Underwater communication using acoustic parametric arrays

The underwater channel is a hard environment for acoustic communications, in addition to suffering a huge loss of energy, the acoustic waves are affected by the agitation of the waves and the mass of water that cause the signal to fluctuate erratically, being able to fade at short intervals of time. Ultrasonic communications are more exposed to its effects. Therefore you are proposing new methods of communicaction, based on non-linear propagation efect that allow to avoid some of these problems in which the high frequencies are emitted and the low ones are obtained in the medium, allowing the design of more compact transducers.

In general, if the emitted wave has a high carrier frequency (primary beam), it interferes and is rapidly absorbed in the medium allowing the low frequencies formed (secondary beam) to propagate at greater distances. As is well known, high frequencies tend to be very directional, unlike with low frequencies, which are more omnidirectional. However, one of the fundamental characteristics of the parametric effect is that the low frequencies that are generated have a rather narrow directivity, comparable to that of the primary beam.

This paper presents a study of different types of parametric signals with application to submarine acoustic telecommunications. In all of them, the carrier frequency is 200 kHz, which corresponds to that resonates the transducer under study, while they differ by the different modulations they present. In this sense, we study modulations with sweeps (2 to 20 kHz), and signals with information contained in binary code (zeros and ones), getting closer to the application in acoustic telecommunications. The different properties of the transmitting signals in terms of communication speed, directivity, efficiency and power needed are discussed as well.