title: Ultrasonic transducers working in the air with the continuous wave within the 50-500 kHz frequency range.
abstract: Transmitting and receiving ultrasonic waves in the air requires high standards of both the transmitters and the receivers of these waves. The paper presents the results of measurements of ultrasonic signals generated by ultrasonic transducers of mean power working with the continuous wave, designed for operating in the air at the frequencies between 50 and 500 kHz. The characteristic feature of these transducers is their high effectiveness and sensitivity, which are necessary for working in the transmission system. Directional characteristics' measurements and the measurements of the acoustic field in the air enabling its visualization on different planes were done on specially built research setups. The results of the measurements of these transducers' admittance were also presented. Because of the forecast applications of these transducers for examining ultrasonic signals transmitted in the air by materials with different degrees of porosity, obtaining the high energy of the generated ultrasonic wave is necessary. This was possible thanks to applying layers of acoustic impedance Z approximately (0.2/1.0)x10(6) kg/(m2 s) matching the high impedance of ceramics with the low impedance of air. The designed and produced transducers had the normalized diameter of D=38 mm and worked at frequencies within the ranges of f=50, 200, 350 and 500 kHz.
authors.affiliation: Institute of Telecommunications and Acoustics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland. gudra@zakus.ita.pwr.wroc.pl
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Gudra
authors.forename: Krzysztof J
authors.initials: KJ
authors.lastname: Opielinski