Recent publications'20

1. Plantar pressure detection with mechanically induced long period fiber grating system

DOI:https://doi.org/10.1117/12.2553049

Abstract

We demonstrate an application of the mechanically induced long period fiber grating system for a foot plantar measurement. The system is designed as a fixed fiber grating platform that can be utilized for monitoring a subject’s foot plantar pressure distribution in static and dynamic activities. The pressure information obtained from the foot loading characteristics can be used for various application such as disease diagnosis of foot problem, foot ware design, sport biomechanics and injury prevention. The system is composed of a strand of a single mode fibers with 800 nm cut off wavelength and circular plastic grooved plates with the grating period of 0.8 and 1.0 mm made by 3 D printing. The sensing units are fixed at biomechanically significant positions; fore-foot, mid-foot and hind-foot of the foot platform for monitoring the foot plantar pressure distribution. The sensing locations are chosen appropriately to contact with sensitive areas of foot and can initially provide enough foot plantar pressure characteristics of a subject. The fiber sensing units with grating having different periods provides different sets of transmission spectra which separately respond to individual perturbed points. Preliminary result shows that the system can be used to classify different types of foot. With some advantageous properties of the optical fiber such as structural flexibility and light weight, the system can successfully be used to monitor the static and dynamic perturbations such as the movement of the body center of mass and foot actions in the stance phase. The study has demonstrated that the proposed fiber-optic sensing systems has a feasibility of being used as an alternative for insole plantar pressure detection systems.

2. Analysis and optimization of Raman scattering for malaria infected blood

DOI:https://doi.org/10.1117/12.2552998

Abstract

Malaria is a disease generally found in a tropical area including Thailand. It is widely known that the biological technique such as PCR normally used for an accurate detection of malaria-infected blood requiring a considerable period to repeat the process. Raman spectroscopy is considered to be an alternative method for the malaria infected blood detection. Theoretically, Raman spectroscopy is based on the scattering process that is less likely in a normal situation. Therefore, an enhancing technique known as “surface-enhanced Raman scattering (SERS)” is required for the signal augmentation. The SERS provides the enhancement of the electric field near the surface of the substrate. With the application of the technique, the main target of this research focuses on the comparison of the SER Raman spectra of the normal red blood cell and malaria infected red blood cell. However, only a single spectrum cannot provide a clear difference between the normal and the infected blood. An additional tool for even more effective discrimination was provided by using PCA analysis. In the sample preparation stage, the spin coating process was applied to spread the red blood cells uniformly on the surface. In addition, the spectra of the red blood cells including media were collected in various conditions in terms of the excitation wavelengths and the types of substrate. This additional information can be used as references for any red blood cell related investigation using Raman spectroscopy.

3. The design of high birefringence hollow core with nested anti-resonance nodeless fiber

DOI:https://doi.org/10.1117/12.2553003

Abstract

We present the design of a high birefringence hollow core with nested anti-resonance nodeless fiber (HC-NANF). This model is designed for terahertz guidance made by TOPAS copolymer. The finite element method is used to study the properties of the proposed fiber: effective material loss, confinement loss, and birefringence. In this model, the cladding consists of four circular anti-resonant tubes: two tubes aligning in the horizontal axis and two tubes aligning in the vertical axis. Each circular anti-resonant tube consists of two circular nested tubes. First, we optimize the thickness of circular nested tubes due to anti-resonance reflecting guidance mechanism to achieve the lowest loss. The simulation results show that the thickness of 0.09 mm is suitable for operating at 1 THz. To achieve the birefringence, we attempted to rotate the inner circular nested tube with two patterns: symmetric and asymmetric rotations. The simulation results show that only the asymmetric rotation can provide the birefringence in the structure. It also shows that the birefringence can be adjusted by rotating the inner circular nested tube with respect to the core radius. Finally, the orthogonal birefringence of the proposed design from HC-NANF is found to be higher than 10-4. This study offers an alternative model to provide the birefringence in THz regime, which might be relevant for future polarization related applications.

4. The study of geometries effect of hexagonal metamaterial absorber in the terahertz regime

DOI:https://doi.org/10.1117/12.2552989

Abstract

Metamaterials (MMs) are the artificially engineered materials that can exhibit particular electromagnetic properties such as negative refractive index, left-handed behavior, extraordinary transmission, etc. These fascinating properties of MMs are of great and increasing interest to be used in various applications in the terahertz regime (0.1-10 THz). In this study, the electromagnetic property of metamaterial that we are interested is an extraordinary transmission for creating a “Metamaterial Absorber (MMA)”. Over the past decade, there has been a number of designed patterns of metamaterial absorbers having high absorptivity and also multi-absorption characteristics such as split-ring resonator, square, U-shape, T-shape and Hexagon. Most of the Hexagons are designed to have the absorption characteristics in GHz frequency. We intend to investigate the effects of the parameters regarding the absorption in the terahertz regime, especially in 0.3-5.0 THz for various applications such as security and medicine. The proposed absorber structure in this study consists of 3 layers which are a periodically arranged metallic hexagonal pattern layer, a dielectric layer, and a continuous metallic layer. Length, width, number of gaps, gap size, the position of a gap of the hexagon in the first layer are the studied parameters. The proposed hexagon metamaterial absorber of the first design having 5 gaps with gap size 5 μm each located at the corner of the hexagon provide 4 absorption bands with high absorptivity. For the other design having 6 gaps with gap size of 5 μm each located at hexagon side show not only 3 narrow bands of perfect absorption but also a broadband absorbance for the terahertz regime around 3 THz.