US Patent 7184898 Contact sensitive device

A contact sensitive device includes a member capable of supporting bending waves and a plurality of sensors mounted on the member for measuring bending wave vibration in the member. The sensors measure the bending wave signals and by calculating a phase angle for each measured bending wave signal and a phase difference between the phase angles of at least two pairs of sensors so that at least two phase differences are calculated, the location of the contact can be determined.