NOISE THEORITICAL INVESTIGATIONS FOR TRI-DIMMENSIONAL NMR CIRCUIT: TOWARDS THE NANOSCALE

Abstract

In recent years, NMR/MRI portable devices have drawn attention of numerous researcher teams. They are used for variety of applications, from medical diagnosis to archaeological analysis, nondestructive material testing evaluation of water presence in building materials and food emulsions. Different magnets designs have been proposed by many groups of research. They can be divided into two groups: the magnets ex-situ and the magnets in situ .The first group has the simple configuration with the sensitive volume near their surface and the samples under test are located outside the magnets. Thus, they can be used for the experimental investigation of objects with any dimension. Although the ex-situ magnets have simple shape and light weight, they are difficult to achieve in terms of homogeneity of the magnetic field in the sensitive volume. 
 In comparison, the in-situ magnets have their static field reinforced inside their bore center and canceled outside of the structure. Thus, their magnetic field is roughly homogeneous inside the structure. 
 But drawbacks still exist and can be amplified, especially the in depth problem of Signal/Noise. Calculations, in a microscopic point of view, are develop, first applied to resistances and inductances imbedded in this circuit. 
 Before, from any point source, we calculate the impedance spreading out. For this, our approach is using Transmission Line Model, over or into a multi-layered substrate; it can be also derived by solving Poisson's equation analytically to obtain the associated Green’s kernel. We implement our algorithms in MATLAB. Thus, it permits to extract impedances between any two embedded contacts, real or virtual, of any shape or thickness.