A 0.9 V 96 μW Fully Operational Digital Hearing Aid Chip

A 0.9 V 96 muW fully operational low-power digital hearing aid chip is proposed and implemented. An internal status controller is introduced to achieve full operation of the adaptive-SNR analog front end. Dedicated DSP with an additional volume control parameter eliminates any internal overflow and enables the hearing aid to be customized for each individual user. When the input audio band is split into a low band and a high band, the audio signal can be processed coarsely. In addition, fine processing of the high-band signal can be obtained with a low-power automatic gain control (AGC) comprising a digital comparator and a subtraction unit. A heterogeneous Sigma-Delta DAC reduces the power consumption of the interpolation filter without degrading performance by allowing different frequencies between the input signal and the sampling clock of the Sigma-Delta modulator. Compared with a conventional Sigma-Delta DAC, the heterogeneous Sigma-Delta DAC reduces the power dissipation by 40.4% and the area occupation by 40.5%, and it has a reported error rate of only 0.16%. The fabricated chip achieves a 79 dB peak SNR with 4.1 muVrms of input-referred noise voltage. The core area is 2.8 mm x 1.1 mm in a 0.18 mum standard CMOS process.     

Chiral Stereoisomer Engineering of Electron Transporting Materials for Efficient and Stable Perovskite Solar Cells

A series of chiral stereoisomers of electron transporting materials with two chiral substituents is rationally designed and synthesized, and the influence of stereoisomerism on their physical and electronic properties is investigated to demonstrate highly efficient and stable perovskite solar cells (PSCs). Compared to mesomeric naphthalene diimide (NDI) derivatives, which have heterochiral side groups with centrosymmetric molecular packing of symmetric‐shaped conformers in the crystalline state, enantiomeric NDI derivatives have homochiral side groups that exhibit non‐centrosymmetric molecular packing of asymmetric‐shaped conformers in the crystalline state and exhibit better solution processability based on one order of magnitude higher solubility. A similar trend is observed in different rylene diimide stereoisomers based on larger semiconducting core perylene diimide. The PSCs based on NDI enantiomers with good film‐forming ability and a very high lowest phase transition temperature (T_lowest) of 321 °C exhibit a high and uniform average power conversion efficiency (PCE) of 19.067 ± 0.654%. These PSCs also have a high temporal device stability, with less than 10% degradation of the PCE at 100 °C for 1000 h without encapsulation. Therefore, chiral stereoisomer engineering of charge transporting materials is a potential approach to achieve high solution processability, excellent performance, and significant temporal stability in organic electronic devices.     

Multi‐band Approach to Deep Learning‐Based Artificial Stereo Extension

In this paper, an artificial stereo extension method that creates stereophonic sound from a mono sound source is proposed. The proposed method first trains deep neural networks (DNNs) that model the nonlinear relationship between the dominant and residual signals of the stereo channel. In the training stage, the band‐wise log spectral magnitude and unwrapped phase of both the dominant and residual signals are utilized to model the nonlinearities of each sub‐band through deep architecture. From that point, stereo extension is conducted by estimating the residual signal that corresponds to the input mono channel signal with the trained DNN model in a sub‐band domain. The performance of the proposed method was evaluated using a log spectral distortion (LSD) measure and multiple stimuli with a hidden reference and anchor (MUSHRA) test. The results showed that the proposed method provided a lower LSD and higher MUSHRA score than conventional methods that use hidden Markov models and DNN with full‐band processing.     

Indicator Sensor Development and Fuel Cell Degradation Imaging

Although extensive research has been conducted, understanding the exact phenomena occurring during the operation of polymer electrolyte fuel cells (PEFCs) remains difficult. This research attempted to identify new reasons for the reduced performance of PEFC using an imaging technique. To begin with, H⁺ and OH⁻ indicator sensors, which display red, blue, and green values (RGB) using digital microscopes, are developed and attached to each electrode of a membrane electrode assembly to enable quantitative analysis of ion generation. The proposed reaction in the fuel cell can be confirmed, and various reactions occurring in the electrode can be examined using this approach. In particular, H⁺ is generated at the anode and cathode of the anion exchange membrane fuel cell, which is found to be a major cause of performance deterioration.     

A high-yield fabrication process for silicon neural probes

There is a great need for silicon microelectrodes that can simultaneously monitor the activity of many neurons in the brain. However, one of the existing processes for fabricating silicon microelectrodes-reactive-ion etching in combination with anisotropic KOH etching-breaks down at the wet-etching step for device release. Here we describe a modified wet-etching sidewall-protection technique for the high-yield fabrication of well-defined silicon probe structures, using a Teflon shield and low-pressure chemical vapor deposition (LPCVD) silicon nitride. In the proposed method, a micro-tab holds each individual probe to the central scaffold, allowing uniform anisotropic KOH etching. Using this approach, we obtained a well-defined probe structure without device loss during the wet-etching process. This simple method yielded more accurate fabrication and an improved mechanical profile.     

Studies on the performance characteristics and improvements of the piezoelectrically-driven micro gas compressors

This study presents the main characteristics of a micro gas compressor produced by microfabrication techniques on silicon wafers. The compressor consists of a compression chamber, check valves and a silicon membrane where the piezoelectric bimorph actuator is installed. Compressor performance was investigated under various working conditions of input voltage and frequency to the actuator at several downstream back pressures. Volume stroke ratio is a critical parameter for gas compressors. However, micro actuators do not generally produce large displacement, so the volume stroke ratio of the micro compressor is expected to be significantly less than that of conventional mechanical compressors. Therefore, the possibility of using dual compression was also investigated in order to improve micro compressor performance. The performance of the micro compressor is evaluated in this study through experiments and simulation.     

Timely Effective Handover Mechanism in Heterogeneous Wireless Networks

Next-generation wireless networks should be able to coordinate and integrate different communication systems. It has been a challenging problem to support a seamless handover in these diverse wireless network environments. Link level triggers can provide information about events which can help handover decision and layer 3 entities better streamline their handover related activities. In most conventional layer 2 triggering approaches, a pre-defined threshold for a specific perspective such as the received signal strength is used. This may cause too late or too early handover executions. In this paper we propose a new predictive handover framework that uses the neighbor network information to generate timely the link triggers so that the required handover procedures can appropriately finish before the current link goes down. First we estimate a required handover time for the given neighbor network conditions, then using a predictive link triggering mechanism the handover start time is dynamically determined to minimize handover costs. The handover costs are analyzed in terms of the total required handover time and the service disruption time. The numerical analysis and simulation results show that the proposed method significantly enhances the handover performance in heterogeneous wireless networks.     

An Area Optimization Method for Digital Filter Design

In this paper, we propose an efficient design method for area optimization in a digital filter. The conventional methods to reduce the number of adders in a filter have the problem of a long critical path delay caused by the deep logic depth of the filter due to adder sharing. Furthermore, there is such a disadvantage that they use the transposed direct form (TDF) filter which needs more registers than those of the direct form (DF) filter. In this paper, we present a hybrid structure of a TDF and DF based on the flattened coefficients method so that it can reduce the number of flip‐flops and full‐adders without additional critical path delay. We also propose a resource sharing method and sharing‐pattern searching algorithm to reduce the number of adders without deepening the logic depth. Simulation results show that the proposed structure can save the number of adders and registers by 22 and 26%, respectively, compared to the best one used in the past.     

A building-transmission model for improved propagation prediction in urban microcells

This paper presents a model for the propagation of radiowaves through buildings. The model can be used as a seamless extension to ray-based propagation prediction models that only consider external reflection and diffraction, as do most current models. This involves the use of so-called transmitted rays, which are traced through building walls. Outdoor-to-indoor propagation (building penetration) is automatically taken into account as a "by-product". The transmission model requires no information about each building's interior other than a specific attenuation factor that describes the global behavior of the field inside the building. This coefficient can be determined for individual buildings by measuring the excess loss associated with the propagation path through the building. It is shown, however, that no large errors are to be expected if all buildings are characterized by the average of the empirical values obtained in this study, at 1.9 GHz. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in accuracy that can be achieved in realistic urban microcell scenarios by taking into account building penetration and transmission.