Needle Micro-Coils for MRS

A process for batch fabrication of low-cost needle-shaped microcoils for magnetic resonance spectroscopy (MRS) is demonstrated. The conductors are embedded inside a cross-section designed to avoid the signal cancellation that can occur with a completely immersed coil. Conductors are fabricated on oxidised silicon substrates by electroplating metals inside a deep resist mould, and then capped with a thick layer of epoxy resist. Through-wafer deep reactive ion etching is used to define needle shapes, and die separation is carried out by snap-out. Prototype coils are robust, and sharp enough to puncture model samples of fruit. At 63.8 MHz, Q-factors on Si substrates are comparable to those obtained on glass, and resonators based on single-turn coils have Q-factors of 14. Total immersion¹H MR imaging and spectroscopy are demonstrated in a 1.5 T field using tomato fruits.