Piezoelectric-controlled tuning capacitor for surface coils.

The design of a piezoelectric-controlled trimmer capacitor and its use as a tuning element of an MRI surface coil at 63.8 MHz are described. It is found that image quality does not depend strongly on match of the coil to the transmission line but that tuning can be a significant factor. The work is intended to lead eventually to an automatic frequency control circuit in which the capacitor serves as the active element in holding the resonant frequency of the nuclei and the resonant frequency of the coil in coincidence.