The calculation of near and far fields for acoustic antennas consisting of piezoelectric rectangular bimorph transducers in flexural vibration

Abstract

In this article the calculation, along with practical examples of near and far fields of acoustic antennas are presented. Knowing the near and far fields is important because the radiation patterns and physical measurements of the antennas depend on them. These antennas designed for measurements in air consist of transducers in flexural vibration, which give the best possibility to match acoustic impedances between air and the transducer. Specific type of transducers for acoustic antennas is described along with their schematic diagrams. Optimal design of the antenna is achieved when the near and far fields of the transducer are available. The near and far fields are described by the distribution of acoustic pressure in the area around the transducer. The necessary expressions for calculating acoustic pressure are supplied. In addition, diagrams of acoustic pressure distribution in chosen planes and lines of the environment are presented. Unidirectional radiation of the evaluated transducer in flexural vibration is achieved by a relatively small increase in the physical dimensions of the antenna. Schematic diagrams of actual antennas along with their radiation patterns are presented. A method for eliminating peripheral radiation of these antennas is also described.