Flexible ultrasonic transducers incorporating piezoelectric fibres

Abstract

It is possible to produce a high-performance, flexible 1-3 connectivity piezoelectric ceramic composite with conventional methods but the process is difficult and time-consuming. Extensive finite element modeling was used to design a piezocomposite structure which incorporated randomly positioned piezoceramic fibers in a polymer matrix. Simple manufacturing techniques were developed which resulted in the production of large numbers of fully populated fiber composites that offered performance comparable with a conventional 1-3 piezocomposite. A modified process facilitated the production of efficient fiber piezocomposite elements separated by polymer channels which conformed to a highly flexible (13 mm radius of curvature), 2-D matrix array configuration. This arrangement has been termed a Composite Element Composite Array Transducer, or CECAT. These devices were evaluated in terms of their impedance spectra, pulse-echo response, and surface displacement characteristics. The random piezoceramic fiber arrangements showed comparable sensitivity and bandwidth to periodic devices while minimizing the parasitic interpillar modes associated with periodic structures. Investigations have indicated that CECAT arrays constructed with 250 microm diameter fibers can be operated at frequencies of up to 3 MHz and transducers incorporating 10 microm diameter fibers can extend the frequency range above 6 MHz. Conversely, improved low-frequency devices can be produced with taller pillars than possible with conventional manufacturing techniques.

Design of a 2D sparse array transducer for integration into an ergonomic transcranial ultrasound system

“…However, the overall ceramic volume fraction of the array device is lower than a comparable 1-3 piezocomposite array due to the fact that only the array elements contain active piezoceramic material. The piezoelectric fibers are randomly placed within the array element area and the experimental results demonstrate that this random fiber structure can achieve similar performance when compared with the conventional dice-and-fill structure [6]. Furthermore, the random fiber structure can help reduce interpillar modes as it breaks the periodicity of the conventional 1-3 piezocomposite microstructure.…”

“…The Composite Element Composite Array Transducer (CECAT) is a piezocomposite configuration which was designed to improve the flexibility of traditional array transducer technology using conventional 1-3 connectivity composite active layer [6]. Elements in the CECAT configuration are individual piezocomposites, consisting of piezoelectric fiber material embedded in a polymer phase [6].…”

“…Furthermore, the random fiber structure can help reduce interpillar modes as it breaks the periodicity of the conventional 1-3 piezocomposite microstructure. The manufacturing process for fiber CECAT is simpler compared to the conventional dice and fill method and more than one active layer can be made from a single manufacturing process [6].…”

“…The performance of each proposed array configuration is evaluated using two parameters: Peak Side-Lobe value (PSL) and Integrated Side-Lobe Ratio (ISLR). Based on the simulation results, a log spiral array configuration has been identified as a promising array design and manufactured using a Composite Element Composite Array Transducer (CECAT) fabrication approach [6].…”

Implementation of a PMN-PT piezocrystal-based focused array with geodesic faceted structure

“…Mechanical forming to focus piezocrystal transducers has been achieved successfully using mechanical hard-press [15] and dimpling techniques [16], but reports are limited to single-element transducers. Other possibilities are to thermally form a 1-3 connectivity piezoelectric -polymer composite into the desired shape [17] or to use flexible polymers for flexible composites [18], but these may be difficult at the frequencies of interest here, below 1.0 MHz, and the values of volume fraction, e.g. VF > 50%, used in focused ultrasound applications.…”