Near-field Image Transfer by Magneto-Inductive Arrays: a Modal Perspective

TL;DR

This paper presents an analytical model for near-field image transfer using magneto-inductive arrays, revealing conditions for effective imaging, the impact of array size, and the importance of operating frequency for fidelity and resolution.

Contribution

It introduces a modal analysis approach to model pixel-to-pixel image transfer in magneto-inductive arrays, providing explicit expressions for imaging parameters and conditions for successful transfer.

Findings

Out-of-band excitation enables image transfer.

Array size must exceed the image size by at least the point spread function.

Imaging fidelity depends on operating frequency and array dimensions.

Abstract

A simple model of near-field pixel-to-pixel image transfer using magneto-inductive arrays is presented. The response of N-dimensional rectangular arrays is first found as an excitation of eigenmodes. This analytical method involves approximating the effect of sources and detectors, and replaces the problem of solving large numbers of simultaneous equations with that of evaluating a sum. Expressions are given for the modal expansion coefficients, and in the low-loss case it is shown that the coefficient values depend only on the difference in reciprocal frequency space of the operating frequency from the resonant frequency of each mode. Analytic expressions are then derived for quasi-optical quantities such as the spatial frequency response, point-spread function and resolving power, and their implications for imaging fidelity and resolution are examined for arrays of different dimension. The results show clearly that there can be no useful image transfer for in-band excitation. Out-of-band excitation allows image transfer. Provided the array is larger than the expected image by at least the size of the point spread function, the effect of the array boundaries may be ignored and imaging is determined purely by the properties of the medium. However, there is a tradeoff between fidelity and throughput, and good imaging performance using thick slabs depends on careful choice of the operating frequency. The approximate analytic method is verified by comparison of exact numerical solution.