Excessively tilted fiber grating sensors

The development of excessively tilted fiber gratings (Ex-TFGs) provides a new type of sensing device with high refractive index (RI) sensitivity, low thermal crosstalk and vector sensing property. Due to the asymmetric grating structure of Ex-TFG, the light in the core is coupled into high order forward-propagating cladding modes and split into two orthogonal polarization states, resulting in dual-peak resonances in the transmission spectrum. The Ex-TFG also exhibits a non-circularly symmetrical near field distribution, which endows an exceptional orientation sensing capability. Benefitting from the unique mode coupling behavior, Ex-TFGs have been studied and developed for many different sensing applications, such as polarization dependent torsion and loading sensors, vector accelerometer and magnetometer, and a variety of low thermal crosstalk bio/chemical sensors. This paper will review the recent study and development of Ex-TFGs in terms of mode coupling mechanism, fabrication method, transmission and sensor characteristics and the novel applications in sensing areas

Considerable Different Frequency Dependence of Dynamic Tensile Modulus between Self-Heating (Joule Heat) and External Heating for Polymer–Nickel-Coated Carbon Fiber Composites

Dynamic tensile moduli of polyethylene–nickel-coated carbon fiber (NiCF) composites with 10 and 4 vol % NiCF contents under electrical field were measured by a homemade instrument in the frequency range of 100–0.01 Hz. The drastic descent of the storage modulus of the composite with 10 vol % was verified in lower frequency range with elevating surface temperature (<i>T</i>_s) by self-heating (Joule heat). The composite was cut when <i>T</i>_s was beyond 108 °C. On the other hand, the measurement of the composite with 4 vol % beyond 88 °C was impossible, since <i>T</i>_s did not elevate because of the disruption of current networks. Incidentally, the dynamic tensile moduli by external heating could be measured up to 130 and 115 °C for 10 and 4 vol %, respectively, but the two composites could be elongated beyond the above temperatures. Such different properties were analyzed in terms of crystal dispersions, electrical treeing, and thermal fluctuation-induced tunneling effect

Appearance of Perfect Amorphous Linear Bulk Polyethylene under Applied Electric Field and the Analysis by Radial Distribution Function and Direct Tunneling Effect

Without melting flow, linear ultrahigh molecular weight polyethylene (UHMWPE) provided X-ray intensity curve from only amorphous halo at 129.0 °C (surface temperature, <i>T</i>_s arisen by Joule heat) lower than the conventionally known melting point 145.5 °C on applying electric field to UHMWPE-nickel-coated carbon fiber (NiCF) composite. Such surprising phenomenon was analyzed by simultaneous measurements of X-ray intensity, electric current, and <i>T</i>_s as a function of time. The calculated radial distribution function revealed the amorphous structure with disordered chain arrangement. The appearance of such amorphous phase was arisen by the phenomenon that the transferring electrons between overlapped adjacent NiCFs by tunneling effect struck together with X-ray photons and some of the transferring electron flown out from the gap to UHMWPE matrix collided against carbon atoms of UHMWPE. The impact by the collision caused disordering chain arrangement in crystal grains