The Role Of Flaps In Biosonar Antenna

In the information age, the artificial antenna as part of a sensing and communication channel plays an important role in many fields of everyday life. Smart antenna technology which can adapt its directivity to meet the challenges of evermore demanding applications is required. For antenna design, the property of the antenna is important. i.e., maximum signal-to-noise ratio minimizes output power, usually a good directivity with which the shape of an antenna has much to do is required. So devising an antenna with a proper shape is important and the study of the relationship between the shape of an antenna and the directivity of the antenna is needed.Through evolutionary optimization, most of bats have evolved a wireless sensing and communication systems (biosonar), which include intricate baffle shapes surrounding the sites of ultrasound emission (noseleaves) and reception (outer ears), they can help bats to shape the sonar beam pattern. In physical view, the electromagnetic wave problems and acoustical problems is similar in essence, so the research of the relationship between such baffle shapes and beamforming can enhance the antenna design. Due to the diversity of species, a lot of morphological features in bat pinna and noseleaves are of interest in the term of functional properties of beamforming. For these complex and irregular systems it is impossible to get analytic solutions. So some numeric methods are used. Finite element method (FEM) is used for getting the solutions. Infinite element method is used for dealing with the boundary of the problem domain. And Kirchhoff Integral is used for the far-field.A pinna sample taken from the carcass of a Brown Long-eared Bat (Plecotus auritus) has been studied numerically. One of features is that there are two inconspicuous flaps on the inner wall of pinna. The pinna was found capable of generating a fan-beam of sensitivity lobes which scan the environment in a systematic fashion as the sound frequency is changed in certain frequency band. Comparing with the functions of tow flaps, the lower flap but not upper flap was found to have larger impact for the sidelobes scanning. From the working of the employed information measure, the Crame'r-Rao Lower Bound (CRLB), we established an immediate and quantitative link between the flap and the direction information it generates. For studying how the small flap diffract the sound wave, wave field decomposition method was used, and the result is that the interaction item generated obviously sensitivity lobes scanning. It is proved that the lower flap is required for the generation of useful spatial information.The relationship between directivity and sound diffraction of intricate shapes of pinna was studied, and some theories have been established. Since the basic principle of operation of the pinna is shared by many mammals including humans, their methods could be applied widely to mammalian and human hearing. Furthermore, the methods and theories can be used for the artificial antenna design.