Systematic analysis and experiment of inductive coupling and induced voltage for inductively coupled wireless implantable neurostimulator application

Abstract

The main strategy for wireless power transfer to implantable devices is to use inductive coupling technology. The induced voltage of implanted devices highly depends on factors such as mutual inductance between the external transmitter coil and the receiver coil, quality factor of the receiver circuit and operation frequency. In this paper, the mutual inductance under a variety of geometries of external coil and under the condition of different vertical distances, lateral displacements and angular misalignments between two coils were theoretically calculated and simulated. To ascertain the condition of maximum power transmission for certain coils’ position requirements, an LC tank (2.7 mm × 2 mm) consisting of a microfabricated gold inductor coil and a small surface mounted capacitor was designed and fabricated as the telemetric part of a neurostimulator. The induced voltage of the LC tank was measured in both air and artificial tissue media under different sizes of power coil and operation frequencies. As a result, the optimum size of a transmitter coil is selected to be of 4 mm inner radius with six turns of coil, while the whole coupling system operates at 94 MHz resonant frequency within 5–11 mm vertical distance, 0–4 mm lateral and 0°–50° angular misalignment between two coils. With the change of the above coils’ positions, the measured induced voltage drops within 30%, satisfying the surgical requirement for neurostimulator implantation.

Optimal Design of Litz Wire Coils With Sandwich Structure Wirelessly Powering an Artificial Anal Sphincter System

“…Previous attempts at design, theoretical analysis, and geometrical optimization of inductive links have been covered extensively (7)(8)(9)(10)(11)(12)(13)(20)(21)(22)(23)(24)(25). However, it is difficult to accurately analyze how a set of coils performs before they are fabricated due to the complexity of estimating the parasitic components and coupling coefficients associated with coils.…”

“…The total induced voltage at the winding position z = d is the sum of the voltage induced at each turn, which can be calculated by integrating the EΦ(r, z) along the winding length as follows: (8) and therefore, the equivalent impedance is…”

“…The former may be further broken down into either rigid or flexible types, which is suited to cases where low power, high frequency, and strict size constraint (intraocular or intracranial space) are required (8,9). The former may be further broken down into either rigid or flexible types, which is suited to cases where low power, high frequency, and strict size constraint (intraocular or intracranial space) are required (8,9).…”

“…Generally, energy coils used in TETS may be grouped into either printed spiral coils (PSC) or filament wire coils. The former may be further broken down into either rigid or flexible types, which is suited to cases where low power, high frequency, and strict size constraint (intraocular or intracranial space) are required (8,9). A typical application example of a flexible PSC fabricated by means of a liquid metal alloy encased in a biocompatible elastomeric substrate is retinal prosthesis systems, which utilize an inductive transfer link wirelessly delivering 100 mW power to the flexible micro-coil implanted inside the eye with 21% PTE (4 MHz) at 12-mm separation (10).…”

Improvement of the Coupling Factor of Litz-Wire Coil Pair With Ferrite Substrate for Transcutaneous Energy Transfer System

“…Generally speaking, two kinds of planar coils have been designed and documented in several researches. The first type is the printed spiral coils (PSC), which may be further broken down into either rigid or flexible types, and such a type is applicable to those cases with requirements of low power, high frequency and strict size constrain (intraocular or intracranial space) [6,7]. One example of a flexible PSC fabricated with a liquid metal alloy encased in a biocompatible elastomeric substrate is the retinal prosthesis system [8].…”