Institute of Electrical and Electronics Engineers Acta Medica Okayama 2644-1284 5 2024 Skewing Technology for Permanent Magnet Synchronous Motors: A Comprehensive Review and Recent Trends 1251 1273 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University This article gives a comprehensive overview of the current research trends in the skewing technique for permanent magnet synchronous motors (PMSMs). The skewing technique has been widely used in many applications to reduce the cogging torque and torque ripple in PMSMs. There are many ways to implement the skew, and new techniques are continually being developed. First, this article summarizes the types of skew structures and presents a survey of existing techniques. Specific emphasis is placed on what kind of skew structure is selected depending on the PMSM configuration. Second, the optimal value of the skew angle for each structure is comprehensively explained, and the discrepancy between theory and finite element analysis is discussed. The definition of skew angle varies across the literature, and one of the purposes of this article is to organize the definition in an easy-to-understand manner. In addition, this article offers three-dimensional finite element analysis (3D-FEA) results of various PMSMs employing the skew for quantitative comparison. Then, this article discusses the properties of PMSMs using the skew by structure and the latest trends, and finally describes future prospects. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 Detecting Unintended Redirects to Malicious Websites on Android Devices Based on URL-Switching Interval 153285 153294 EN Toshihiro Yamauchi Faculty of Environmental, Life, Natural Science and Technology, Okayama University Rintaro Orito Graduate School of Natural Science and Technology, Okayama University Koji Ebisu Graduate School of Natural Science and Technology, Okayama University Masaya Sato Faculty of Computer Science and Systems Engineering, Okayama Prefectural University Website clicks that redirect Android-phone users to malicious websites with fake virus alerts or phishing attacks are increasing exponentially. Although a uniform resource locator (URL) blocklist is considered a suitable countermeasure to such attacks, it is difficult to efficiently identify malicious websites. To the best of our knowledge, no research has focused on detecting attacks that redirect Android-phone users to malicious websites. Therefore, we propose a redirect-detection method that focuses on the URL bar-switching interval of Android-based Google Chrome browser. The proposed method, which can be easily installed as an Android application, uses the Android accessibility service to detect unintended redirects to malicious websites without collecting information about these websites in advance. This paper details the design, implementation, and evaluation results of the proposed application on an actual Android device. We determined the threshold values for the number of times the URL bar switches and the elapsed time to determine redirects to malicious websites for the proposed method. Based on the results, we investigated the causes of false-positive detection of redirects to benign websites and offer solutions on handling them. We also present the threshold values that can minimize the false positive and negative rates, as well as the detection accuracy of the proposed method based on these threshold values. Additionally, we present the evaluations results based on the access logs of actual users participating in the WarpDrive project experiment, which indicate that the proposed method minimizes false positives and successfully detects most redirects to malicious websites. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 A Protection Scheme With Speech Processing Against Audio Adversarial Examples 146551 146559 EN Yuya Tarutani Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Taisei Yamamoto Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yukinobu Fukushima Faculty of Environmental, Life, Natural Science and Technology, Okayama University Tokumi Yokohira Faculty of Interdisciplinary Science and Engineering in Health Systems, Okayama University Machine learning technologies have improved the accuracy of speech recognition systems, and devices using those systems, such as smart speakers and AI assistants, are now in wide use. However, speech recognition systems have security vulnerabilities. In particular, a known machine learning vulnerability called audio adversarial examples (AAEs), which causes misrecognition in speech recognition systems, has become a problem. We propose a scheme for using speech processing to protect speech recognition systems from AAEs, preventing misrecognitions by slight processing of input speech that does not affect the recognition of normal speech. We use two kinds of processing: speed and frequency. Evaluation results show that the proposed scheme can reduce the success rate of attack speech to about 1% while maintaining about 85% recognition rates for normal speech. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 MUSIC Spectrum Based Interference Detection, Localization, and Interference Arrival Prediction for mmWave IRS-MIMO System 142592 142605 EN Yafei Hou Faculty of Environmental, Life, Natural Science and Technology, Okayama University Kazuto Yano Wave Engineering Laboratories, Advanced Telecommunications Research Institute International Norisato Suga Wave Engineering Laboratories, Advanced Telecommunications Research Institute International Julian Webber Wave Engineering Laboratories, Advanced Telecommunications Research Institute International Satoshi Denno Faculty of Environmental, Life, Natural Science and Technology, Okayama University Toshikazu Sakano Wave Engineering Laboratories, Advanced Telecommunications Research Institute International For a millimeter wave (mmWave) intelligent re-configurable surface (IRS)-MIMO system, if it can correctly detect the interference occurrence and their locations, the patterns of interference signal can be collected and learned using machine learning for the prediction of interference arrival. With the information of interference location and activity pattern, the capacity of the system can be largely improved using many techniques such as beamforming, interference cancellation, and transmission scheduling. This paper aims to detect interference occurrence using a low-complexity MUSIC (MUSIC: multiple signal classification) spectrum-based method, and then localize their sources for mmWave IRS-MIMO system. The MUSIC spectrum of wireless system can be regarded as somehow the 'signature' related to the signals transmitted from different users or interference. We utilize such property to detect the occurrence of interference, and then localize their sources in a low-complexity way. Finally, the pattern of interference occurrence can be learned to predict the interference arrival from the collected data. This paper also proposed an efficient probabilistic neural network (PNN)-based predictor for the interference arrival prediction and showed its prediction accuracy. From simulated results, our proposed method can achieve the correct results with the accuracy near to 100% when the fingerprint samples is over 10. In addition, the localization error can be within 1 m with more than 65% and 43% for Y-axis and X-axis, respectively. Finally, based on the results of the interference occurrence, the proposed PNN-based predictor for the interference arrival prediction can capture correctly the similar distribution function of the coming continuous idle status. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 Adaptive Resonance Theory-Based Global Topological Map Building for an Autonomous Mobile Robot 111371 111385 EN Yuichiro Toda Faculty of Environmental, Life, Natural Science and Technology, Okayama University Naoki Masuyama Graduate School of Informatics, Osaka Metropolitan University 3D space perception is one of the key technologies for autonomous mobile robots that perform tasks in unknown environments. Among these, building global topological maps for autonomous mobile robots is a challenging task. In this study, we propose a method for learning topological structures from unknown data distributions based on competitive learning, a type of unsupervised learning. For this purpose, adaptive resonance theory-based Topological Clustering (ATC), which can avoid catastrophic forgetting of previously measured point clouds, is applied as a learning method. Furthermore, by extending ATC with Different Topologies (ATC-DT) with multiple topological structures for extracting the traversable information of terrain environments, a path planning method is realized that can reach target points set in an unknown environment. Path planning experiments in unknown environments show that, compared to other methods, ATC-DT can build a global topology map with high accuracy and stability using only measured 3D point cloud and robot position information. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 Feasibility of Active Reactance Compensator for Autonomously Maximizing Repeater Coil Current of Wireless Power Transfer System Against Variations in Resonant Frequency and Magnetic Coupling Intensity 98175 98188 EN Masataka Ishihara Faculty of Life, Environment, Natural Science and Technology, Okayama University Kazuhiro Umetani Faculty of Life, Environment, Natural Science and Technology, Okayama University Akihiro Konishi Graduate School of Science and Engineering, Chiba University Eiji Hiraki Faculty of Life, Environment, Natural Science and Technology, Okayama University In resonant inductive coupling wireless power transfer systems, a repeater resonator is crucial in expanding the charging area, enabling efficient power supply to receivers, such as small Internet of Things (IoT) devices sparsely distributed in a wide area. However, the repeater current is highly susceptible to deviations in resonance frequency due to manufacturing tolerance and aging, as well as to the magnetic coupling between the transmitter and repeater coils, potentially leading to insufficient amplitude. Consequently, the magnetic field generated by the repeater decreases and the receiver may be difficult to obtain sufficient power from the transmitter via the repeater. To address this problem, this paper proposes a wireless power transfer system with active reactance compensators incorporated in the repeater and the transmitter. The proposed system can equivalently adjust the resonant frequencies of the transmitter and repeater to stably maximize the repeater coil current regardless of the variations in the resonant frequency and the magnetic coupling intensity. Experiments successfully verify that the proposed system can provide a more stable and larger repeater current and output power than the conventional system against the variations in the magnetic field intensity and the resonant frequency of the repeater, validating the feasibility of the proposed system for practical utilization of the repeater in expanding the charging area. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 12 2024 WLAN Channel Status Duration Prediction for Audio and Video Services Using Probabilistic Neural Networks 28201 28211 EN Yafei Hou Faculty of Environmental, Life, Natural Science and Technology, Okayama University Satoshi Denno Faculty of Environmental, Life, Natural Science and Technology, Okayama University Due to massive increase in wireless access from smartphones, IoT devices, WLAN is aiming to improve its spectrum efficiency (SE) using many technologies. Some interesting techniques for WLAN systems are flexible allocation of frequency resource and cognitive radio (CR) techniques which expect to find more useful spectrum resource by modeling and then predicting of channel status using the captured statistics information of the used spectrum. This paper investigates the prediction accuracy of busy/idle duration of two major wireless services: audio service and video service using neural network based predictor. We first study the statistics distribution of their time-series busy/idle (B/I) duration, and then analyze the predictability of the busy/idle duration based on the predictability theory. Then, we propose a data categorization (DC) method which categorizes the duration of recent B/I duration according the their ranges to make the duration of next data be distributed into several streams. From the predictability analysis of each stream and the prediction performance using the probabilistic neural network (PNN), it can be confirmed that the proposed DC can improve the prediction accuracy of time-series data in partial streams. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 A Proposal of an Axial-Flux Permanent-Magnet Machine Employing SMC Core With Tooth-Tips Constructed by One-Pressing Process: Improving Torque and Manufacturability 109435 109447 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd. Tomoyuki Ueno Sumitomo Electric Industries Ltd. This study aims to improve the torque performance and manufacturability of axial-flux permanent magnet (AFPM) machines. Hence, we propose a novel AFPM machine that employs a soft magnetic composite (SMC) core with tooth-tips constructed by a one-pressing process and die. In this paper, the proposed AFPM machine is compared to two conventional AFPM machines using an SMC core. One of them has open-slot structure without tooth-tips. Another model employs an SMC core with tooth-tips pressed by a conventional pressing process that requires multiple operations and dies. As a result of the comparison, the proposed AFPM machine realizes a much higher torque than the two conventional machines. Additionally, the manufacturability of an SMC core with tooth-tips pressed by the proposed method is superior to the conventional one because the proposed structure can be realized by the one-pressing process and die. Furthermore, two prototypes of the proposed AFPM machine and the conventional one with an open-slot structure are fabricated, and then, they are compared by experiments. Consequently, the proposed AFPM machine achieves a 15.7% higher torque than that of the conventional machine using an open-slot structure. Finally, this paper presents an improved design of an AFPM machine with SMC cores using the proposed pressing process. As a result, the proposed AFPM realizes a 20% larger torque than that of a conventional model employing an open-slot structure. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 Design and Analysis of Hybrid-Excitation Variable Flux Memory Motor for Traction Applications: Improving Output Power in High-Speed Area During Six-Step Operation Mode 82024 82036 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Keito Yokomichi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Variable flux motors with adjustable magnetic flux have been gaining attention because of their capability to simultaneously achieve a high torque density and high efficiency. In addition, the output power characteristic, which is related to acceleration performance, in high-speed areas is important in traction applications. However, typical traction motors have lower output power in high-speed areas. In this paper, a Hybrid-Excitation Variable Flux Memory Motor (HE-VFMM) is therefore proposed to enhance output power characteristics under six-step operation mode in high-speed area. The proposed HE-VFMM can perform magnetic flux adjustment with two components: field winding and variable flux permanent magnet (VPM), thus dramatically increasing flux adjustment range. The simulation results show the proposed HE-VFMM achieves 23.7% higher output power at 17,000 rpm than that of an existing traction motor in Prius 4th generation that has the same size while maintaining high efficiency in the frequently used operating area. Additionally, it was found that variable magnetic flux is very effective in enhancing the output power, especially in the high-speed region because the magnetic saturation in the stator core is mitigated by field-weakening control. Consequently, as the rotational speed increases, an increase ratio of the output power caused by the adjustable magnetic flux becomes higher. This paper shows that the proposed HE-VFMM is an effective method for improving the problem of low output power in high-speed regions in traction motors. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 Stargazer: Long-Term and Multiregional Measurement of Timing/ Geolocation-Based Cloaking 52750 52762 EN Shota Fujii Graduate School of Natural Science and Technology, Okayama University Takayuki Sato Research and Development Group, Hitachi Ltd. Sho Aoki Research and Development Group, Hitachi Ltd. Yu Tsuda National Institute of Information and Communications Technology Nobutaka Kawaguchi Research and Development Group, Hitachi Ltd. Tomohiro Shigemoto Research and Development Group, Hitachi Ltd. Masato Terada Research and Development Group, Hitachi Ltd. Malicious hosts have come to play a significant and varied role in today's cyber attacks. Some of these hosts are equipped with a technique called cloaking, which discriminates between access from potential victims and others and then returns malicious content only to potential victims. This is a serious threat because it can evade detection by security vendors and researchers and cause serious damage. As such, cloaking is being extensively investigated, especially for phishing sites. We are currently engaged in a long-term cloaking study of a broader range of threats. In the present study, we implemented Stargazer, which actively monitors malicious hosts and detects geographic and temporal cloaking, and collected 30,359,410 observations between November 2019 and February 2022 for 18,397 targets from 13 sites where our sensors are installed. Our analysis confirmed that cloaking techniques are widely abused, i.e., not only in the context of specific threats such as phishing. This includes geographic and time-based cloaking, which is difficult to detect with single-site or one-shot observations. Furthermore, we found that malicious hosts that perform cloaking include those that survive for relatively long periods of time, and those whose contents are not present in VirusTotal. This suggests that it is not easy to observe and analyze the cloaking malicious hosts with existing technologies. The results of this study have deepened our understanding of various types of cloaking, including geographic and temporal ones, and will help in the development of future cloaking detection methods. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 Artificial Neural Network Based Audio Reinforcement for Computer Assisted Rote Learning 39466 39483 EN Parisa Supitayakul Graduate School of Natural Science and Technology, Okayama University Zeynep Yücel Graduate School of Natural Science and Technology, Okayama University Akito Monden Graduate School of Natural Science and Technology, Okayama University The dual-channel assumption of the cognitive theory of multimedia learning suggests that importing a large amount of information through a single (visual or audio) channel overloads that channel, causing partial loss of information, while importing it simultaneously through multiple channels relieves the burden on them and leads to the registration of a larger amount of information. In light of such knowledge, this study investigates the possibility of reinforcing visual stimuli with audio for supporting e-learners in memorization tasks. Specifically, we consider three kinds of learning material and two kinds of audio stimuli and partially reinforce each kind of material with each kind of stimuli in an arbitrary way. In a series of experiments, we determine the particular type of audio, which offers the highest improvement for each kind of material. Our work stands out as being the first study investigating the differences in memory performance in relation to different combinations of learning content and stimulus. Our key findings from the experiments are: (i) E-learning is more effective in refreshing memory rather than studying from scratch, (ii) Non-informative audio is more suited to verbal content, whereas informative audio is better for numerical content, (iii) Constant audio triggering degrades learning performance and thus audio triggering should be handled with care. Based on these findings, we develop an ANN-based estimator to determine the proper moment for triggering audio (i.e. when memory performance is estimated to be declining) and carry out follow-up experiments for testing the integrated framework. Our contributions involve (i) determination of the most effective audio for each content type, (ii) estimation of memory deterioration based on learners' interaction logs, and (iii) the proposal of improvement of memory registration through auditory reinforcement. We believe that such findings constitute encouraging evidence the memory registration of e-learners can be enhanced with content-aware audio incorporation. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 9 2021 Development of an Eye-Gaze Input System With High Speed and Accuracy through Target Prediction Based on Homing Eye Movements 22688 22697 EN Atsuo Murata Department of Intelligent Mechanical Systems, Graduate School of Natural Science and Technology, Okayama University Toshihisa Doi Department of Intelligent Mechanical Systems, Graduate School of Natural Science and Technology, Okayama University Kazushi Kageyama Department of Intelligent Mechanical Systems, Graduate School of Natural Science and Technology, Okayama University Waldemar Karwowski Engineering and Management Systems, University of Central Florida In this study, a method to predict a target on the basis of the trajectory of eye movements and to increase the pointing speed while maintaining high predictive accuracy is proposed. First, a predictive method based on ballistic (fast) eye movements (Approach 1) was evaluated in terms of pointing speed and predictive accuracy. In Approach 1, the so-called Midas touch problem (pointing to an unintended target) occurred, particularly when a small number of samples was used to predict a target. Therefore, to overcome the poor predictive accuracy of Approach 1, we developed a new predictive method (Approach 2) using homing (slow) eye movements rather than ballistic (fast) eye movements. Approach 2 overcame the disadvantage (inaccurate prediction) of Approach 1 by shortening the pointing time while maintaining high predictive accuracy. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 9 2021 Capacity Loss From Localization Error in MIMO Channel Using Leaky Coaxial Cable 15929 15938 EN Junjie Zhu Graduate School of Natural Science and Technology, Okayama University Yafei Hou Graduate School of Natural Science and Technology, Okayama University Kenta Nagayama Graduate School of Natural Science and Technology, Okayama University Satoshi Denno Graduate School of Natural Science and Technology, Okayama University Leaky coaxial (LCX) cable has been employed as antennas for wireless traffic over many linear-cell scenarios such as railway station, tunnels and shopping malls. In addition, LCX can be used for user localization and wireless power transfer (WPT). Compared with the equal power allocation method, the power allocation method for LCX system using positional information (PI) can improve its capacity with the same level of computational complexity. In this paper, we will investigate the level of capacity loss on the 2.4 GHz and 5 GHz band for the conventional equal power (EP) allocation method, the water-filling (WF) based power allocation, and our proposed low-complexity power allocation method for LCX system with PI. The results show that LCX system with our proposed method using PI can reduce the capacity loss due to localization error than that of others. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 15566013 15 2019 Near-Optimal Detection for Binary Tardos Code by Estimating Collusion Strategy 2069 2080 EN Tatsuya Yasui Graduate School of Science and Technology, Okayama University Minoru Kuribayashi Graduate School of Science and Technology, Okayama University Nobuo Funabiki Graduate School of Natural Science and Technology, Okayama University Isao Echizen National Institute of Informatics A previously proposed optimal detector for bias-based fingerprinting codes such as Tardos and Nuida requires two kinds of important information: the number of colluders and the collusion strategy used to generate the pirated codeword. An estimator has now been derived for these two parameters. The bias in the pirated codeword is measured by observing the number of zeros and ones and compared with possible bias patterns calculated using information about the collusion strategy and number of colluders. Computer simulation demonstrated that the collusion strategy and number of colluders can be estimated with high probability and that the traceability of a detector using the proposed estimator is extremely close to being optimal. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 1999 Application of pneumatic parallel manipulator as haptic human interface 185 190 EN Masahiro Takaiwa Toshiro Noritsugu When humans and robots implement a cooperative task, information (intention) transfer between them is an important problem as the task becomes complicated. In the paper, a haptic interface using a pneumatic parallel manipulator is developed to realize “information transfer by means of contact”. The contact information given by the human, namely contact force vector and contact point on the manipulator, is detected by the interface itself and such information is transferred to the robot by being connected with some reference signal. The pneumatic parallel manipulator works as a kind of elastic body even when its position is controlled owing to the air compressibility. Focusing on this characteristic and introducing an idea of compliance center with a spherical shell, contact force vector and contact point are detected without a force sensor. The validity of the proposed method is confirmed through some experiments. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2 1996 Development of a tactile sensing flexible actuator 723 728 EN Yutaka Tanaka Akio Gofuku Yuji Fujino <p>The disadvantages of flexible artificial fingers have been improved. The finger is provided with the tactile sense by two types of sensors to detect when the finger tip touches an object and to estimate both the finger force and object size. The rigidity is enhanced by equipping the finger with a reinforcing material similar to that of human bone. A prototype robot hand with four fingers has been manufactured for experiments and mounted on an industrial articulated robot. The effectiveness of the improved robot hand finger was confirmed throughout experimental tests of grasping action</p> No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 1999 Development of a video-rate range finder using dynamic threshold method for characteristic point detection 932 937 EN Yutaka Tanaka Akio Gofuku Nobuo Takeda Isaku Nagai This study develops a video-rate stereo range finding circuit to obtain the depth of objects in a scene by processing video signals (R, G, B, and brightness signals) from binocular CCD cameras. The electronic circuit implements a dynamic threshold method to decrease the affect of signal noise in characteristic point detection, where a video signal from each CCD camera is compared with multiple thresholds, shifting dynamically by feeding back the previous comparison result. Several object depth measurement experiments for simple indoor scenes show that the dynamic threshold method gives high acquisition and correct rates of depth data compared with those by a fixed threshold method for the video signals and a relative method for R, G, and B signals utilized in the authors' previous range finders. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 1997 Visual tracking of redundant features 51 51 EN Koichi Hashimoto Atsuhito Aoki Toshiro Noritsugu This paper presents how the control performance of the feature-based visual servo system is improved by utilizing redundant features. Effectiveness of the redundant features is evaluated by the smallest singular value of the image Jacobian which is closely related to the accuracy in the world coordinate system. An LQ control scheme is used to resolve the controllability problem. Usefulness of the redundant features is verified by the real time experiments on a PUMA 560 manipulator. No potential conflict of interest relevant to this article was reported.