Design and simulation of a RF coil for a dedicated low-field MRI system

Magnetic resonance imaging (MRI) has not yet been exploited for on-line quality control of agricultural and food products. For such applications, the RF coil is a major part of the system which must satisfy not only to usual MRI criterions but also to mechanical constraints (conveyors). The classical structure of an optimized solenoid coil as proposed by Hoult [1] is well adapted to on-line quality control of oranges. However, we show by calculations and measurements that even at our low working frequency (15 MHz) the stray capacitance of the optimized coil is greater than the tuning capacity. In order to obtain the required homogeneity we have carried out the design and numerical simulation of a variable step solenoid. We show that the obtained homogeneity is enhanced compared to a constant step solenoid.