Two-Port Networks to Model Galvanic Coupling for Intrabody Communications and Power Transfer to Implants

Abstract

Galvanic coupling, or more precisely, volume conduction, can be used to communicate with and to transfer power to electronic implants. Since no bulky components for power, such as coils or batteries, are required within the implants, this strategy can yield very thin devices suitable for implantation by injection. To design the circuitry of both the implants and the external systems, it is desirable to possess a model that encompasses the behavior of these circuits and also the volume conduction phenomenon. Here we propose to model volume conduction with a two-port network so that the whole system can be studied in circuit simulators. The two-port network consists only of three impedances whose values can be obtained through simple measurements or through numerical methods. We report a validation of this modeling approach in a geometrically simple in vitro setup that allowed us to determine the impedances of the two-port network not only by performing measurements or through a finite element method study but also through an analytical solution.

A Wireless Power Method for Deeply Implanted Biomedical Devices via Capacitively Coupled Conductive Power Transfer

“…6. The result is consistent with what has been reported for volume conduction in [21]; however, the proposed model is a Pi equivalent network rather than a T network. This indicates that the capacitive coupling does not change the fundamental power transfer mechanism of volume conduction.…”

Powering electronic implants by high frequency volume conduction: in human validation

“…Experimental measurements versus computational model. The transmission channel formed by the band electrodes, the tissues and the needle electrodes was modeled as a two-port impedance network (see Figure 3a) 44 . The impedance (Z) parameters of the network were numerically computed using the 3D computational model of the limb obtained after segmenting the MRI images.…”

Injectable Sensors Based on Passive Rectification of Volume-Conducted Currents

“…where V 1 is the voltage across the two external electrodes (i.e., v ex ) and V 2 is the voltage across the implant electrodes (i.e., v implant ), I 1 is the current through the two external electrodes and I 2 is the current through the implant [22]. For the sake of simplicity, the impedances in the two-port network can be substituted by resistances so that…”

“…This can be done experimentally (i.e. applying signals and performing measurements), by means of numerical modeling and, in some simple cases, by means of analytical expressions [22]. For instance, for R 22 (i.e.…”

“…where σ is the conductivity of the medium [24]. As explained in [22], once the network model for the coupling between the external electrodes and the implant electrodes is obtained, the behavior of any circuit topology-including those that are non-linear -for the implant or for the external system can be easily studied with the help of circuit simulators. For that, the T or π models of the two-port network can be employed.…”