US Patent 7026943 Acoustic wave ice and water detector

An acoustic wave sensor utilizes one or more acoustic waves trapped in an acoustic wave cavity to detect the presence of one or more substances on a surface of the acoustic wave cavity. To detect the presence of ice, a trapped torsional acoustic wave is used. To detect water, an acoustic wave with flexural or compressional components is used. The sensor includes a number of transducers adjacent the acoustic wave cavity where a controller drives different sets of the transducers to generate different acoustic waves.