Yanjun Zhang

A pressure and temperature sensor based on dual Fabry-Perot interferometers (F-PIs) using Vernier effect and fiber Bragg grating (FBG) in hollow silica microsphere-cavity (HSMC) structure is demonstrated theoretically and experimentally. The sensor consists of a F-P cavity formed by inserting the FBG into the HSMC and a reference F-P cavity. Two structures are connected by a 50% coupler to generate the Vernier effect. The change of external pressure will change the length of the microsphere F-P cavity. Utilizing the characteristics that FBG is temperature sensitive and not effected by pressure, the simultaneous detection of temperature and pressure can be realized by demodulating equation. With a pressure sensitivity of 49.5nm/MPa and a temperature sensitivity of 14.3pm/°C, the sensor is achieved pressure detection at 300°C ranging from 0 to 0.8 MPa. The sensor has the characteristics of temperature compensation, high production efficiency, low cost, strong robustness, self-encapsulation and so on. It has a broad prospect in the field of high temperature and high pressure detection.

Currently, there are several thermoelectric materials, such as Ag₂Te, Bi₂Te₃, and Sb₂Te₃, that have been investigated for thermoelectric applications. However, the toxicity and rarity of most of these materials make them unsuitable for practical applications. In contrast, silver selenide (Ag₂Se) is an abundant and environment-friendly thermoelectric material. This study provides a facile synthetic approach for preparing high-performance, low-cost, and flexible Ag₂Se thermoelectric films. Ag₂Se nanomaterials were prepared based on the chemical template method, and the reaction solution concentration was varied to systematically investigate the effects of reaction solution concentration on the characterization and thermoelectric properties of Ag₂Se nanomaterials. For convenience of testing, the flexible Ag₂Se films were prepared on porous nylon membranes using vacuum-assisted filtration. The prepared thermoelectric films were tested using an X-ray diffractometer, scanning electron microscope, Seebeck coefficient tester, and Hall tester. The film prepared from the solution with the lowest concentration (18.0 mM) demonstrated the best thermoelectric performance, with a maximum power factor of 382.18 μW∙m⁻¹∙K⁻² at ~400 K. Additionally, a cold-pressing treatment could effectively enhance the electrical conductivity of the film, without damaging the substrate, as the conductivity of the film remained at 90% of the original value after 1500 bending cycles.

In recent years, the preparation of flexible thermoelectric generators by screen printing has attracted wide attention due to easy processing and high-volume production. In this work, we propose an n-type Ag₂Se/polymer polyvinylpyrrolidone (PVP) film based on screen printing and investigate the effect of PVP on thermoelectric performance by varying the ratio of PVP. When the content ratio of Ag₂Se to PVP is 30:1, i.e., PI30, the fabricated PI30 film has the best thermoelectric property. The maximum power factor (PF) of the PI30 is 4.3 μW·m⁻¹·K⁻², and conductivity reaches 81% of its initial value at 1500 bending cycles. Then, the film thermoelectric generator (F-TEG) fabricated by PI30 is tested for practical application; the output voltage and the maximum output power are 21.6 mV and 233.3 nW at the temperature difference of 40 K, respectively. This work demonstrates that the use of PVP combined with screen printing to prepare F-TEG is a simple and rapid method, which provides an efficient preparation solution for the development of environmentally friendly and wearable flexible thermoelectric devices.