Tunable ultrasonic phononic crystal controlled by infrared radiation

• Published in: Applied physics letters Vol. 105; no. 14
• Main Authors: Walker, Ezekiel, Reyes, Delfino, Rojas, Miguel Mayorga, Krokhin, Arkadii, Wang, Zhiming, Neogi, Arup
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 06.10.2014
• Subjects: Applied physics; Banded structure; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CRYSTALS; CYLINDERS; FILTERS; Forbidden bands; Hydrogels; Infrared filters; INFRARED RADIATION; Isopropylacrylamide; Periodic structures; PHYSICAL PROPERTIES; POLYMERS; REFRACTIVE INDEX; STIMULATION; STIMULI; TRANSMISSION; ULTRASONIC WAVES; Wave propagation
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4894489

A tunable phononic crystal based ultrasonic filter was designed by stimulating the phase of the polymeric material embedded in a periodic structure using infrared radiation. The acoustic filter can be tuned remotely using thermal stimulation induced by the infrared radiation. The filter is composed of steel cylinder scatterers arranged periodically in a background of bulk poly (N-isopropylacrylamide) polymer hydrogel. The lattice structure creates forbidden bands for certain sets of mechanical waves that cause it to behave as an ultrasonic filter. Since the bandstructure is determined by not only the arrangement of the scatterers but also the physical properties of the materials composing the scatterers and background, modulating either the arrangement or physical properties will alter the effect of the crystal on propagating mechanical waves. Here, the physical properties of the filter are varied by inducing changes in the polymer hydrogel using an electromagnetic thermal stimulus. With particular focus on the k00-wave, the transmission of ultrasonic wave changes by as much as 20 dBm, and band widths by 22% for select bands.