Coupled Field Circuit Model Of Implantable Devices Energy Delivery Through Volume Conduction

All implantable devices need electricity, power technology is one of the keytechnologies to provide energy security for its reliable operation and influent thefunction, miniaturization and life. So the research on energy delivery process acrossskin tissue efficiently has important academic and medical significance. Althoughbatteries and magnetic induction technology are practical, but the service life of animplantable device powered by a battery is short because of the limited battery capacity,while magnetic inductive conversion efficiency is generally poor due to the conductivebiological tissue and exits strong radio frequency interference. Energy supply throughvolume conduction is a new technology which can avoid the major drawback of existingmethods.In order to simulate the volume conduction system truly, dynamically andintegrally, it is necessary to establish the field-circuit coupling volume conductionmodel.For field-circuit coupled problem with complex boundary conditions，potentialequation and boundary condition formulation of quasi-static electric field problem areexpressed by using scalar voltage potential method. And circuit equation of voltage andcurrent in electrodes is presented. Furthermore, mathematic model of field-circuitcoupled directly is derived．Numerical calculation is adopted here, Finite elementformulation is derived by using Galerkin method as volume conduction．Solution stepsof finite element analysis are given and some of key problems were described in detail.On the basis of field-circuit coupling volume conductive model, this dissertationexplores the relationship between each physical factors and energy transferefficiency.The finite element modes of field-circuit coupling for circular cylinderelectrode have been built. The size and edge distance of electrodes effects on energytransfer efficiency have been investigated. The results show that the impedancedistribution of system is changed by the cross sectional area and spacing of electrode,and the current transfer efficiency increases with the increase of them. The powerparameters effects on energy transfer efficiency have been investigated. The resultsshow that system impedance is changed by power supply frequency, current crossingskin tissue is changed by voltage magnitude, but both of them does not influent thedistribution of system impendence and the energy transfer efficiency. The circuitparameters effects on energy transfer efficiency have been investigated. The results show that when the unit of skin electrode was fixed, engineers could make efforts tomodify the input impedance of the device to adjust current transfer ratio, to modify thepower impedance to adjust voltage transfer ratio, and the theoretical maximum transferratio is achieved by a pure inductance circuit.Loader-changing method based on field-circuit have been proposed to calculationthe lumped parameter of skin-electrode unit, and the network impedance parameters indifferent electrode edge distance, cross sectional area and power supply frequency wereand simulated calculated. Firstly, the skin-electrode unit is equivalently expressed as atwo-port network and the relationship between port voltage and current is established inconsideration of the coupling model does not involve complex circuit calculation in skinelectrode unit. By the use of all phase FFT spectrum analysis, the amplitude and phaseof the power signal is extracted. On this basis, equivalent circuit impedance parametersof the skin electrode unit under various conditions are obtained by the application ofvariable load method and the validity of the method is verified.Based on the calculation of skin electrode unit lumped parameter and the Xequivalent circuit model of skin electrode unit, voltage and current transfer function arederived. By means of concrete circuit data, the influence of voltage transfer ratio by invitro circuit and the influence of current transfer ratio by in vivo circuit impendencewere analyzed, which could be used as the basis of circuit design and evaluating systemperformance.Theoretical analyses and simulation have proved that Volume conduction canprovide another energy transfer technology for implanted devices.