Acoustic Properties of Porous Lead Zirconate Titanate Backing for Ultrasonic Transducers

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 67; no. 8; pp. 1656 - 1666
• Main Authors: Kuscer, Danjela, Bustillo, Julien, Bakaric, Tina, Drnovsek, Silvo, Lethiecq, Marc, Levassort, Franck
• Format: Journal Article
• Language: English
• Published: United States IEEE 01-08-2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers
• Subjects: Acoustic attenuation; Acoustic characterization; Acoustic measurement; Acoustic measurements; Acoustic properties; Acoustics; Attenuation; Back propagation; backing; Backups; Ceramics; Chemical Sciences; Engineering Sciences; Frequency ranges; Lead zirconate titanates; Material chemistry; Multilayers; Piezoelectricity; Pore size; Porosity; porous Pb(Zr₀.₅₃Ti₀.₄₇)O₃ (PZT); Powders; Substrates; Thick films; Thickness; Thin films; Transducers; Ultrasonic transducers
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2020.2983257

For transducer design, it is essential to know the acoustic properties of the materials in their operating conditions. At frequencies over 15 MHz, standard methods are not well adapted because layers are very thin and backings have very high attenuation. In this article, we report on an original method for measuring the acoustic properties in the 15-25 MHz frequency range, corresponding to typical skin-imaging applications, using a backing/piezoelectric multilayer structure. Onto a porous Pb(Zr 0.53 Ti 0.47 O 3 (PZT) substrate, a piezoelectric PZT-based layer with a thickness of <inline-formula> <tex-math notation="LaTeX">\sim 20~\mu \text{m} </tex-math></inline-formula> was deposited and directly used to excite an acoustic signal into water. Herein, the measured signal corresponds to the wave that is first reflected on a target in water, then propagates back to the multilayer structure, and is transmitted through the thick film and further to the rear face of the porous backing, where it is again reflected and returns to the piezoelectric thick film, thus avoiding overlap with the electrical excitation signal. Two types of PZT backings with similar porosity of ~20% and spherical pores with size of 1.5 and 10 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> were processed. The ultrasound group velocities were measured at ~3500 m/s for both samples. The acoustic attenuation of the backings with pore size of 1.5 and 10 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> were 12 and 33 dB/mm, respectively, measured at 19 MHz. This advanced measuring technique demonstrated potential for the simple measurements of acoustic properties of backing at high frequencies in operating conditions. Importantly, this method also enables rapid determination of the minimum required thickness of the backing to act as a semi-infinite medium, for high-frequency transducer applications.