Broadband sound sink/absorber via a structure with deep sub-wavelength thickness is of great and continuing interest in physics and engineering communities.An intuitive technique extensively used is to combine compone...Broadband sound sink/absorber via a structure with deep sub-wavelength thickness is of great and continuing interest in physics and engineering communities.An intuitive technique extensively used is to combine components(resonators)with quasi-perfect absorption to piece together a broad absorbing band,but the requirement of quasi-perfect absorption substantially places a very strict restriction on the impedance and thickness of the components.Here,we theoretically and experimentally demonstrate that a compact broadband acoustic sink that quasi-perfectly absorbs broadband arriving sound waves can be achieved with coherently coupled‘‘weak resonances"(resonant sound absorbing systems with low absorption peaks).Although each component exhibits rather low absorption peak alone,via manipulating the coherent coupling effect among the components,they collectively provide a remarkably improved performance over a wide frequency range with a significantly compressed thickness.To illustrate the design principle,a hybrid metasurface utilizing the coaction of parallel and cascade couplings is presented,which possesses an average absorption coefficient of 0.957 in the quasi-perfect band(a>0:9)from 870 to 3224 Hz with a thickness of only 3.9 cm.Our results open new avenues for the development of novel and highly efficient acoustic absorbers against low frequency noise,and more essentially,suggest an efficient approach towards on-demand acoustic impedance engineering in broadband.展开更多
We design an asymmetric transmission system(ATS)with two flat acoustic metasurfaces(AMs)to yield bidirectional asymmetric acoustic focusing(BAAF).The acoustic waves could be focused on both sides of the ATS with diffe...We design an asymmetric transmission system(ATS)with two flat acoustic metasurfaces(AMs)to yield bidirectional asymmetric acoustic focusing(BAAF).The acoustic waves could be focused on both sides of the ATS with different focal lengths and intensities.To achieve high intensity energy concentration,the accelerating acoustic beams are selected to realize the BAAF.The working bandwidth of the BAAF based on our ATS could reach ～0.4 k Hz.It is found that by adjusting the distance between two flat AMs,the focal length and intensity of the bidirectional focusing could easily be modulated.Because the distance between two flat AMs is large enough,the BAAF even could be converted into a unidirectional acoustic focusing.The proposed BAAF may find applications in non-destructive evaluation,biomedical imaging and medical diagnosis.展开更多
基金supported by the National Natural Science Foundation of China(11704284 and 11774265)the Young Elite Scientists Sponsorship by CAST(2018QNRC001)+2 种基金the Shanghai Science and Technology Committee(18JC1410900)the Shanghai Pujiang Program(17PJ1409000)the Stable Supporting Fund of Acoustic Science and Technology Laboratory.
文摘Broadband sound sink/absorber via a structure with deep sub-wavelength thickness is of great and continuing interest in physics and engineering communities.An intuitive technique extensively used is to combine components(resonators)with quasi-perfect absorption to piece together a broad absorbing band,but the requirement of quasi-perfect absorption substantially places a very strict restriction on the impedance and thickness of the components.Here,we theoretically and experimentally demonstrate that a compact broadband acoustic sink that quasi-perfectly absorbs broadband arriving sound waves can be achieved with coherently coupled‘‘weak resonances"(resonant sound absorbing systems with low absorption peaks).Although each component exhibits rather low absorption peak alone,via manipulating the coherent coupling effect among the components,they collectively provide a remarkably improved performance over a wide frequency range with a significantly compressed thickness.To illustrate the design principle,a hybrid metasurface utilizing the coaction of parallel and cascade couplings is presented,which possesses an average absorption coefficient of 0.957 in the quasi-perfect band(a>0:9)from 870 to 3224 Hz with a thickness of only 3.9 cm.Our results open new avenues for the development of novel and highly efficient acoustic absorbers against low frequency noise,and more essentially,suggest an efficient approach towards on-demand acoustic impedance engineering in broadband.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11704193,11674175,and 11704192)the "333" Project of Jiangsu Province,China(Grant No.BRA2017451)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX18_1185)
文摘We design an asymmetric transmission system(ATS)with two flat acoustic metasurfaces(AMs)to yield bidirectional asymmetric acoustic focusing(BAAF).The acoustic waves could be focused on both sides of the ATS with different focal lengths and intensities.To achieve high intensity energy concentration,the accelerating acoustic beams are selected to realize the BAAF.The working bandwidth of the BAAF based on our ATS could reach ～0.4 k Hz.It is found that by adjusting the distance between two flat AMs,the focal length and intensity of the bidirectional focusing could easily be modulated.Because the distance between two flat AMs is large enough,the BAAF even could be converted into a unidirectional acoustic focusing.The proposed BAAF may find applications in non-destructive evaluation,biomedical imaging and medical diagnosis.
