Kejia Wei

Bio: Kejia Wei is an academic researcher from Tianjin Polytechnic University. The author has contributed to research in topics: Arrayed waveguide grating & Fiber Bragg grating. The author has an hindex of 2, co-authored 7 publications receiving 97 citations.

Wearable sensors in intelligent clothing for measuring human body temperature based on optical fiber Bragg grating.

Abstract: Measuring body temperature is considerably important to physiological studies as well as clinical investigations. In recent years, numerous observations have been reported and various methods of measurement have been employed. The present paper introduces a novel wearable sensor in intelligent clothing for human body temperature measurement. The objective is the integration of optical fiber Bragg grating (FBG)-based sensors into functional textiles to extend the capabilities of wearable solutions for body temperature monitoring. In addition, the temperature sensitivity is 150 pm/°C, which is almost 15 times higher than that of a bare FBG. This study combines large and small pipes during fabrication to implant FBG sensors into the fabric. The law of energy conservation of the human body is considered in determining heat transfer between the body and its clothing. The mathematical model of heat transmission between the body and clothed FBG sensors is studied, and the steady-state thermal analysis is presented. The simulation results show the capability of the material to correct the actual body temperature. Based on the skin temperature obtained by the weighted average method, this paper presents the five points weighted coefficients model using both sides of the chest, armpits, and the upper back for the intelligent clothing. The weighted coefficients of 0.0826 for the left chest, 0.3706 for the left armpit, 0.3706 for the right armpit, 0.0936 for the upper back, and 0.0826 for the right chest were obtained using Cramer's Rule. Using the weighting coefficient, the deviation of the experimental result was ± 0.18 °C, which favors the use for clinical armpit temperature monitoring. Moreover, in special cases when several FBG sensors are broken, the weighted coefficients of the other sensors could be changed to obtain accurate body temperature.

Design of 1 × 8 silicon nanowire arrayed waveguide grating for on-chip arrayed waveguide grating demodulation integration microsystem

Abstract: The integration of fiber grating demodulation system is a research emphasis in the study of demodulation systems. On-chip arrayed waveguide grating (AWG) demodulation integration makes integration possible in a demodulation system. A 1 × 8 silicon nanowire AWG for on-chip AWG demodulation integration microsystem is proposed and designed. The center wavelength is 1550.918 nm, the waveguide width is 350 nm, the waveguide thickness is 220 nm, and the effective area is 267 × 259 μm 2 . The single-mode waveguide cross-section structure is designed according to the refractive index of the silicon-on-insulator material. The mask layout territory of the 1 × 8 AWG is designed and opti- mized using the beam propagation method. A cone-shaped mold spots converter is proposed in the design process. Furthermore, the wave- length-division-multiplexing-phasar simulation system is established to simulate the stable output optical propagation characteristics of the designed AWG. The simulation result shows that the insert loss of the AWG is 10.658 dB, and the crosstalk is 3.037 dB, which is lower under the same waveguide, thickness, and size. This condition makes the AWG design the best choice for a fiber Bragg grating demodulation micro- system. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1 .OE.51.12.123001)

Method for improving C-wave band LED emergent light efficiency by using two-dimensional photon crystal

Abstract: The invention discloses a method for improving C-wave band LED emergent light efficiency by using a two-dimensional photon crystal The method comprises the steps of: 1, based on a finite different time domain (FDTD) algorithm theory, constructing a two-dimensional photon crystal structure model; analyzing a two-dimensional photon crystal band structure based on the FDTD algorithm; and 3, selecting an optimal band structure and completing the design of two-dimensional photon crystal parameters In the invention, the band solution is carried out on the two-dimensional photon crystal structure model by adopting the FDTD algorithm, two-dimensional photon crystal structure and parameters for improving the C-wave band LED emergent efficiency are designed Through simulation calculation, the C-wave band LED emergent efficiency can be increased by the two-dimensional photon crystal structure and parameters provided by the invention

Research on demodulation system for human body temperature measurement of intelligent clothing based on arrayed waveguide grating

Abstract: A system for demodulating distributed fiber Bragg grating sensors of the intelligent clothing was researched and realized, which is based on arrayed waveguide grating. The principle of demodulation method based on arrayed waveguide grating was analyzed, intensity--demodulating method was used to interrogate the wavelength of the fiber Bragg grating based on the building up of an experimental platform, and demodulation experiment of pre and post series of fiber Bragg grating was completed. The results show that the wavelength demodulation of the system has high linearity for fiber Bragg grating, the system gives a wavelength accuracy of 0.001 nm, and demodulation error caused by crosstalk between different sensors is 0.0005 nm. The measurement error of human body temperature is +/- 0.16 degrees C. It can be applied to the human body temperature measurement.

Enhanced light extraction of C-band on-chip LED by photonic crystals for arrayed waveguide grating demodulation integrated microsystems

Abstract: The main disadvantage of using a light-emitting diode (LEDs) as the on-chip light source for arrayed waveguide grating demodulation integrated microsystems is its low light extraction efficiency. Using photonic crystals (PCs) is an efficient method to increase the extraction efficiency of LEDs. This paper calculated the band structure of two-dimensional (2D) PCs with different arrangements and ratios using the finite-difference time-domain (FDTD) method, and the best structural parameters of 2D PCs were determined using the band gap theory. Furthermore, a FDTD simulation system was established, and the energy flow of the surface of LED was calculated to verify the effect of PCs on the light extraction efficiency of C-band LEDs. Results show that the best structure is an air hole PC with a triangular arrangement having a lattice constant of 500 nm and a ratio of 0.44. This model increased the light extraction efficiency of C-band LEDs by 1.77 times.

Wearable Sensors for Remote Health Monitoring.

Abstract: Life expectancy in most countries has been increasing continually over the several few decades thanks to significant improvements in medicine, public health, as well as personal and environmental hygiene. However, increased life expectancy combined with falling birth rates are expected to engender a large aging demographic in the near future that would impose significant burdens on the socio-economic structure of these countries. Therefore, it is essential to develop cost-effective, easy-to-use systems for the sake of elderly healthcare and well-being. Remote health monitoring, based on non-invasive and wearable sensors, actuators and modern communication and information technologies offers an efficient and cost-effective solution that allows the elderly to continue to live in their comfortable home environment instead of expensive healthcare facilities. These systems will also allow healthcare personnel to monitor important physiological signs of their patients in real time, assess health conditions and provide feedback from distant facilities. In this paper, we have presented and compared several low-cost and non-invasive health and activity monitoring systems that were reported in recent years. A survey on textile-based sensors that can potentially be used in wearable systems is also presented. Finally, compatibility of several communication technologies as well as future perspectives and research challenges in remote monitoring systems will be discussed.

Wearable Pressure Sensors for Pulse Wave Monitoring

Abstract: Cardiovascular diseases remain the leading cause of death worldwide. The rapid development of flexible sensing technologies and wearable pressure sensors have attracted keen research interest and have been widely used for long‐term and real‐time cardiovascular status monitoring. Owing to compelling characteristics, including light weight, wearing comfort, and high sensitivity to pulse pressures, physiological pulse waveforms can be precisely and continuously monitored by flexible pressure sensors for wearable health monitoring. Herein, an overview of wearable pressure sensors for human pulse wave monitoring is presented, with a focus on the transduction mechanism, microengineering structures, and related applications in pulse wave monitoring and cardiovascular condition assessment. The conceptualizations and methods for the acquisition of physiological and pathological information related to the cardiovascular system are outlined. The biomechanics of arterial pulse waves and the working mechanism of various wearable pressure sensors, including triboelectric, piezoelectric, magnetoelastic, piezoresistive, capacitive, and optical sensors, are also subject to systematic debate. Exemple applications of pulse wave measurement based on microengineering structured devices are then summarized. Finally, a discussion of the opportunities and challenges that wearable pressure sensors face, as well as their potential as a wearable intelligent system for personalized healthcare is given in conclusion.

Fiber Bragg Gratings for Medical Applications and Future Challenges: A Review

Abstract: In the last decades, fiber Bragg gratings (FBGs) have become increasingly attractive to medical applications due to their unique properties such as small size, biocompatibility, immunity to electromagnetic interferences, high sensitivity and multiplexing capability. FBGs have been employed in the development of surgical tools, assistive devices, wearables, and biosensors, showing great potentialities for medical uses. This paper reviews the FBG-based measuring systems, their principle of work, and their applications in medicine and healthcare. Particular attention is given to sensing solutions for biomechanics, minimally invasive surgery, physiological monitoring, and medical biosensing. Strengths, weaknesses, open challenges, and future trends are also discussed to highlight how FBGs can meet the demands of next-generation medical devices and healthcare system.

Wearable E-Textile Technologies: A Review on Sensors, Actuators and Control Elements

Abstract: Wearable e-textiles are able to perform electronic functions and are perceived as a way to add features into common wearable textiles, building competitive market advantages. The e-textile production has become not only a research effort but also an industrial production challenge. It is important to know how to use existing industrial processes or to develop new ones that are able to scale up production, ensuring the behavior and performance of prototypes. Despite the technical challenges, there are already some examples of wearable e-textiles where sensors, actuators, and production techniques were used to seamlessly embed electronic features into traditional wearable textiles, which allow for daily use without a bionic stigma.

Flexible Sensors—From Materials to Applications

Abstract: Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications.