High Frequency Transducer Applications Research Articles

Dielectric polarization and electrical properties of Modified PbTiO3 Piezoelectric Ceramics for high frequency transducer applications

PbTiO3 ceramics which modified by chiral symmetry material LiYW2O8 for the applications of high frequency transducers or actuators were investigated. The densification test results show that the LiYW2O8 modified PbTiO3 ceramics have good sintering properties at 900 °C. The dipole relaxation of PbTiO3 ceramics occurred at around 107 Hz, the difference of dipole relaxation time between polarized and unpolarized sample shows strong correlation with the piezoelectric constant. The d33, K33, and Np are close related to Tetragonality. The Tetragonality is higher, the value of d33, and K33 are also higher, and the value of Np is lower. The PbTiO3-0.35wt.% LiYW2O8 ceramic shows the relatively good properties of 68 pC/N and 245.4 for d33 and K33, respectively, which can meet the applications of high frequency transducers.

Porous lead zirconate titanate ceramics with optimized acoustic properties for high-frequency ultrasonic transducer applications

Acoustic properties of porous PZT ceramics intended to be used as backing in high-frequency transducer applications are investigated using a novel method where an electroded piezoelectric thick film is deposited on the backing under test. Two backings with pore sizes 1.5 μm and 10 μm were obtained by sintering a mixture of ceramic powder and an organic template, their porosity was evaluated by scanning electron microscopy at 15%, leading to a density around 6.5 g/cm3. The electroacoustic impulse responses of these devices were measured considering the backing as a propagation medium, the initial thickness of which was chosen small enough to allow back-wall echoes to be detected and large enough to be able to separate the signals in time domain. Then the thickness of the backing was reduced (from around 2 mm to less than 1 mm) and the measurements were repeated. Acoustic properties were then deduced: attenuation coefficients reaching 4 dB/mm/MHz and group velocities around 3400 m/s were obtained, leading to an acoustic impedance around 22 MRa. Such combination of high attenuation and moderate acoustical impedance make these materials an interesting solution for high-resolution ultrasonic imaging transducers.

Silver Doped 0.9PMN-PT-0.1PZT Composite Films for very High Frequency Ultrasonic Transducer Applications.

A series of silver doping concentration into the 0.9PMN-PT-0.1PZT (PMN-PT-PZT) films via the composite sol-gel technique were prepared. The crystallographic properties and microstructures of PMN-PT-PZT films with the silver dopant were investigated. Additionally, the effect of silver doping on dielectric and ferroelectric properties was examined. The results show that in general, the dielectric permittivity and remnant polarization increase as the silver doping concentration is increased. The PMN-PT-PZT+ 2.5 mol% Ag film exhibits a dielectric constant of 3,610 at 1 kHz and a remnant polarization of 57.6 µC/cm2 at room temperature. From this silver doped film, very high frequency ultrasonic needle transducers were fabricated and evaluated. The representative transducer had the center frequency of 225 MHz with a -6 dB bandwidth of 29% (65 MHz) and 62 dB insertion loss. The performance of this transducer is comparable to other composite sol-gel films transducer. The results suggest that this silver-doped PMN-PT-PZT film is a promising candidate as an alternative piezoelectric film for very high frequency transducer applications.

Aerosol-deposited KNN–LSO lead-free piezoelectric thick film for high frequency transducer applications

In this report, we fabricated and characterized a high frequency transducer with lead-free piezoelectric thick film, 0.948(K 0.5Na 0.5)NbO 3–0.052LiSbO 3, formed on a platinized silicon substrate by aerosol-deposition. X-ray diffraction analysis and scanning electron microscopy revealed that the film had well-crystallized perovskite structure and was dense and crack-free microstructure. The film showed the dielectric constant of 766 at 1 kHz and the remnant polarization of 13.2 μC/cm 2. The film was used to fabricate a high frequency needle transducer with an aperture size of ∼200 μm. The center frequency of the transducer was 197 MHz and the −6 dB bandwidth was 50% which was comparable to the PZT-based transducers. A 6-μm tungsten wire phantom was imaged to assess the −6 dB axial and lateral resolution of the transducer, which were found to be 12 and 66 μm, respectively.

Self-separated hydrothermal lead zirconate titanate thick films for high frequency transducer applications

Using a simple rapid heating process, Pb(Zr(0.52)Ti(0.48))O(3) (PZT) thick films prepared by hydrothermal method were separated from a Ti substrate. Scanning electron microscopy (SEM) revealed that the self-separated films were crack-free. After solution infiltration and high temperature annealing, the PZT thick films were shown to possess good electric properties. At 1 kHz, the dielectric constant and the loss were 593 and 0.05, respectively. The remnant polarization was 30.0 muCcm(2) at room temperature. A high frequency single element ultrasound transducer fabricated with these films showed a bandwidth at -6 dB of 73% at a center frequency of 67 MHz.

25 MHz ultrasonic transducers with lead- free piezoceramic, 1-3 PZT fiber-epoxy composite, and PVDF polymer active elements

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 zirconate titanate thick film with enhanced electrical properties for high frequency transducer applications

Piezoelectric Pb(Zr0.52Ti0.48)O3 thick film with the thickness around 10μm has been deposited on the (111) Pt∕Ti∕SiO2∕Si substrate using a ceramic powder/sol-gel solution modified composite method. X-ray diffraction analysis and scanning electron microscopy revealed that the film was in the well-crystallized perovskite phase and crack-free. At 1kHz, the dielectric constant and the loss were 1925 and 0.015, respectively. The remnant polarization was 42.0μC∕cm2 at room temperature. A high frequency single element acoustic transducer fabricated with this film showed a bandwidth at −6dB of 50% at 156MHz.

PSmT Ceramic Fibers for High Frequency Transducer Applications

Samarium and manganese doped lead titanate (PSmT) ceramic fibers with diameters of 35–75 μm have been prepared using a sol-gel method. The effects of hydrolysis, pyrolysis and sintering on the fiber fabrication have been studied. X-ray diffraction (XRD) study shows that the fibers have a pure perovskite structure with a high c/a = 1.043. Scanning electron microscopy investigations show that the grain size of the fiber increases as the annealing temperature increases. A single PSmT fiber has been poled and its electrical impedance measured.

Lead Free Piezoelectric Materials

Lead oxide based ferroelectrics, represented by lead zirconate titanate (Pb(Zr,Ti)O-3) or PZT) are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is interest in developing piezoelectric materials that are biocompatible and environmentally friendlier. The low density of non-lead based materials can also be an advantage in transducers for underwater and medical imaging due to expected lower acoustical impedance. Another impetus for seeking alternative to lead based compositions is the need for piezoelectric materials for operation at high temperatures. Several classes of materials are now being reconsidered as potentially attractive alternatives to PZT for special applications. The potassium niobate family, KNbO3, exhibits low dielectric constants, large thickness coupling coefficient along certain non-polar directions, and low density, all of which have advantages for high frequency transducer applications. Several compositions belonging to bismuth titanate family, Bi4Ti3O12, such as SrTi4Bi4O15, are promising candidates for high temperature applications. Lead free materials alone (eg. (Na0.5Bi0.5)TiO3) or in solution with PT (BiSCO3-PbTiO3) are also potentially interesting as they combine high piezoelectric activity and, in some cases, relatively high T-c. For these families of piezoelectric materials, the processing and piezoelectric response under different conditions of pressure, frequency, and temperature are presently much less understood than for the classical lead containing systems. In this presentation we review and discuss piezoelectric properties of selected lead free compositions (principally for members of the potassium niobate family and bismuth titanate layered compounds) in relation to structural and microstructural features as well as extrinsic contributions (domain walls displacement, conductivity) to their electromechanical properties. It is shown that it is possible to obtain remarkably stable piezoelectric response in some compositions, while others exhibit strong dependence of piezoelectric properties on driving field and frequency. Origins of these different behaviours are discussed.

Ultra-Fine Particle Processing for Fine Grain Piezoelectric Ceramics

ABSTRACT Reliable fine-scale piezoelectric ceramics are essential in meeting high frequency transducer applications, offering benefits to product machinability and the increased demand for device miniaturization trends. Processing routes involving the reassessment of grinding technologies were explored in lieu of chemical synthesis routes in order to achieve ultrafine precursor powders. De-agglomeration and Theological properties of non-aqueous ceramic slurries were carefully studied to improve the colloidal pressing of dense, fine-scale Sm and Mn doped PbTiO3 ceramics.