Abstract
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(Zr0.53Ti0.47O3 (PZT) substrate, a piezoelectric PZT-based layer with a thickness of [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] 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.
Highlights
P OROUS piezoelectric ceramics have been largely studied as an active layer for ultrasonic transducer applications
It was demonstrated that ∼30-μm-thick PZT with a relative density of 85%, a dielectric constant of ∼500, and a thickness coupling coefficient kt of ∼0.4–0.5 can be processed on a porous ceramic substrate by screen printing or electrophoretic deposition, and consequent sintering at 800 ◦C–950 ◦C [8]–[11]
The backings with tailored amount of porosity, homogeneous distribution of the pores having predefined size and shape were processed by a template method in combination with HC process and sintering
Summary
P OROUS piezoelectric ceramics have been largely studied as an active layer for ultrasonic transducer applications. According to the porosity content, several properties of the piezoelectric can be adjusted such as acoustic impedance, dielectric constant, and piezoelectric coupling factors [3]–[6]. Some properties of the porous ceramic can even be improved when compared with those of the dense ceramic with the same composition, in particular, the thickness coupling factor [7]. It was demonstrated that ∼30-μm-thick PZT with a relative density of 85%, a dielectric constant of ∼500, and a thickness coupling coefficient kt of ∼0.4–0.5 can be processed on a porous ceramic substrate by screen printing or electrophoretic deposition, and consequent sintering at 800 ◦C–950 ◦C [8]–[11]
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