Adjustable Acoustic Delay Line as a Phase Shifter

An acoustic delay line consisting of two Y–X-cut lithium niobate plates 0.2 mm thick placed on top of each other was experimentally investigated. An interdigital transducer is located at the edge of each plate. An rf voltage (pulsed or continuous-wave) is fed to one transducer, which excites a piezoelectrically active acoustic wave with transverse–horizontal polarization propagating in the first plate. The electric field of this wave penetrates the second plate to excite an acoustic wave therein, which is converted into an electrical signal using the second interdigital transducer. The phase and delay time of the output signal can be changed by varying the distance between the transducers by shifting one plate relative to the other.