Bats Sonar Calls and its Application in Sonar Systems

Abstract

Sonar system operating in gas medium (air) are based on echolocation phenomenon (active sonar). Many scientist and specialists in the field of air coupled ultrasound localisation systems have been inspired by echolocation mechanism of bats. Those mammals mastered echolocation perfectly using ultrasound waves. A resolution of so called real time biosonar is out of range of human made equivalent due to scientific and technological limitations. The main aim of the chapter presented below is to introduce book readers with the echolocation mechanism, evolved in bats, which are an example of animals that have achieved perfection in biosonar usage. The next problem that authors cover is an evolution of sonar systems from simple one beam ranging echolocation devices to advanced multibeam array beamformers operating with digital signal as serviceable form of information representation. Some properties of ultrasound waves in gas medium and physical phenomena involved with air coupled ultrasoundwaves generation, transmission and detection are described in the chapter as follows: (1) generation of ultrasound wave in gas medium, (2) a short review of air operating transducers including piezoceramics, sandwich, electrostatic, EMFi and MEMS, (3) problem of ultrasound wave transmission in gas medium (the influence of temperature and static pressure on speed of sound, attenuation in air) and range equation, (4) reception and detection of ultrasound waves, target strength. Considering the fact that the detection of echo signal does not give us an information about target a review of signal processing methods is also presented. Taking into account global trend in applying digital signal processing methods to sonar application authors describe some of DSP solutions which are adaptation of echo signal processing by bats at higher level of their auditory system. In order to explain some important issues from bat echo analysis, authors to present some information about bat auditory system and the role of its particular organs and auditory pathways in spatial information processing.