One aspect of the invention relates to a composite member for a resonator having an active piezoelectric element and a passive piezoelectric element. The active piezoelectric element causes the resonator to vibrate and detects the frequency of the vibration. The passive piezoelectric element changes...http://www.google.es/patents/US6943484?utm_source=gb-gplus-sharePatente US6943484 - Tunable piezoelectric micro-mechanical resonator
