Design and Assessment of Phononic Crystals for Controlling Ultrasonic Wave via Optical Measurement Method

Using an optical visualization technique, we experimentally measure ultrasonic propagation in phononic crystals consisting of a two-dimensional square array of copper wires in the water. Two different phononic crystals are designed and fabricated to exhibit waveguiding property and negative refraction of an ultrasonic wave at 200 kHz. The Fresnel diffraction method is employed to directly visualize intensity profile of the wavefront propagating in the phononic crystals, proving waveguiding and negative refraction of the ultrasonic wave. Non-invasive time-resolved imaging of an ultrasonic wave in artificial acoustic structures is thereby demonstrated, paving the way toward an efficient device design for an advanced ultrasonic wave control.