An electrically controllable square-loop metamaterial based on vanadium dioxide (VO ₂ ) thin film was proposed in the terahertz frequency regime. The square-loop shaped metamaterial was adopted to perform roles not only as a resonator but also as a micro-heater for the electrical control of the VO ₂ . A dual-resonant square-loop structure was designed to realize band-pass characteristics in the desired frequency band. The measured Q -factors of the basic and scaled-down metamaterials fabricated on VO ₂ thin films were 2.22 and 1.61 at the center frequencies of 0.44 and 1.14 THz in the passbands, respectively. The transmittances of the proposed metamaterial were successfully controlled by applying a bias voltage without an external heater. The measured transmittance on–off ratios of the metamaterials were over 40 at the center frequencies in the passbands. In the future, electrically controllable terahertz metamaterial based on VO ₂ metamaterial could be employed as high-performance active filters or sensors.

In this paper, we propose an asymmetric split-loop resonator with an outer square loop (ASLR-OSL) based on vanadium dioxide (VO₂) which can actively control the transmission characteristics of a terahertz wave while maintaining a high quality factor of the asymmetric split-loop resonator (ASLR) by adding an outer square loop. The proposed ASLR-OSL demonstrated transmission characteristics similar to those of ASLR, and the transmission characteristics of ASLR-OSL were successfully controlled by directly applying a bias voltage. These results show a simple method for imposing active properties on a common metamaterial having a high quality factor by adding a loop structure.

The construction site is one of the most dangerous industries because the number of occupational injuries and fatalities is significantly higher compared to other industries. Proper use of personal protective equipment (PPE) by workers can reduce the risk of occupational injuries and fatalities. However, for a variety of reasons, workers tend not to wear their personal protective equipment properly. To address these issues, we propose a vision-based framework for monitoring wearing personal protective equipment. The developed framework is based on the real-time pixel-level detect model YOLACT, which employs MobileNetV3 as a backbone to lightweight the proposed framework. In addition, the framework uses DeepSORT of object tracking algorithm to interpolate frames not predicted by the model. The post-processing algorithm in our framework classifies the correlation between workers and PPE into four statuses based on the results predicted by YOLACT and the interpolated results from DeepSORT. The results showed that the fine-tuned model achieved 66.4 mAP₅₀, and the algorithm successfully determined workers’ PPE-wearing status detection with 91.3% accuracy. This study shows the potential to prevent occupational injuries and reduce social costs by automating monitoring at construction sites in real-time.

A Ta/TaO_x/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaO_x mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaO_x thin film at the LRS.

We report a high-speed (~2 kHz) dynamic multiplexed fiber Bragg grating (FBG) sensor interrogation using a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter. The scanning frequency of the WSL is 18 kHz, and the 10 dB scanning bandwidth is more than 90 nm around a center wavelength of 1,540 nm. The output from the WSL is coupled into the multiplexed FBG array, which consists of five FBGs. The reflected Bragg wavelengths of the FBGs are 1,532.02 nm, 1,537.84 nm, 1,543.48 nm, 1,547.98 nm, and 1,553.06 nm, respectively. A dynamic periodic strain ranging from 500 Hz to 2 kHz is applied to one of the multiplexed FBGs, which is fixed on the stage of the piezoelectric transducer stack. Good dynamic performance of the FBGs and recording of their fast Fourier transform spectra have been successfully achieved with a measuring speed of 18 kHz. The signal-to-noise ratio and the bandwidth over the whole frequency span are determined to be more than 30 dB and around 10 Hz, respectively. We successfully obtained a real-time measurement of the abrupt change of the periodic strain. The dynamic FBG sensor interrogation system can be read out with a WSL for high-speed and high-sensitivity real-time measurement.