Performance of improved probabilistic location update scheme forcellular mobile networks

This paper suggests an improved probabilistic location update (IPLU) scheme for advanced cellular mobile networks. The location management cost with IPLU is analyzed, and various performance characteristics of IPLU are investigated. It is shown that IPLU has the parameter q that can be used as a control parameter to achieve the best performance when the unit location update cost (U) and the unit paging cost (P) are given. In addition, this paper provides some recommendable values of q in two cases, P>U and P⩽U. As a result, we demonstrate a merit of IPLU, that is, simple implementation with an acceptable performance level, especially, under the future cellular mobile network environments where a vast number of microcells/picocells exist and the relative user mobility is very high     

Improvement of kink and beam steering characteristics of 0.98-μmGaInAs-GaInP high-power lasers utilizing channel ion implantation

We demonstrate a kink and beam steering free operation of 0.98-μm GaInAs-GaInP high-power ridge waveguide (RW) lasers utilizing channel ion implantation. The ion-implanted regions along the both sides of the ridge effectively suppressed the excitation of higher order lateral modes, which causes beam steering and kink. The maximum power without beam steering and kink has been achieved over 250 mW for channel ion-implanted RW lasers with 1.8-3.7-μm ridge width, compared to 120-mW maximum power without the channel ion implantation     

Highly Customizable All Solution–Processed Polymer Light Emitting Diodes with Inkjet Printed Ag and Transfer Printed Conductive Polymer Electrodes

Inkjet and transfer printing processes are combined to easily form patterned poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as top anodes of all solution–processed inverted polymer light emitting diodes (PLEDs) on rigid glass and flexible plastic substrates. An adhesive PEDOT:PSS ink is formulated and fully customizable patterns are obtained using the inkjet printing process. In order to transfer the patterned PEDOT:PSS films, adhesion properties at interfaces during multistep transfer printing processes are carefully adjusted. The transferred PEDOT:PSS film on the plastic substrates shows not only a sheet resistance of 260.6 Ω/□ and a transmittance of 92.1% at 550 nm wavelength but also excellent mechanical flexibility. The PLEDs with spin‐coated functional layers sandwiched between the transferred PEDOT:PSS top anodes and inkjet‐printed Ag bottom cathodes are fabricated. The fabricated PLEDs on the plastic substrates show a high current efficiency of 10.4 cd A^?1 and high mechanical stability. It is noted that because both Ag and PEDOT:PSS electrodes can be patterned with a high degree of freedom via the inkjet printing process, highly customizable PLEDs with various pattern sizes and shapes are demonstrated on the glass and plastic substrates. Finally, with all solution process, a 5 × 7 passive matrix PLED array is demonstrated.     

Microparticle‐Based Soft Electronic Devices: Toward One‐Particle/One‐Pixel

While microparticle (MP) assemblies have long attracted academic interest, few practical applications of assembled MPs have been achieved because of technological difficulties related to MP synthesis, MP position registration, and the absence of device concepts. The precise positioning of functional MPs in a proper stencil can produce flexible/stretchable electronic devices, even when the MPs themselves are rigid. In recent years, remarkable progress has been made in the programmable position registration of MPs, production of functional MPs, and concepts for MP‐based, pixel‐type electronic devices. This progress report reviews the recent technological advances in MP assembly and discusses the technological challenges preventing the realization of the one‐particle/one‐pixel concept.     

Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.     

Non‐Volatile Polymer Electroluminescence Programmable with Ferroelectric Field‐Induced Charge Injection Gate

Electroluminescence (EL) of organic and polymeric fluorescent materials programmable in the luminance is extremely useful as a non‐volatile EL memory with the great potential in the variety of emerging information storage applications for imaging and motion sensors. In this work, a novel non‐volatile EL memory in which arbitrarily chosen EL states are programmed and erased repetitively with long EL retention is demonstrated. The memory is based on utilizing the built‐in electric field arising from the remnant polarization of a ferroelectric polymer which in turn controls the carrier injection of an EL device. A device with vertically stacked components of a transparent bottom electrode/a ferroelectric polymer/a hole injection layer/a light emitting layer/a top electrode successfully emits light upon alternating current (AC) operation. Interestingly, the device exhibits two distinctive non‐volatile EL intensities at constant reading AC voltage, depending upon the programmed direct current (DC) voltage on the ferroelectric layer. DC programmed and AC read EL memories are also realized with different EL colors of red, green and blue. Furthermore, more than four distinguishable EL states are precisely addressed upon the programmed voltage input each of which shows excellent EL retention and multiple cycle endurance of more than 10⁵ s and 10² cycles, respectively.     

Strain‐Visualization with Ultrasensitive Nanoscale Crack‐Based Sensor Assembled with Hierarchical Thermochromic Membrane

As eidetic signal recognition has become important, displaying mechanical signals visually has imposed huge demands for simple readability and without complex signal processing. Such visualization of mechanical signals is used in delicate urgent medical or safety‐related industries. Accordingly, chromic materials are considered to facilitate visualization with multiple colors and simple process. However, the response and recovery time is very long, such that rapid regular signals are unable to be detected, i.e., physiological signals, such as respiration. Here, the simple visualization of low strain ≈2%, with ultrasensitive crack‐based strain sensors with a hierarchical thermochromic layer is suggested. The sensor shows a gradient color change from red to white color in each strain, which is attributed to the hierarchical property, and the thermal response (recovery) time is dramatically minimized within 0.6 s from 45 to 37 °C, as the hierarchical membrane is inspired by termite mounds for efficient thermal management. The fast recovery property can be taken advantage of in medical fields, such as monitoring regular respiration, and the color changes can be delicately monitored with high accuracy by software on a mobile phone.     

Tunnel lane‐positioning system for autonomous driving cars using LED chromaticity and fuzzy logic system

Currently, studies on autonomous driving are being actively conducted. Vehicle positioning techniques are very important in the autonomous driving area. Currently, the global positioning system (GPS) is the most widely used technology for vehicle positioning. Although technologies such as the inertial navigation system and vision are used in combination with GPS to enhance precision, there is a limitation in measuring the lane and position in shaded areas of GPS, like tunnels. To solve such problems, this paper presents the use of LED lighting for position estimation in GPS shadow areas. This paper presents simulations in the environment of three‐lane tunnels with LEDs of different color temperatures, and the results show that position estimation is possible by the analyzing chromaticity of LED lights. To improve the precision of positioning, a fuzzy logic system is added to the location function in the literature [1]. The experimental results showed that the average error was 0.0619 cm, and verify that the performance of developed position estimation system is viable compared with previous works.