Acoustic Properties of Porous Lead Zirconate Titanate Backing for Ultrasonic Transducers

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Porous lead zirconate titanate ceramics with optimized acoustic properties for high-frequency ultrasonic transducer applications

International audienceAcoustic properties of porous PZT ceramics intended to be used as backing in high-frequency transducer applications are investigated using a novel method where an electroded piezoelectric thick film is deposited on the backing under test. Two backings with pore sizes 1.5 μm and 10 μm were obtained by sintering a mixture of ceramic powder and an organic template, their porosity was evaluated by scanning electron microscopy at 15%, leading to a density around 6.5 g/cm3. The electroacoustic impulse responses of these devices were measured considering the backing as a propagation medium, the initial thickness of which was chosen small enough to allow back-wall echoes to be detected and large enough to be able to separate the signals in time domain. Then the thickness of the backing was reduced (from around 2 mm to less than 1 mm) and the measurements were repeated. Acoustic properties were then deduced: attenuation coefficients reaching 4 dB/mm/MHz and group velocities around 3400 m/s were obtained, leading to an acoustic impedance around 22 MRa. Such combination of high attenuation and moderate acoustical impedance make these materials an interesting solution for high-resolution ultrasonic imaging transducers

High-frequency acoustic characterization of porous lead zirconate titanate for backing applications

International audienceAn original method to measure the acoustic properties of porous Pb(Zr0.53Ti0.47)O3 (PZT) backings at high-frequencies (HF, i.e. between 15 and 25 MHz), was developed. To this end, a piezoelectric PZT-based thick film was deposited onto the porous ceramic backing and directly used to generate an acoustic signal in water. Here, the considered signal is the one that was generated in water, reflected on a target, back toward the multilayer structure, transmitted through the piezoelectric thick film and then to the rear face of the porous backing and finally back to the active film. This method avoids the overlap of the electrical excitation and the measured signal. In this study, two types of porous PZT backings with 1.5 and 10 micrometers pore sizes (volume fraction around 20%) were characterized. For both samples, group velocities were around 3500 m/s and for the 10 micrometers pores size sample, the measured acoustic attenuation coefficient was 1.7 dB/mm/MHz in the frequency range of the transducer bandwidth. Finally, this method is found to be an easy way to determine, in operating conditions, the minimum required thickness of the porous PZT to be used as a backing (in order to be considered as a semi-infinite medium) for HF transducer applications

Effect of Pore Size and Porosity on Piezoelectric and Acoustic Properties of Pb(Zr0.53Ti0.47)O3 Ceramics

International audienceWe studied the effect of porosity and pore morphology on the functional properties of Pb(Zr0.53Ti0.47)O3 (PZT) ceramics for application in high frequency ultrasound transducers. By sintering a powder mixture of PZT and polymethylmetacrylate spherical particles (1.5 and 10 μm) at 1080°C, we prepared ceramics with ∼30% porosity with interconnected micrometer sized pores and with predominantly ∼8 μm spherical pores. The acoustic impedance was ∼15 MRa for both samples, which was lower than for the dense PZT. The attenuation coefficient α (at 2.25 MHz) was higher for ceramics with ∼8 μm pores (0.96 dB mm− 1 MHz− 1), in comparison to the ceramic with smaller pores (0.56 dB mm− 1 MHz− 1). The high α value enables the miniaturisation of the transducer, which is crucial for medical imaging probes. The dielectric and piezoelectric coefficients, polarisation, and strain response decreased with increased porosity and decreased pore/grain size. We suggest a possible role of pore/grain size on the switching behaviour