This work presents the fabrication of a 30 MHz, linear-array transducer based on a KN, 1-3 piezocomposite. Performances of the transducer were characterized and compared to a PZT-based linear array with similar structure. The composites were designed to minimize lateral modes of vibration which can severely degrade imaging performances. Fabrication steps were optimized to achieve a 40 MHz resonant frequency in air with a composite thickness of 69 microns. The measured thickness coupling factor was around 50 %. A 128element, linear array was then fabricated with 100 m pitch and 1,5 mm elevation aperture. The structure of the transducer (backing, matching layers, and electric components) was optimized to deliver good fractional bandwidth and sensitivity. The final probe was integrated in a prototype, real-time, 128channel scanner to acquire high-resolution images of the human skin in vivo. Results showed that, compared to PZT ceramics, KN single crystals provide low density and high acoustic velocity, both highly desirable for the manufacturing of HF transducers. The central frequency of the linear-array transducer was 30 MHz despite the KN composite being 20% thicker than equivalent PZT-based composites and the relative bandwidth was about 50%. High-resolution images of the human skin were acquired. A large ultrasound penetration due to good signal sensitivity was obtained and detailed features could be visualized.

A complete and consistent set (elastic, dielectric, and piezoelectric tensors) of a commercial lead-free (YXt)-45° cut KNbO3 single crystal is reported. These data were obtained using several samples and the resonance-antiresonance method. Particular attention was paid to the consistency of this delivered database. A genetic algorithm with an appropriate criterion was used. Electromechanical characterization revealed a high thickness coupling factor of approximately 60%. These properties make this single crystal a good candidate for several applications such as medical imaging. This complete set provides a basis for simulation designs of such devices integrating this piezoelectric lead-free material, especially for ultrasonic transducers.

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