Modelling the Generation of the Cochlear Microphonic

<p>The human ear is a remarkable sensory organ. A normal healthy human ear is able to process sounds covering a wide range of frequencies and intensities, while distinguishing between different components of complex sounds such as a musical chord. In the last four decades, knowledge about the cochlea and the mechanisms involved in its operation has greatly increased, but many details about these mechanisms remain unresolved and disputed. The cochlea has a vulnerable structure. Consequently, measuring and monitoring its mechanical and electrical activities even with contemporary devices is very difficult. Modelling can be used to fill gaps between those measurements that are feasible and actual cochlear function. Modelling techniques can also help to simplify complex cochlear operation to a tractable and comprehensible level while still reproducing certain behaviours of interest. Modelling therefore can play an essential role in developing a better understanding of the cochlea. The Cochlear Microphonic (CM) is an electrical signal generated inside the cochlea in response to sound. This electrical signal reflects mechanical activity in the cochlea and the excitation processes involved in its generation. However, the difficulty of obtaining this signal and the simplicity of other methods such as otoacoustic emissions have discouraged the use of the cochlear microphonic as a tool for studying cochlear functions. In this thesis, amodel of the cochlea is presented which integrates bothmechanical and electrical aspects, enabling the interaction between them to be investigated. The resulting model is then used to observe the effect of the cochlear amplifier on the CM. The results indicate that while the cochlear amplifier significantly amplifies the basilar membrane displacement, the effect on the CM is less significant. Both of these indications agree with previous physiological findings. A novel modelling approach is used to investigate the tuning discrepancy between basilar membrane and CMtuning curves. The results suggest that this discrepancy is primarily due to transversal phase cancellation in the outer hair cell rather than longitudinal phase cancellation along the basilar membrane. In addition, the results of the model suggest that spontaneous cochlear microphonic should exist in the cochlea. The existence of this spontaneous electrical signal has not yet been reported.</p>

Modelling the Generation of the Cochlear Microphonic

<p>The human ear is a remarkable sensory organ. A normal healthy human ear is able to process sounds covering a wide range of frequencies and intensities, while distinguishing between different components of complex sounds such as a musical chord. In the last four decades, knowledge about the cochlea and the mechanisms involved in its operation has greatly increased, but many details about these mechanisms remain unresolved and disputed. The cochlea has a vulnerable structure. Consequently, measuring and monitoring its mechanical and electrical activities even with contemporary devices is very difficult. Modelling can be used to fill gaps between those measurements that are feasible and actual cochlear function. Modelling techniques can also help to simplify complex cochlear operation to a tractable and comprehensible level while still reproducing certain behaviours of interest. Modelling therefore can play an essential role in developing a better understanding of the cochlea. The Cochlear Microphonic (CM) is an electrical signal generated inside the cochlea in response to sound. This electrical signal reflects mechanical activity in the cochlea and the excitation processes involved in its generation. However, the difficulty of obtaining this signal and the simplicity of other methods such as otoacoustic emissions have discouraged the use of the cochlear microphonic as a tool for studying cochlear functions. In this thesis, amodel of the cochlea is presented which integrates bothmechanical and electrical aspects, enabling the interaction between them to be investigated. The resulting model is then used to observe the effect of the cochlear amplifier on the CM. The results indicate that while the cochlear amplifier significantly amplifies the basilar membrane displacement, the effect on the CM is less significant. Both of these indications agree with previous physiological findings. A novel modelling approach is used to investigate the tuning discrepancy between basilar membrane and CMtuning curves. The results suggest that this discrepancy is primarily due to transversal phase cancellation in the outer hair cell rather than longitudinal phase cancellation along the basilar membrane. In addition, the results of the model suggest that spontaneous cochlear microphonic should exist in the cochlea. The existence of this spontaneous electrical signal has not yet been reported.</p>

Secrecy Analysis and Error Probability of LIS-aided Communication Systems under Nakagami-m Fading

In this work, we derive the spectral efficiency, secrecy outage probability, and bit error rate of a communication system assisted by a large intelligent surface (LIS). We consider a single-antenna user and an array of antennas at the transmitter side and the possibility of a direct link between transmitter and receiver. Additionally, there is a single-antenna eavesdropper with a direct link to the transmitter, which is modeled as a Nakagami-m distributed fading coefficient. The channels from transmitter to the LIS and from the LIS to the user may or may not have the line-of-sight (LoS) and are modeled by the Nakagami- m distribution. Moreover, we assume that the LIS elements perform non-ideal phase cancellation leading to a residual phase error that assumes a Von Mises distribution. We show that the resulting channel can be accurately approximated by a Gamma distribution whose parameters are analytically estimated using the moments of the equivalent signal-to-noise ratio. We also provide an upper bound for the error probability for M-QAM modulations. With the derived formulas, we analyze the effect of the strength of the LoS link by varying the Nakagami parameter, m.

Design of a miniaturized ultrawideband and low scattering antipodal vivaldi antenna array

This paper presents a miniaturized ultra-wideband (UWB) antipodal Vivaldi antenna (AVA) array with low-scattering characteristics integrated a hybrid diffusive-absorptive metasurface. Periodic elliptical slots at the outer edges and a dielectric lens are utilized for antenna element to improve performances including miniaturized size, wide bandwidth, and high gain. The optimized element is fabricated and measured, the results demonstrate that the − 10 dB impedance bandwidth is 4.5–50 GHz with a ratio bandwidth (fH/fL) of 11.1:1, and the maximum gain at 35 GHz is 12.7 dBi, which are in good agreement with simulation. By loading an optimized Minkowski-shaped metasurface as the ground reflector, which combines the multielement phase cancellation (MEPC) and EM absorption technology, the 4 × 4 array realizes a low radar cross section (RCS) without the radiation performance degradation. Simulated and measured results show that the proposed low-scattering array has a 10-dB RCS reduction band ranging from 5 to 50 GHz at normal incidence for both polarizations. Furthermore, the array structure shows extremely low-observable capability, which is larger than 15 dB of the RCS reduction from 7.1 to 50 GHz with a ratio bandwidth of 7.0:1. The results verify the feasibility of improving the performance of antenna and the UWB low-scattering functionality.

An infrared energy harvester based on radar cross-section reduction of chiral metasurfaces through phase cancellation approach

Conventional metasurface absorbers rely on high dissipation losses by incorporating lossy materials. In this paper, we propose a novel mechanism of absorption based on phase cancellation of polarization states of scattered fields emerging from adjacent L-shaped chiral meta-atoms (unit cells). A linearly polarized wave forms helicoidal currents in each meta-atom leading to diagonally polarized radiated waves. When phase cancellation is employed by reorienting four such meta-atoms in a supercell configuration, contra-directed chiral currents flow in adjacent cells to cancel all the radiated fields in far-field region leading to a minimal broadside radar cross-section. From the reciprocity, the currents that are induced in the meta-atoms produce a null towards the incident direction which can be utilized for infrared energy harvesting. Full wave electromagnetic simulation indicates near perfect resonant absorption around 52.2 THz frequency. Enhanced bandwidth is shown by adding smaller resonators inside the supercell in nested form leading to dual band absorption at 45.2 THz and 53.15 THz.