Patent ID: 6637268
Filing Date: 2003-10-28
Classification: G01N

Abstract:
A vibration displacement sensing system comprising:a piezoelectric substrate; a first comb-shaped electrode formed on an upper end surface of said piezoelectric substrate; a second comb-shaped electrode formed on said upper end surface of said piezoelectric substrate; a counter electrode formed on a lower end surface of said piezoelectric substrate and in contact with a medium having a material therein; and a signal analyzer, said first- and second comb-shaped electrodes forming an interdigital arrangement, said first comb-shaped electrode and said counter electrode receiving input electric signals, radiating longitudinal waves into said medium along the direction vertical to said lower end surface of said piezoelectric substrate, and making said material reflect said longitudinal waves back, said second comb-shaped electrode and said counter electrode detecting electrical coupled-signals from said input electric signals, respectively, as well as reflected longitudinal waves as delayed electric signals Di (i=1, 2, . . . , n) in accordance with distances Zi (i=1, 2, . . . , n) between said counter electrode and said material which vibrates in response to times Ti (i=1, 2, . . . , n), said signal analyzer causing said electrical coupled-signals and said delayed electric signals Di to interfere respectively, making respective interference signals Ri (i=1, 2, . . . , n), clarifying a relationship between respective amplitudes of said interference signals Ri and said times Ti, and estimating the vibration displacement of said material from the amplitude change of said relationship.