COMMUNICATIONS:

Communication is one of the biggest challenges in many underwater applications. Hydro Technologies is developing several technologies that promise to radically improve on the current state of the art capabilities in this area.

After several years of development and testing, the Hydro Technologies Hull Penetrator Replacement System (HPRS) is currently making its debut in a Navy submarine application. HPRS is based upon a digital communication technology capable of communicating through any hull material without the need for compromising the hull integrity by drilling holes for wire feed-through or RF waveguides. To date HPRS has been tested through fiberglass, marine grade aluminum, stainless steel, and several Navy ship and submarine hull alloys including HY80 up to 3" thick.

The low data rates inherent in transmission from an unmanned underwater vehicle (UUV) back to a host ship have limited the usefulness of UUVs in many applications. Hydro Technologies has been involved in several pioneering efforts to increase the data rate achievable between submerged nodes. Since the underwater acoustic channel has inherently limited bandwidth, one technique for increasing the achievable data rate is to attempt to pack more data on a given bandwidth using advanced digital communications algorithms. The leading candidate for this is known as Quadrature Amplitude Modulation (QAM). It was the application of QAM by the telephone companies that allowed for high speed DSL internet access using the same phone lines that were normally limited to dial-up speeds of 20 times slower than DSL. Many researchers are hopeful that the same speed enhancements can be applied to underwater communications.

In support of these high speed underwater communications efforts, Hydro Technologies worked with the Massachusetts Institute of Technology AUV Laboratory to help develop a custom electronics module capable of communications using advanced algorithms such as QAM. In addition to this work, Hydro Technologies assisted engineers at Woods Hole Oceanographic Institute in the design of a next generation MicroModem capable of driving underwater piezoelectric transducers with QAM signals.

 

The other option for increasing the data rate of underwater communications is to increase the usable transducer bandwidth. Hydro Technologies has been developing and evaluating technologies in this area since the company was founded. To support our internal efforts, we have installed an acoustic test facility on site at Hydro Technologies. This facility consists of a 2000 gallon acoustic tank outfitted with broadband hydrophones. Our data acquisition and signal generation hardware is capable of evaluating the frequency response of devices under test as well as establishing a communications link using algorithms such as FM, AM, ASK, FSK, and QAM. Our custom software also allows for the full suite of acoustic characterizations such as signal-to-noise ratio and total-harmonic-distortion measurements.

Hydro Technologies, in cooperation with one of our corporate partners, is currently heading up the development and testing of novel transducer designs capable of achieving nearly an order of magnitude higher bandwidth than off-the-shelf transducers.

In addition to underwater acoustic communications, Hydro Technologies has been active in optical communications. Our basic experimentation in lasers for underwater communications has led to several other applications such as a laser beam break sensor for time-of-flight measurements. One of the more esoteric applications of the optical technology developed at Hydro Technologies is a low cost optical emitter shown by the MIT Quantum Communications laboratory to generate quantum entangled photons usable in quantum cryptography research. To our knowledge, this experiment done in 2003 was the first in which a non-coherent optical source was used to generate entangled photons.