High-Frequency Linear Array (20 MHz) Based on Lead-Free BCTZ Crystal

Abstract

Centimeter-sized BaTiO3-based crystals grown by top-seeded solution growth from the BaTiO3−CaTiO3−BaZrO3 system were used to process a high-frequency (HF) lead-free linear array. Piezoelectric plates with (110)pc cut within 1° accuracy were used to manufacture two 1-3 piezo-composites with thicknesses of 270 and 78 m for resonant frequencies in air of 10 and 30 MHz, respectively. The electromechanical characterization of the BCTZ crystal plates and the 10 MHz piezocomposite yielded thickness coupling factors of 40% and 50%, respectively. We quantified the electromechanical performance of the second piezocomposite (30 MHz) according to the reduction in the pillar sizes during the fabrication process. The dimensions of the piezocomposite at 30 MHz were sufficient for a 128-element array with a 70 m element pitch and a 1.5 mm elevation aperture. The transducer stack (backing, matching layers, lens and electrical components) was tuned with the characteristics of the lead-free materials to deliver optimal bandwidth and sensitivity. The probe was connected to a real-time HF 128channel echographic system for acoustic characterization (electroacoustic response, radiation pattern) and to acquire high-resolution in vivo images of human skin. The center frequency of the experimental probe was 20 MHz, and the fractional bandwidth at -6 dB was 41%. Skin images were compared against those obtained with a lead-based 20-MHz commercial imaging probe. Despite significant differences in sensitivity between elements, in vivo images obtained with a BCTZ-based probe convincingly demonstrated the potential of integrating this piezoelectric material in an imaging probe.

Two orientation effects and large anisotropy of parameters in piezo-active 2–1–2 composites based on [0 1 1]-poled crystals

“…Advanced composites based on ferroelectric domainengineered single crystals (SCs) with important physical properties are of significant interest not only in an academic sense but also in a variety of transducer applications. Numerous two-component piezo-active SC-based composites, which were manufactured and studied recently, are characterised by either 2-2 [1][2][3] or 1-3 [4][5][6][7][8][9][10][11] connectivity written in terms of [12]. The connectivity indices such as 2-2 or 1-3 indicate [12,13] the number of axes of a rectangular coordinate system along which the first and second components of the composite are continuously distributed, respectively.…”

“…The presence of high-performance SC as the main piezoelectric component with high properties becomes a stimulus to study the 'composition-structure-property' relationships [13] that can facilitate specific piezotechnical applications of novel composites. As follows from recent papers on piezo-active composites, their main components are often chosen among perovskite-type solid-solution compositions, for instance, lead-containing (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 −xPbTiO 3 (PMN-xPT) [5,6,9,10,14], Pb(In 1/2 Nb 1/2 )O 3 -Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 [1,7,11] or lead-free BaTiO 3 -CaTiO 3 -BaZrO 3 [8].…”

“…The 2-2 and 1-3 composite structures are well reproducible in the manufacturing sense [3,[8][9][10], so it is of interest to develop piezo-active composites [13,[15][16][17] and predict their effective (or homogenised, overall) physical properties by means of various methods. These methods include analytical methods, finite element modelling, resonator methods and matrix methods, which are applicable to heterogeneous electro-elastic media.…”