An AT cut quartz crystal resonator has an unbalanced electrode geometry to induce a particularly strong electrical field in a surface of the resonator adjacent a medium. The electrical field will interact with ions and dipoles in the medium and may be used to accurately and repeatably measure the electrical...http://www.google.ca/patents/US5455475?utm_source=gb-gplus-sharePatent US5455475 - Piezoelectric resonant sensor using the acoustoelectric effect
