Figure 1: Overview of picoRing mouse, enabling 30-500 uW-class ultra-low-power wireless ring mouse for ubiquitous finger input.The ring can potentially operate over a month on a single charge of a 27 mAh battery (https://youtu.be/7RazVNMx0Ms).

Wearable devices for life-logging and healthcare have been studied, but the need for frequent charging imposes inconvenience for long-term use. Integrating textile-based wireless chargers (i.e., coil) into clothing enables sustainable wearable computing by charging the on-body devices in use. However, the electromagnetic field generated by conventional coil chargers strongly interferes with human body, and the high resistance of conductive threads leads to inefficient power delivery. This paper presents Meander Coil++, enabling safe, energy-efficient, and body-scale wireless power delivery. Meander Coil++ uses a wiring pattern that suppresses electromagnetic exposure to the human body without compromising power delivery performance and a liquid-metal-based low-loss conductive cord. With these advancements, Meander Coil++ transmits a few watts of power to on-body devices at 25% DC-to-DC efficiency while complying with international safety guidelines regarding electromagnetic exposure. We envision Meander Coil++ can maintain multiple devices on body for weeks beyond the confines of their small battery capacity.

In the past several years, research in soft and flexible electronics has promised to yield developments in wearable technology, including health and fitness monitoring tools, independence and mobility aids for the disabled, and human-computer interfaces for virtual and augmented reality. However, as these devices become thinner and lighter, they demand efficient power supplies with similar mechanical properties. Organic photovoltaics (OPVs)--known for their high flexibility, lightweight, and scalable fabrication methods-have recently attained power conversion efficiencies of over 17% and are excellent candidates to power these next-generation wearable devices. In this paper, we discuss recent developments in flexible OPVs, including advances in materials, structure, and integration with additional wearable components, such as sensors and displays. In addition, we describe our recent work in developing a self-powered actuator for a tactile feedback system.

We demonstrate ultrathin, ultraflexible, large-area pressure sensors based on an organic transistor integrated circuit. A 10-μm-thick plastic film with an organic transistor active matrix is developed that can be bent to a bending radius of less than 1 mm to create an electrical artificial skin (E-skin). The thin-film, flexible pressure-sensor matrix is implemented on a curved surface, and the spatial distribution of pressure is successfully obtained in real time.

Flexible electronics have attracted much attention since they enable promising applications such as low-cost RFID tags and e-paper. Thin-film transistors (TFTs) are considered as an ideal candidate to implement flexible electronics on low-cost substrates. Most TFT technologies, however, have only mono-type - either n- or p-type - devices and thus modern design technologies for silicon-based electronics cannot be directly applied. In this paper, we propose a novel design style Pseudo-CMOS for flexible electronics that uses only mono-type TFTs while achieving comparable performance with the complementary-type designs. The manufacturing cost and complexity can therefore be significantly reduced while the circuit yield and reliability are also enhanced with the built-in capability of post-fabrication tuning. Some standard cells have been designed and fabricated in p-type organic and n-type InGaZnO (IGZO) TFT technologies which successfully verify the superiority of the proposed Pseudo-CMOS design style. To the best of our knowledge, this is the first design solution that has proven superior performance for both types of TFT technologies.

Organic electronics is attracting a lot of attention for large-area pervasive electronics applications, because organic transistors can be fabricated using printing technologies on arbitrary substrates and this enables both high-throughput and low-cost production. In this paper, some examples of the large area electronics with the organic transistors including a wireless power transmission sheet and a communication sheet are presented. Challenges for future large area electronics are also described.

In line-of sight (LOS) environments, the performance of Multiple-Input Multiple-Output (MIMO) systems depends largely on the difference of the phase difference of direct paths from transmit antennas to each receive antenna. When the phase difference of direct paths are close to each other, the spatial division multiplexing (SDM) channel is not orthogonal to each other so that the signal detection becomes difficult. In this paper, we propose a MIMO system with relative phase difference time-shift modulation (RPDTM) in Rician fading environments. The proposed scheme transmits independent signals from each antenna at each time slot where relative phase difference between signal constellations used by transmit antennas varies with a pre-determined pattern. This transmission virtually changes the phase difference of direct paths from transmit antennas to each receive antenna without lowering data rate and without knowledge of the channels. In addition, forward error correction coding (ECC) is applied to exploit the time slots where the receiver can detect the signals easily to improve the detection performance. From the results of computer simulation, we show that MIMO system with RPDTM can achieve the better bit error rate (BER) than the conventional MIMO system. We also show that the MEMO system with RPDTM is effective by about Rician factor K = 10 dB.

In recent years, multiple-input multiple-output (MIMO) systems, which use several transmit and receive antennas, have attracted much attention for high performance radio systems. In MIMO systems, the channel estimation is important to distinguish transmit signals from multiple transmit antennas. While the space-alternating generalized expectation-maximization (SAGE) algorithm is known to offer good channel estimation and data detection. We proposed earlier the minimum mean square error (MMSE)-based SAGE algorithm for MIMO systems where the MMSE estimation is used for channel estimation. We showed that the proposed MMSE-based SAGE algorithm can achieve the better bit error rate (BER) than the maximum likelihood (ML) detection with training symbols. The MMSE channel estimation needs the knowledge of the maximum Doppler frequency Fdfor deriving the covariance matrix of the channel and the variance sigma2of additive white Gaussian noise (AWGN). Additionally, the computation of the MMSE channel estimation requires O(L3) operations where L is the transmitted frame length. Thus, its computational complexity is high. In this paper, we propose a zero-forcing (ZF)-based SAGE algorithm for channel estimation and data detection in MIMO systems that does not need the knowledge of Fd and sigma2. Since the computation of the proposed ZF-based SAGE algorithm requires O(N3) operations where N is the number of transmit antennas, its computational complexity is low. We show that the proposed ZF-based tracking SAGE algorithm with less computational complexity can achieve almost the same BER as that of the MMSE-based tracking SAGE algorithm

In MIMO systems, channel estimation is important to distinguish transmit signals from multiple transmit antennas. The space-alternating generalized expectation-maximization (SAGE) algorithm is known to be good for channel estimation and data detection. However, the SAGE algorithm has not been applied to MIMO systems. In this paper, we propose a SAGE algorithm for the channel estimation and data detection in MIMO systems. In addition, we propose a simplified SAGE algorithm for the channel estimation and data detection by tracking the channel variation in MIMO systems. In the simplified SAGE algorithm, we divide a transmit frame into some subblocks and apply the SAGE algorithm to each subblock, and we use the channel estimates in the previous subblock as the initial channel estimates in the current subblock. According to the division of the transmit frame, the computational complexity is decreased. In addition, the simplified SAGE algorithm can track the channel variation by using the channel estimates transferred between the subblocks.