Circularly polarized array antenna with corporate-feed network and series-feed elements

In this paper, corporate-feed circularly polarized microstrip array antennas are studied. The antenna element is a series-feed slot-coupled structure. Series feeding causes sequential rotation effect at the element level. Antenna elements are then used to form the subarray by applying sequential rotation to their feeding. Arrays having 4, 16, and 64 elements were made. The maximum achieved gains are 15.3, 21, and 25.4 dBic, respectively. All arrays have less than 15 dB return loss and 3 dB axial ratio from 10 to 13 GHz. The patterns are all quite symmetrical.     

An alternative method to fabricate the planar-type resonant-cavity light-emitting diodes by using silicon oxide for short-reach communications

In this article, the silicon oxide (SiO_x) planarization technique is presented to fabricate the 650-nm resonant-cavity light-emitting diodes (RCLEDs). The performances of RCLEDs are characterized by forward voltage, light output power, external quantum efficiency, emission spectrum, and dynamic response. As a result, the device with the SiO_x-planarized layer exhibits a low operating voltage of 2.3 V at 20 mA, a maximum light output power of 304 μW at 15 mA, and the best external quantum efficiency of 3% at 1.2 mA. In addition, the SiO_x-planarized device exhibits temperature insensitivity as compared to the device without it. The RCLED with a 30-μm diameter shows the maximum 3 dB frequency bandwidth of 275 MHz at a driving current of 40 mA. Finally, the RCLED with a SiO_x-planarized layer shows a clear eye-opening feature as operating at 100 Mbit/s at 20 mA. These results indicate that such LEDs are excellent candidates for use in high-speed short-reach plastic optical fiber communications.     

Digital Laser Micropainting for Reprogrammable Optoelectronic Applications

Structural coloration is closely related to the progress of innovative optoelectronic applications, but the absence of direct, on-demand, and rewritable coloration schemes has impeded advances in the relevant area, particularly including the development of customized, reprogrammable optoelectronic devices. To overcome these limitations, a digital laser micropainting technique, based on controlled thin-film interference, is proposed through direct growth of the absorbing metal oxide layer on a metallic reflector in the solution environment via a laser. A continuous-wave laser simultaneously performs two functions—a photothermal reaction for site-selective metal oxide layer growth and in situ real-time monitoring of its thickness—while the reflection spectrum is tuned in a broad visible spectrum according to the laser fluence. The scalability and controllability of the proposed scheme is verified by laser-printed painting, while altering the thickness via supplementary irradiation of the identical laser in the homogeneous and heterogeneous solutions facilitates the modification of the original coloration. Finally, the proof-of-concept bolometer device verifies that specific wavelength-dependent photoresponsivity can be assigned, erased, and reassigned by the successive application of the proposed digital laser micropainting technique, which substantiates its potential to offer a new route for reprogrammable optoelectronic applications.     

A Liquid Metal Based Multimodal Sensor and Haptic Feedback Device for Thermal and Tactile Sensation Generation in Virtual Reality

Virtual reality (VR) has been widely used for training, gaming, and entertainment, and the value of VR is continually increasing as a contact-free technology. For an immersive VR experience, measuring finger movements and providing appropriate feedback to the hand are as important as visual information, given the necessity of the hands for activities in daily life. Thus, a hand-worn VR device with motion sensors and haptic feedback is desirable. In this paper, a multimodal sensing and feedback glove is developed with soft, stretchable, lightweight, and compact sensor and heater sheets manufactured by direct ink writing (DIW) of liquid metal, eutectic gallium-indium (eGaIn). In the sensor sheet, ten sensors and three vibrators are embedded to measure finger movements and provide vibro-haptic feedback. The other heater sheet provides thermo-haptic sensation in accurate and rapid manner via model-based feedback control even under stretched conditions. The multimodal sensing and feedback glove allows users to feel the contact status and discriminate materials with different temperature. Performance of the proposed multimodal glove is verified under VR environments including touching and pushing two blocks of different materials and grabbing a heated metal ball submerged in hot water.     

Modal analysis of radial-resonator waveguide diode mounts

A method of calculating the driving-point and transfer admittances of waveguide diode mounts with radial resonators is presented. The method is applicable to a variety of mount configurations, including the widely used resonant-cap mount. The analysis uses multimodal admittance matrices to represent the radial regions and their coupling and includes the influence of the waveguide boundary conditions. The analysis proceeds by first determining (from the matching of tangential fields at the common boundary) the coupling between radial regions in the form of a mode-coupling matrix. By multiplying this matrix with the generalized admittance matrices of connecting radial regions to form an overall admittance matrix, the driving-point and transfer admittances for a general radial-resonator mount can be extracted. The method is demonstrated by application to the resonant-cap mount. The accuracy of the analysis is confirmed by comparison with experimental results     

Self-Organization of Microlens Arrays Caused by the Spin-Coating-Assisted Hydrophobic Effect

A simple, low-cost, low-temperature, and shape-controllable approach has been demonstrated to fabricate polymer microlens arrays (MLAs). By using microcontact printing of the self-assembled monolayers and then spin coating, the microlenses were able to organize themselves on the patterned glass substrate. High-quality MLAs made of NOA65 prepolymer with lens-diameters of 50, 75, and 100 mum have been fabricated by this method. Lens shapes can be controlled by changing the spin rates of the prepolymer coating. Optical measurements have revealed an excellent light-collecting capability from the fabricated MLAs. It is anticipated that the technique will be ideally suited to low-cost and high-volume production     

Nitride-Based Schottky Barrier Sensor Module With High Electrostatic Discharge Reliability

In this study, we proposed and realized a nitride-based Schottky barrier sensor module with high electrostatic discharge (ESD) reliability. By including a Si-based ESD protection chip into the module, we can significantly enhance endurable ESD voltages under both forward and reverse human-body-mode (HBM) ESD stresses. It was found that the fabricated module can endure reverse HBM ESD stress of 7.5 KV and forward HBM ESD stress larger than 8 KV. It was also found that the inclusion of the Si-based ESD protection chip will not result in a decrease in detector responsivity     

Nitride-Based High-Power Flip-Chip LED With Double-Side Patterned Sapphire Substrate

A nitride-based high-power flip-chip (FC) light-emitting diode (LED) with a double-side patterned sapphire substrate (PSS) was proposed and realized. Under 350-mA current injection, it was found that forward voltages were 3.24, 3.26, and 3.25 V for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. It was found that the 350-mA LED output powers were 79.3, 98.1, and 121.5 mW for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. In other words, we can enhance the electroluminescence intensity by 53% without increasing operation voltage of the fabricated LED     

Low temperature annealing behaviors of the titanium films formed by the ionized sputtering process on (001) silicon substrates

We investigated the low temperature reactions between the Ti films created by the ionized sputtering process and the (001) single crystal silicon wafers using high resolution transmission electron microscopy and x-ray diffractometry. We observed that the amorphous Ti-Si intermixed layer is formed at the Ti-Si interface whose thickness increased with the thickness of the deposited Ti films. The amorphous interlayer grew upon annealing treatments at the temperatures below 450°C. We also observed that the crystallization of the amorphous interlayer occurred upon annealing at 500°C. The first formed phase is Ti₅Si₃ in contact with Ti films, which is epitaxial with Ti films. Upon further annealing at 500°C, the Ti₅Si₄ phase and C49 TiSi₂ phase formed in the regions close to Ti films and Si substrates, respectively.     

A handover-aware seamless video streaming scheme in heterogeneous wireless networks

With the development of wireless technologies, video streaming services over heterogeneous wireless networks have become more popular in recent years. Video streaming schemes for heterogeneous networks should consider vertical handover in which the link capacity is varied significantly, because the quality experienced for a video streaming service is affected by the network status. When a vertical handover occurs, an abrupt bandwidth change and substantial handover latency lead to bursty packet loss and discontinuity of the video playback. In this paper, we propose a handover-aware video streaming scheme to provide seamless video streaming services over heterogeneous wireless networks. The proposed scheme adjusts its sending rate and the quality level of the transmitted video streams according to the significant bandwidth variation that occurs in a vertical handover. To expedite the response to the bandwidth variation due to a handover, our scheme uses an explicit notification message that informs the streaming server of a client's handover occurrence. In order to evaluate the performance, we use a simulation environment for a vertical handover between wireless local area networks and cellular networks. Through the simulation results, we prove that our scheme improves the experienced quality of video streaming in vertical handovers.