Choon Sik Cho

This paper presents a method of introducing novel bar shaped multiple patches to enhance the gain of the often-ignored North Atlantic Treaty Organization (NATO) radio frequencies E-band, that is from 2–3 GHz while maintaining high gain through the entire bandwidth of the antenna. The patches are introduced in the vicinity of the antenna flares. The length of the patches increases subsequently in the end fire direction to cater for different frequency fields. This approach improves the gain and directivity by field coupling, without getting a tradeoff with the absolute bandwidth of the antenna. This new antenna prototype has dimensions of 100 mm × 90 mm × 1.5 mm with measured gain from 3.8–7.8 dBi from 2–10 GHz and for NATO E-band the gain ranges from 3.8–5 dBi which is better than the previous designs with respective antenna size.

—Frequency Diverse Array (FDA) radar uses small frequency offsets across antenna array elements to generate a range-angle dependent beampattern. A well-known limitation, however, is that the received echo is time-variant, preventing direct target localization. In this work, we experimentally demonstrate that time variance can be effectively cancelled after reception, yielding a stable, time-invariant range-angle map that accurately reflects the true target location. Implementation of this concept gives rise to some subtle experimental challenges which are caused by the hardware complexity of FDA radar. We implement the transceiver using two Universal Software Radio Peripherals (USRPs). This configuration causes several practical challenges, including random initial phase offsets across Rx channels and the limited instantaneous bandwidth available for realizing a short-range laboratory prototype. These challenges are addressed through offline processing of independently collected I/Q samples for each FDA frequency offset. This approach alleviates the hardware constraints but introduces new difficulties, such as target motion synchronization and maintaining positional accuracy, which we analyze and mitigate through careful calibration and measurement design. To validate the proposed methodology, we first conduct wired-channel experiments, where RF cables of varying lengths emulate controlled, time-invariant range-angle steering. We then perform free-space FDA radar measurements and compare the resulting range-angle maps with simulations, evaluating localization accuracy and Peak Side Lobe Level (PSLL). The results demonstrate the practical feasibility of low-complexity, short-range, time-invariant FDA radar prototyping.

The amyloid- beta (Aβ) protein is a peptide that plays a central role in the development and progression of Alzheimer's disease, originating from the cleavage of the amyloid precursor protein (APP). The peptide's structural variability is linked to different stages and manifestations of Alzheimer's pathology, making it a critical focus for understanding the disease. Current therapeutic strategies primarily involve pharmacological interventions, but they have met with limited success in altering the course of the disease. Our research introduces an innovative approach to address this challenge by employing electromagnetic waves, specifically at a frequency of 900 MHz We performed comprehensive electromagnetic simulations to explore the effects of this frequency on Aβ structures, aiming to offer an alternative non-invasive treatment avenue. Following these electromagnetic simulations, molecular dynamics (MD) simulations were carried out using the Large Scale Atomic/Molecular Massively Parallel Simulation (LAMMPS) software to further investigate the peptide’s response at the atomic and molecular level. These simulations provided insights into the structural dynamics of Aβ under electromagnetic influence, enabling a deeper understanding of the peptide’s behavior. To substantiate the findings from our simulations and the theoretical framework, we conducted a Thioflavin T (ThT) assay and western blot analysis on in vitro Aβ fibril samples which are treated with electromagnetic (EM) wave exposure using a TEM cell device. After 3 hours of EM wave exposure, a noticeable decrease in Aβ fibrils was observed. This experimental validation was essential in confirming the simulation results and reinforcing the theoretical basis of our approach. Together, simulations and experimental evidence provide a strong foundation for exploring electromagnetic-based treatments as a potential therapeutic intervention for Alzheimer’s disease.

This paper proposes a new method to find the optimum frequency offsets in a Frequency Diverse Array (FDA) radar transmit beampattern that minimizes the Peak Side Lobe Level (PSLL) and Half Power Beamwidth (HPBW). This method uses a modified Bayesian Optimization (BO) framework where Bayesian Neural Network (BNN) is used for surrogate modelling of FDA radar transmit beampattern objective function. By resampling the weights and biases of BNN, we get a distribution of predictions whose mean and standard deviation are used to compute the Expected Improvement (EI). A population of frequency offsets where the EI is higher is used to initialize Genetic Algorithm (GA). Unlike the traditional method of random initialization, this method guides GA, which in turn, searches and updates the BNN with function evaluations. Hence, each sub-optimal GA run trains the BNN, and this cycle is repeated until convergence. Simulation results show that this method yields PSLL and HPBW that are lower than state-of-the-art.

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)

This paper proposes a 500 MS/s 4-bit flash analog-to-digital converter (ADC) featuring a differential input voltage range of 1.2 Vpp operating at a supply voltage of 1.2 V. Although the proposed circuit utilizes a conventional flash ADC structure, its track and hold circuit, driving buffer, and preamp circuits corresponding to the analog stages are designed using complementary architecture to attain a sufficient swing range even at a low supply voltage. Notably, the proposed structure satisfies the error requirements. The error source of the flash ADC, such as the comparator’s input referred offset, did not degrade its performance, while the use of a calibration circuit, characterized by power consumption and area burdens and increased complexity, could also be avoided. Therefore, the proposed flash ADC met the error requirements, such as the comparator’s input referred offset, without the need for calibration circuits. The chip, fabricated using the TSMC 65 nm process, covers an area of 1,160 × 950 μm2 and consumes 78 mW of power. Furthermore, its signal-to-noise and distortion ratio and spurious-free dynamic range were measured to be 23.36 dB and 30.26 dB, respectively, at a sampling frequency of 500 MHz.

Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation technique used to treat a variety of neurological disorders, including major depression. The development of the deep brain TMS coil for stimulating subcortical structures expands the use of TMS beyond the stimulation of superficial cortical targets. Deep brain stimulation may have beneficial effects on neurological disorders such as Parkinson's disease, post-traumatic stress disorder and mild traumatic brain injury. Previous studies have shown that cerebellum plays a very big role in behavior and motor planning. To stimulate the specific areas of the human brain we require TMS coil with precise focal abilities for that the material, design, and position of a TMS coil plays a significant role in adjusting focusing power of the coil. Therefore, in this letter, we studied stimulation of frontal brain and cerebellum with two different new coil designs positioning on different locations. A rare design of TMS coil made with Litz wire is proposed to enhance excitation focality in the brain and compared with traditional figure-of-eight (FOE) coil and double cone coil (DC). Finite-element simulation tool ANSYS Maxwell 3D has been used to simulate and compare the magnetic field and electric field induced inside the model of human brain. The coil studies are as follows: a figure-of-eight (FOE) coil, an overlapped copper coil, and a Litz wire overlapped coil. This was followed by experimental validation which shows great agreement with the simulation results.

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)

Repetitive transcranial magnetic stimulation (rTMS) is attracting attention as a new treatment technique for brain lesions, and many animal studies showing its effects have been reported. However, the findings of animal application researches cannot directly represent the effects of rTMS in human, mainly due to size difference and mechanistic characteristics of rTMS. Therefore, the authors purposed to develop a mouse rTMS to simulate clinical application and to confirm. Firstly, a virtual head model was created according to magnetic resonance images of murine head. Then, simulations of rTMS stimulation with different coils were performed on the murine head phantom, and an rTMS device for mice was fabricated based on the optimal voltage conditions. Lastly, strengths of magnetic fields generated by the two rTMS devices, for human (conventional clinical use) and mouse (newly fabricated), were measured in air and on mouse head and compared. Resultantly, the magnetic field intensity generated by coil of mouse was lower than human’s (p < 0.01), and no differences were found between the predicted simulation values and the measured intensity in vivo (p > 0.05). Further in vivo researches using miniaturized rTMS devices for murine head should be followed to be more meaningful for human.