HIGH-SPEED photography1 and an acoustic doppler method2,3 have shown that rapid ear movements of Rhinolophus ferrumequinum4,5 are closely correlated to the production of the constant frequency signals used for echolocation. In addition to independent “searching” movements, the pinnae make alternating movements with an excursion of up to 1 cm at the tip, thus describing an arc of about 30°. The simultaneous movements (forwards by one ear, backwards by the other) may take less than 20 ms and are generally associated with the emission of one ultrasonic pulse through the nose-leaf. The one to one correspondence is not always exact but is seldom much in error even at the highest recorded pulse repetition rates of up to 60–80 pulses/s.

Ear Movements in a Hipposiderid Bat

The reflected fields of a slightly divergent ultrasonic beam on a liquid-solid interface are recorded by a Schlieren system, and the lateral beam displacements on the interface are measured. The range of the incident angle θ i is ±5° around the Rayleigh angle θ c . The displacements Δ are found to decrease as the incident angle increases. Theoretical calculation reveals that the displacements decrease with the increase in the incident angle for a divergent incident beam, but increase with that for a convergent one. The calculated curve of Δ - θ i are in agreement with the experimental results.

P. Steffen

Papers

Ultrasonic model experiments for simulation of a chirp Doppler sonar