Electromagnetic modeling of NMR stripline chips (Advanced Technology / Applied Physics / Electrical Engineering)

Student assignment: Electromagnetic modeling of NMR stripline chips

In previous research the MCS group, in collaboration with the Radboud University in Nijmegen, has developed a microfluidic/microelectronic chip for NMR spectrometry, which operates with less than 1 microliter of liquid sample [1]. The current design of the device consists of a liquid-filled capillary aligned on the stripline electrode, see figure. The operating principle is that the stripline, when an alternating current with radiofrequency (RF) passes through it, generates a magnetic field in the liquid, which rotates and aligns the nuclear spins. When the RF current is switched off, the nuclear spins relax back to their original position (aligned with the main static magnetic field of the NMR system). This relaxation occurs via a precession motion, at the Larmor frequency (the resonance frequency of the spins). This precession is picked up by the stripline because the moving magnetic fields that the spins generate create an alternating current in the stripline. Out of the electrical signal, the resonance frequencies of different spins (with different so-called "chemical shift") are determined via Fourier Transformation, which then gives the NMR spectrum.


The important parameters in the stripline measurements are sensitivity (what is the minimum number of spins that can be detected?) and spectral resolution (how sharp are the peaks in the NMR spectrum?). These parameters are related to the strength and the uniformity of the magnet field that is generated in the liquid sample by the stripline. Experimental results have shown that the choice of the material on which the stripline is positioned can effect the spectral resolution. It is unknown what the exact reason for this material dependence is, and the goal of this assignment is to study this via a 2-dimensional numerical electromagnetic model (COMSOL software).

This assignment consists of the following tasks:

i) study the existing designs and the experimental results that are available, to get acquainted with the stripline principle;

ii) identify which material properties could be relevant for stripline performance;

iii) make a model to calculate electromagnetic behavior of striplines, and perform modeling with different materials


[1] J. Bart et al., A microfluidic high resolution NMR flow probe, Journal of the American Chemical Society 131 (2009) 5014-5015; DOI: 10.1021/ja900389x

Contact information

Han Gardeniers; Email: j.g.e.gardeniers@utwente.nl