The programmable nature of smart textiles makes them an indispensable part of an emerging new technology field. Smart textile-integrated microelectronic systems (STIMES), which combine microelectronics and technology such as artificial intelligence and augmented or virtual reality, have been intensively explored. A vast range of research activities have been reported. Many promising applications in healthcare, the internet of things (IoT), smart city management, robotics, etc., have been demonstrated around the world. A timely overview and comprehensive review of progress of this field in the last five years are provided. Several main aspects are covered: functional materials, major fabrication processes of smart textile components, functional devices, system architectures and heterogeneous integration, wearable applications in human and nonhuman-related areas, and the safety and security of STIMES. The major types of textile-integrated nonconventional functional devices are discussed in detail: sensors, actuators, displays, antennas, energy harvesters and their hybrids, batteries and supercapacitors, circuit boards, and memory devices.

Smart Textile-Integrated Microelectronic Systems for Wearable Applications

Ultra-high bandwidth, negligible latency and seamless communication are envisioned as milestones that will revolutionize the way by which societies create, distribute and consume information. The remarkable expansion of wireless data traffic has advocated the investigation of suitable regimes in the radio spectrum to satisfy users’ escalating requirements and allow the exploitation of massive capacity and massive connectivity. To this end, the Terahertz (THz) frequency band (0.1-10 THz) has received noticeable attention in the research community as an ideal choice for scenarios involving high-speed transmission. As such, in this work, we present an up-to-date review paper to analyze key concepts associated with the THz system architecture. THz generation methods are first addressed by highlighting the recent progress in the devices technology. Moreover, the recently proposed channel models available for propagation at THz band frequencies are introduced. A comprehensive comparison is then presented between the THz wireless communication and its other contenders. In addition, several applications of THz communication are discussed taking into account various scales. Further, we highlight the milestones achieved regarding THz standardization activities. Finally, a future outlook is provided by presenting and envisaging several potential use cases and attempts to guide the deployment of the THz frequency band.

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Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems

Featuring a combination of ultrathin and lightweight properties, excellent mechanical flexibility, low power-consumption, and widely tunable saturated emission, flexible displays have opened up a new possibility for optoelectronics. The demands for flexible displays are growing on a continual basis due not only to their successful commercialization but, more importantly, their endless possibilities for wearable integrated systems. Up to now, self-emissive technologies for displays, flexible active-matrix organic light-emitting diodes (flex-AMOLED), flexible quantum dot light-emitting diodes (flex-QLEDs), and flexible perovskite light-emitting diodes (flex-PeLEDs) have been widely reported, but despite the significant progress made in these technologies, enormous obstacles and challenges remain for the vision of truly wearable applications, in particular with flex-QLEDs and flex-PeLEDs. Here, a review of the recent progress of all three self-emissive technologies for flexible displays is conducted, including the emissive active materials, device structures and approaches to manufacturing, the flexible substrates, and conductive electrodes, as well as the encapsulation techniques. The fast-paced improvement made to the efficiency of flexible devices in recent years is also summarized. The review concludes by making suggestions on the future development in this area, and is expected to help researchers in gaining a comprehensive understanding about the newly emerging technologies for flexible displays.

Emerging Self-Emissive Technologies for Flexible Displays

DOI: 10.1002/admt.201800371 wearable displays, and conceptual lighting panels. In addition, besides the excellent designs, a flexible OLED (FOLED)[7,20–40] has several other advantages, the displays and lighting panels are thinner, lighter, more cost effective, shatterproof, and durable compared to glass or silicon based OLEDs. They are impact resistance and less prone to break than glass. At present, both flexible displays and lighting panels are being mass produced (Samsung and LG on displays, LG and Konica Minolta on lighting). FOLEDs are becoming most promising and popular next-generation display technology in consumer electronics and lighting panels. In order to develop the FOLEDs and realize their practical application, many great efforts have been conducted. The key components of the FOLEDs are flexible substrate, bottom and top electrode, organic functional layers, encapsulation layer, and optional light extraction layers. Differed from conventional OLEDs on rigid glass or silicon substrate, FOLEDs are fabricated on flexible substrates. Up to now, metal foil, flexible glass, and plastic film have been commonly used as flexible substrates for FOLEDs. On the other hand, actual fabric materials, natural silk fibroin films, bacterial cellulose, and rubbery poly (urethane acrylate) have also been developed to achieve the requirements of wearable and stretchable displays. The electrode is also very important for FOLEDs. Compared with the top electrode, more research has been conducted on the bottom electrode because its surface roughness, conductivity, and transmittance for bottom emitting OLEDs play a key role in the performance of FOLEDs. As conventional indiumtin-oxide (ITO) is not suitable for flexible devices as it is brittle, many great alternatives such as thin metal film, conducting polymer, dielectric–metal–dielectric (DMD) multilayers, metal nanowires, graphene, carbon nanotubes (CNTs), and their compound have been studied. It should be mentioned that the performance of organic layers has almost no difference with rigid OLEDs because of their inherent excellent ductility and identical working mechanism. Moreover, for practical and commercial applications, stability and efficiency are two factors of crucial importance. As a consequence, the encapsulation technique and light extraction of FOLEDs are also two research hotspots in recent years. This review will summarize the key components, discuss the method of implementation, highlight the recent research progresses, and conclude the challenges and prospects of FOLEDs. As the demand for display technology in consumer electronics and lighting panels increases, thin, light, high-quality, and more cost-effective light-emitting devices are required. Organic light-emitting devices (OLEDs), satisfying the criteria exactly, have been considered the most promising next-generation display and lighting technique. In particular, an OLED based on flexible substrate enables the device to be applied to curved displays, electronic newspapers, wearable displays, and conceptual lighting panels, has been always in the spotlight both in science and industry. Great advances on flexible OLEDs (FOLEDs) have been made over the past three decades. The fundamental elements of FOLEDs including substrates, electrodes, fabrication and encapsulation techniques, as well as the strategies of efficiency improvement are discussed herein. Moreover, emerging electrodes such as graphene, carbon nanotubes, metal nanowire network and their composite, flexible perovskite light emitting devices, and stretchable light emitting devices are also considered. Finally, the future challenges and prospects for these devices are put forward.

Recent Developments in Flexible Organic Light-Emitting Devices

Through the manipulation of co-polarized reflection and cross-polarized reflection from a periodic array of metal-dielectric-metal resonators, a plethora of unprecedented metamaterial devices have been successfully demonstrated, such as perfect absorber and polarization converter. Recently, some broadband absorbers based on anisotropic resonators have been reported, which are actually poor absorbers when the cross-polarized reflection is considered. Here, we demonstrate that an ultra-wideband and high-efficiency reflective cross-polarization convertor can be achieved by breaking the symmetry of the resonator unit of a perfect absorber. Simulation results show that the polarization conversion ratio of the proposed metasurface is above 90% in the frequency range from 6.67 to 17.1 GHz and the relative bandwidth reaches 87.7%. The experimental results are in good agreement with the simulation results. The method paves a new way for the design of broadband polarization convertor, which can also be extended to the terahertz band.

Ultra-broadband linear polarization converter based on anisotropic metasurface

We investigate and compare the performance of star-shaped 16-ary quadrature amplitude modulation (Star-16QAM) and square-shaped 16QAM (Square-16QAM) in the probabilistic shaping (PS) and uniform schemes with coherent detection. With the help of PS technology, the bit error ratio (BER) improvement achieved in the PS-Star-16QAM scheme is greater than that of the PS-Square-16QAM when compared with the uniform schemes in our numerical simulation and experiment. Therefore, the PS-Star-16QAM shows superiority over the PS-Square-16QAM in terms of the BER improvement.

Performance Comparison of PS Star-16QAM and PS Square-Shaped 16QAM (Square-16QAM)

We propose and experimentally demonstrate a photonics-aided 2 × 2 multiple-input multiple-output (MIMO) wireless Terahertz-wave (THz-wave) signal transmission system, which realizes 6 × 20-Gb/s six-channel polarization division multiplexing quadrature-phase-shift-keying THz-wave signal delivery over 10-km wireline single-mode fiber- link and 142-cm wireless 2 × 2 MIMO link with a bit-error ratio under the hard-decision forward-error-correction threshold of 3.8 × 10−3. Our employed multi-carrier frequencies are located within the range of 375 GHz to 500 GHz. To the best of our knowledge, this is the first experimental demonstration of 2 × 2 MIMO wireless transmission of multi-channel THz-wave signal. Here, it is worth noting that our wireless 2 × 2 MIMO link, which offers point-to-point straight transmission and brings neither interference nor gain, is different from the traditional MIMO link defined in the field of wireless communications.

120 Gb/s Wireless Terahertz-Wave Signal Delivery by 375 GHz-500 GHz Multi-Carrier in a 2 × 2 MIMO System

We experimentally demonstrated single-lane EML-based IM/DD 106-Gbaud PAM-4 and PS-PAM-8 signals transmission over 1-km NZDSF based on Pre-EQ and clipping technique. 260-Gb/s PS-PAM-8 signal transmission can be achieved.

Demonstration of 260-Gb/s Single-Lane EML-Based PS-PAM-8 IM/DD for Datacenter Interconnects

The 16QAM signal adopting probabilistic shaping (PS) technology is transmitted in a photonics-aided wireless Terahertz-wave system. The experimental results show an improvement of BER performance compared to the uniform distribution.

Probabilistically Shaped 16QAM Signal Transmission in a Photonics-aided Wireless Terahertz-Wave System

We experimentally demonstrate 132-Gb/s (12-Gbaud) photonics-aided single-carrier PDM-64QAM-PS5.5 THz-wave signal transmission at 450GHz over 20-km fiber-optics and 1.8-m wireless distance with BER under 4×10−2. The employment of probabilistic-constellation-shaping significantly improves transmission capacity and system performance.

Miao Kong

Papers

Performance Comparison of PS Star-16QAM and PS Square-Shaped 16QAM (Square-16QAM)

120 Gb/s Wireless Terahertz-Wave Signal Delivery by 375 GHz-500 GHz Multi-Carrier in a 2 × 2 MIMO System

Demonstration of 260-Gb/s Single-Lane EML-Based PS-PAM-8 IM/DD for Datacenter Interconnects

Probabilistically Shaped 16QAM Signal Transmission in a Photonics-aided Wireless Terahertz-Wave System

132-Gb/s Photonics-Aided Single-Carrier Wireless Terahertz-Wave Signal Transmission at 450GHz Enabled by 64QAM Modulation and Probabilistic Shaping