Ji-Woong Choi

Daegu Gyeongbuk Institute of Science and Technology | DGIST · Department of Information and Communication Engineering

The piezoelectric mechanism represents a promising approach for advanced sensors that measure physical factors such as pressures, strain levels and even temperature responses to various stimuli. However, a conventional analysis of piezoelectric signals is mainly related to the peak output voltage for normal force, meaning that there remain numerous...

Dynamic wireless power transfer (DWPT) has emerged as a technology for delivering sustainable energy to mobile electric vehicles without charging cables. Magnetic beamforming is a wellknown DWPT strategy for increasing power transfer efficiency (PTE) by calculating an optimal weight for focusing the magnetic fields from the transmitting (TX) coils...

Parkinson's disease is a neurodegenerative disease characterized by progressive dopaminergic neuronal loss. Motor deficits experienced by patients with Parkinson's disease are well documented, but non-motor symptoms, including mood disorders associated with circadian disturbances, are also frequent features. One common phenomenon is "sundowning syn...

Electrophysiological biomarkers reflecting the pathological activities in the basal ganglia are essential to gain an etiological understanding of Parkinson's disease (PD) and develop a method of diagnosing and treating the disease. Previous studies that explored electrophysiological biomarkers in PD have focused mainly on oscillatory or periodic ac...

The dysregulation of dopamine, a neuromodulator, is associated with a broad spectrum of brain disorders, including Parkinson’s disease, addiction, and schizophrenia. Quantitative measurements of dopamine are essential for understanding dopamine functional dynamics. Fast-scan cyclic voltammetry (FSCV) is the most widely used electrochemical techniqu...

Micro size antennas have significant merits due to the small size effect, enabling new device concepts. However, the low‐quality factor (Q‐factor), the large size of impedance matching components, and the poor selectivity of the multi‐array design remain challenging issues. To solve these issues, a floating coil structure stacked on a loop micro‐an...

In vivo calcium imaging is a standard neuroimaging technique that allows the simultaneous observation of neuronal population activity. In calcium imaging, the activation signals of neurons are key information for the investigation of neural circuits. For efficient extraction of the calcium signals of neurons, selective detection of the region of in...

Electrophysiological biomarkers reflecting the pathological activities in the basal ganglia are essential to gain an etiological understanding of Parkinson′s disease (PD) and develop a method of diagnosing and treating the disease. Previous studies that explored electrophysiological biomarkers in PD have focused mainly on oscillatory or periodic ac...

Detecting Alzheimer's disease (AD) is an important step in preventing pathological brain damage. Working memory (WM)-related network modulation can be a pathological feature of AD, but is usually modulated by untargeted cognitive processes and individual variance, resulting in the concealment of this key information. Therefore, in this study, we co...

Background: Parkinson’s disease is a neurodegenerative disease characterized by progressive dopaminergic (DAergic) neuronal loss. Motor deficits experienced by patients with Parkinson’s disease are well documented, but non-motor symptoms, including mood disorders associated with circadian disturbances, are also frequent features. One common phenome...

Magnetic beamforming techniques can enhance the power transfer efficiency using focused magnetic fields by the multiple transmitters to the receivers. However, the intra-couplings that cause power leakage and phase distortion among the arrayed coils inevitably occur due to the deployment of coils having strong couplings between each other. Here, we...

As a promising future treatment for stroke rehabilitation, researchers have developed direct brain stimulation to manipulate the neural excitability. However, there has been less interest in energy consumption and unexpected side effect caused by electrical stimulation to bring functional recovery for stroke rehabilitation. In this study, we propos...

Transfer printing is a technique that integrates heterogeneous materials by readily retrieving functional elements from a grown substrate and subsequently printing them onto a specific target site. These strategies are broadly exploited to construct heterogeneously integrated electronic devices. A typical wet transfer printing method exhibits limit...

As a surrogate for human tactile cognition, an artificial tactile perception and cognition system are proposed to produce smooth/soft and rough tactile sensations by its user's tactile feeling; and named this system as “tactile avatar”. A piezoelectric tactile sensor is developed to record dynamically various physical information such as pressure,...

In article number 2002362, Ji‐Woong Choi, Jae Eun Jang, and co‐workers suggest a tactile avatar system as a surrogate for human tactile cognition producing smooth/soft and rough tactile sensation. Because the tactile responses vary among humans, the deep learning network is designed considering the cognitive processing of independent tactile featur...

As a promising future treatment for stroke rehabilitation, researchers have developed direct brain stimulation to manipulate the neural excitability. However, there has been less interest in energy consumption and unexpected side effect caused by electrical stimulation to bring functional recovery for stroke rehabilitation. In this study, we propos...

Deep brain stimulation (DBS) refers to a neurosurgical process in which electrical stimulation is delivered via electrodes implanted within deep brain regions. DBS has become the most established clinical therapy for patients with movement disorders, although recent studies have investigated its application in a broad range of neurological and psyc...

Symptoms of Parkinson's disease (PD) caused by loss of dopaminergic neurons are accompanied by movement disorders, including tremors, rigidity, bradykinesia, and akinesia. Non-human primate (NHP) models with PD play an essential role in the analysis of PD pathophysiology and behavior symptoms. As impairments of hand dexterity function can affect ac...

The controller area network (CAN) is the de facto standard for in-vehicle networks. Numerous vehicles are equipped with a CAN for the networking of electronic control units. Since the CAN has no intrinsic secured identification protocol, however, it is vulnerable to security attacks. In this paper, we propose a convolution neural network (CNN)-base...

Background: Gait analysis in non-human primate models has been performed to elucidate the neural systems involved in controlling quadrupedal locomotor behavior. This study aimed to use a pressure-sensing walkway to identify characteristics of species-specific quadrupedal locomotion in rhesus monkeys. A total of nine healthy adult female rhesus monk...

Reducing the input data of tactile sensory systems brings a large degree of freedom to real-world implementations from the perspectives of bandwidth and computational complexity. For this, we suggest efficient active-cell formations with a high classification accuracy of tactile materials. By revealing that averaged Kullback-Leibler (KL)-divergence...

Symptoms of Parkinson's disease (PD) caused by loss of dopaminergic neurons are accompanied by movement disorders, including tremors, rigidity, bradykinesia, and akinesia. Non-human primate (NHP) models with PD play an essential role in the analysis of PD pathophysiology and behavior symptoms. As impairments of hand dexterity function can affect ac...

Gait analysis in non-human primate models has been performed to elucidate the neural systems involved in controlling quadrupedal locomotor behavior. This study aimed to use a pressure-sensing walkway to identify characteristics of species-specific quadrupedal locomotion in rhesus monkeys. A total of nine healthy adult female rhesus monkeys ( Macaca...

In research on cognitive function, the use of experimental animals is essential for the study of human cognitive processes and mechanisms. Furthermore, non-human primates are necessary for understanding higher cognitive functions in humans. However, there are few cognitive function tests available for non-human primates, Thus, we modified a finger...

Cognitive decline (CD) is a major symptom of mild cognitive impairment (MCI). Patients with MCI have an increased likelihood of developing Alzheimer’s disease (AD). Although a cure for AD is currently lacking, medication therapies and/or daily training in the early stage can alleviate disease progression and improve patients’ quality of life. Accor...

This paper presents numerical analysis and simulation results in order to study the impact of interference between fixed service (FS) systems and 5G cellular networks at 28 GHz, 38 GHz, and 60 GHz millimeter-wave (mmWave) bands. For this study, two different scenarios were considered, i.e., the aggregation of interference from small cells into an F...

An artificial tactile system has attracted tremendous interest and intensive study, since it can be applied as a new functional interface between humans and electronic devices. Unfortunately, most previous works focused on improving the sensitivity of sensors. However, humans also respond to psychological feelings for sensations such as pain, softn...

Functional connectivity derived from resting-state functional near infrared spectroscopy has gained attention of recent scholars because of its capability in providing valuable insight into intrinsic networks and various neurological disorders in a human brain. Several progressive methodologies in detecting resting-state functional connectivity pat...

Tactile sensors mimicking the human sense of touch have been studied and various technologies for the sensing of external stimuli have been suggested as well. Humans detect certain external stimuli and become aware of related sensations, such as roughness or smoothness. Among the various physical parameters, surface information is the most informat...

Many researchers have provided meaningful insights for physical layer security (PLS) in various wireless communication systems. However, few works have carried out an intensive PLS analysis for magnetic inductive coupling (MIC)-based simultaneous wireless information and power transfer (SWIPT). This paper analyzes the effect of the angular position...

Array beamforming (BF) has received considerable attention as a means of anti-jamming (AJ) by combining desired signals constructively and jamming signals destructively. However, even with BF, the state-of-the-art reactive jammer (RJ) can easily detect the target channels from the leakage of the transmit power and concentrate its own power to the d...

Crosstalk between coil array components in magnetic systems has to be minimized to achieve enhanced performance, such as high data rate, high power transfer efficiency, and simultaneous wireless information and power transfer. This paper presents a scalable non-coupling coil array composed of perpendicularly arranged quadrupole loop coils. The prop...

Given the increased amount of data traffic in in-vehicle networks with more systems now included in vehicles, enormous amounts of research have recently focused on providing reliable and inexpensive quality of service (QoS) for in-vehicle communication systems. To support high-speed data processing while maintaining backward compatibility with cont...

[This corrects the article on p. 210 in vol. 11, PMID: 28572760.].

While many companies have launched various wireless chargers in mobile industries, conventional wireless power transfer (WPT) technologies are available only for a very short distance due to large attenuation of the magnetic fields. A magnetic beamforming WPT system achieves an enhanced power transfer efficiency (PTE) with a longer wireless chargin...

This paper proposes a near-field magnetic multiple input multiple output (MIMO) scalable noncoupling coil array for achieving high-rate data transmission for implantable devices. While small path loss of near-field magnetic communication enables effective implementation of implantable devices, it is difficult to support high-rate applications. In t...

The aim of this work is to develop an effective brain-computer interface (BCI) method based on functional near-infrared spectroscopy (fNIRS). In order to improve the performance of the BCI system in terms of accuracy, the ability to discriminate features from input signals and proper classification are desired. Previous studies have mainly extracte...

The mechanism of tinnitus suppression after cochlear implantation (CI) in single-sided deafness (SSD) is not fully understood. In this regard, by comparing pre- and post-CI quantitative electroencephalography (qEEG), we explored cortical changes relevant to tinnitus improvement. In SSD patients who underwent CI, qEEG data were collected: (1) before...

While many companies have provided wireless charging technologies to users recently, a charging distance is very short due to a drastic drop of magnetic fields. A lot of researches have been carried out steadily to increase the wireless charging distance. Magnetic beamforming is one of promising technologies to achieve this vision. However, convent...

In the growing field of brain-machine interface (BMI), the interface between electrodes and neural tissues plays an important role in the recording and stimulation of neural signals. To minimize tissue damage while retaining high sensitivity, a flexible and a smaller electrode with low impedance is required. However, it is a major challenge to redu...

A magnetodielectric substrate is firstly proposed for implantable antennas in medical implant communication service (MICS) band. Ba3Co2Fe24O41 (Co2Z), Z-type hexaferrite flakes synthesized by molten-salt method were incorporated with a polymer matrix, having a real permeability of 2.88 and a magnetic loss of 0.029 at 402 MHz. A spiral antenna with...

Due to the necessity of the low-power implementation of newly-developed electrocardiogram (ECG) sensors, exact ECG data reconstruction from the compressed measurements has received much attention in recent years. Our interest lies in improving the compression ratio (CR), as well as the ECG reconstruction performance of the sparse signal recovery. T...

Array beamforming for anti-jamming means that jamming signals are superposed destructively, while superposing information signals constructively at a receiver. However, according to channel state variation, the anti-jamming performance of the beamforming can be degraded because of large beamwidth of the sidelobe and lower selectivity of the mainlob...

This article presents a near-field magnetic multi-input multi-output (MIMO) communication system test bed using software defined radio (SDR). We propose a heterogeneous multi-pole loop antenna array for near-field magnetic MIMO system. In this paper, we show improved performance of the proposed near-field magnetic MIMO communication system over a c...

In this paper, we propose a multi-input multi-output (MIMO) magnetic communication using heterogeneous multi-pole loop antenna array with a crosstalk cancellation effect for increasing channel capacity. To extend the number of antennas in array, we present a quasi-static analysis of the crosstalk cancellation in cylindrical coordinate and additiona...

Electroencephalograms (EEGs) measure a brain signal that contains abundant information about the human brain function and health. For this reason, recent clinical brain research and brain computer interface (BCI) studies use EEG signals in many applications. Due to the significant noise in EEG traces, signal processing to enhance the signal to nois...

In this paper, we propose a novel method realizing multi-input-multi-output (MIMO) transmission in near-field magnetic induction (NFMI) communication for increasing channel capacity where limited capacity is a major bottleneck problem in magnetic communication systems. Since conventional magnetic communication systems using the same antenna pattern...

The effects of transmission (Tx) coil structure have been studied for micro-size magnetic induction coil. The size of the receiving (Rx) coil should be shrunk to the micrometer level for the various new applications such as micro-robot and wireless body implanted devices. In case of the macro-scale magnetic induction coil, the power transmission ef...

Ultra-fast diode structures based on non-semiconductive materials employing tunneling mechanism have been investigated. Applying the structurally asymmetric effect of multi-wall carbon nanotube (MWCNT) to a vertical metal-insulator-MWCNT (MIC) tunneling diode structure, the ‘on-off’ ratio (∼104) and the current density (38.2MA/cm2) are drastically...