Though the initial concept of the face-mounted resonator was ahead of
fabrication technology, the solidly-mounted resonator (SMR) is now a
practical resonator design yielding high Qs in a space-efficient and
robust mounting configuration. An agile tunable piezoelectric SMR is now
provided with a resonator and alternating stacks of high mechanical
impedance and low mechanical impedance, piezoelectric layers
advantageously stacked on a substrate with the piezoelectric layers
connected to an adaptive circuit that alternates with an external
electrical impedance having values anywhere between an open circuit and a
short circuit. The piezoelectric Bragg stacks with alternating layers of
high and low mechanical impedance and properties made variable via the
additional piezoelectric properties of the stack materials overcomes
difficulties caused by the limitations of manufacturing techniques,
acoustic power leakage and inability to meet the single-frequency,
quarter-wavelength criterion due to manufacturing deviations.