Relationship between head size and biosonar transmit and receive beams in odontocetes

Abstract

The unique shape of a dolphin head, the different specie specific shape and the internal head structure suggest a very complex propagation mechanism for the biosonar signals to travel from the phonic lips into the water. Despite these factors, a circular planar aperture of the appropriate diameter can produce a transmission beam that resembles the corresponding beam of a dolphin. In the similar manner, the reception process is also very complex and not completely understood. Once again, despite the complexity involving the reception of biosonar echoes, a simple circular planar aperture of the right diameter can have a receiving beam that approximate or resemble the receiving beam of odontocetes. For both transmission and reception of broadband biosonar signals, the size of the head compared to the wavelength of the signal will determine the degree of directionality of the beams in odontocetes in a similar manner as a planar transducer. Beam pattern data from Tursiops truncates, Delphinapterus leucas, Pseudorca crassidens, and Phocoena phocoena will be used to demonstrate the relationship between head size and directionality for the transmit signal. Receiving beam pattern data from Tursiops truncates and Phocoena phocoena will be used in a similar manner as for the transmit beam.