Three novel methods for acoustic nonlinearity parameter B/A imaging in reflection mode are developed in this paper. They are: (1) the acoustic nonlinearity parameter B/A tomography by detecting reflective second harmonic wave, (2) the B/A tomography in reflection mode via the measurement of the difference frequency wave generated by a parametric array, and (3) the C-scan imaging of B/A via the measurement of the echo second-harmonic signal. A theoretical analysis and the experimental imaging of normal and pathological biological tissues by using these methods are also present and discussed. Results show that using the acoustic nonlinearity parameter imaging we can more easily distinguish the diseased tissue from the normal one than using the linear acoustic parameters.

Acoustic carpet cloak in air has become an attractive topic in the past few years and has been realized in many feasible ways. However, underwater acoustic carpet cloak still suffers from lacking operator flexibility. Inspired by those works before, we design an impedance matching underwater acoustic carpet cloak using pentamode materials under normal incidence. The carpet cloak employs an effective velocity lower than water to restore the distorted reflected waves and its effective density is tuned to guarantee impedance matching with water. It is also demonstrated that a cloaked area with a higher height can be formed by simply using more microstructures in the cloak. Simulation results depict that the proposed carpet cloak has a great performance in a wide range of frequency. Our investigation may have potential applications in simplifying the underwater acoustic carpet cloak design.

LI Xiao-rong(% ?&)2, CHEN Xi(K#)l, ZHANG Qin-lan(%Fg)2