Abstract
A coupled resonant acoustic waveguide (CRAW) in a phononic crystal (PnC) was engineered to manipulate the propagation of ultrasonic waves within a conventional phononic bandgap for wavelength division multiplexing. The PnC device included two, forked, distinct CRAW waveguide channels that exhibited strong frequency and mode selectivity. Each branch was composed of cavities of differing volumes, with each giving rise to deep and shallow ‘impurity’ states. These states were utilized to select frequency windows where transmission along the channels was suppressed distinctly for each channel. Though completely a linear system, the mode sensitivity of each CRAW waveguide channel produced apparent nonlinear power dependence along each branch. Nonlinearity in the system arises from the combination of the mode sensitivity of each CRAW channel and small variations in the shape of the incident wavefront as a function of input power. The all-acoustic effect was then leveraged to realize an ultrasonic, spatial signal modulator, and logic element operating at 398 and 450 kHz using input power.
Highlights
Phononic crystals (PnCs), or elastic bandgap materials, are periodic arrangements of scatterers with divergent elastic properties from an ambient medium [1, 2]
The experimental transmission setup is shown in figure 1(c), where an emitter and detector are placed at opposing ends of the coupled resonant acoustic waveguide (CRAW) device
The input is a CRAW based on Model I that is forked into two defect waveguide branches comprised of Models I and II cavities
Summary
Phononic crystals (PnCs), or elastic bandgap materials, are periodic arrangements of scatterers with divergent elastic properties from an ambient medium [1, 2]. The result is the transmission of limited modes and frequencies that would otherwise be forbidden [3, 4] These guided acoustic modes are analogous to guided optical modes in photonic crystals and discrete states in the bandgap of a semiconductor with linear defects [5]. Similar to electromagnetic wave propagation in photonic crystal structures, the propagation of acoustic modes influenced by these localized defect modes in phononic structures can be designed to realize sensors [7], filters and waveguides [8, 9], and acoustic logic elements [10, 11] in the ultrasonic frequency domain
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