Research Of Midfield Wireless Power Transfer For Microimplants

By the stability and safety,wireless powering could enable the long-term usage of microimplants within the human body.Although the wireless powering can be achieved by both the inductive coupling and magnetic resonance coupling,the devices suffers from the “big” size of receive antennas,while the size is proportional to the wavelength.However,the dielectric loss in tissue begins to play a role at high frequency.We believe that the optimal frequency for wireless power transmission into deep tissue is in the range of 0.5～4.5GHz.First,some basic conceptions and theories were expounded.Secondly,the Cole-Cole relaxation model was substitute into Maxwell equation to get the field pattern of electromagnetic waves in muscle tissue.The air gap between the magnetic dipole and tissue was 1 mm thick.The diameter of dipole was 0.5 mm.Thirdly,the received power was calculated from the electromotive force in the receive coil,which was 50 mm beneath the tissue surface.The diameter of receive coil was 5 mm.Then,the specific absorption rate(SAR)in muscle tissue hemisphere was calculated to figure out the power absorbed by muscle.The radius of the muscle hemisphere was twice the depth of the implanted receiving antenna,and the center was same as the transmitting dipole.The transmission efficiency was defined as the ratio of the received power to the absorbed power.The most efficient frequency was 0.84 GHz for parallel receive coil,and 1.53 GHz for vertical receive coil.Finally,the phased array antenna was designed for vertical receive coil using the magnetic dipole model at 1.53 GHz.Using the genetic algorithm and CST simulation,the phased array antenna was proved to be 2.62 times as efficient as magnetic dipole transmitter.A measurement platform conforming to the IEC62209 standard was built.An adjustable antenna fixture was designed and manufactured.Formulas of biological tissue-equivalent phantoms were list.The optimal frequency for microimplants power transmission was proof by vitro experiments.The round of pork was used as human muscle.The results show that the coil transmitter can be used as a magnetic dipole,and the optimal frequency for midfield wireless power transmission is 0.84 GHz while the receive coil is parallel to the transmitter,and 1.53 GHz while the receive coil is vertical to the transmitter.