Hyoungsuk Yoo

Among the various methods to develop flexible wearable antennas, a serpentine, mesh structure has been a great interest because of its mechanical reliability upon applied strain. However, there is still a significant lack of design guidelines for the open-mesh concept that account for both material and electromagnetic (EM) properties of antennas. In this work, we introduce a comprehensive study of materials, mechanics, fabrication, and system integration for the development of stretchable dipole

A miniaturised implantable antenna with dual‐band operation the Medical Implant Communications Service (MICS) (402–405 MHz) and Industrial, Scientific, and Medical (ISM) (2400.0–2483.5 MHz) bands is presented. The size of the proposed antenna is 31.5 mm 3 (8.75 mm × 7.2 mm × 0.5 mm) which is the smallest size compared to previous implantable antennas. A serpentine‐shaped radiating patch and open‐end slot placed on the ground plane are used for miniaturisation. The performance of the antenna was

In high-field magnetic resonance imaging (MRI) systems, B₀ fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B₀ fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected reg

Abstract This study presents an innovative wirelessly powered stent rectenna system for endovascular aneurysm repair (EVAR), targeting abdominal aortic aneurysm (AAA) treatment. The system includes an on‐body flexible transmitter (Tx) antenna and an in‐body rectifier‐integrated stent receiver (Rx) antenna, operating in the industrial, scientific, and medical (ISM) band of 868 MHz. The Rx stent antenna, made from a biocompatible nylon‐coated metallic wire, ensures mechanical stretchability, bioco

MRI has the potential to produce clear anatomic, as well as functional, images of the human body. However, the ability to diagnose is limited by signal‐to‐noise ratio (SNR) and the resolution of current medical systems. To remove the challenges prevalent due to the use of high‐field scanners, dedicated RF coils are used. Transverse electromagnetic (TEM) coils have the advantage of providing a homogeneous magnetic field throughout the region, but with a low SNR, while surface coils have the advan

The radio frequency coils in magnetic resonance imaging (MRI) systems induce scattered electric fields in the implanted medical lead and result in tissue heating. A novel structure of the medical lead has been designed to reduce the scattered field. Proposed metal nails are placed along the medical lead. The scattered electric field is calculated near the medical lead tip at 64 MHz (1.5 T MRI). By installing this design on the conventional lead, a significant decrease in the scattered electric f

The higher static magnetic fields $B_0$, in MRI systems result in higher signal to noise ratios. However, as the wavelength decreases linearly with the higher static magnetic field, image inhomogeneity occurs. This paper demonstrates the use of the convex optimization with an iterative method to improve $B_1Λ +$ uniformity in an anatomic region of interest by varying the magnitude and phase of each RF channel element independently. The simulation results for 16 channels for 9.4 T systems are dis

Abstract We present a compact and broadband balun based on the concept of a synthetic left‐handed transmission line and right‐handed transmission line.The compact balun uses lumped, discrete LC elements only to reduce the circuit size dramatically. For the frequency range of 0.6–1.2 GHz, this circuit maintains 180 ± 9.5° phase difference at the outputs, whereas the maximum insertion loss is −1.78 dB, and the minimum return loss is −10.2 dB at all three ports, yet the circuit size is merely 12 ×

In a multi-element microstrip transmission line (MTL) transmit array coil, the transmit field (B1+) distribution is inhomogeneous due to its standing-wave nature, and the interference effects can severely degrade the B1+ and imaging. Therefore, to improve the homogeneity and strength of B1+, this study focuses on the development of a multi-element MTL transmit array coil integrated with a dielectric liner (DL) material. Furthermore, the transmission efficiency (Tx,eff) is improved in the head re

The combined field integral equation (CFIE) method is used to calculate the RF magnetic <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> field produced by a transmission-line resonator element for high-field magnetic resonance systems. The method calculates the surface currents on a homogeneous phantom with triangular patches with the Rao-Wilton

Abstract A 9‐cm wavelength in the human brain at the 400‐MHz Larmor frequency for 9.4‐T leads to pronounced B 1 field contours and consequential image inhomogeneity. The objective of this study was to develop a new technique to control this nonuniformity by designing the phase and magnitude of radiofrequency (RF) power emanating from RF coil antenna elements in a multichannel transceiver array. Nonuniformity was used to steer a constructively interfering B 1 field node to spatially correlate wit

A broadband tunable phased array antenna system was fabricated using a broadband and linear phase shifter. For the frequency between 1.6 and 2.4 GHz, more than ±19° of beam steering was achieved with a 1 × 4 array. The main part of this system consists of a low loss, compact, linear tunable phase shifter which is implemented with left-handed transmission line theory. For the same frequency range, the phase shifter showed less than 5.1 dB insertion loss for the whole 360° phase variation with ±21

To analyze dielectric waveguides, an iterative procedure coupling the finite-element method in the interior to an integral equation of the exterior domain is developed. The robustness of this method is confirmed by the numerical results presented in this paper and corresponding the computation of the propagation constant.

This reported work demonstrates the use of convex optimisation to localise the transverse magnetic B + 1 field in regions of interest for recently proposed multi‐sectioned alternating impedance coils and the traditional transmission line coil. An approach based on different axial slices to identical radio frequency (RF) coils except upper stripline structure is investigated. Electromagnetic simulation results are compared for RF coils and discussed in detail at 7.0 T.