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The manuscript introduces a radio wave-based wireless communication system tailored for Autonomous Underwater Vehicles (AUVs), optimized for underwater deployment. Initial experiments to ascertain the fundamental properties of a loop antenna were conducted in a small-scale water tank, followed by comprehensive communication and video transmission trials in a larger tank with an AUV. A specialized waterproof enclosure was developed to house a waterproof antenna, a Vector Network Analyzer (VNA), and a communication board. This setup facilitated the evaluation of the loop antenna’s radio propagation attributes and the identification of frequencies conducive to underwater communication. Designed with practical deployment in mind, the system incorporates a 2-meter loop antenna for signal transmission and a 0.5m by 0.8m rectangular loop antenna integrated into the AUV for signal reception. Utilizing a wavelet Orthogonal Frequency Division Multiplexing (OFDM) communication board and tuning to lower frequencies, the system successfully established User Datagram Protocol (UDP) and Transfer Control Protocol (TCP) communications within a few meter radius from the transmitting antenna, achieving data transfer rates up to 6.8 Mbps.

Various human assistance robots that effectively assist the daily activities of persons with perception deficits have recently been developed. In this paper, a perception assist method with an upper limb power assist exoskeleton robot is proposed for meal activities, which are important in daily living. The proposed robot-based method assists users by appropriately assessing utensil trajectories and posture performance according to the target position of the user. A method to predict the user’s target position based on the user’s motion trajectories and shoulder muscle electromyographic (EMG) signals is also proposed. Two kinds of virtual tunnels (for the utensil trajectory and utensil posture) corresponding to the user’s target position are defined in the proposed method to monitor the accuracy of the executed motion. The spatial relationship between the virtual tunnels is controlled to perform the eating task with the assistance of the power assist robot. The user’s hand motion is automatically modified by the robot in real time if the utensil trajectory and/or posture exits the respective virtual tunnel during meal activities. The effectiveness of the proposed method is evaluated through experiments.

The purpose of this study is to facilitate knowledge discovery about the relationship between driving and health among the elderly. In the Iwaki Health Promotion Project that is an annual project conducted by Hirosaki University, we have included a survey on driving for the first time in 2019. After linking the data obtained from the survey with four years of health data for 2016–2019, we have utilized PLSA as a machine learning method to cluster those data in an integrated manner. As a result, we have found latent classes broadly classified according to whether the health level has been generally high or low. Also, when we have focused on a specific health item, for example, cognitive function, we have found some people with higher and lower maintenance of cognitive function over four years, even if they have belonged to a same latent class. To characterize these differences in detail, we have utilized t-SNE as a machine learning method. As a result, we have found that “I like driving” as a factor related to the Kansei (sensitivity) may characterize the high maintenance of cognitive function. For those who like driving, it is considered that the high maintenance of cognitive function may be occurred because they enjoy driving, have a wider range of activities, and increase the possibility of multitasking.

The conductivity of tungsten disulfide (WS2) films using sputtering, which is a physical vapor deposition (PVD), was enhanced using a chlorine (Cl2)-plasma treatment and sulfur-vapor annealing (SVA). For WS2 films to be used in thermoelectric devices, its carrier concentration must be controlled. Therefore, we exposed WS2 films to Cl2-plasma as a doping method. In addition, SVA was performed to improve the crystallinity of the film and potentially introduce activating dopants. Consequently, the conductivity of the Cl2-plasma-treated PVD-WS2 films (0.440 S/m) more than doubled compared with that of an untreated PVD-WS2 film (0.201 S/m). The doping type in this experiment is considered to be n-type on the basis of a positive peak shift observed in the X-ray photoelectron spectra.

This paper presents a guaranteed-cost disturbance observer and controller design to achieve accurate path tracking control for a powered paraglider (PPG) in the presence of unknown rudder trim and wind disturbances. The key contribution of this paper is a theoretical approach that ensures given flight control performance even in the presence of these unknown variables. Due to the complex and highly nonlinear nature of PPG dynamics, our approach utilizes a nonlinear control framework based on Takagi-Sugeno fuzzy models. Although this paper designs a nonlinear controller that compensates the rudder input not only with the trim but also with the wind estimated by the disturbance observer, it successfully derives guaranteed-cost design conditions that allow the separate design of the disturbance observer and the nonlinear controller within this framework. In addition, the influence of observer estimation errors on control performance degradation is discussed in terms of considering the upper bound of given control performance. The effectiveness of the proposed approach is demonstrated through extensive flight simulations using a high-precision PPG simulator, which accurately models the real-world flight dynamics of two rigid bodies with seven degrees of freedom. This validates the practical utility of the guaranteed-cost disturbance observer and controller design in maintaining control performance under unknown rudder trim and wind disturbances.

The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an increased focus on the routine analysis of vital signs such as breathing and pulse rates. Radar technology has proven effective for non-contact, long-term monitoring of these vital signs, with frequency analysis being the default method for processing signals from Doppler radar owing to their inherent noise. However, conventional analysis approaches often struggle to detect weak signals buried within the sidelobes of other signals. Some data analysis techniques for Doppler radar rely on machine learning, but they struggle to generate clear time-frequency diagrams, complicating heartbeat detection. In this study, we employed non-harmonic analysis (NHA) as a frequency analysis method to mitigate sidelobe interference and implemented semantic segmentation for precise heartbeat detection. To validate the proposed approach, we conducted heartbeat detection tests both in stationary, low-noise conditions and in a noisy driving simulation environment. The results indicated that the NHA method successfully analyzed heartbeat harmonics, suggesting its potential for detecting heartbeat components through machine learning. To validate these findings, we determined the detection accuracy by comparing true and false positive rates, allowing us to quantify the detectability of heartbeats under both resting and driving simulation conditions.

Robotic prosthetic hands can help perform the intended sophisticated movements of the upper limb, which can assist amputees to perform their daily activities. Although a robotic prosthetic hand can be controlled in real-time using the user’s electromyography (EMG), which directly reflects the user’s motion intention, some important EMG signals are usually lost owing to muscle deficiency. This study proposes a muscle activity estimator that is inspired by the muscle synergy across subjects to estimate the activity of the missing muscles in amputees in real-time. The proposed estimator learns muscle synergy from the EMG balance, finger joint angles, and the grasping force of healthy persons. The proposed estimator is developed as an artificial neural network (ANN) with a novel cell structure that combines long-short-term memory and damping neurons to analyze muscle dynamics. Furthermore, to improve the accuracy of learning muscle synergy, the muscles to be input to the estimator are selected by focusing on the enslavement of muscles and anatomical relationships. The effectiveness of the proposed estimator is evaluated by experiments. The results showed that the proposed estimator can contribute well to the realization of the intended sophisticated motions of the user.

Wireless powered communication network (WPCN) is a novel structure of the network that integrates wireless information communication (WIT) and wireless energy transfer(WET). The scheduling design is a key factor for performance improvement for WPCN. As an effective scheduling design approach, “Harvest-then-Access” has been proposed. This approach requires optimizing control parameters in the scheduling. Therefore, some approaches, such as machine learning or simulation, have been used. This paper proposes a Markov-chain model-based analytical model of Harvest-then-Access scheduling for WPCN. We propose a new Markov-chain model, which includes the essential operation in WPCN with Harvest-then-Access. From the analytical model, we derive the optimal time interval of WET in the network with Harvest-then-Access, which simultaneously provides throughput improvement and fairness among devices. The validity of the proposed analytical model is demonstrated by comparing the analytical and simulation result. Then, we evaluate the performance of Harvest-then-Access scheduling through comparison to the other scheduling.

Several studies have been published on noncontact heartbeat detection recently. Particularly, a few studies have found that radar for noncontact detection is effective for long-term monitoring. As the novel coronavirus continues to spread worldwide, the use of radar is expected to prevent the contamination of equipment by the virus and enable heartbeat detection from a safe distance. To monitor heartbeat fluctuation, heartbeat signals must be detected over a short period; however, conventional methods require approximately 5 s for detection in the stationary state of the human body. This study developed a method for detecting heartbeat in approximately 2.5 s based on nonharmonic analysis (NHA) to suppress sidelobes. The method has nearly no data length limitations in terms of frequency resolution. To validate the method, heartbeat detection is performed in a stationary state with reduced noise and a driving simulation environment with high noise. Frequency analysis of the received signals enabled the detection of heartbeat harmonics, suggesting the possibility of detecting the fundamental heartbeat frequency from its harmonics. To test this aspect, the detectability of heartbeat harmonics is determined under the stationary and driving simulation conditions from a comparison of the conventional short-time Fourier transform, continuous wavelet transforms, and the proposed NHA method.

Arrhythmias are conditions characterized by a faster, slower, or irregular heart rhythm. Some of them may be harmless and brief, but others can lead to sudden cardiac arrest. Thus, procedures that safely restore a normal heartbeat are a matter of interest. Laboratory experiments have evidenced that some arrhythmia exhibit nonlinear deterministic behavior, which justifies the need to build mathematical models for heartbeat description. The study of these models may contribute to a better understanding of arrhythmias mechanism and new heartbeat control treatments. This paper addresses a model-based tracking control method for heart rhythm regulation in a cardiac model. Since there is no consensus on the equations describing the heart dynamics, we leverage a nonlinear oscillator that is able to reproduce a variety of electrocardiogram-like waveforms when adjusting a parameter. First of all, the nonlinear system under study is represented as a Takagi-Sugeno fuzzy model. Due to its multiple local linear systems structure, tracking control design conditions for both nominal and uncertain slave systems are formulated as linear matrix inequalities. The simulation examples show that the proposed feedback control framework can restore the heart rhythm dynamics from a non-desirable situation to the normal behavior given by the reference system, which reveals a proof of concept to use tracking control techniques to suppress pathological behaviors.

In this study, we experimentally demonstrated concepts for realizing doping-free Tungsten Diselenide (WSe2) complementary metal-oxide-semiconductor (CMOS) inverter by developing alloys and compound metals used as source/drain (S/D) contacts. Aluminum – scandium alloy (AlSc) and tungsten oxide (WOx)-based S/D contacts enable efficient electron and hole injection into WSe2 for n-type and p-type FET operation because the work function (WF) of AlSc and WOx are aligned to neighboring the conduction and valence band edge of WSe2, respectively. A dual-gate bias architecture is used to improve electrical characteristics of FETs and enhance CMOS inverter performance after device fabrication. By utilizing AlSc and WOx-based S/D contacts in conjunction with the dual-gate bias architecture, our fabricated WSe2 CMOS inverter realized a higher gain at $\text{V}_{\mathrm{ dd}}$ of 1 V or higher than those in the literatures. Furthermore, the fabricated WSe2 CMOS inverter is operated at a power supply voltage ( $\text{V}_{\mathrm{ dd}}$ ) of as low as 0.5 V. This study paves the way towards research and development of transition metal dichalcogenides-based devices and circuits.

We propose and demonstrate a stable single-longitudinal mode (SLM) thulium-doped fiber laser (TDFL) with a Fabry- Pérot (F-P) fiber Bragg grating (FBG) filter and a triple-coupler based double-ring cavity (TC-DRC) filter. For the first time, this structure of TC-DRC filter is used to select a single mode from dense longitudinal-modes in a ring cavity TDFL. The design and fabricate methods of TC-DRC filter are revealed and the principle of SLM selection is also analyzed in detail. The experimental results demonstrated the good performance of the proposed filter. The central wavelength of proposed TDFL is 2049.49 nm and its OSNR is higher than 35 dB. There is no obvious wavelength drift during the test, and the power fluctuation is less 0.5 dB. The SLM operation is verified through the self-homodyne method, this laser can be stably maintained in a SLM state after operating for one hour under laboratory condition. In addition, the linewidth is measured less than 10 kHz based on the phase noise demodulation method.

Sheet resistance (Rsheet) reduction of a-few-layered molybdenum disulfide (MoS2) film using sputtering is investigated in this study. To enhance the carrier density, chlorine (Cl2) gas excited by inductively coupled plasma is introduced as a substitute for sulfur. To electrically activate the Cl dopants and simultaneously prevent out-diffusion of sulfur, a furnace annealing was performed in sulfur-vapor ambient. Consequently, the Rsheet in the MoS2 film with the Cl2 plasma treatment remarkably reduced by one order lower than that without one, because of the activation of Cl dopants in the MoS2 film.

A multiaperture along-track interferometric synthetic aperture radar (MA-ATI SAR) theory was proposed to obtain velocity vectors of moving objects. This theory utilizes two antennas to estimate two velocity components (aft- and fore-looking directions) by multi/sublook processing. The moving direction can then be calculated by the two velocity components. Combining it with the conventional range velocity estimation, the velocity vector can be estimated. In order to validate its methodology, the present study applies MA-ATI SAR to airborne polarimetric interfereometric SAR-2 (Pi-SAR2) for estimating the directions of moving water surface currents of rivers. The results were in good agreement with the true moving directions. The estimated accuracy showed the direction error of approximately 20° for the three cases out of four. One case showed the higher error, since there may be complicated flow patterns. The findings of this study have implications for the applicability of the MA-ATI method to an airborne SAR system.

Robotic-assisted microsurgeries provide several benefits to both patients and surgeons. Nevertheless, there are still some limitations and challenges associated with their outcome, one of which is a lack of force feedback. Without force information, the risk of delicate tissue damage from the excessive force applied by surgeons would be increased. Since it is difficult to install force sensors on microsurgical tools, a novel approach for estimating a force vector from the deformation of the surgical tool is proposed in this paper. In the proposed approach, a surgical instrument that deforms according to the magnitude of the tool-to-tissue force is designed, and a time series convolution neural network is used to make the nonlinear relationship between the visual information of the deformation of the surgical tool and the applied forces in such a way that the tool-to-tissue force can be estimated according to the deformation of the surgical instrument in a real-time manner. The experimental results prove that the applied force can be successfully estimated with high accuracy in three dimensions using the proposed method.

A method for improving the estimation accuracy of the velocity of cruising ships is proposed using synthetic aperture radar (SAR) sublook images in the spotlight mode. The main purpose of spotlight SAR is to obtain high resolution utilizing longer integration times than those of other imaging modes, and the proposed method is based on these long integration times. The principal methodology is to produce successive N sublook images of a cruising ship, where N is more than approximately 10. The positions of the look-1 and look-N subimages differ by a substantial distance proportional to the cruising speed and the long interlook time difference. The distance, and hence the velocity of the cruising ship, can be computed from the cross-correlation function of these two sublook images with improved accuracy compared with other modes. We tested using PALSAR-2 spotlight subimages with N = 2, 10, and 20, and the results are compared with the automatic identification system data. Five images of ships cruising close to the azimuth direction were tested; the best result was obtained for the 10-look images with an average error of 13.8%, followed by 17.9% and 40.5% errors for the 20- and 2-look images, respectively. The reason is also given for the best result of the 10-look case over the 20-look case.

A layered polycrystalline WS2 film is formed by radio-frequency (RF) magnetron sputtering and sulfur-vapor annealing (SVA). Its $p$ MISFET is successfully demonstrated with TiN/HfO2 top-gate stack, TiN contact, and ultra-thin body and box technologies. A WS2 film with a (002) plane is formed parallel to a substrate surface using RF magnetron sputtering, and its crystallinity is drastically enhanced by the SVA. $I$ – $V$ characteristics with $p$ -type operation are confirmed in WS2 MISFETs with a maximum field effect mobility of $1.5\times10$ −2 cm2V−1s−1. Therefore, our film-formation method is a promising candidate for $p$ MOSFETs in CMOS circuits.

To prevent accidents occurring in daily life, such as the collision between objects in the environment and our body, the perception-assist technique, which can automatically change a dangerous motion to a safe motion, has been considerably studied. In addition, it has recently been found by the authors that a human's motion is different from his/her intended motion if vibration stimulation is presented on an antagonist muscle. In this study, a method to change human motion in a controlled manner using vibration stimulation is proposed for the perception-assist and applied for elbow-joint-extension motion change. In this study, it is elucidated that the amount of elbow-joint-extension motion change can be changed with respect to the frequency change of the vibration stimulation. Furthermore, it is elucidated that the change in the human elbow-joint-extension motion can be generated soon after the vibration stimulation is provided. Based on the characteristics of motion change with respect to vibration stimulation, the proposed method controls the change of the user's elbow-joint-extension motion by adjusting the frequency of the vibration stimulation to achieve the target motion, which is different from the user's intended motion. The effectiveness of the proposed method toward the change in the human elbow-joint-extension motion was experimentally evaluated.

Recent advances in AI technologies are dramatically changing the world and impacting our daily life. However, human users still essentially need to cooperate with AI systems to complete tasks as such technologies are never perfect. For optimal performance and safety in human-AI cooperation, human users must appropriately adjust their level of trust to the actual reliability of AI systems. Poorly calibrated trust can be a major cause of serious issues with safety and efficiency. Previous works on trust calibration have emphasized the importance of system transparency for avoiding trust miscalibration. Measuring and influencing trust are still challenging issues; consequently, not many studies have focused on how to detect improper trust calibration nor how to mitigate it. We approach these research challenges with a behavior-based approach to capture the status of calibration. A framework of adaptive trust calibration is proposed, including a formal definition of improper trust calibration called “a trust equation”. It involves cognitive cues called “trust calibration cues (TCCs)” and a conceptual entity called “trust calibration AI” (TCAI), which supervises the status of trust calibration. We conducted empirical evaluations using a simulated drone environment with two types of cooperative tasks: a visual search task and a real-time navigation task. We designed trust changing scenarios and evaluated our framework. The results demonstrated that adaptively presenting a TCC could promote trust calibration more effectively than a traditional system transparency approach.

Tremor, which is one of the most common movement disorders, is a repetitive movement that is caused by periodic muscle contraction and relaxation. To suppress tremors of upper-limb tremor patients, such as essential tremor (ET) patients, many kinds of devices have been developed. On the other hand, when mechanical vibration stimulation is applied to a human muscle, sustained muscle contraction, which is referred to as the tonic vibration reflex (TVR), is induced in the stimulated muscle. In this study, a novel tremor suppression method that utilizes the periodic TVR to induce muscle contraction/relaxation to generate the counterphase motion of the ET is proposed and applied to the forearm pronation-supination ET. In the proposed method, periodic vibration stimulation is applied to generate the periodic TVR in the pronator teres muscle and/or supinator muscle. First, the results confirmed that the TVR can be induced by applying mechanical vibration stimulation to the pronator teres muscle and supinator muscle since the forearm pronation-supination tremor is one of the key features of the ET. Furthermore, the findings also confirmed that the TVR intensity that is induced in these muscles can be adjusted by changing the vibration stimulation frequency. Second, the results show that the counterphase motion of the ET (i.e., periodic pronation-supination motion) can be generated by applying the proposed method. The effectiveness of the proposed method for tremor suppression is evaluated by comparing the generated motion with the ET motion.

Low-carrier density and high-crystallinity molybdenum disulfide (MoS2) films were fabricated by low-temperature and clean process based on a UHV RF sputtering system. This paper focuses on improving crystallinity and reducing the number of sulfur defects of sputtered-MoS2 film. We have fabricated MoS2 films at lower than 400°C using the sputtering and H2S post-deposition annealing processes. Consequently, MoS2 films with high crystallinity and appropriate S/Mo ratio were obtained. Eventually, a low carrier density of 3.5 × 1017 cm-3 and the Hall-effect mobility of 12 cm2 V-1 s-1 were achieved.

To the best of our knowledge, a phase-modulated hybrid high-speed Internet/wireless local area network (WLAN) wireless fidelity (Wi-Fi)/pre-fifth-generation (Pre-5G) in-building network over an integration of single-mode fiber (SMF), phonic crystal fiber (PCF), and graded index-plastic optical fiber (GI-POF)/invisible laser light communication (IVLLC) transmission is feasibly demonstrated for the first time. An effective fiber Bragg grating (FBG)-based phase modulation (PM)-to-intensity modulation (IM) conversion scheme is adopted to replace the sophisticated dispersion-induced PM-to-IM conversion scheme or costly delay interferometer (DI). This proposal is the first one to deliver high-speed Internet, WLAN Wi-Fi, and Pre-5G broadband heterogeneous services so as to bridge fiber backhaul and in-building network. The light is phase-modulated with 4-Gb/s four-level pulse amplitude modulation (PAM4) (high-speed Internet), 24-Mbps/2.4-GHz microwave (MW) (WLAN Wi-Fi), and 5-Gb/s/3.5-GHz 16-quadrature amplitude modulation-orthogonal frequency-division multiplexing (Pre-5G) data signals over 41.44-km fiber link (40-km single-mode fiber +1.44-km photonic crystal fiber) with 30-m GI-POF/IVLLC transmission. Bit error rate, PAM4 eye diagrams, error vector magnitude, and constellation map are examined to perform well to reveal the practicality of constructing a phase-modulated hybrid high-speed Internet/Wi-Fi/Pre-5G in-building network.

A high Hall-effect mobility of 1,250 cm2V1s−1 is achieved in ZrS2 film as a two-dimensional semiconductor. A large-area atomic-layered polycrystalline ZrS2 film was obtained by sputtering and sulfurization. It was confirmed that a layered ZrS2 film on a SiO2/Si substrate was successfully achieved by a high-temperature sputtering and sulfur compensation process. We demonstrated that the Hall-effect mobility and the carrier density were greatly improved to 1,250 cm2V−1s−1 and $8.5 \times 10^{17}$ cm−3, simultaneously. High-mobility two-dimensional ZrS2 film is a strong candidate for advanced MISFETs.

In this paper, we investigated the source/drain recessed contact structure to mitigate the self-heating-effects in vertically stacked-nanowire FETs. As a result, lattice temperature of nanowire regions during device operation was considerably decreased by using the source/drain recessed contact structure. This is attributed to an increase in heat dissipation mainly from heat source to bulk wafer. Moreover, we proposed the p/n-stacked nanowire on bulk FinFET and its 6T-SRAM layout. Area of the proposed SRAM was reduced approximately 15%, as compared to the conventional cell layout.

We have fabricated large area integrated top-gate ${n}$ MISFETs with sputter-deposited-MoS2 film having n-type operation. A sputtering method enables us to form a large-area MoS2 thin film followed by H2S annealing to compensate sulfur vacancies. Two passivation films of ALD-Al2O3 enhance the process endurance of MoS2 channel. Therefore, we demonstrate TiN-top-gate ${n}$ MISFET, which is a substantial first step to realize industrial chip-level LSIs with MoS2-channel FETs.