Study of two contact-less tuning principles for small monolithic radiofrequency MRI coils and development of an automated system based on piezoelectric motor

•Two contact-less tuning principles for small monolithic NMR coils were studied.•The coil can be tuned up or down over a large frequency range.•Piezoelectric-based automated system was built to implement the tuning principles.•The automated system allows real-time tuning during an MRI experiment.•MRI compatibility of the automated system was validated by imaging experiment.