Mechanical stress was applied to the specimen by four points bending tests while measuring electromotive force (EMF) between the two electrodes. EMF proportional to the applied stress was observed. EMF was significantly dependent on the electrode material, but was almost independent of the electrolyte material. These results indicated that lithium chemical potential varied under mechanical stress both in the electrode and electrolyte but the influence of mechanical stress appeared more notably in the electrode than the electrolyte. The lithium chemical potential changes in the electrode and the electrolyte under mechanical stress were discussed based on the idea of local equilibrium.
This paper presents a control method intended to suppress the effects of manufacturing variations on nanomechanical systems. Often, the resonance characteristics of nanoscale devices are inconsistent, due to unavoidable variations in the fabrication process. This is important because resonant vibrations enhance the sensitivities of the devices. As such, the sensitivities of these systems can be degraded if the device characteristics are not identified. To address this fundamental problem, this paper presents a multidisciplinary method based on control theory, nanotechnology, and communication technology. A stochastic optimal feedback controller is employed to enhance an average sensitivity by regarding the variations as stochastic parameters. This method is applied to nanoscale receivers that detect transmitted binary data based on binary phase-shift keying in communication systems. The proposed method controls the vibrations of carbon nanotubes (CNTs) that serve as the antennas of the receiver. The proposed method is demonstrated via a numerical simulation using nanoscale receivers with the manufacturing variation. The simulation based on experimental data obtained from CNTs shows that the average performance of the devices is enhanced. INDEX TERMS Nanoelectromechanical systems, optimal control, stochastic systems.
The field-emission phenomenon is exploited in a broad variety of applications and systems. Previous studies have reported that the current induced by field emission strongly and inherently depend on the temperature. This dependence enhances the noise in the current, which results in performance degradation in, for example, signal detection and communications in nanoscale receivers. In this paper, a mathematical model is presented for the suppression of the noise based on its probability density. Our experiment and analysis revealed that the density follows a Gaussian distribution, and the dependence on temperature is observed to be exponential. This result is intriguing because in the field of signal processing and communication, the influence of temperature is often considered with a noise-temperature model, namely, linear dependence. Using our derived model, we theoretically evaluated the communication performance of a nanoscale receiver; owing to the exponential dependence on temperature, severe performance degradation was found with increasing temperature. This means that, as field-emission technology continues to be developed, the temperature should be kept low, for example, at room temperature, to secure the reliability of nanoscale communication devices.INDEX TERMS Bit-error rate, field emission, nanoscale communication, nonlinear temperature dependence.
Modified solid surfaces exhibit unique wetting behavior, such as hydrophobicity and hydrophilicity. Such behavior can passively control the fluid flow. In this study, we experimentally demonstrated a wettability-designable cell array consisting of unetched and physically etched surfaces by reactive ion etching on a silicon substrate. The etching process induced a significant surface roughness on the silicon surface. Thus, the unetched and etched surfaces have different wettabilities. By adjusting the ratio between the unetched and etched surface areas, we designed one- and two-dimensional wettability gradients for the fluid channel. Consequently, fine-tuned channels passively realized unidirectional and curved fluid motions. The design of a wettability gradient is crucial for practical and portable systems with integrated fluid channels.
We experimentally evaluated the influence of stress on the Li chemical potential (µLi) and phase equilibrium in the two-phase battery electrode materials through the emf measurements while applying a mechanical load. In our measurements, we prepared an electrochemical cell by depositing a thin film of a two-phase electrode material (LiFePO4 or LiCoO2 in the two-phase region) on each of the solid electrolyte surfaces. Then we applied a mechanical load to the electrochemical cell through four-point bending, and the resulting µLi variation in the electrode material was measured as the emf between the two thin films. Our results indicated that µLi in the two-phase electrode materials immediately changed just after loading and then gradually changed while maintaining a constant mechanical load. Besides, the loading and unloading led to the µLi variation in the opposite direction. Such characteristic µLi variations could be explained by considering the change in the phase equilibrium between the two phases, which led to the Li content variation in the two phases and the stress relaxation due to the volume fraction variation of the two phases. Our results can provide valuable insights regarding the influence of stress on the performances of energy storage devices with two-phase electrode materials.
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