BACKGROUND: Solid surfaces possessing both superhydrophobic and superoleophilic properties have attracted great interest for fundamental research and potential application. However, fabrication of the reported surfaces is usually time-consuming and the wetability of the surfaces could not be achieved to the desired level in rugged environments.
The Gerchberg-Saxton (GS) algorithm is widely used to calculate the phase-only computer-generated hologram (CGH) for holographic three-dimensional (3D) display. However, speckle noise exists in the reconstruction of the CGH due to the uncontrolled phase distribution. In this paper, we propose a method to suppress the speckle noise by simultaneously reconstructing the desired amplitude and phase distribution. The phase-only CGH is calculated by using a double-constraint GS algorithm, in which both the desired amplitude and phase information are constrained in the image plane in each iteration. The calculated phase-only CGH can reconstruct the 3D object on multiple planes with a desired amplitude distribution and uniform phase distribution. Thus the speckle noise caused by the phase fluctuation between adjacent pixels is suppressed. Both simulations and experiments are presented to demonstrate the effective speckle noise suppression by our algorithm.
The purpose of this study is to implement speckle reduced three-dimensional (3-D) holographic display by single phase-only spatial light modulator (SLM). The complex amplitude of hologram is transformed to pure phase value based on double-phase method. To suppress noises and higher order diffractions, we introduced a 4-f system with a filter at the frequency plane. A blazing grating is proposed to separate the complex amplitude on the frequency plane. Due to the complex modulation, the speckle noise is reduced. Both computer simulation and optical experiment have been conducted to verify the effectiveness of the method. The results indicate that this method can effectively reduce the speckle in the reconstruction in 3-D holographic display. Furthermore, the method is free of iteration which allows improving the image quality and the calculation speed at the same time.
BackgroundFabrication of superhydrophobic surfaces has attracted much interest in the past decade. The fabrication methods that have been studied are chemical vapour deposition, the sol-gel method, etching technique, electrochemical deposition, the layer-by-layer deposition, and so on. Simple and inexpensive methods for manufacturing environmentally stable superhydrophobic surfaces have also been proposed lately. However, work referring to the influence of special structures on the wettability, such as hierarchical ZnO nanostructures, is rare.MethodologyThis study presents a simple and reproducible method to fabricate a superhydrophobic surface with micro-scale roughness based on zinc oxide (ZnO) hierarchical structure, which is grown by the hydrothermal method with an alkaline aqueous solution. Coral-like structures of ZnO were fabricated on a glass substrate with a micro-scale roughness, while the antennas of the coral formed the nano-scale roughness. The fresh ZnO films exhibited excellent superhydrophilicity (the apparent contact angle for water droplet was about 0°), while the ability to be wet could be changed to superhydrophobicity after spin-coating Teflon (the apparent contact angle greater than 168°). The procedure reported here can be applied to substrates consisting of other materials and having various shapes.ResultsThe new process is convenient and environmentally friendly compared to conventional methods. Furthermore, the hierarchical structure generates the extraordinary solid/gas/liquid three-phase contact interface, which is the essential characteristic for a superhydrophobic surface.
Owing to the rapid growth of mobile data communication and spectrum crunch at lower radio frequency, utilizing high frequency spectrum such as millimeter wave for ultra-high data rate mobile communications becomes necessary. Yet the propagation behaviors of high frequency radio waves make mobile communications rather challenging with a lot of technical problems, such as very large propagation loss. In this paper, we propose a novel approach, referred to as optical mobile communications (OMC), to cater to the need for high data rate mobile communication by exploiting optical beams. Taking spatial light modulator as an exemplary means of laser beam adaptation, we first present the system model of OMC. It is shown that the downlink channels in OMC are different from that in a system equipped with antennas emitting radio frequency signals. That is, the OMC channels for different mobile terminals are controllable to a large extent. This new feature creates a new dimension for performance optimization of OMC. We then investigate the achievable rate region of OMC using different multiple access schemes in a two-user downlink system. Numerical results show that expanded rate region can be achieved in OMC compared to the case where channels are not controllable, which shows the potential of OMC as a promising technique. Index Terms-Optical mobile communications, multiple access, achievable rate region, beam adaptation. I. INTRODUCTION W ITH the fast development of mobile communication systems (MCSs), radio spectrum has a limitation to provide extreme high throughput services -. On the other hand,
Piezoelectric sensors with high performance and low-to-zero power consumption meet the growing demand in the flexible microelectronic system with small size and low power consumption, which are promising in robotics and prosthetics, wearable devices and electronic skin. In this review, the development process, application scenarios and typical cases are discussed. In addition, several strategies to improve the performance of piezoelectric sensors are summed up: (1) material innovation: from piezoelectric semiconductor materials, inorganic piezoceramic materials, organic piezoelectric polymer, nanocomposite materials, to emerging and promising molecular ferroelectric materials. (2) designing microstructures on the surface of the piezoelectric materials to enlarge the contact area of piezoelectric materials under the applied force. (3) addition of dopants such as chemical elements and graphene in conventional piezoelectric materials. (4) developing piezoelectric transistors based on piezotronic effect. In addition, the principle, advantages, disadvantages and challenges of every strategy are discussed. Apart from that, the prospects and directions of piezoelectric sensors are predicted. In the future, the electronic sensors need to be embedded in the microelectronic systems to play the full part. Therefore, a strategy based on peripheral circuits to improve the performance of piezoelectric sensors is proposed in the final part of this review.
Wearable sensors with water resistance and mechanical durability are of great value in dealing with long‐term movement and remote control in harsh environments. However, achieving high sensitivity with long‐term stability and real‐time remote control in a watery environment is still a challenge. Herein, the waterproof wearable sensors with good mechanical robustness composed of laser‐induced graphene and in situ‐coated protective silicone layers are reported. By being integrated with high‐capacitance ion‐gel dielectrics, the conformal sensors can detect multiple stimuli, including strain, temperature, and pressure. The long‐term water resistance of strain sensors is evaluated by continuously monitoring the resistance in underwater, sweat, and saline environment for up to 5.5 h. Underwater wireless remote control of a robotic hand is further demonstrated by mounting five sensor arrays. Moreover, different finger gestures are well recognized, making these sensor devices promising candidates for versatile waterproof wearable electronics and robotics technology.
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