First experimental demonstration of broadband acoustic invisibility cloak
Our work entitled “Broadband Acoustic Cloak for Ultrasound Waves” has potential significant impact in fundamental understanding of manipulation and control of acoustic waves with engineered materials.
In the past few years, study of novel acoustic device based on transformation optics design gained strong momentum from the promising applications of their electromagnetic counterpart. For example, acoustic shielding cloak based on coordinate transformation are theoretically proposed to reduce the shadowing and scattered waves and thus limiting the visibility of hidden object under sonar detection. However, due to the complexity of the building blocks involved in this anisotropic metamaterial with spatial gradient, most of the proposed designs of acoustic elements are narrow band and solely studied in numerical ways.
In this work, we constructed for the first time, an acoustic cylindrical cloak using a two dimensional network of acoustic circuit elements. Because the cloak is synthesized from a set of nonresonant units, the acoustic metamaterial cloak is highly transparent (loss ~ 6dB/m) to the underwater ultrasound waves. Our experimental results clearly indicate a broad frequency band of underwater ultrasonic waves can be bent and guided through the acoustic metamaterial cloak. As a result, the measured visibility of the hidden object is significantly reduced for underwater sonar. Because of the small size of the elements (about 1/10 of wavelength), it promises novel strategies of camouflage and shielding for navel research applications. Moreover, our approach offers the possibility for a variety of compact and miniature novel acoustic devices based on conformal mapping, with potential applications in medical imaging and noise control.
