Airborne Ultrasonic Transducers for Ultrasonic Transmission Tomography in Gaseous Media

Ultrasonic transmission tomography is one of the measurement methods used for imaging of internal structure of various media. The method can be used in gaseous media, e.g. to identify the shape, size and location of objects, to determine the spatial distribution of temperature in a studied area (if here is a heterogeneous field of that quantity) and to determine concentration of components of selected binary gas mixtures. The non-invasive nature and short duration measurement process are the great advantages of this method. All applications of the method in gas media it is necessary to use suitable ultrasonic transducers intended for operation in a gaseous medium in the frequency band of 20 kHz – 100 kHz, that generate cylindrical wave. The paper presents the designed ultrasonic transducers constructed using piezoelectric film. They are capable of generating cylindrical wave at the frequency f = 31.5 kHz, f = 63 kHz and f = 90 kHz and are intended to work in gaseous media. The focus is on electromechanical model of transmitting and receiving transducer and the properties of EMFi film and powering systems (using burst type signal) are taken into consideration. It also presents the results of measurements of characteristics of directivity of transmitting transducers and the results of measurements performed using those transducers operating as ultrasonic wave receivers. Additionally, examples of applications of ultrasonic transmission tomography in gaseous media are presented.