Study Of Implantable Ultrasonic-coupled Wireless Power Transfer System

Implantable devices are gaining more and more attention in the modern medical field.Many new medical treatments emerge by using implantable devices.However,these implantable devices are usually powered by lithium-ion batteries,requiring surgery to replace the battery when they run out,which will bring great pain to the patient.By using wireless power transfer technology,the weaknesses of implantable devices can be effectively overcome.The implantable Ultrasonic-coupled wireless Power Transfer(UPT)technology which is studied in this paper is an emerging technology.Unlike Inductive-coupled wireless Power Transfer(IPT)technology and Capacitive-coupled wireless Power Transfer(CPT),using UPT technology can not only transmit energy in metallic media,but also concentrate energy easier.Thus in many occasions such as deep implanted medical applications,it has higher energy transfer efficiency.In addition,the UPT technology has the advantages of no electromagnetic radiation and electromagnetic interference,and the adaptability and reliability to the working environment.However,the current UPT technology still has problems of low transmission efficiency.In this paper,the modeling of UPT system is carried out.Based on the modelling,omnidirectional UPT system by virture of the cubic structure piezoelectric transducer is studied,and the transmission impedance transformation network is designed to obtain maximum power in the system.Firstly,the current research situation of UPT technology is introduced.The system model and basic working principles of UPT are analyzed.Secondly,a UPT system with cubic piezoelectric transducer for the receiving end is designed for solving the problem of "dead zone"(i.e.,without energy is received because of non-coaxal between the transmitting and receving ends in the traditional disc-shaped structure receiving end when it is implanted into the human body).The effects of the rotational offset on the receiving end of the cubic and disc-shaped structures are qualitatively compared by COMSOL Multiphysics simulation and verified by experiments.The experimental results show that the receiving end of piezoelectric transducer with cubic structure can solve the problem of "dead zone".Finally,the conditions of the UPT system at maximum power transmission are derived,and the impedance transformation network is designed according to this condition.Three different impedance transformation networks,i.e.,LC-type,π-type and T-type,are designed on the transmitting and receiving ends of the system,respectively.The calculation methods of the corresponding matching network parameters are given.Because of few components for the LC-type and consequently less loss to the system in general,the LC-type impedance transformation network with is chosen finally and verified by simulations and experiments.The experimental results show that the output power of the system increased by nearly 10 times after using the matching network.