김상혁 교수

We analyze wireless power transfer between a source and a weakly coupled implant on the heart. Numerical studies show that mid-field wireless powering achieves much higher power transfer efficiency than traditional inductively coupled systems. With proper system design, power sufficient to operate typical cardiac implants can be received by millimeter-sized coils.

This paper examines transmitter optimization for wirelessly powering a small implant embedded in tissue. The wireless link between the transmitter and receiver is first modeled as a two-port network and an expression for the power transfer efficiency derived. For a given small receiver in a multilayer tissue model, the transmitter is abstracted as a sheet of magnetic current density for which the optimal distribution is analytically found. The optimal transmitter is compared to the point and uni

Implantable bioelectronic devices are becoming useful and prospective solutions for various diseases owing to their ability to monitor or manipulate body functions. However, conventional implantable devices (e.g., pacemaker and neurostimulator) are still bulky and rigid, which is mostly due to the energy storage component. In addition to mechanical mismatch between the bulky and rigid implantable device and the soft human tissue, another significant drawback is that the entire device should be s

We obtain an analytical bound on the efficiency of wireless power transfer to a weakly coupled device. The optimal source is solved for a multilayer geometry in terms of a representation based on the field equivalence principle. The theory reveals that optimal power transfer exploits the properties of the midfield to achieve efficiencies far greater than conventional coil-based designs. As a physical realization of the source, we present a slot array structure whose performance closely approache

Recently, stationary wireless power transfer (WPT) has been widely adopted in commercial devices. However, the current WPT configuration is limited in its operational area and susceptible to operating condition changes, impeding its applications for dynamic environments. To overcome the limitations, we propose a WPT system with laterally aligned neutral elements in parity-time (PT) symmetry, which can widen the operational area with the number of neutrals <i>N</i>. Compared to the conventional m

We propose a biomedical sensor system for continuous monitoring of glucose concentration. Despite recent advances in implantable biomedical devices, mm sized devices have yet to be developed due to the power limitation of the device in a tissue. We here present a mm sized wireless system with backscattered frequency-modulation communication that enables a low-power operation to read the glucose level from a fluorescent hydrogel sensor. The configuration of the reader structure is optimized for a

We introduce a method to measure the fat thickness by harnessing the physics of destructive interference. At certain frequencies, when the fat thickness equals a quarter wavelength, the amplitude of the reflected wave is minimized due to the destructive interference. Therefore, by observing the frequency where the reflection is minimized, we are able to deduce the fat thickness. This work demonstrates that this simple method can operate not only on a planar tissue model but also on a cylindrical

Implantable medical devices will play an important role in modern medicine for preventive and post-surgery monitoring, drug delivery, local stimulation, and biomimetic prosthesis. To reduce the risk of wire snapping, and replacement and corrosion of embedded batteries, wireless delivery of energy to these devices is desirable. Current studies in wireless power transmission into biological tissue tend to operate below 10 MHz because of the common belief that lower operating frequency yields highe

RF wireless interface enables remotely powered implantable devices. To maximize the received power under the safety constraint, we analytically solved the optimal current source distribution and investigated the theoretical upper-bound of the efficiency obtainable with planary vertical magnetic current sources. The optimal solution reveals that a finite dimensional source is sufficient to approach the theoretical upper-bound. At the low MHz-range, a coil of approximately 2 cm in diameter is adeq

S-parameters of electrical networks are often extracted using an electromagnetic (EM) simulator, and imported directly or after conversion to rational function models into a transient circuit simulator. However, there are several issues related to frequency-defined models that might prevent successful transient simulation. In this work, the requirements for S-parameter and rational function models in the frequency domain leading to successful transient simulations are studied in detail. Applicat

The Salisbury‐screen characteristics of the human abdomen are demonstrated. The skin–fat–muscle structure in the human abdomen resembles that of the Salisbury screen, which consists of a resistive sheet, a dielectric slab, and a conducting plane. Using this similarity, the authors can estimate the degree of obesity based on the reflectivity of electromagnetic waves. The Salisbury screen acts as a wave absorber when the thickness of the dielectric matches the quarter wavelength. This characterist

With the rapid advancement of information and communication technology, the number of items users encounter increased exponentially. Consequently, the importance of recommendation systems emerged to reduce the time and effort required for users to make item selections. Recently, among various studies on recommendation systems, there has been significant interest in leveraging review text as auxiliary information. This study proposes a novel model to enhance recommendation performance by effectiv