Analysis And Experimental Study On The Characteristics Of Through-metal-wall Wireless Power Transmission Channels Based On Piezoelectric Ultrasonic Transducers

Sealed metal structures are widely used in modern equipments in order to sustain high temperature,high pressure,radioactive,highly toxic and other special environments.Power must be provided for sensors enclosed in the hermitical structures for inside condition monitoring.Due to the strong Faraday shielding effect,for effective power wireless transmission through metal barriers it is hard using electromagnetic approaches.Ultrasound waves have capabilities of easy penetration of metal and good convergence.So it is of great engineering importance to design efficient ultrasonic wireless power transmission systems.The core of the ultrasonic wireless energy transmission system is usually composed of a pair of piezoelectric ultrasonic transducers and a metal wall which is called acoustic-electric power transmission channel.In this paper,the effective modeling methods of the ultrasonic wireless power transmission channel is studied and the power transmission characteristics of the channel are analyzed by the simulation analysis and experiment test which provides reference for the optimization design of the ultrasonic wireless power transmission systems through the metal wall.The main contents of this paper include:1.The T type equivalent circuit models of the transmission medium and the piezoelectric medium oscillating in thickness extensional mode are established based on the acoustic wave propagation equation,the piezoelectric equation and the electromechanical equivalent methods.Then,the T type model of the acoustic-electricity power transmission channel is established according to the cascade principle of multiple medium layers.Finally,the equivalent input impedances of a single piezoelectric ultrasonic transducer and the channel are simulated and compared with the measured data.The results are consistent which shows that correctness of the T type equivalent circuit model.2.The T type models are not suitable for circuit simulation software.In order to overcome the disadvantage,Pspice circuit simulation models of the single piezoelectric ultrasonic transducer and the acoustic-electric power transmission channel are built in the PSpice-Multisim software based on the T type equivalent circuit model and the lossy transmission line model.The equivalent input impedances of the single piezoelectric ultrasonic transducer and the channel are simulated and measured.The results verified the correctness of the Pspice modeling methods which shows that the Pspice circuit simulation models can be used in the PSpice-Multisim software to simulate the acoustic-electric power transmission system.3.In the case of complex geometric metal wall,both the previous modeling methods are difficult to establish the channel model effectively.A finite element modeling method is studied in the paper.Finite element models for the single piezoelectric ultrasonic transducer and the through-metal-wall(flat and cylindrical metal wall)acoustic-electricity power transmission channel are established based on multi-physical field coupling principle using Comsol-Multiphysics simulation software.The equivalent input impedances of the single piezoelectric ultrasonic transducer and the channel are simulated and measured.The results showed the effectiveness of the finite element methods for the channel through the metal wall with arbitrary complex geometric shape.4.The actual through-metal-wall piezoelectric ultrasonic wireless power transmission channels are built and the power transmission characteristics(output-to-input voltage ratio of the channel and power transmission efficiency)of the channel are tested.Combined with the simulation analysis,the influences of various factors which include the geometry size of the transducer,the thickness and species of the metal wall,the coupling effect of the coupling agent and the change of the load resistance on the transmission characteristics of the power transmission channels are tested and concluded,which provide references for the optimization design of the ultrasonic wireless power transmission system through the metal wall.