Borehole acoustic imaging techniques have become a crucial tool in subsurface investigations, combining advances in signal processing and sensor technology to produce detailed images of geological ...

And although they are “acoustic” waves, they are below the range of human hearing – the only way to pick up and record them is using hydrophones, special microphones that work underwater.

To control the movements of particles within acoustic wells, another kind of energy is required. These are in the form of electrical fields, generated by using microscopic electrodes.