Kai Xie

In order to improve the response time of fiber optical temperature sensors, a fast response temperature sensor based on the Venturi structure is proposed. This sensor takes advantage of the Venturi structure to increase fluid flow velocity, thereby increasing thermal conductivity and reducing the temperature response time. Simulation analysis of the Venturi temperature sensor based on fiber Bragg grating (VFBGT) showed that it has a shorter response time compared to a bare FBG at different flow velocities. The structure of the VFBGT was optimized to achieve the minimum response time. Experimental results confirmed that the VFBGT can reduce the temperature response time of the bare FBG sensor from 420ms to 210ms at a flow velocity of 1m/s, providing a new approach for dynamic temperature measurement and real-time fast temperature compensation in high-precision systems.

A method of monitoring the transmission line galloping based on fiber Bragg grating (FBG) fitting sensor is proposed and verified by video monitoring method in the overhead transmission line experiment. The proposed method can be used to measure the line tension, the galloping mode and amplitude in horizontal and vertical directions in real-time, simultaneously. The functions of this method were confirmed by the 92 hours transmission line galloping results and the influence of the wind speed and direction to the galloping measurement were also analyzed. Compared with the video monitoring method, it has the advantage of being able to measure the tension and galloping mode of line, higher resolution of galloping amplitude monitoring and real-time monitoring regardless of weather condition. This method can be widely used in transmission line monitoring and has positive significance to promote smart grid.

Silicon-germanium (Si-Ge) is used as a high-temperature thermoelectric material due to its high figure of merit and good thermal stability at high temperatures. This article focuses on the high-temperature thermoelectric energy conversion devices using Si ₈₀ Ge ₂₀ thick films prepared by laser sintering of nano/micro particles. The Si ₈₀ Ge ₂₀ thick films were prepared by ball milling of Si-Ge material to achieve nano/micro particles and then laser sintering to achieve thick films. The device consists of three pairs of n-type phosphorus-doped Si ₈₀ Ge ₂₀ legs and p-type boron-doped Si ₈₀ Ge ₂₀ legs. The maximum temperature difference of 200 K was achieved when the hot-side temperature was 873 K and the cold-side was kept in the air (no water cooling). The corresponding maximum thermovoltage and output-power were 311.6 mV and 15.85 $\mu \text{W}$ . The effective power density was calculated as 8.8 mW/cm ² . The performance of the device could be further improved by increasing the hot side temperature to about 1000 °C and cooling the cold side by water circulation, to generate a larger temperature difference. We demonstrate that this novel fabrication method as an easier, faster, and lower-cost way to fabricate the thick film type thermoelectric devices with high performance. Our demonstrated approach will be suitable for thermoelectric devices for large-area applications on arbitrary shapes. The presented method will also find applications for on-chip cooling and powering, which could substitute MEMS-based fabrication methods for $\mu $ -thermoelectric generators (TEGs) or other microthermoelectric modules with a simpler, cheaper, and faster fabrication process.

Silicon-germanium (SiGe) is an important thermoelectric material for high-temperature applications. In this study, we show that the Seebeck coefficient of the laser sintered thin films of phosphorous (P)-doped Si₈₀Ge₂₀ nanoparticles increases from -144.9 μV/K at room temperature to -390.1 μV/K at 873 K. The electrical conductivity increases from 16.1 S/cm at room temperature to 62.1 S/cm at 873 K and demonstrates an opposite trend when compared to bulk nanostructured materials. The thermal conductivity from room temperature to 573 K is essentially constant within the measurement error of our system at ∼1.35 W/m⋅K. Therefore, if the thermal conductivity follows a similar temperature dependent trend as reported in past scientific literature, the figure of merit of the thin film Si₈₀Ge₂₀ is estimated to be 0.60 at 873 K which is comparable to a value of ∼1 for bulk nanostructured materials. This result indicates that thin film P-doped SiGe can provide comparable performance with bulk nanostructured SiGe materials by using nanoparticle laser sintering as an easier, quicker, and more cost-effective processing method.

Silicon-germanium is an important thermoelectric material for high temperature applications. In this study, thin films composed of SiGe nanoparticles were synthesized in a plasma reactor and sintered by a millisecond pulse width, quasi continuous wave, near infrared laser of wavelength 1070 nm. We demonstrate that laser sintered SiGe thin films have high electrical and low thermal conductivity, dependent on the surface morphology and dopant concentration. Substrate wetting of laser heating induced molten SiGe was found to play an important role in the final surface morphology of the films. Interconnected percolation structures, formed when proper substrate wetting occurs, were found to be more conductive than the balling structure that formed with insufficient wetting. Laser power was adjusted to maximize dopant reactivation while still minimizing dopant evaporation. After optimizing laser sintering process parameters, the best electrical conductivity, thermal conductivity, and Seebeck coefficient were found to be 70.42 S/cm, 0.84 W/m K, and 133.7 μV/K, respectively. We demonstrate that laser sintered SiGe thin films have low thermal conductivity while maintaining good electrical conductivity for high temperature thermoelectric applications.

In this work, Li : Al alloy was fabricated by co-evaporation of Li₃N and Al and was confirmed by x-ray diffraction and x-ray photoelectron spectroscopy measurements. An optimized green organic light-emitting diode with the Li : Al alloy as the electron injection layer shows about 20% higher efficiency compared with the control device using a LiF/Al cathode. Furthermore, the photovoltaic measurement shows that the Li : Al/Al cathode has a lower electron injection barrier than the LiF/Al cathode.