Environment-friendly lead-free piezoelectric materials with excellent piezoelectric properties are needed for high frequency ultrasonic transducer applications. Recently, lead-free 0.915(K0.45Na0.5Li0.05)NbO3-0.075BaZrO3-0.01(Bi0.5Na0.5)TiO3 (KNLN-BZ-BNT) textured piezoelectric ceramics have high piezoelectric response, superior thermal stability, and excellent fatigue resistance, which are promising for devices applications. In this work, the KNLN-BZ-BNT textured ceramics were prepared by tape-casting method. Microstructural morphology, phase transition and electrical properties of KNLN-BZ-BNT textured ceramics were investigated. High frequency needle type ultrasonic transducers were designed and fabricated with these textured ceramics. The tightly focused transducers have a center frequency higher than 80 MHz and a -6 dB fractional bandwidth of 52%. Such transducers were built for an f-number close to 1, and the desired focal depth was achieved by press-focusing technology associated with a set of customer design fixture. Its lateral resolution was better than 90 μm by scanning a 15 μm tungsten wire target. These promising results demonstrate that the lead-free KNLN-BZ-BNT textured ceramic is a good candidate for high frequency ultrasonic transducer applications.

( $1- {x}$ )BiScO ₃ - ${x}$ PbTiO ₃ (BS-PT) ceramics have excellent piezoelectricity and high Curie temperature at its morphotropic phase boundary (MPB) ( ${x} =0.64$ ), so it is a promising piezoelectric material for fabricating high-temperature ultrasonic transducer (HTUT). Electric properties of 0.36BS-0.64PT ceramics were characterized at different temperatures, and an HTUT with the center frequency of about 15 MHz was designed by PiezoCAD based on the measuring results. The prepared HTUT was tested in a silicone oil bath at different temperatures systematically. The test results show that the HTUT can maintain a stable electrical resonance until 290 °C and get a clear echo response until 250 °C with slight changes of the center frequency. Then, a stepped metal block submerged in silicone oil was imaged by the HTUT until 250 °C. Velocity of silicone oil and axial resolution of the HTUT at different temperatures was calculated. The results verify the capability of 0.36BS-0.64PT-based HTUT for high-temperature ultrasonic imaging applications.

In order to meet the urgent need for high temperature piezoelectric materials with a Curie temperature over 400 °C, the Mn/Nb co-doped strategy has been proposed to improve the weak piezoelectric performance of the Aurivillius-type Na_0.5Bi_4.5Ti₄O₁₅ (NBT) high temperature piezoelectric ceramics. In this paper, the crystal structure, electrical properties, and thermal stability of the B-site Mn/Nb co-doped Na_0.5Bi_4.5Ti_4-x(Mn_1/3Nb_2/3)_xO₁₅ (NBT-100x) ceramics were systematically investigated by the conventional solid-state reaction method. The crystal structural analysis results indicate that the NBT-100x ceramics have typical bismuth oxide layer type phase structure and high anisotropic plate-like morphology. The lattice parameters and the grain sizes increase with the B-site Mn/Nb co-doped content. The electrical properties were significantly improved by Mn/Nb co-doped modifications. The maximum of the piezoelectric coefficient d₃₃ was found to be 29 pC/N for the NBT-2 ceramics, nearly twice that of the unmodified NBT ceramics. The highest values of the planar electromechanical coupling factor k_p and thickness electromechanical coupling factor k_t were also obtained for the NBT-2 ceramics, at 5.4% and 31.2%, respectively. The dielectric spectroscopy showed that the Curie temperature Tc of the Mn/Nb co-doped NBT-100x ceramics is slightly higher than that of unmodified NBT ceramics (646 °C). The DC resistivity of the NBT-2 ceramics is higher than 10⁶ Ω∙cm at 500 °C. All the results together with the good thermal stability demonstrated the Mn/Nb co-doped ceramics as an effective method to improve the NBT based piezoelectric ceramics and the potential candidates of the Mn/Nb co-doped NBT-100x ceramics for high temperature piezoelectric applications.

Ultrasound is one of the most promising methods for blood pressure monitoring due to its harmless, non-invasive, and high-precision characteristics. To further enhance the biocompatibility of ultrasound blood pressure monitors, this work reports wearable ultrasonic patches for blood pressure monitoring based on lead-free KNN (potassium sodium niobate)-based materials. The patches are designed and fabricated with a center frequency of 5 MHz and dimensions of 2.8 mm × 2.8 mm, optimized for both electrical impedance matching and vascular detection. Moreover, biocompatible silicone rubber is used for the packaging. The wearable ultrasonic patches are demonstrated to effectively transmit and receive signals. The diameter of artificial blood vessels is measured to validate the vascular diameter detection capability of the patches. The relationship between blood pressure and vascular diameter is then calculated. A radial artery vascular system platform is built to simulate changes in human blood pressure. Finally, the patches are shown to successfully measure the variation in vessel diameters on this platform. These patches exhibit sufficient detection ability, good biocompatibility, and can adhere tightly to human skin without coupling agents, providing the possibility for safe, sustainable, comfortable, and wearable long-term blood pressure monitoring.