Underwater Communication – Acoustic Modems and Transducers

Wireless Underwater Communications

While underwater communications can be performed via cables and tethers, this limits the versatility and flexibility of the systems involved, particularly in the case of submarines and robotic vehicles. Wireless underwater communications can be deployed rapidly and can be utilized in environments where it may be dangerous or impractical to lay cables.

Sound waves are attenuated and absorbed less quickly than RF (radio frequency) waves or laser pulses, and thus acoustic communications are the most widely used form of underwater wireless technology. Acoustic waves can be used to achieve practical communications distances of multiple kilometers without the need for an extremely high-powered transmitter.

Acoustic Communication Systems

Acoustic Modems

Subsea communications systems that utilize sound waves require an acoustic modem. This device decodes captured acoustic waves into digital data that can be handled by a computer, and also encodes any digital data that needs to be broadcast into acoustic waveforms.
Digital information may be transformed into an acoustic signal using one of a number of modulation techniques, including:

• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK),
• Orthogonal Frequency-Division Multiplexing (OFDM)

Acoustic modems may also apply error correction algorithms to enhance the robustness of the data transmission in challenging underwater environments.

Acoustic Transducers

Acoustic modems interface with acoustic transducers, which are devices that convert electrical energy into sound waves and vice versa. These transducers are installed into projectors, which transmit acoustic waves, and hydrophones, which receive them. Piezoelectric transducers are mostly commonly used, with material types including ceramics, single crystals, polymers and composites.

Acoustic Communications Applications

Subsea acoustic communications systems are utilized for a wide range of applications in the commercial, industrial, defense and scientific sectors. They can be used to keep track of submarines, underwater vehicles and other assets, and to pass data and information to and from the surface. They can also be used to extract information gathered by networks of underwater and seafloor sensors, such as oceanographic and marine environmental data.