Inverse Design of Terahertz Nanoresonators through Physics-Informed Machine Learning

The rapid development of 6G communications using terahertz (THz) electromagnetic waves has created a demand for highly sensitive THz nanoresonators capable of detecting these waves. Among the potential candidates, THz nanogap loop arrays show promising characteristics but require significant computational resources for accurate simulation. This requirement arises because their unit cells are 10 times smaller than millimeter wavelengths, with nanogap regions that are 1,000,000 times smaller. To address this challenge, we propose a rapid inverse design method for terahertz nanoresonators using physics-informed machine learning, specifically employing double deep Q-learning combined with an analytical model of the THz nanogap loop array. Through approximately 200,000 iterations in about 39 hours on a middle-level personal computer (CPU: 3.40 GHz, 6 cores, 12 threads, RAM: 16 GB, GPU: NVIDIA GeForce GTX 1050), our approach successfully identifies the optimal structure, resulting in an experimental electric field enhancement of 32,000 at 0.2 THz, 300% stronger than previous achievements. By leveraging our analytical model-based approach, we significantly reduce the computational resources required, providing a viable alternative to the impractical numerical simulation-based inverse design that was previously impractical

Detection of Single Nanoparticles inside a Single Terahertz Resonator

With the rapid advancement of 5G/6G communications using millimeter wavelengths, the concomitant usage of these long wavelength radiation for remote sensing and monitoring of biological and chemical agents is anticipated. However, the ability to detect and identify these agents with sizes ranging from nanometers to microns is hampered by its millimeter wavelength, which drastically reduces the interaction cross-section. Herein, it is reported that single gold nanoparticles (NPs) drop-casted on the nanoresonator can be observed by monitoring the far-field transmitting spectra of individual terahertz (THz) nanoresonators, which enhance the electric field hundreds of times on the nanoscale. Despite the enormous mismatch in length scales, full-wave 3D numerical modeling of the single THz nanoresonator is also performed to interpret the experimental results, indicating the possibility to turn off the resonance using only one NP embedded in the hotspot of the nanoresonator. Such NP detection becomes the most sensitive when the particle, whose size is comparable to the gap width, is tightly fitted into the nanoresonator. This work unveils the potential associated with refractive index sensing and hyperspectral absorption spectroscopy for detecting and fingerprinting ultra-low density of bio/chemical molecules such as viruses, lipid vesicles, and explosives

Measuring Complex Refractive Indices of a Nanometer-Thick Superconducting Film Using Terahertz Time-Domain Spectroscopy with a 10 Femtoseconds Pulse Laser

Superconducting thin films are widely applied in various fields, including switching devices, because of their phase transition behaviors in relation to temperature changes. Therefore, it is important to quantitatively determine the optical constant of a superconducting material in the thin-film state. We performed a terahertz time-domain spectroscopy, based on a 10 femtoseconds pulse laser, to measure the optical constant of a superconducting GdBa2Cu3O7-x (GdBCO) thin film in the terahertz region. We then estimated the terahertz refractive indices of the 70 nm-thick GdBCO film using a numerical extraction process, even though the film thickness was approximately 1/10,000 times smaller than the terahertz wavelength range of 200 mu m to 1 mm. The resulting refractive indices of the GdBCO thin film were consistent with the theoretical results using the two-fluid model. Our work will help to further understand the terahertz optical properties of superconducting thin films with thicknesses under 100 nm, as well as provide a standard platform for characterizing the optical properties of thin films without the need of Kramers-Kronig transformation at the terahertz frequencies

High sensitivity bolometers based on metal nanoantenna dimers with a nanogap filled with vanadium dioxide

One critical factor for bolometer sensitivity is efficient electromagnetic heating of thermistor materials, which plasmonic nanogap structures can provide through the electric field enhancement. In this report, using finite element method simulation, electromagnetic heating of nanorod dimer antennas with a nanogap filled with vanadium dioxide (VO2) was studied for long-wavelength infrared detection. Because VO2 is a thermistor material, the electrical resistance between the two dimer ends depends on the dimer's temperature. The simulation results show that, due to the high heating ability of the nanogap, the temperature rise is several times higher than expected from the areal coverage. This excellent performance is observed over various nanorod lengths and gap widths, ensuring wavelength tunability and ultrafast operating speed, thereby making the dimer structures a promising candidate for high sensitivity bolometers

The C677 Mutation in Methylene Tetrahydrofolate Reductase Gene: Correlation with Uric Acid and Cardiovascular Risk Factors in Elderly Korean men

The C677T mutation in the methylene tetrahydrofolate reductase (MTHFR) gene results in elevated homocysteine levels and, presumably, in increased cardiovascular risk. Moreover, elevated homocysteine levels are reportedly associated with high serum uric acid levels. We evaluated the MTHFR genotype and a panel of biochemical, hematological variables, and lifestyle characteristics in 327 elderly Korean men (age range 40-81 yr; mean, 51.87). This study shows that mutation of the MTHFR gene may be a risk for hyperuricemia. The mean uric acid levels for the C/C, C/T and T/T genotypes were 5.54, 5.91 and 6.33 mg/dL, respectively (p=0.000). The T/T genotype was significantly more frequent in subjects with high uric acid levels (p=0.003). Thus, this mutation of the MTHFR gene is implied by the study results to be a risk factor of hyperuricemia in elderly Korean men. However, the relationship between the MTHFR mutation and uric acid metabolism remains unclear. Therefore, further studies are necessary to explain the associated between the MTHFR mutation and elevated uric acid levels, and to examine potential relationships between it and conventional cardiovascular risk factors

Clinical Characteristics of Dialysis Related Sclerosing Encapsulating Peritonitis: Multi-center Experience in Korea

Sclerosing encapsulating peritonitis (SEP) is a rare but serious complication in patients with continuous ambulatory peritoneal dialysis (CAPD), and is characterized by a progressive, intra-abdominal, inflammatory process resulting in the formation of sheets of new fibrous tissue, which cover, bind, and constrict the viscera, thereby compromising the motility of the bowel. No satisfactory estimate is available on the comparative incidence of dialysis related SEP and the pathogenesis of SEP still remains uncertain. Although recent therapeutic approaches have reported varying degrees of success, an efficient measure to detect, at an early stage, patients at risk for SEP would be beneficial and a standardized treatment regimen to prevent the illness is urgently needed. This study aimed to evaluate the clinical features of SEP and to identify the possible risk factors for the development of SEP in CAPD patients. We retrospectively reviewed by questionnaire SEP cases among CAPD patients from 7 university hospital dialysis centers in Korea, including Yonsei University, Ajou University, Catholic University, Inha University, Kyungpook University, Seoul National University and Soonchunhyang University, from January 1981 to December 2002. Out of a total of 4,290 CAPD patients in these centers, 34 cases developed SEP with an overall prevalence of 0.79%. The male to female ratio was 17:17. The median age of these patients was 44.5 years (range 19 - 66). The median duration of CAPD before SEP was 64 months (9 - 144) and 68% of patients (23/34) had been on CAPD for more than 4 years. Peritonitis (including two fungal cases) was the main cause of catheter removal in SEP (27 cases, 79%). Seventy-five percent of the cases (15/20) were administered β-blocker for a mean duration of 85 months (26 - 130). Among 10 cases with available peritoneal equilibration test (PET) data, 8 showed high transporter characteristics, and the remaining 2 were high average. Eighteen cases were diagnosed by clinical and radiologic methods, and 16 were surgically diagnosed. Eleven cases were surgically treated and the others were treated conservatively with intermittent total parenteral nutrition (TPN). The overall mortality rate was 24%. SEP is a serious, life threatening complication of CAPD. Most cases had a PD duration of more than 4 years, a history of severe peritonitis, and high transporter characteristics in PET. Therefore, to reduce the incidence of SEP, careful monitoring and treatment, including early catheter removal in patients with severe peritonitis, should be considered for long-term CAPD patients with the above characteristics

Large-area nanogap fabrication for terahertz switching

Here, I will introduce new lithography techniques that fabricate an array of metal gaps of nanometer to ??ngstrom scale. Furthermore, the related optical applications in the terahertz (THz) region are also covered. A fundamental challenge was to fabricate THz???resonant nano-patterns over, at least, a square sub-millimeter. At the beginning of these studies, the focused ion beam and electron-beam lithography techniques were used for fabricating the THz???resonant nanostructures such as nano-slot antennas and cloased-loop nano-gaps, but the fabrications with those techniques were expensive and slow. To overcome these fabrication issues, new lithography techniques such as nanoimprint, nanosphere lithography, and atomic layer lithography have recently been developed for large???area nanogap arrays in thin metal films. In particular, atomic layer lithography, which combines atomic layer deposition with standard lithography techniques, produced an array of nanogaps with gap widths of 1 nm in metal films over a wafer-scale substrate. Funneling of THz waves through the resulting 1 nm gaps led to a record field enhancement factor of 25 000. THz waves and nanometer gaps have become a great combination for dramatically enhancing light???matter interactions by contacting the large-area nanogaps to the phase-transition materials