Bats are mammals which have acquired the ability of flight and of echolocation. Echolocation involves using vibrating membranes to direct a high frequency sound, with frequencies ranging from 12 kHz to 150 kHz. If the sound encounters a flying insect or obstacle which is larger than the wavelength of the sound, then a portion of the sound wave is reflected, and the bat detects it.
Beyond this basic framework, different species of bats use different strategies in echolocation. Some species emit a series of pulses, determining the distance to an object by the delay in return of the signal. Some emit a constant frequency, using the frequency of the returned sound to determine information about the velocity of the insect. Others use a sweep of frequencies, presumably to determine size information or directional information. Some emit a sound with a high harmonic content. Many use some combination of these strategies.
Several adaptations provide for better processing of the returned signal, including isolation of the detection apparatus from the emitting apparatus and specializations in the middle ear.
For the questions, use the following: The speed of sound is 343 m/s, and the Doppler-shifted frequency for a detector and emitter moving relative to each other is
What is a possible reason for using a sound with high harmonic content?