostic procedures require the use of lead-free piezoelectric materials as active elements in transducers. With this goal in mind, we investigated the substitution of Ba(2+) cations in a lead-free piezoelectric system of K(1/2)Na(1/2)NbO(3)-LiTaO(3)-LiSbO(3) (KNN-LT-LS) with perovskite structure. The Ba(2+) was added to the system as an A-site dopant in the range of 0-2 mol% in increments of 0.5 mol%. The addition of Ba(2+) improved the piezoelectric charge coefficient, d(33), and longitudinal coupling coefficient, k(33). The composition with 1 mol% Ba2+ had 36% and 58% higher d(33) and k(33), respectively, than the undoped composition. It appeared that the addition of Ba(2+) induced "soft" characteristics in this lead-free piezoelectric system. This was verified by the increase of remnant polarization along with the decline of coercive field. The Ba(2+) behaved as a grain growth inhibitor and caused a drastic reduction in polarization level (approximately 60%) when the grain size became smaller than approximately 1.5 microm. Incorporation of Ba(2+) up to 1.5 mol% increased the bulk resistivity of the KNN-LT-LS system and then reduced it drastically at higher dopant concentrations. The electron-hole compensation model fit well with the results obtained in this study and verified the A-site substitution of donor-doped barium. KNN-LT-LS ceramics with 0 mol% and 1 mol% Ba(2+) were used to fabricate single-element ultrasonic transducers resonating at 5.5 MHz. The -6 dB fractional bandwidth and -20 dB pulse length of the probe made of doped ceramic were 50% and 1.68 micros, respectively. This indicated that this system could be considered as a candidate for invasive and/or embedded medical ultrasound applications.

Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1-100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized.

Epitaxial and (110) oriented paraelectric thin films of Ba0.60Sro.40TiO3 were grown on (100) oriented NdGaO3 orthorhombic substrates, and the nonlinear dielectric properties were studied at 10 GHz along selected in-plane crystallographic directions in the film thickness range of 25-1200 nm. The measured dielectric properties show strong residual strain and in-plane directional dependence. For instance, the in-plane relative permittivity is found to vary from as much as 500 to 150 along [110] and [001], respectively, in the 600 nm film. Tunability was found to vary from as much as 54% to 20% in all films and directions. In a given film, the best tunability is observed along the compressed axis in a mixed strain state, 54% along [110] in the 600 nm film. It is shown that, by nanoscale manipulation of epitaxy and planar anisotropy, the return loss and phase shift in a paraelectric can be tuned over a rather wide range. The approach presented herein opens avenues for obtaining various degrees of phase shift on the same film, enabling one with an additional degree of freedom in device design and fabrication as well as multifunctionality.

In the last 25 years, piezoelectric ceramic-polymer composites have been conceptualized, prototyped, fabricated, and implemented in an array of applications encompassing medical imaging and military missions, among others. A detailed snapshot of the materials used, and a detailed account of the major innovative methods developed in making various piezoelectric ceramic-polymer composites are presented. The salient aspects of processing of such composites are summarized, and structure-processing-property relations are described using connectivity as the unifying central concept. Computer-aided design (CAD)-based fabrication methods, which result in composites whose structural complexity surpass that of composites obtained with traditional methods, are described to introduce the reader to novel concepts in processing of piezocomposites. A brief survey of some recent advances made in modeling of (0-3), (1-3), and (2-2) composites also is provided.

This paper presents a two-dimensional analytical model of a spiral-shaped PZT ceramic actuator. Developed using elasticity theory and a zero-stress assumption, the theoretical analysis has been formulated for a piecewise semicircular representation of the spiral-shaped actuator. Closed-form solutions of the tangential displacement of the equivalent spiral under applied electrical field in the poling direction have been obtained. To develop confidence in the theoretical model, results are compared with those obtained using finite element analysis (FEA). Results from both are then compared with previously reported experimental findings, and reasonable agreement is achieved.