Research On Acoustically Coupled Power Transfer In Seawater

Electromechanical devices are indispensable in exploitation of marine resources and monitoring of marine environment. How to power or charge these devices safely and conveniently is a problem. Electrical hazards and inconvenience exist in use of waterproof connectors, but these problems can be avoided if Acoustically Coupled Power Transfer (ACPT) is used. ACPT is to achieve power transmission through the way of electricity-sound-electricity by means of ultrasonic waves. Since ultrasonic waves have characteristics like strong directional transmission, no electromagnetic interference and not being affected by conductivity of the media, ACPT has a bright and wide application prospect in ocean development.This dissertation is aimed at studying the energy transfer characteristics of the ACPT system in seawater and how to improve performance of the system through impedance transformation and impedance matching. The specific research work and findings mainly include the following aspects:Theoretical analysis for the ACPT system in seawater is carried out, including loss mechanism of the propagating ultrasonic waves, principles of electromechanical analogy and the electromechanical equivalent circuit of the piezoelectric transducer. And then the equivalent circuit of the ACPT system in seawater while transducers are working at the resonance state is built.Impedance transformation methods for the piezoelectric transducers are studied. At the transmitting terminal, impedance transformation is aimed at eliminating reactive power and making the transmitting transducer get controllable active power output. Impedance transformation methods specific to high-frequency voltage and current source are proposed respectively. At the receiving terminal, impedance transformation is aimed at eliminating reactive power and getting stable output voltage. Impedance transformation methods are proposed according to the equivalent load resistance. Experimental results verify the efficiency of the proposed impedance transformation methods.Normally, a transmission line which is hundreds of meters long is needed to connect the high-frequency power source on the mobile-surface platform or the bank with the transmitting transducer when ACPT is applied under the sea. Impedance matching methods between the transmission line and transducer is studied in this dissertation, so as to eliminate reflected waves at the joint. Lossless matching lines are designed based on the impedance transformation principle of quarter-wave (?/4) losses lines. T-shape and ?-shape circuits are respectively used to equal the matching lines, so as to obtain the approximate impedance matching network composed of lumped elements and to save the long matching lines. Experimental results verify the efficiency of the proposed impedance matching methods.For comparison, Inductively Coupled Power Transfer (ICPT) in seawater is studied in this dissertation. First, the equivalent circuit of the ICPT system in seawater is built. Then ICPT and ACPT are compared in the relationship between power transmission efficiency and operating frequency, the relationship between power transmission efficiency and coupling distance, and the magnitude of transmitted power. The experiment results show that, within a certain frequency range, power transmission efficiency of ICPT and ACPT under seawater both increase first and then decrease with increasing operating frequency. Both ICPT and ACPT can transfer high-power energy under seawater. ICPT is appropriate for transferring energy through a short distance, and ACPT has higher energy efficiency when the distance is long.