Phase tracking algorithms detect both real and imaginary components of outer hair cell nonlinear membrane capacitance that exhibits dielectric loss.

Outer hair cell (OHC) nonlinear membrane capacitance (NLC) represents voltage-dependent sensor charge movements within prestin (SLC26a5) that drive OHC electromotility. Dielectric loss, a shift in charge movement phase from purely capacitive to resistive, is likely indicative of prestin interaction with the viscous lipid bilayer and has been suggested to correspond to prestin power output. The frequency response of NLC in OHC membrane patches has been measured with phase tracking and complex capacitance methodologies. While the latter approach can directly determine the presence of dielectric loss by assessing charge movement both in and out of phase with driving voltage, the former has been suggested to fail in this regard. Here we show that standard phase tracking in the presence of dielectric loss does indeed register this loss. Such estimates of NLC correspond to the absolute magnitude of complex NLC, indicating that total charge movement regardless of phase is assessed, thereby validating past and present measures of NLC frequency response that limits its effectiveness at high frequencies. This observation has important implications for understanding the role of prestin in cochlear amplification.

Study of a Nonlinear Membrane Absorber Applied to 3D Acoustic Cavity for Low Frequency Broadband Noise Control

As a new approach to passive noise control in low frequency domain, the targeted energy transfer (TET) technique has been applied to the 3D fields of acoustics. The nonlinear membrane absorber based on the TET can reduce the low frequency noise inside the 3D acoustic cavity. The TET phenomenon inside the 3D acoustic cavity has firstly investigated by a two degrees-of-freedom (DOF) system, which is comprised by an acoustic mode and a nonlinear membrane without the pre-stress. In order to control the low frequency broadband noise inside 3D acoustic cavity and consider the influence of the pre-stress for the TET, a general model of the system with several acoustic modes of 3D acoustic cavity and one nonlinear membrane is built and studied in this paper. By using the harmonic balance method and the numerical method, the nonlinear normal modes and the forced responses are analyzed. Meanwhile, the influence of the pre-stress of the nonlinear membrane for the TET is investigated. The desired working zones of the nonlinear membrane absorber for the broadband noise are investigated. It can be helpful to design the nonlinear membrane according the dimension of 3D acoustic cavity to control the low frequency broadband noise.

Noise Reduction in an Acoustic Cavity Using a Nonlinear Membrane Driven by an Electroacoustic Device

In this paper an electro-Acoustic Nonlinear Absorber (ANLA) is described. It is composed of a baffled nonlinear membrane with its front face coupled to an acoustic cavity and the other one enclosed. The enclosure includes a feedback loop composed of a microphone and a loudspeaker that control the acoustic pressure seen by the rear face of the membrane. Due to the nonlinear geometrical properties of the membrane, the ANLA can synchronize it resonance with one of the resonances of the cavity. It allows to bring out the energy transfer toward the ANLA and thus to reduce pressure in the cavity. The feedback loop tunes the resonance frequency of the ANLA at low level, wich is a key factor for the triggering threshold of the targeted energy transfer. An numerical study of the efficiency of the ANLA to reduce noise in a cavity is presented including the influence of the feedback loop parameters.