The design of impedance matching between long cable and ultrasonic transducer under seawater

Ultrasonic energy transmission (UET) will become novel measures to power the devices under deep seawater, because the energy can be transmitted in the form of conductive contactless. But a long cable must be often required to transmit high frequency electric energy from platform to ultrasonic transducer (UT) for producing ultrasonic energy. However, the input impedance of UT would not match with the characteristic impedance of the long cable. Therefore, the energy transfer effect will be affected by the reflected wave produced in the joint position. In order to eliminate the reflected wave, the impedance matching method between long cable and UT was studied in this paper. A symmetric T type or Π type two-port matching network was designed by means of one-quarter wavelength cable. By this method, the capacitive UT impedance can be transformed into the resistive impedance, which equals to the characteristic impedance of the long cable. Hence, the reflected wave in long cable would be ignored. In the paper, the calculating formulas of inductance and capacitance in the matching network were derived based on the series expedition of hyperbolic functions in the transmission line equations. The experiments were made to show the effectiveness of the method.