Papers by Nathan Seongheon Jeong
Snow Depth Measurements With Ultra-Wideband Compact FMCW Radar on a Small Unmanned Aircraft System
IEEE Journal of Radio Frequency Identification
Current Research in Food Science
Microwave imaging technology is a useful method often applied in medical diagnosis and can be use... more Microwave imaging technology is a useful method often applied in medical diagnosis and can be used by the food industry to ensure food safety and quality. For fruit, ripeness is the primary characteristic which determines quality for the consumer. This paper proposes a novel microwave imaging system to determine the ripeness of watermelon as a proof of concept. The design employs a circular array with 10 Coplanar Vivaldi antennas offering wide bandwidth, high gain, and high efficiency. S-parameters between antennas are collected quickly via automated channel switching for fast image generation. Eight different watermelon samples of varying ripeness, type, dimensions, and origin are scanned and imaged. Comparisons with sample cross-sections show distinct differences in image characteristics based on watermelon maturity. Sugar concentration of unripe and ripe watermelon is also measured and plotted for further validation of the imaging technique.
Ultra-Wideband Ceramic-Based Dielectric Resonator Antenna Array For Radar Applications
2022 International Workshop on Antenna Technology (iWAT)
Sensors
This paper presents a plantar pressure sensor system (P2S2) integrated in the insoles of shoes to... more This paper presents a plantar pressure sensor system (P2S2) integrated in the insoles of shoes to detect thirteen commonly used human movements including walking, stooping left and right, pulling a cart backward, squatting, descending, ascending stairs, running, and falling (front, back, right, left). Six force sensitive resistors (FSR) sensors were positioned on critical pressure points on the insoles to capture the electrical signature of pressure change in the various movements. A total of 34 adult participants were tested with the P2S2. The pressure data were collected and processed using a Principal Component Analysis (PCA) for input to the multiple machine learning (ML) algorithms, including k-NN, neural network and Support-Vector Machine (SVM) algorithms. The ML models were trained using four-fold cross-validation. Each fold kept subject data independent from other folds. The model proved effective with an accuracy of 86%, showing a promising result in predicting human moveme...
Sensors
Extreme angles in lower body joints may adversely increase the risk of injury to joints. These in... more Extreme angles in lower body joints may adversely increase the risk of injury to joints. These injuries are common in the workplace and cause persistent pain and significant financial losses to people and companies. The purpose of this study was to predict lower body joint angles from the ankle to the lumbosacral joint (L5S1) by measuring plantar pressures in shoes. Joint angle prediction was aided by a designed footwear sensor consisting of six force-sensing resistors (FSR) and a microcontroller fitted with Bluetooth LE sensors. An Xsens motion capture system was utilized as a ground truth validation measuring 3D joint angles. Thirty-seven human subjects were tested squatting in an IRB-approved study. The Gaussian Process Regression (GPR) linear regression algorithm was used to create a progressive model that predicted the angles of ankle, knee, hip, and L5S1. The footwear sensor showed a promising root mean square error (RMSE) for each joint. The L5S1 angle was predicted to be RMS...
Design of mmWave Foldable Vertically Stacked Yagi–Uda Antenna Inspired by Origami and Kirigami Theories
IEEE Antennas and Wireless Propagation Letters
A Miniaturized Ultra-Wideband Radar for UAV Remote Sensing Applications
IEEE Microwave and Wireless Components Letters, 2022
This letter presents a novel approach to build a compact lightweight unmanned aerial vehicle (UAV... more This letter presents a novel approach to build a compact lightweight unmanned aerial vehicle (UAV) radar for remote sensing applications. The proposed radar exploits the recent advancement of an automotive radar chip for broadband chirp generation and rapid data processing. To compensate for the path losses and improve penetration at the millimeter-wave (mm-wave) frequency range, up- and down-converters are developed to generate an ultra-wideband (UWB) (3.25–5.15 GHz) chirp signal. The total payload of the radar is 2.5 kg. The proposed radar is installed on an UAV and tested in the field at a 100-m altitude above the ground surface. The results show that the compact low-power UWB radar can be used to map vegetation and soil moisture with fine resolution.
Sensors, 2021
Ankle injuries may adversely increase the risk of injury to the joints of the lower extremity and... more Ankle injuries may adversely increase the risk of injury to the joints of the lower extremity and can lead to various impairments in workplaces. The purpose of this study was to predict the ankle angles by developing a footwear pressure sensor and utilizing a machine learning technique. The footwear sensor was composed of six FSRs (force sensing resistors), a microcontroller and a Bluetooth LE chipset in a flexible substrate. Twenty-six subjects were tested in squat and stoop motions, which are common positions utilized when lifting objects from the floor and pose distinct risks to the lifter. The kNN (k-nearest neighbor) machine learning algorithm was used to create a representative model to predict the ankle angles. For the validation, a commercial IMU (inertial measurement unit) sensor system was used. The results showed that the proposed footwear pressure sensor could predict the ankle angles at more than 93% accuracy for squat and 87% accuracy for stoop motions. This study conf...
IEEE Access
This paper details a new approach for enhancing the radiation characteristics of a coplanar Vival... more This paper details a new approach for enhancing the radiation characteristics of a coplanar Vivaldi antenna (CVA) array. First, the inter-element mutual coupling is reduced by introducing slots in the conventional CVA array. Then, a low-profile dielectric patch antenna (DPA) is situated between the CVA flares when it acts as a traveling wave radiator at the higher frequency band. The DPA is excited by the loop current at the radiation part of the CVA, and a set of TE modes with omnidirectional radiation patterns are excited. This combination enhances the directivity in the broadside direction of the CVA and suppresses the grating lobes by as much as 10 dB. The 4 × 1 linear array covers the frequency range of 2.77-13.6 GHz, with 132% fractional bandwidth. Then, four of the proposed linear arrays are connected to constitute an 8 × 2 planar array to achieve a gain of 15.2-24.6 dBi. The proposed arrays are fabricated, tested, and mounted on a small unmanned aerial system (sUAS) for radar measurements. The real-life field radar results with the proposed arrays are presented including an echogram of the scanned area. INDEX TERMS High gain antennas, radar applications, radiation pattern enhancement.
Applied Computational Electromagnetics Society, 2021
In this paper, a new approach to create frequency band rejection is applied to a wideband H-shape... more In this paper, a new approach to create frequency band rejection is applied to a wideband H-shaped dielectric resonator antenna (DRA). In order to create a notch characteristic in the operating band of the TEy1δ1 and TEy2δ1 modes, and guided by their theoretical and simulated electric field distributions, a narrow conductive strip is incorporated around the mid-section of the H-shaped DRA. The orientation of the notching strip is determined based on the electric field distribution of the selected modes for the frequency rejection. Furthermore, the selected feeding method improves the radiation patterns for this DRA shape compared to its previous designs. The new design offers an operating frequency range that extends from 4.15 to 9.8 GHz, allowing 81% of fractional bandwidth. The first notch is created at 6.5 GHz, while the second one is at 8 GHz. Average radiation efficiency of 95% across the frequency of interest is achieved with overall dimensions of 40x30x11.4 mm3. The proposed ...
2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, 2019
Рассмотрены вопросы получения оксида алюминия из техногенных материалов; различия в структуре, со... more Рассмотрены вопросы получения оксида алюминия из техногенных материалов; различия в структуре, составе и свойствах глиноземов, получаемых различными технологическими способами; обеспечения высокоглиноземистыми материалами отечественной керамической, электронной и огнеупорной промышленности.
Loosely Coupled Wireless Charging of Footwear-based Sensor System
2019 IEEE 20th Wireless and Microwave Technology Conference (WAMICON), 2019
This paper presents a wireless charging system that can power up footwear-based sensors. Loosely ... more This paper presents a wireless charging system that can power up footwear-based sensors. Loosely coupled magnetic resonant technique was applied to achieve a 20 mm-long charging distance relative to the conventional Qi charging, which requires close proximity and precise alignment. Transmitting and receiving resonators are modeled and simulated with a full-wave solver, ANSYS HFSS. Simulation results match measured results with respect to coupling coefficient (k). The resonator coupling efficiency (RCE) for the loosely coupled wireless charging system over a 20 mm gap is 65%, which seems feasible for a small battery-operated sensor system.
A Hybrid Inductive and Resonant Transmitter for Dual-mode Wireless Charging
2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, 2018
As wireless charging becomes popular, a transmitter that can support multi-mode operation seems t... more As wireless charging becomes popular, a transmitter that can support multi-mode operation seems to be essential for broad and rapid deployment. In this paper, a dual-mode transmitter is proposed to accommodate the tightly inductive coupled and loosely magnetic resonant coupled charging technologies. The challenge is to meet charging distance requirements, as they have opposite characteristic with respect to coupling coefficients. When two different coils are stacked on top of each other, proximity effect due to the nearby two sets of coils should also be mitigated. The coexistence issue is resolved by stacking and separating the different types of coils on top of each other and by making use of the tightly inductive charging coils to extend the charging distance of the magnetic resonant charging, allowing a further physical separation between the two sets of coils. The details of design stackup, prototype, and measurement result are presented.
2021 IEEE Radar Conference (RadarConf21), 2021
To accommodate a high number of automotive radars operating at the same frequency band while avoi... more To accommodate a high number of automotive radars operating at the same frequency band while avoiding mutual interference, we propose a sparse step-frequency waveform (SSFW) radar to synthesize a large effective bandwidth to achieve high range resolution profiles (HRRP). To mitigate high range sidelobes in the SSFW radars, we propose a joint sparse carriers selection and weighting approach, where the sparse carriers are first optimally selected via the particle swarm optimization (PSO) techniques, and then a weighting vector is optimized and applied such that the peak sidelobe level of range spectrum is minimized. As a result, targets with relatively small radar cross section are detectable without introducing high probability of false alarm. We extend the SSFW concept to multi-input multioutput (MIMO) radar by applying phase codes along slow-time to synthesize a large virtual array aperture. Numerical simulations are conducted to demonstrate the performance of the proposed SSFW MIMO radar.
Liquid Metal Broadband Monopole for Stretchable Electronics
2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, 2019
This paper presents a broadband monopole antenna made out of smart materials for stretchable elec... more This paper presents a broadband monopole antenna made out of smart materials for stretchable electronics. The antenna consists of a liquid conductor and a thermoplastic - Galinstan (gallium indium and tin) for the radiating element and SEBS (styrene-ethylene-butylene-styrene) for the antenna substrate. The antenna is simulated with a full-wave solver and is compared to measurement. The simulated result is in a good agreement with the measured. The reflection coefficients show broadband characteristics from 1.4 GHz to 6 GHz.
A recent development of antenna-in-package for 5G millimeter-wave applications (Invited paper)
2018 IEEE 19th Wireless and Microwave Technology Conference (WAMICON), 2018
Millimeter-wave technology brings a new paradigm of wireless communication in various areas inclu... more Millimeter-wave technology brings a new paradigm of wireless communication in various areas including mobile devices, automotive, IoT (Internet of Things), medical, military and many others. In this paper, we present our recently developed antenna in a package and system for 5G (Fifth-Generation) millimeter-wave applications. The antenna is configured to be an array to compensate path loss and maintain data link budget. The antenna is designed with a multi-layer laminate substrate and is integrated with a 5G mmW RFIC. 5G NR (New Radio) wireless connection is demonstrated with a RFIC transceiver at 28 GHz band. Interoperability test is conducted to ensure compatibility with the 3GPP standard. Finally, indoor and outdoor field test including beamforming and beamtracking are presented to show realistic system-level throughput performance.
Fast Estimation of Wireless Charging System in a Large Tissue
Wireless charging technology enables designers to miniaturize medical implants and eliminates the... more Wireless charging technology enables designers to miniaturize medical implants and eliminates the redundant surgical procedure to replace batteries. In this paper, we propose a precise and fast method of predicting mutual coupling inside a human body. A magnetic field at 6.78 MHz is generated with two different types of resonant coils - circumferential and Helmholtz coils. The circumferential coil generates a vertical magnetic field while the Helmholtz coil produces a horizontal field. They can operate individually or simultaneously. The combined field mitigates orientation mismatch and increases ability to charge the implant wirelessly within the volume of interest. To predict M precisely and rapidly, a theoretical derivation is presented and compared to a commercial full-wave solver. The results show that the theoretical value is well aligned with the simulated one. The time required to produce an estimation of the coupling within the entire constellation can be substantially redu...
2019 IEEE 20th Wireless and Microwave Technology Conference (WAMICON), 2019
The task of decision-making under uncertainty is daunting, especially for problems which have sig... more The task of decision-making under uncertainty is daunting, especially for problems which have significant complexity. Healthcare policy makers across the globe are facing problems under challenging constraints, with limited tools to help them make data driven decisions. In this work we frame the process of finding an optimal malaria policy as a stochastic multi-armed bandit problem, and implement three agent based strategies to explore the policy space. We apply a Gaussian Process regression to the findings of each agent, both for comparison and to account for stochastic results from simulating the spread of malaria in a fixed population. The generated policy spaces are compared with published results to give a direct reference with human expert decisions for the same simulated population. Our novel approach provides a powerful resource for policy makers, and a platform which can be readily extended to capture future more nuanced policy spaces.
IEEE Open Journal of Antennas and Propagation, 2021
─ This paper presents the capabilities of an 8×8 Rectangular Dielectric Resonator Antenna (RDRA) ... more ─ This paper presents the capabilities of an 8×8 Rectangular Dielectric Resonator Antenna (RDRA) planar array with broad bandwidth and high gain. To improve shielding of a multi-stage feeding network, the proposed array is designed using a stripline feeding network with two different substrates. To enhance impedance matching while keeping a sufficient F/B ratio of 20 dB, the lower ground of the stripline has a smaller dimension than the upper ground plane. The proposed array covers the frequency band from 3.79 to 6.29 GHz with 50% fractional bandwidth. The peak realized gain ranges from 18 to 22 dBi, with 85% of radiation efficiency throughout the frequency of interest. The overall size and weight of the array is 215×215×14.5 mm 3 and 650 g, respectively. Furthermore, the radiation patterns appear as low as 15 dB of peak-to-side lobe level with 25 dB cross polarization level, which makes the proposed array suitable for UAS (Unmanned Aerial System) radar applications. The measurements and simulations agree considerably.
Origami-Inspired Radiation Pattern and Shape Reconfigurable Dipole Array Antenna at C-Band for CubeSat Applications
IEEE Transactions on Antennas and Propagation, 2021
This article presents an antenna structure with a reconfigurable pattern and polarization for Cub... more This article presents an antenna structure with a reconfigurable pattern and polarization for CubeSat applications. The proposed antenna is based on spatial-mapping origami theory and consists of a center-fed four-way Gysel power divider, delay lines, inside lamina emergent torsion (LET) joints, and four thick planar dipole antennas. The LET joints are used to distribute the mechanical stress of a rigid planar material to form a flexible planar spring structure. The proposed antenna has monopole-like omnidirectional linearly polarized gain patterns in planar mode. Its gain value is about 0.5 dBi at 5.8 GHz. In folded mode, the antenna has about a circularly polarized gain value of about 8.07 dBic and broadside radiation patterns. The measured cross-polarization suppression ratio is about 25 dB, and the axial ratio (AR) value is 1.13 dB at 5.8 GHz. The size of the antenna in planar mode with a cross-shape is <inline-formula> <tex-math notation="LaTeX">$100\times 100\times0.5$ </tex-math></inline-formula> mm<sup>3</sup>, and its size is in folded mode is <inline-formula> <tex-math notation="LaTeX">$32.5\times 32.5\times32.5$ </tex-math></inline-formula> mm<sup>3</sup>. The size of the antenna in inactive mode is <inline-formula> <tex-math notation="LaTeX">$35\times 35\times 3$ </tex-math></inline-formula> mm<sup>3</sup>, and its total weight is only 4.73 g.
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Papers by Nathan Seongheon Jeong