title: Hydrogel microphones for stealthy underwater listening.
abstract: Exploring the abundant resources in the ocean requires underwater acoustic detectors with a high-sensitivity reception of low-frequency sound from greater distances and zero reflections. Here we address both challenges by integrating an easily deformable network of metal nanoparticles in a hydrogel matrix for use as a cavity-free microphone. Since metal nanoparticles can be densely implanted as inclusions, and can even be arranged in coherent arrays, this microphone can detect static loads and air breezes from different angles, as well as underwater acoustic signals from 20 Hz to 3 kHz at amplitudes as low as 4 Pa. Unlike dielectric capacitors or cavity-based microphones that respond to stimuli by deforming the device in thickness directions, this hydrogel device responds with a transient modulation of electric double layers, resulting in an extraordinary sensitivity (217 nF kPa(-1) or 24 μC N(-1) at a bias of 1.0 V) without using any signal amplification tools.
authors.affiliation: State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics and School of Aerospace, Collaborative Innovation Center of Suzhou Nano Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China.|Department of Mechanical and Materials Engineering, University of Nebraska, Lincoln 68588-0526, Nebraska, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Physics and Astronomy, University of Nebraska, Lincoln 68588-0299, Nebraska, USA.|Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln 68588-0298, Nebraska, USA.
authors.forename: Jingfeng
authors.initials: J
authors.lastname: Song
authors.affiliation: Department of Mechanical and Materials Engineering, University of Nebraska, Lincoln 68588-0526, Nebraska, USA.|Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln 68588-0298, Nebraska, USA.
authors.forename: Shumin
authors.initials: S
authors.lastname: Li
authors.affiliation: Center for Biotechnology, University of Nebraska, Lincoln 68588-0665, Nebraska, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Elowsky
authors.affiliation: Center for Biotechnology, University of Nebraska, Lincoln 68588-0665, Nebraska, USA.
authors.forename: You
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Physics and Astronomy, University of Nebraska, Lincoln 68588-0299, Nebraska, USA.|Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln 68588-0298, Nebraska, USA.
authors.forename: Stephen
authors.identifier: 0000-0003-0936-7995
authors.initials: S
authors.lastname: Ducharme
authors.affiliation: State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics and School of Aerospace, Collaborative Innovation Center of Suzhou Nano Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China.
authors.forename: Yong Mei
authors.initials: YM
authors.lastname: Chen
authors.affiliation: Department of Mechanical and Materials Engineering, University of Nebraska, Lincoln 68588-0526, Nebraska, USA.|Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln 68588-0298, Nebraska, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Department of Mechanical and Materials Engineering, University of Nebraska, Lincoln 68588-0526, Nebraska, USA.|Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln 68588-0298, Nebraska, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Tan