Nam Kim

Chungbuk National University · School of Computer and Communication Engineering

Wireless communication technology’s ubiquity means constant exposure to radiofrequency electromagnetic fields (RF-EMF). While concerns exist about RF-EMF’s effects on fetal brain development, studying this in pregnant women poses ethical and safety challenges. Our study examined 1.7 GHz LTE RF-EMF’s impact on early human fetal brain development usi...

The skin is the largest body organ that can be physiologically affected by exposure to radiofrequency electromagnetic fields (RF-EMFs). We investigated the effect of RF-EMFs on melanogenesis; Mel-Ab melanocytes were exposed to 1760 MHz radiation with a specific absorption rate of 4.0 W/kg for 4 h/day over 4 days. Exposure to the RF-EMF led to skin...

Vehicular Internet of Things (IoT) is facilitated by efficient RF front ends with suppressed mutual coupling for enhanced spatial diversity and increased channel capacity. This paper presents a mutual coupling suppressed MIMO antenna with a hybrid decoupling technique for Vehicle-to-Everything (V2X) communications, enabling IoT in automotive system...

Radiofrequency electromagnetic fields (RF-EMFs) can penetrate tissues and potentially influence endocrine and brain development. Despite increased mobile phone use among children and adolescents, the long-term effects of RF-EMF exposure on brain and endocrine development remain unclear. This study investigated the effects of long-term evolution ban...

A metamaterial-based non-uniform dipole array antenna is presented for high gain 5G millimeter-wave applications with a wideband characteristic. Initially, a non-uniform dipole array is designed on a 0.202 mm thick Rogers RO4003C substrate, offering a wide operating bandwidth ranging from 23.1 GHz to 44.8 GHz. The dipole array antenna emits unidire...

The article investigates a conformal millimeter-wave (mmWave) meander dipole array antenna that provides end-fire radiation with improved performance. The antenna offers various benefits including high gain, wider bandwidth, low side lobe level (SLL), and a simple feeding structure. The design comprises of microstrip fed eight meander dipoles, prin...

In this study, we introduce a deep learning-based depth estimation network for a light field microscopy system. Using a micro-lens array, elemental images were captured to generate orthographic view images. Depth estimation was performed using the attention UNET network architecture.

This paper presents the design and isolation enhancement of a filtering MIMO antenna with a radiation null for out-of-band suppressions suited for 5G sub-6 GHz communications. The MIMO antenna offers -10 dB impedance bandwidth functionality at the most prominent partial spectrum of the 5G NR n78 band for enabling wireless applications in base stati...

This article presents the design and implementation of a dipole array antenna based on a radial waveguide power divider for millimeter-wave IoT sensing applications. The dipole array and radial waveguide power divider techniques are used in tandem to achieve high gain with omnidirectional radiation properties. The proposed antenna is comprised of e...

Subjective visual examination by human dermatologists is associated with inter-observer variability and error. To address this problem, we present a method to accurately diagnose the 23 most common skin conditions, using an adaptive GrabCut approach with the EfficientNetB3 model, for accurate segmentation and classification, respectively. Using a c...

This study focuses on advancing precision in Electromagnetic Compatibility (EMC) measurements through the innovative optimization of Horn antenna performance. Utilizing a multi-layer lens with strategically varied radii, the proposed design significantly enhances antenna directivity and sensitivity across a wide frequency spectrum. Beyond addressin...

A 4-port MIMO antenna with a low specific absorption rate (SAR) is presented in this paper for 3.5 GHz 5G, and 5.8 GHz ISM (Industrial, Scientific, and Medical) band applications. The antenna is developed on a 0.252 mm thick Rogers 5880 substrate with a compact size of 36.2 mm × 36.2 mm. The designed antenna offers a bandwidth of more than 100 MHz...

In this article, an ultra-wideband (UWB) antenna featuring two reconfigurable quasi-perfect stop bands at WLAN (5.25–5.75 GHz) and lower 5G (3.4–3.8 GHz) utilizing electromagnetic bandgaps (EBGs) and positive-intrinsic-negative (P-I-N) diodes is proposed. A pair of EBG structures are applied to generate sharp notch bands in the targeted frequency s...

Long-term evolution (LTE) radiofrequency electromagnetic field (RF-EMF) is widely used in communication technologies. Thus, the influence of RF-EMF on biological systems is a major public concern and its physiological effects remain controversial. In our previous study, we showed that continuous exposure of various human cell types to 1.7 GHz LTE R...

We present a deep learning-based method that corrects motion artifacts and thus accelerates data acquisition and reconstruction of magnetic resonance images. The novel model, the Motion Artifact Correction by Swin Network (MACS-Net), uses a Swin transformer layer as the fundamental block and the Unet architecture as the neural network backbone. We...

This paper presents a conformal, miniaturized, and geometrically simple monopole antenna designed for Vehicle–to–Everything (V2X) communications. The antenna consists of a flexible substrate, radiating patch, ground, and metallic stubs. Meandered lines are added to the U-shaped radiator to achieve the required bandwidth of the antenna. The antenna...

Citation: Hossain, M.B.; Shinde, R.K.; Oh, S.; Kwon, K.-C.; Kim, N. A Systematic Review and Identification of the Challenges of Deep Learning Techniques for Undersampled Magnetic Resonance Image Reconstruction. Sensors 2024, 24, 753. Abstract: Deep learning (DL) in magnetic resonance imaging (MRI) shows excellent performance in image reconstruction...

We present a novel augmented reality (AR) display system utilizing a holographic optical element (HOE)-based approach, featuring seamless switching between three-dimensional (3D) and two-dimensional (2D) modes through a liquid-crystalline microlens array (LC-MLA). The proposed system aims to capture and present comprehensive spatial information on...

Citation: Hossain, M.B.; Shinde, R.K.; Oh, S.; Kwon, K.-C.; Kim, N. A Systematic Review and Identification of the Challenges of Deep Learning Techniques for Undersampled Magnetic Resonance Image Reconstruction. Sensors 2024, 24, 753. Abstract: Deep learning (DL) in magnetic resonance imaging (MRI) shows excellent performance in image reconstruction...

This article describes the design of a tri-band antenna that operates at 2.45 GHz (ISM band), 3.5 GHz (5G sub-6-GHz band), and 5.8 GHz (WLAN band). The antenna design is inspired by a conventional quarter-wave monopole which is fed using a coplanar waveguide feed. Initially, the radiator is loaded with an inverted L-shaped stub to attain broadband...

A quad-port MIMO antenna based on a quasi-binomial series-fed array is presented in this paper for n257 and n258 millimeter-wave applications with an investigation of additional loaded patches on performance enhancement of the conventional binomial series-fed array. The single element of the proposed MIMO is a 3 × 3 element planar binomial series-f...

In this paper, a high-gain and low-mutual-coupling four-port Multiple Input Multiple Output (MIMO) antenna based on a Partially Reflective Surface (PRS) for 28 GHz applications is proposed. The antenna radiator is a circular-shaped patch with a circular slot and a pair of vias to secure a wide bandwidth ranging from 24.29 GHz to 28.45 GHz (15.77%)....

Long-term evolution (LTE) radiofrequency electromagnetic field (RF-EMF) is widely used in communication technologies. As a result, the influence of RF-EMF on biological systems is a major public concern, and its physiological effects remain controversial. In our previous study, we showed that continuous exposure of various human cell types to 1.7 G...

Four-dimensional (4D) light-field (LF) microscopes can acquire 3D information about target objects using a microlens array (MLA). However, the resolution and quality of sub-images in the LF images are reduced because of the spatial multiplexing of rays by the element lenses of the MLA. To overcome these limitations, this study proposes an LF one-sh...

We propose a high-quality, three-dimensional display system based on a simplified light field image acquisition method, and a custom-trained full-connected deep neural network is proposed. The ultimate goal of the proposed system is to acquire and reconstruct the light field images with possibly the most elevated quality from the real-world objects...

In ultra-wideband (UWB) communications, highly selective notch bands are required to avoid interference with other licensed bands. This study presents a highly selective triple-notch UWB-MIMO antenna, which consists of a four-radiating patch antenna and an isolator. The single-element antenna consists of a radiating patch, substrate, ground plane,...

We propose a dual-domain deep learning technique for accelerating compressed sensing magnetic resonance image reconstruction. An advanced convolutional neural network with residual connectivity and an attention mechanism was developed for frequency and image domains. First, the sensor domain subnetwork estimates the unmeasured frequencies of k-spac...

An ultra-wideband (UWB), geometrically simple, compact, and high-gain antenna with a WLAN notch band is presented for future wireless devices. The antenna is printed on the top side of the Rogers RT/Duroid 5880 substrate and has a small dimension of 10 mm × 15 mm × 0.254 mm. The primary radiator of the proposed coplanar waveguide-fed monopole anten...

This paper investigates the design and optimization of the dipole array antenna. Unlike conventional dipoles, the presented work contains eight dipole antennas connected to a feedline having an angle of 250. Moreover, the non-uniform distance between consecutive elements as well as different dipole lengths helps in achieving a wideband antenna havi...

This article presents a dual notch band Ultra-wideband (UWB) reconfigurable antenna. The antenna consists of a radiation patch, coplanar ground, electromagnetic bandgap (EBG) structures, and switches. The lower edges of the radiating patch are truncated to enhance the antenna's UWB spectral bandwidth, and pairs of EBG structures are utilized to for...

In this paper, a modified series-fed array antenna with wideband characteristics is presented for the 5G mmWave applications. Additional loaded patches in both the E-plane and H-plane of the proposed antenna offer wider bandwidth and high gain with side lobe suppression of the conventional rectangular series-fed antenna. The proposed antenna is sim...

We have previously found that long-term effects of exposure to radiofrequency electromagnetic fields in 5×FAD mice with severe late-stage Alzheimer’s disease reduced both amyloid-β deposition and glial activation, including microglia. To examine whether this therapeutic effect is due to the regulation of activated microglia, we analyzed microglial...

We propose a light-field microscopy display system that provides improved image quality and realistic three-dimensional (3D) measurement information. Our approach acquires both high-resolution two-dimensional (2D) and light-field images of the specimen sequentially. We put forward a matting Laplacian-based depth estimation algorithm to obtain nearl...

This paper investigates the performance enhancement of a quarter-wave monopole antenna by etching slots and loading multiple stubs. These techniques were exploited to achieve a compact size antenna for modern-day multi-band applications. The antenna covers three distinct band spectrums of 2.35-2.5, 3.3-3.55, and 5.18-7.63 GHz along with respective...

This paper presents the design and analysis of an integrated microwave and millimeter-wave antenna. The antenna offers four distinct brands in the microwave band spectrum while an additional band in the mm-wave band is also achieved. The antenna structure is inspired by a triangular quarter-wave monopole antenna which is then loaded by five stubs o...

In this article, a 2×2 Multiple-Input-Multiple-Output (MIMO) antenna for UWB applications is presented. A plus-shaped parasitic decoupler is used to reduce mutual coupling between the single elements. The single element antenna comprises a square patch with lower end truncated, rectangular-shaped EBG, and SRR on its backside. The EBGs and SRR are p...

This paper presents the design of a series fed planar array-based 4-port multiple-input-multiple-output (MIMO) antenna for 28 GHz Internet of Things (IoT) applications. The unit element comprises a conventional rectangular patch-shaped series array antenna offering high gain along with loaded patches to suppress the side lobe level. The unit elemen...

An advanced three-dimensional/two-dimensional switchable augmented-reality system is proposed. A camera captures the images of real objects, and it is displayed as it is or the elemental image array generated from a captured image and estimated depth information via a one-shot learning model, is reconstructed by a liquid-crystalline lens array.

Simple Summary Skin cancer is a life-threatening condition. It is difficult to diagnose in its early stages; therefore, we proposed an easy-to-use telemedicine device to tackle skin cancer without expert intervention. The deep learning model automatically detects skin cancer patches on lesions with a credit-card-sized device named Raspberry Pi and...

When sparsely sampled data are used to accelerate magnetic resonance imaging (MRI), conventional reconstruction approaches produce significant artifacts that obscure the content of the image. To remove aliasing artifacts, we propose an advanced convolutional neural network (CNN) called fully dense attention CNN (FDA-CNN). We updated the Unet model...

A holographic display provides natural-view three-dimensional (3D) images with exact depth and parallax information for given objects and reconstructs the actual 3D visualization. The depth map-based methods have the advantages that rapid calculation of CGHs than the point cloud-based methods; and provides a better image quality. However, it has di...

The complete coverage of the operating frequency bands from microwave bands to millimeter (mm-wave) is required for the realization of the fifth-generation (5G) internet-of-thing (IoT) systems. Here, we present a multi-band antenna operating at the microwave (2.5/3.5/5.5/7.5 GHz) and mm-wave bands (23 -31 GHz), and its 12-port MIMO configuration wi...

A full-color reflection holographic optical element (HOE) with uniform diffraction efficiency, achieved via time-scheduled exposure, is proposed in which 660, 532, and 473 nm wavelengths are used for recording. To enhance the diffraction efficiency, the exposure energy of three wavelengths should be controlled to react uniformly in the photopolymer...

Radiofrequency radiation (RFR) can generate heat in living organisms. In this study, we monitored the body temperature of healthy animals during RFR exposure in real time using an implantable iButton data logger. A reverberation chamber system for small animals was used for this radiofrequency (RF) exposure in vivo study. Healthy male Sprague-Dawle...

Air-writing is a growing research topic in the field of gesture-based writing systems. This research proposes a unified, lightweight, and general-purpose deep learning algorithm for a trajectory-based air-writing recognition network (TARNet). We combine a convolutional neural network (CNN) with a long short-term memory (LSTM) network. The architect...

To avoid mixing of the undesired frequencies in a free‐space, the point sources of gratings, defined by a spatially varying refractive index, should be sinusoidally rather than binarily arranged. This long‐lasting but gold standard lesson attainable from a classical Fourier optics, however, is underutilized in the practical materialization of grati...

HIoT, AR/VR, Sensors, Remote monitoring

Using a microlens array (MLA), integral imaging microscopy (IIM) captures angular information in three dimensions. In this paper, we provide a three-dimensional display system using a deep neural network and augmented reality (AR) for the IIM that renders a true 3D image. There are three parts to this procedure: image capture using the IIM system [...

This paper presents a compact two-element MIMO antenna with improved isolation for triple-band applications. The antenna consists of two radiating elements with the shared ground plane and a novel decoupling structure. Each antenna element has three stubs with different lengths, which work as quarter-wavelength monopoles to give a triple-band opera...

Recently, the impacts of 5G electromagnetic radiation (EMR) with 28 GHz on human health have been attracting public attention with the advent of 5G wireless communication. Here, we report that 5G (28 GHz) EMR can attenuate the skin pigmentation in murine melanoma cells (B16F10) and a 3D pigmented human epidermis model (Melanoderm™). B16 cells were...

We proposed an end-to-end MRI reconstruction method based on the generative adversarial networks (GAN) where the generator network maps the relationship between under-sampled and fully sampled k-data. The discriminator network judges whether the reconstructed image is real or fake and it is determined by adversarial loss. The perceptual, pixel-wise...

This paper presents the design of wideband and high gain Frequency Selective Surface (FSS) loaded antenna for ultra-wideband (UWB) wireless applications requiring high-gain. The antenna consists of a monopole and an FSS reflector. Initially, a conventional rectangular monopole antenna is modified using slot and stub to achieve wide operational band...

This study proposes a robust depth map framework based on a convolutional neural network (CNN) to calculate disparities using multi-direction epipolar plane images (EPIs). A combination of three-dimensional (3D) and two-dimensional (2D) CNN-based deep learning networks is used to extract the features from each input stream separately. The 3D convol...