Multilayer Systems Driven by Elastic Standing Waves

Abstract

An elastic standing wave propagating in a cubic piezoelectric multilayer structure, parallel to or at an angle with the direction of growth, induces a standing wave of strains, which results in a standing wave of piezoelectric fields. The thickness of each layer is chosen equal to half the wavelength in that layer. This choice corresponds to an even-order zone-center folded acoustic mode with zero minigap. The field will produce an ac voltage signal across the system at the frequency of the wave.We have found that in well-known systems grown along [111] with a thickness of 2 pm per period, the amplitude of the signal induced by a longitudinal standing wave can be of the order of a few volts, for an energy-flux density of 0.1 W/cm2. As an ultrasonic receiver, this system is expected to have higher sensitivity than general transducers. Infrared light modulators operating in the range of GHz are also discussed as a possible application of the same system.

On the Piezoelectric Signals of Multilayer Systems

“…We assume that the two layer thicknesses are not matched to the half wavelengths as in [27], but are related to them through h n kl n /2 where k is a positive constant common to both layers, not to be confused with the wavevectors K n . Thus…”

“…In the present work, the above analysis is extended to ESWs with wavelengths beyond exact matching; it therefore constitutes a generalization of the work in [27]. We invoke the Stokes recurrent relation connecting the generalized reflection coefficients of an interface with those of adjacent interfaces.…”

“…For the same reason, a cubic piezoelectric multilayer system (called the system or MS, from now on) driven by an elastic standing wave (ESW) was proposed in Ref. [27]. In the presence of an ESW in the direction of growth, a standing wave of strains is produced which, via the PZ field, leads to a PZ ac voltage signal across the MS at the driving frequency of the ESW.…”

“…The MS considered in [27] consisted of m periods, with two layers per period (layer thicknesses h 1 , h 2 , thickness per period h h 1 h 2 ). The basic condition in [27] was the exact matching between the ESW wavelength halves l n /2 and the two layer thicknesses h n , n 1,2.…”

“…The basic condition in [27] was the exact matching between the ESW wavelength halves l n /2 and the two layer thicknesses h n , n 1,2. Under this condition, the crests of the ESW occur at the interfaces of adjacent layers; the nodes and the maximum signal occur halfway between successive interfaces.…”