We designed and built a functional prototype of a device intended to assist in
locating a diving partner in situations of unexpectedly reduced visibility or limited
communication. The system is based on three ultrasonic receivers positioned at
the vertices of an equilateral triangle. The phase of the detected sinusoidal signal
was determined using I/Q demodulation, while the direction of the transmitter in
the plane of the receivers was calculated from the phase differences using phase
interferometry.
We designed the electronic circuitry of the receiving system, constructed the
underwater preamplifiers and their waterproof protection, and developed a signal-
processing algorithm in Python for determining the angle of incidence. The system
was tested in a swimming pool at different angles of incidence and at different
distances between the transmitter and the receivers.
The results showed that the direction of the transmitter could be determined,
but the accuracy depended on the angle of incidence and the distance. Consecutive
measurements at the same setup were generally highly repeatable, while larger sys-
tematic deviations from the expected direction were present in some configurations.
The prototype therefore demonstrates the feasibility of the basic principle, although
further improvements to the mechanical setup, calibration, and electronic circuitry
would be required for practical use.
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