title: Acoustic Coherent Perfect Absorbers as Sensitive Null Detectors.
abstract: We report the experimental realization of acoustic coherent perfect absorption (CPA) of four symmetric scatterers of very different structures. The only conditions necessary for these scatterers to exhibit CPA are that both the reflection and transmission amplitudes of the scatterers are 0.5 under one incident wave, and there are two collinear and counter-propagating incident waves with appropriate relative amplitude and phase. Nearly 1000 times in the modulation of output power has been demonstrated by changing the relative phase of the incident waves over 180°. We further demonstrate that these scatterers could potentially be sensitive devices to detect the small differences between two nearly equal incident waves. A 27% change in the strength of the scattering wave has been demonstrated for every degree of phase deviation from the optimum condition between the incident waves.
authors.affiliation: Department of Physics, the Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong, China.
authors.forename: Chong
authors.initials: C
authors.lastname: Meng
authors.affiliation: Department of Physics, the Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong, China.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Physics, the Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong, China.
authors.forename: Suet To
authors.initials: ST
authors.lastname: Tang
authors.affiliation: Department of Physics, the Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong, China.
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Physics, the Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong, China.
authors.forename: Zhiyu
authors.initials: Z
authors.lastname: Yang