The high power properties of piezoelectric transducers were evaluated considering a complex nonlinear elastic constant. The piezoelectric LCR equivalent circuit with nonlinear circuit parameters was utilized to measure them. The deformed admittance curve of piezoelectric transducers was measured under a high stress and the complex nonlinear elastic constant was calculated by curve fitting. Transducers with various piezoelectric materials, Pb(Zr,Ti)O3, (K,Na)NbO3, and Ba(Zr,Ti)O3–(Ba,Ca)TiO3, were investigated by the proposed method. The measured complex nonlinear elastic constant strongly depends on the linear elastic and piezoelectric constants. This relationship indicates that piezoelectric high power properties can be controlled by modifying the linear elastic and piezoelectric constants.

Ultrasonic sensors fabricated using (K,Na)NbO 3 KTiNbO 5 (KNNNTK)-based lead-free piezoelectric ceramics were fabricated, their sensor characteristics were compared with those of sensors fabricated using Pb(Zr,Ti)O 3 (PZT)-based piezoelectric ceramics, and effects of material properties on sensor performance were investigated. The sound pressure, sensitivity, temperature increase during driving, and the responsiveness of the KNNNTKbased sensor equaled those of the PZT-5A-based sensor. PZT-5A is generally used for ultrasonic sensors and has the same mechanical quality factor Q m as the KNNNTK ceramics. Most sensor characteristics are explained based on the electromechanical coupling factor and Q m. However, the change in frequency characteristics under high applied power was observed that is attributed to the tendency of the nonlinear phenomenon of KNNNTKbased ceramics to be weaker than that of PZT-based ceramics.

To achieve wide-frequency (20 kHz-2 MHz) high-power output (10 MPa) of Double Parabolic refLectors wave-guided Ultrasonic tranSducers (DPLUS), this paper investigated the DPLUS with hard-type PZTs. Under resonant excitation of the DPLUS waveguide, around 30 harmonic longitudinal modes from the thin waveguide (1 mm in diameter and 40 mm long) can be excited between 20 kHz to 2 MHz. From 20 kHz to 0.4 MHz, the maximum peak vibration velocity was 7.5 m/s; for high-frequency modes (1-2 MHz), the maximum peak vibration velocity of hard-type PZT DPLUS (7 m/s) was 3.5 times of soft-type piezoelectric materials DPLUS (2 m/s). Acoustic evaluation revealed the large acoustic pressure at a wide frequency range: 0.46 MPa (31 kHz), 10 MPa (590 kHz), 7.7 MPa (1.154 MHz), and 7.2 MPa (1.322 MHz). Results proved wide-frequency and high-power operation of DPLUS, which are significant for realizing various applications.

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To suit double parabolic reflectors wave-guided ultrasonic transducer (DPLUS) for high-power ultrasound applications, we investigated the selection criteria of piezoelectric materials for DPLUS. Four piezoelectric materials were prepared: two lead–zirconate–titanate (PZT) types and two lead-free types. For non-resonant excitation of the DPLUS waveguide, the piezoelectric constant e and the thickness of piezoelectric materials are two important evaluation indexes. PZT 5H was found as the best candidate. For resonant excitation of the DPLUS waveguide, two situations should be distinguished. For low-frequency modes excitation, the discussed modes matching issue is essential. For high-frequency modes excitation, high-power properties of the piezoelectric material are important for improving the vibration output of DPLUS; LFP 0202 was found as the best candidate. Low-frequency modes can achieve 8 m s−1 of maximum peak vibration velocity, but high-frequency modes were smaller than 2 m s−1. Results are important to design the DPLUS for various high-power ultrasound applications.