Research On Wireless Power And Information Transfer For Body Area Network

Body area network(BAN)is a wireless network composed of the human body and related network elements.Wearable and implantable medical devices are important parts of the BAN.With the increase of their number and functions,the total energy consumption of the BAN increases.In addition,to make the human body comfortable,the battery size of the implanted device needs to be reduced as much as possible,which leads to a further reduction in battery life and increase in replacement surgeries.Therefore,relying on energy-saving technology to reduce the power consumption and extend the battery life cannot solve the problem completely.So,it is necessary to find a new power supply method to meet the growing power demands of the BAN.On the other hand,the wireless communication function of the BAN also improves,with new difficulties and challenges follow.Due to the limitation of their volume and energy consumption,some implantable devices cannot use the existing communication technology for uplink communication.Hence,it is required to introduce new communication technology to realize uplink communication function for those devices.In order to shrink or even completely remove the battery without compromising the utilization of the device,wireless power transfer(WPT)technology is being applied to the BAN in this dissertation.Meanwhile,the principle and implementation method of existing communication technology are studied and a new communication scheme is proposed in this dissertation to help the implants realizing the uplink communication with other devices in vitro or in vivo.The main contributions and innovations of this dissertation are listed as follows:(1)According to the characteristics and requirements of WPT system in BAN,two compensation networks with good interoperability and security are determined.In order to select suitable compensation networks for the BAN,nine compensation networks combined with S-type,P-type and LC-type circuits are fully studied.The mathematical models of these networks are established and their characteristics are analyzed with coupling coefficient and load change.Besides,the risks of overvoltage and overcurrent in these networks are studied when abnormal conditions occur.Finally,LC-LC and LC-S compensation networks,which have good interoperability and security,are recommended for the BAN.(2)In order to have a large current through transmitting(Tx)coil to establish the magnetic field only with low power supply,this dissertation proposes a design combining boost inverters(Z-source inverter and interleave Buck/Boost inverter)with WPT system,which can realize the efficient boost function,reduce the difficulties and complexity of the control,and further improve the safety.This dissertation analyzes the output characteristics of the boost inverter under different control algorithms,studies and solves the problem that the inverter works abnormally after it is connected to the resonant networks connected at its back end,and puts forward the design guidance on auxiliary inductors and compensation capacitors.On the receiving(Rx)side,a semi-active rectifier is proposed and used to realize the power control of the receiver itself.(3)A wireless information transfer(WIT)scheme based on pulsed magnetic field(PMF)technology was proposed for the implants to transmit the information through long distance with low energy available.In order to reduce the size of the device,the scheme uses one pair of coils for power and information transmission.A new pulsed magnetic Field(PMF)generator with tapped coil is designed in this paper.The energy in a capacitor of PMF device is passed through the tapped coil to generate a high-intensity pulsed magnetic field(PMF)that oscillates at the same frequency as the WPT power transmission carrier.Therefore,it can affect the voltage and current on Tx side over the same WPT channel,realizing wireless information transmission.Compared with the load shift keying(LSK)method,the PMF method can significantly improve the signal strength and transmission distance.(4)In order to facilitate the implantation and obtain efficient energy transmission when the coil is wrapped around the outside of the columnar tissue in the body,a double-helix(DH)coil is designed in this dissertation.By modeling analysis and simulation experiments,it is proved that DH coil is more suitable for implantable device to transfer energy than the traditional solenoid coil.On the basis of this research,a DH coil is further upgraded to the structure with a tap,which can be used not only for receiving energy,but also for sending signals in the PMF scheme.Finally,the prototype was designed and manufactured,and the simulation and experiment were carried out to verify the correctness of the theoretical analysis and the feasibility of the design scheme.