Acoustic impedance matching of piezoelectric transducers to the air

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 51; no. 5; pp. 624 - 633
• Main Author: ALVAREZ-ARENAS, Tomas E
• Format: Journal Article
• Language: English
• Published: New York, NY Institute of Electrical and Electronics Engineers 01.05.2004
• Subjects: Acoustics; Exact sciences and technology; Fundamental areas of phenomenology (including applications); General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Transducers; Ultrasonics, quantum acoustics, and physical effects of sound; Electroacoustic transducer; Piezoelectric sensor; Impedance matching; Air coupling; Insertion loss; Membrane; Boundary condition; Low frequency; Acoustic impedance
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2004.1308697

The purpose of this work is threefold: to investigate material requirements to produce impedance matching layers for air-coupled piezoelectric transducers, to identify materials that meet these requirements, and to propose the best solution to produce air-coupled piezoelectric transducers for the low megahertz frequency range. Toward this end, design criteria for the matching layers and possible configurations are reviewed. Among the several factors that affect the efficiency of the matching layer, the importance of attenuation is pointed out. A standard characterization procedure is applied to a wide collection of candidate materials to produce matching layers. In particular, some types of filtration membranes are studied. From these results, the best materials are identified, and the better matching configuration is proposed. Four pairs of air-coupled piezoelectric transducers also are produced to illustrate the performance of the proposed solution. The lowest two-way insertion loss figure is -24 dB obtained at 0.45 MHz. This increases for higher frequency transducers up to -42 dB at 1.8 MHz and -50 at 2.25 MHz. Typical bandwidth is about 15-20%.