Ultrasonic transducers for use in air

Fewer applications were found for the use of ultrasonics in air than for ultrasonics in liquids or solids. This was primarily because of the inherent limitations of generating high-intensity sound levels in a gaseous medium, and also because of the extremely high attenuation that accompanies in the propagation of ultrasonic energy through air. Several types of transducers are described for the generation and reception of ultrasonic sound in air. Data are presented in the form of engineering design charts which include several quantitative relationships between piston displacements, acoustic power, sound pressure level, beam patterns, attenuation, and additional fundamental information for use in the design of ultrasonic equipment to achieve the transmission of high-frequency sound over a specified range. Due to the natural limitations in the transmission of ultrasonics in air over large distances, the major applications have been in remote control systems, proximity indicators, automatic counting, burglar- and fire-protection systems, and short-range carrier telephony.