Patent ID: 7647814

Claim:
An environment difference detector, comprising: an elastic surface wave element equipped with a substrate including a surface having at least one annular and circular path along which a surface acoustic wave circulates, a surface acoustic wave exciting/receiving unit exciting a surface acoustic wave along the circular path and receiving the surface acoustic wave excited and circulated along the circular path, and a sensitive film disposed on at least one part of the circular path to change an elastic nature in accordance with a predetermined change in an adjacent environment; a speed/intensity measuring unit measuring a circulating speed and intensity of the surface acoustic wave from an electric signal generated by the surface acoustic wave exciting/receiving unit when the surface acoustic wave exciting/receiving unit receives the surface acoustic wave circulating along the circular path; and an environment evaluation unit evaluating the predetermined change in the environment adjacent to the sensitive film from at least one of the circulating speed and the intensity measured by the speed/intensity measuring unit, wherein the speed/intensity measuring unit measures the circulating speed from the electric signal by using at least one of circulating speed corresponding values selected from a group including a phase shift of the surface acoustic wave circulated along the circular path, a delay time of the circulated surface acoustic wave, and a resonance frequency of the circulated surface acoustic wave at which the vibration intensity of the circulated surface acoustic wave becomes maximum, the predetermined change of the environment to be measured includes a plurality of ranges, and the environment evaluation unit uses at least one of the circulating speed and the intensity, which is most suitable to evaluate the predetermined change in each of the ranges of the predetermined change of the environment to be measured.