Graphene, as a novel thermoelectric (TE) material, has received growing attention because of its unique microstructure and excellent thermoelectric properties. In this paper, graphene fibers (GFs) are synthesized by a facile microfluidic spinning technique using a green reducing agent (vitamin C). The GFs have the merits of high electrical conductivity (2448 S/m), high flexibility, and light weight. Further, a flexible temperature sensor based on GF and platinum (Pt) with a sensitivity of 29.9 μV/°C is proposed, and the thermal voltage output of the sensor can reach 3.45 mV at a temperature gradient of 120 °C. The sensor has good scalability in length, and its sensitivity can increase with the number of p-n thermocouples. It has good cyclic stability, repeatability, resistance to bending interference, and stability, showing great promise for applications in real-time detection of human body temperature.

Thin-Film Thermocouples (TFTCs) are characterized by their high spatial resolutions, low cost, high efficiency and low interference on the air flow. However, the thermal stability of TFTCs should be further improved for application since their accuracy is influenced by joule heat and temperature time drift. In this paper, 3D molecular dynamics and finite element analysis are used for structural design. The effects of RF magnetron sputtering power and gas flow rate on conductivity and temperature time drift rate (DT) of high thermal stability tungsten–rhenium (95% W/5% Re vs. 74% W/26% Re) TFTCs were analyzed. According to the experimental results, the average Seebeck coefficient reached 31.1 µV/°C at 900 °C temperature difference (hot junction 1040 °C) with a repeatability error at ±1.37% in 33 h. The conductivity is 17.1 S/m, which is approximately 15.2 times larger than the compared tungsten-rhenium sample we presented, and the DT is 0.92 °C/h (1040 °C for 5 h), which is 9.5% of the old type we presented and 4.5% of compared ITO sample. The lumped capacity method test shows that the response time is 11.5 ms at 300 °C. This indicated an important significance in real-time temperature measurement for narrow spaces, such as the aero-engine combustion chamber.

A double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) as a terahertz (THz) detector at 315 GHz frequency is proposed and fabricated in this paper. The structure of the epitaxial layer material in the detector is optimized, and the performance of the GaN HEMT THz detector is improved. The maximum responsivity of 10 kV/W and minimum noise equivalent power (NEP) of 15.5 pW/Hz^0.5 are obtained at the radiation frequency of 315 GHz. The results are comparable to and even more promising than the reported single-channel (SC) GaN HEMT detectors. The enhancement of THz response and the reduction of NEP of the DC GaN HEMT detector mainly results from the interaction of 2DEG in the upper and lower channels, which improves the self-mixing effect of the detector. The promising experimental results mean that the proposed DC GaN/AlGaN HEMT THz detector is capable of the practical applications of THz detection.

In this paper, a novel micro-displacement sensor with double optical fiber probes is proposed and designed, which can realize the highly sensitive sensing of longitudinal or lateral micro-displacements. The optical fiber probes are made through photopolymer formulation, and the effects of reaction time and optical power on the growth length of the probe are illustrated. The relationship between light intensity and longitudinal micro-displacement is a power function in the range of 0–100 μm at room temperature with a correlation coefficient of 98.92%. For lateral micro-displacement, the sensitivity is −2.9697 dBm/μm in the range of 0–6 μm with a linear fit of 99.61%. In addition, the linear correlation coefficient decreases as the initial longitudinal distance increases, and the function of these correlation coefficients is also linear with a linearity of 96.14%. This sensor has a simple manufacturing process, low cost, high sensitivity, and fast response speed. It is suitable for harsh environments such as strong electromagnetic interference and corrosivity, and has a broad application prospect in the field of micro-displacement sensing.

With polymerization duration and Au³⁺ concentration of the electrolyte regulated, a desirable nitrate-doped polypyrrole ion-selective membrane (PPy(NO₃⁻)-ISM) and Au solid contact layer of anticipate surface morphology were obtained, and the performance of nitrate all-solid ion-selective electrodes (NS ISEs) was improved. It was found that the roughest PPy(NO₃⁻)-ISM remarkably increases the actual contact surface area of the PPy(NO₃⁻)-ISMs with nitrate solution, which leads to better adsorption of NO₃⁻ ions upon the PPy(NO₃⁻)-ISMs, and produces a larger number of electrons. The most hydrophobic Au solid contact layer avoids the formation of the aqueous layer at the interface between the PPy(NO₃⁻)-ISM and Au solid contact layer, and ensures unimpeded transporting of the produced electrons. The PPy-Au-NS ISE for polymerization duration 1800 s and at Au³⁺ concentration 2.5 mM of the electrolyte displays an optimal nitrate potential response, including a Nernstian slope of 54.0 mV/dec, LOD of 1.1 × 10⁻⁴ M, rapid average response time less than 1.9 s, and long-term stability of more than 5 weeks. This indicates that the PPy-Au-NS ISE is an effective working electrode for the electrochemical determination of NO₃⁻ concentration.

Although arrayed waveguide gratings (AWGs) are widely used in fibre Bragg grating (FBG) demodulation systems, their applications in real environments have been limited due to their narrow dynamic range and inability to continuously demodulate FBGs because of the finite bandwidth of AWG channels. Here, we developed a wide-dynamic-range, high-precision, continuous-demodulation FBG interrogator utilizing a dual-input channel on-chip silicon AWG. The introduction of two input channels in the AWG allowed two spectral peaks in each channel; therefore, staggered spectral peaks were realized. A joint-peak demodulation method based on this spectrum is proposed to improve the dynamic range and demodulation precision. With the proposed structure and method, we achieved continuous interrogation with a demodulation precision of 25.58 pm and a dynamic range of 24.5 nm in the 1537.5-1565.3 nm wavelength region. The relative demodulation accuracy within the full range reaches 0.1%. The dynamic range of adjacent channels is 5.4 nm, which is approximately 4 times greater than the dynamic range of an FBG conventional demodulation system using an AWG, and the relative demodulation accuracy is 0.47%. To our knowledge, the relative demodulation accuracy is currently the highest reported. This developed interrogator, with a core size of 420 µm × 300 µm, theoretically explained and experimentally verified the possibility of the accurate measurement of an arbitrary FBG wavelength with high demodulation accuracy in the measurement range. This work achieved continuous monitoring of external temperature by FBGs and demonstrated their significant potential in expanding the application field of FBGs.