Human Activity Recognition (HAR) has gained significant attention due to its broad range of applications, such as healthcare, industrial work safety, activity assistance, and driver monitoring. Most ...prior HAR systems are based on recorded sensor data (i.e., past information) recognizing human activities. In fact, HAR works based on future sensor data to predict human activities are rare. Human Activity Prediction (HAP) can benefit in multiple applications, such as fall detection or exercise routines, to prevent injuries. This work presents a novel HAP system based on forecasted activity data of Inertial Measurement Units (IMU). Our HAP system consists of a deep learning forecaster of IMU activity signals and a deep learning classifier to recognize future activities. Our deep learning forecaster model is based on a Sequence-to-Sequence structure with attention and positional encoding layers. Then, a pre-trained deep learning Bi-LSTM classifier is used to classify future activities based on the forecasted IMU data. We have tested our HAP system for five daily activities with two tri-axial IMU sensors. The forecasted signals show an average correlation of 91.6% to the actual measured signals of the five activities. The proposed HAP system achieves an average accuracy of 97.96% in predicting future activities.
Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest. Since the mid-infrared spectrum can ...provide non-destructive identification and quantitative analysis of unknown substances, miniaturized mid-infrared spectrometers for on-site diagnosis have attained great concern. Filter-array based on-chip spectrometer has been regarded as a promising alternative. In this study, we explore a way of applying a pillar-type plasmonic nanodiscs array, which is advantageous not only for excellent tunability of resonance wavelength but also for 2-dimensional integration through a single layer process, to the multispectral filter array for the on-chip spectrometer. We theoretically and experimentally investigated the optical properties of multi-periodic triangular lattices of metal nanodiscs array that act as stopband filters in the mid-infrared region. Soft-mold reverse nanoimprint lithography with a subsequent lift-off process was employed to fabricate the multispectral filter array and its filter function was successfully extracted using a Fourier transform infrared microscope. With the measured filter function, we tested the feasibility of target spectrum reconstruction using a Tikhonov regularization method for an ill-posed linear problem and evaluated its applicability to the infrared spectroscopic sensor that monitors an oil condition. These results not only verify that the multispectral filter array composed of stopband filters based on the metal nanodiscs array when combined with the spectrum reconstruction technique, has great potential for use to a miniaturized mid-infrared on-chip spectrometer, but also provide effective guidance for the filter design.
There is a rapidly growing demand for highly efficient ultraviolet (UV) light sources for a wide variety of applications. In particular, state-of-the-art AlGaN deep UV light-emitting diodes (DUV ...LEDs) exhibit inadequately low external quantum efficiencies (EQEs). The low efficiencies are attributed to the inherent material properties of high-Al-content AlGaN including strained epitaxial layers, low carrier concentrations, and strong transverse magnetic (TM)-polarized light emission. Extensive efforts have been made to tackle these challenging issues and technological developments have been achieved and enabled the fabrication of reasonable EQE LEDs. In this review, recent advances in the growth of high-quality AlGaN epitaxial layers, transparent and reflective ohmic contacts, and light extraction for AlGaN-based UV LEDs are reviewed.
Recording human gestures from a wearable sensor produces valuable information to implement control gestures or in healthcare services. The wearable sensor is required to be small and easily worn. ...Advances in miniaturized sensor and materials research produces patchable inertial measurement units (IMUs). In this paper, a hand gesture recognition system using a single patchable six-axis IMU attached at the wrist via recurrent neural networks (RNN) is presented. The IMU comprises IC-based electronic components on a stretchable, adhesive substrate with serpentine-structured interconnections. The proposed patchable IMU with soft form-factors can be worn in close contact with the human body, comfortably adapting to skin deformations. Thus, signal distortion (i.e., motion artifacts) produced for vibration during the motion is minimized. Also, our patchable IMU has a wireless communication (i.e., Bluetooth) module to continuously send the sensed signals to any processing device. Our hand gesture recognition system was evaluated, attaching the proposed patchable six-axis IMU on the right wrist of five people to recognize three hand gestures using two models based on recurrent neural nets. The RNN-based models are trained and validated using a public database. The preliminary results show that our proposed patchable IMU have potential to continuously monitor people's motions in remote settings for applications in mobile health, human-computer interaction, and control gestures recognition.
Sb2Se3 has great potential for applications in near‐infrared sensors because of its narrow bandgap, environmental friendliness, and high absorption coefficient. However, the low conductivity of ...Sb2Se3 is an obstacle to the further development of high‐performance optoelectronic devices. In this study, to address this challenge, the selenization process is adopted. The incorporation of Se atoms into Sb2Se3 facilitates the crystallization of the films and the formation of hk0‐textured grains at a lower temperature than unselenized Sb2Se3. The selenized films possess larger grains than the unselenized ones at the same temperature. X‐ray photoelectron spectroscopy (XPS) results show that annealing causes the generation of donor‐like point defects (e.g., Vse and SbSe) and SeO2. The 250 °C‐annealed selenized Sb2Se3‐based photodetectors (PDs) have a high responsivity of 1130 mW A−1 and a specific detectivity of 4.62 × 1011 Jones. The PDs exhibit a fast response time (i.e., rise/fall time of 4.54 ms/8.50 ms), sensitivity of 94.2 at 20 mW cm−2, and external quantum efficiency of 155% at 200 µW cm−2. Further, the selenized PDs have good stability to moisture and air. Based on the XPS, X‐ray diffraction, and transmission electron microscope results, the improved performance of the selenized Sb2Se3‐based PDs is described and discussed.
Highly crystalline selenized Sb2Se3 films are firstly investigated and applied to near‐infrared photodetectors (PDs). The 250 °C‐annealed selenized PDs are found to give a significantly enhanced responsivity and shorter response time than previous studies. The improved performance is attributed to the combined effect of the formation of donor‐like defects, inclusion of larger hk0‐textured grains, and less inclusion of SeO2.
We report high performance flexible Sn-doped In2O3 (ITO) films prepared by in-line type vertical plasma arc ion plating for high performance flexible perovskite solar cells. Even at room temperature ...deposition, the ion-plated ITO film showed a low sheet resistance of 15.75 Ohm per square, a high average optical transmittance of 85.88% and a small outer bending radius of 5 mm because energetic ITO ions accelerated to the substrate led to better crystallinity and adhesion than sputtered ITO films. In addition, the ion-plated ITO films showed atomically flat and smooth surfaces due to different growth mechanisms and the absence of resputtering effects during the ion plating process. Flexible perovskite solar cells fabricated on the ion-plated ITO electrodes showed a higher power conversion efficiency of 16.8% than the sputtered ITO-based perovskite solar cell, indicating the potential of ion plated ITO films as promising flexible and transparent electrodes for perovskite solar cells.
Formamidinium lead triiodide (FAPbI3) exhibits excellent thermal and chemical stability, making it a suitable alternative for methylammonium lead triiodide (MAPbI3) in high‐performance ...photodetectors. However, FAPbI3 faces the challenge of transforming from the metastable photoactive black phase α‐FAPbI3 to the photoinactive yellow phase δ‐FAPbI3 at room temperature. This phase transition is accelerated in humid atmospheric conditions. To realize high‐performance FAPbI3‐based photodetectors, it is crucial to form stable and highly crystalline phase‐pure α‐FAPbI3 films. Herein, is fabricate highly stable and crystalline FAPbI3 films and photodetectors through anti‐solvent additive engineering (AAE) using a green anti‐solvent (isopropanol, IPA) and an organic spacer (phenethylammonium iodide, PEAI). It is found that PEAI‐AAE treatment induced 001‐preferred orientation growth in FAPbI3 films, and passivated defects within the crystal. The photodetectors based on PEAI‐AAE‐treated FAPbI3 film exhibits a fast response time of 485 µs/525 µs (rise time/fall time), high responsivity of 24.89 A W−1, and excellent specific detectivity of 1.56 × 1013 Jones. Moreover, the PEAI‐AAE‐treated FAPbI3 photodetector retained over 80% of its initial performance even after exposure to ambient air for over 720 h, demonstrating excellent long‐term stability. This study provides a green processing method that paves the way for future commercialization of perovskite‐based optoelectronic devices.
Using PEAI (organic spacer) and IPA (green anti‐solvent), FAPbI3 films are fabricated via PEAI‐anti‐solvent additive engineering (AAE) and implemented in photodetectors. PEAI‐AAE treatment induces (001)‐preferred orientation growth of FAPbI3 films, thereby enhancing their crystallinity. The PEAI‐AAE‐treated FAPbI3 photodetectors exhibit high responsivity, fast response speed, and excellent long‐term stability.
The fabrication of ultra-high-resolution micro-displays with low power consumption is essential for applications in virtual reality and augmented reality systems. In this regard, GaN-based ...light-emitting diodes (LEDs) have been regarded as a promising candidate for self-emissive micro-displays. However, micro-LEDs suffer from sidewall defects and low quantum efficiency at a low current. Thus, we investigated the electrical and optical properties of InGaN-based green (520 nm) LEDs as functions of V pits and chip size. With decreasing chip size, the forward voltage of all samples increased at the same injection current. The samples with V pits exhibited markedly higher current density than those without V pits. With decreasing chip size, the current densities of all the samples increased, whereas the output power at the same current density decreased. As the chip size decreased, the peak external quantum efficiency of all the samples decreased, which was attained at high current densities. Furthermore, the samples with V pits displayed more efficient current spreading behavior, smaller ideality factors, and a smaller S parameter than the ones without V pits. The emission wavelength of the small samples (<300 μm) was blue-shifted with increasing current density. Based on the cathodoluminescence results, the effects of chip size, current density, and V pits on the electroluminescence spectral shift of green LEDs are described and discussed.
•First investigated combined effects of chip size and V pits on the performance of green micro-LEDs.•The samples with V pits exhibited higher current density and output power than the ones without V pits.•Efficiency, the ideality factor and S parameter sensitively depend on the size and V-shaped defects.•Optimization of chip size and V pits is found to be crucial for micro-LEDs for LED-based displays and other applications.
Anthropomorphic robotic hands are designed to attain dexterous movements and flexibility much like human hands. Achieving human-like object manipulation remains a challenge especially due to the ...control complexity of the anthropomorphic robotic hand with a high degree of freedom. In this work, we propose a deep reinforcement learning (DRL) to train a policy using a synergy space for generating natural grasping and relocation of variously shaped objects using an anthropomorphic robotic hand. A synergy space is created using a continuous normalizing flow network with point clouds of haptic areas, representing natural hand poses obtained from human grasping demonstrations. The DRL policy accesses the synergistic representation and derives natural hand poses through a deep regressor for object grasping and relocation tasks. Our proposed synergy-based DRL achieves an average success rate of 88.38% for the object manipulation tasks, while the standard DRL without synergy space only achieves 50.66%. Qualitative results show the proposed synergy-based DRL policy produces human-like finger placements over the surface of each object including apple, banana, flashlight, camera, lightbulb, and hammer.
In this study, two-channel thin-film transistors (TC TFTs) using sputtered-deposited amorphous indium-gallium-zinc oxide (a-IGZO) as a channel layer and atomic-layer-deposition Al 2 O 3 as gate ...insulator (GI) are proposed for wearable and portable device application. Symmetric-TC (S-TC) TFT structure consisted of conventional bottom gate (BG) TFT stacked on top of top gate (TG) TFT. Asymmetric-TC (A-TC) TFT contained BG TFT with tandem structure on the TG TFT. It was shown that the TC TFTs exhibited excellent performance such as high field-effect mobility (<inline-formula> <tex-math notation="LaTeX">\mu _{\text {FE}} </tex-math></inline-formula>) and ON/ OFF current ratio (<inline-formula> <tex-math notation="LaTeX">I_{\scriptstyle{\text{ON/OFF}}} </tex-math></inline-formula>) at low voltages (< 2 V). For instance, the S-TC TFTs gave <inline-formula> <tex-math notation="LaTeX">\mu _{\text {FE}} </tex-math></inline-formula> of 19.67 cm 2 /Vs and <inline-formula> <tex-math notation="LaTeX">I_{\scriptstyle{\text{ON/OFF}}} </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">5.48\times 10^{{8}} </tex-math></inline-formula>. Furthermore, the A-TC TFTs with tandem structure yielded <inline-formula> <tex-math notation="LaTeX">\mu _{\text {FE}} </tex-math></inline-formula> of 30.15 cm 2 /Vs, a small threshold voltage of −1.25, a low subthreshold swing of 89 mV/decade, and a high <inline-formula> <tex-math notation="LaTeX">I_{\scriptstyle{\text{ON/OFF}}} </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">1.70\times 10^{{9}} </tex-math></inline-formula>. It was found that the TC TFTs demonstrated better electrical performance than the sum of individual TG and BG TFTs. Under bias stress tests, the TC TFTs experience less <inline-formula> <tex-math notation="LaTeX">{V}_{\text {th}} </tex-math></inline-formula> shift (<inline-formula> <tex-math notation="LaTeX">\Delta {V}_{\text {th}} </tex-math></inline-formula>) than the TG and BG TFTs.
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