Lead-free high-frequency linear-array transducer (30 MHz) for in vivo skin imaging

Abstract

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.

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

“…The main advantages of KNN over other lead-free compositions are the good temperature stability of the piezoelectric properties [19,20], the high mechanical quality factors [21,22], the fatigue resistance [23,24], the low density [25], the biocompatibility [26], and, as shown recently, the compatibility with low-cost, base-metal electrodes [27]. In addition to the scientific community, these materials have also attracted the attention of industry and the first prototypes and products started to appear: ultrasonic transducers [28], ultrasonic motors [29], multilayer actuators [30], knock sensors [31], and piezoelectric transformers [32]. …”

(K,Na)NbO3-based piezoelectric single crystals: Growth methods, properties, and applications

“…In this range, lead-based piezoelectrics are often limited in resolution, whereas the low density of KNN enables to achieve higher frequencies (at same thicknesses) and thus improved imaging resolution. This concept was first demonstrated by Bantignies et al using KNbO 3 single crystals [157]. The [001] C -oriented crystals were cut at 45°and assembled into a 1-3 piezocomposite array with 128 elements and a thickness of 69 lm to minimize the lateral vibration modes [ Fig.…”

Composite microstructures and piezoelectric properties in tantalum substituted lead-free K0.5Na0.5Nb1-xTaxO3 ceramics

“…To conclude on the results summarized in Table 1, SPS sintering techniques appears to be a powerful way to produce highly densified K0,5Na0,5Nb1-xTaxO3 ceramics with improved piezoelectric properties. Indeed, thanks to transducer's element or energy harvesting devices for applications [62], preparing thus the "after PZT" devices. Table 1 …”