The Fessenden Oscillator: The first sonar transducer

When the RMS Titanic sunk in 1912, there was a call placed forth by ship owners for inventors to offer solutions for ship collision avoidance methods. Canadian born inventor Reginald A. Fessenden answered this call while working at the former Boston Submarine Signal Company with the invention and development of the first modern transducer used in a sonar. The Fessenden oscillator was an edge clamped circular metal with a radiating head facing the water on one side while the interior side had a copper tube attached that moved in and out of a fixed magnetic coil. The coil consisted of a direct-current (DC) winding to provide a magnetic field polarization and an alternating-current (AC) coil winding to induce the current into the copper tube and thus translate the magnetic field polarization to the radiating plate with vibrations that translated from the radiating head to the water medium. The prototype and early model versions operated at 540 Hz. Later developments included adaptation of this same transducer for use in underwater communications, obstacle avoidance with WW I retrofits onto British submarines for both transmitting and receiving applications including mine detection. This presentation will discuss design details including a modern numerical modelling effort.