Lead-free piezoelectric materials and ultrasonic transducers for medical imaging

Abstract

Piezoelectric materials have been vastly used in ultrasonic transducers for medical imaging. In this paper, firstly, the most promising lead-free compositions with perovskite structure for medical imaging applications have been reviewed. The electromechanical properties of various lead-free ceramics, composites, and single crystals based on barium titanate, bismuth sodium titanate, potassium sodium niobate, and lithium niobate are presented. Then, fundamental principles and design considerations of ultrasonic transducers are briefly described. Finally, recent developments in lead-free ultrasonic probes are discussed and their acoustic performance is compared to lead-based transducers. Focused transducers with different beam focusing methods such as lens focusing and mechanical shaping are explained. Additionally, acoustic characteristics of lead-free probes including the pulse-echo results as well as their imaging capabilities for various applications such as phantom imaging, in vitro intravascular ultrasound imaging of swine aorta, and in vivo or ex vivo imaging of human eyes and skin are reviewed.

Designing properties of (Na1/2Bix)TiO3-based materials through A-site non-stoichiometry

“…1 Considerable progress has been made in the development of these materials, which under certain conditions display even better properties than lead containing materials. [2][3][4][5][6][7] Moreover, recent works demonstrated that ionic conductivity in NBT-based materials can be enhanced by several orders of magnitude by controlling their B-site defect chemistry. Despite the promising advancements, there is still a significant lack of knowledge considering the defect chemistry of NBT and its implications on microstructure, transport properties, and electromechanical properties.…”

Advanced Synthesis on Lead‐Free KxNa(1−x)NbO3 Piezoceramics for Medical Imaging Applications

“…Finally, a large acoustic impedance mismatch existing between piezoceramics (25–35 MRayls) and body tissue (1.5 MrRayls), affects significantly the ultrasound device performance. For this reason, a matching layers elements together with its microstructure and geometry properties, being crucial for developing high performing ultrasonic transducers for medical imaging application …”

“…For this reason, a matching layers elements together with its microstructure and geometry properties, being crucial for developing high performing ultrasonic transducers for medical imaging application. [7] The most-commonly piezoceramics materials used, the highly dense PZT ceramics with general formula Pb-(Zr x Ti 1Àx )O 3 , are characterized by high values of density and relative permittivity, which negatively influence the performance and limit their application in the ultrasonic devices. Dense PZT-type materials, in fact, show low hydrostatic figure of merit (HFOM) and poor acoustic coupling to the media with which it is in contact and are therefore not suitable for these applications.…”

Dielectric and piezoelectric performance of gadolinium‐doped lead lanthanum zirconate titanate

“…The piezoelectric charge coefficient is the ability of the material to transfer electrical energy into mechanical waves and vice versa. We used the pulse‐echo response to check the performance of the selected sample acting an ultrasonic transducer. The measurement was carried out on a V2 standard reference block with thickness 12.5 mm, and due to the mechanical damping of the sample, a damped oscillation is produced.…”