Infrared thermography technology is a noninvasiveness and real-time imaging method, it has attracted enormous attentions for blood flow imaging. However, the implementation of infrared thermography technology is still limited by the poor imaging quality caused by the low temperature discrimination between the target blood vessel and background. Herein, we reported a flexible and low-cost MXene based photothermal microheater for enhancing the infrared imaging of blood flow. In the experiment, MXene films with specific thickness was prepared by vacuum filtering different concentrations of MXene colloidal solutions. Thereafter, the microheaters were fabricated by assembling the MXene films on the PU tape/PDMS substrate, and then sealed with another layer of pure PDMS film on the top of MXene film. The photothermal performance of the microheaters were evaluated by using an 808-nm laser as the exciting source. Experimental results show that the optimal microheater (MXene content: 17.5 mg) can reach a safe temperature of 41.5 °C with 43.9 s under the light irradiation of 100 mW·cm −2 . Moreover, it can be stabilized at the equilibrium temperate for over 25 min. Finally, the above optimal microheater was used to accurately heat the simulated blood vessel. It shows that temperature difference of 3.3 °C can be induced between the heated blood vessel and environment. As a result, it significantly enhances the quality of the infrared imaging of the blood flow in the simulated vascular network.
A new flow calorimeter is developed to analyze the isobaric heat capacity of liquid. The characteristics of calorimeter have been studied at temperatures from 293 K to 353 K and pressures from 0.1 MPa to 15 MPa. The design of the calorimeter includes the innermost part of the calorimeter with two thick-walls, aluminum shields and microheater. The function of thick-walls with aluminum shields is to replace the conventional constant temperature bath for minimizing heat loss and precisely controlling the temperature of calorimeter. In order to verify the feasibility and reliability of the apparatus, the heat loss is checked by pure water under given pressure and various temperatures. The heat capacity of toluene, heptane and cyclohexane are measured at various temperatures and pressures. The experimentally measured data as a whole is in good agreement with the literature values available. Compared with the literature data, the experimental results by using the new calorimeter show that the deviations are less than 2%.
A novel gas microsensor combining SnO 2 submicron/nanostructured porous sensitive film with Micro-Electro-Mechanical systems (MEMS) microheater was successfully fabricated. The film was made of hierarchically mixed Pd/SnO 2 (HM-PTO) composites composed of Pd/SnO 2 hollow submicrospheres (Pd/SnO 2 -HSs) and Pd/SnO 2 nanoparticles (Pd/SnO 2 -NPs) deposited on the microheater platform using the microdispensing method. The as-prepared HM-PTO sensors exhibited high sensitivities, fast response/recovery rates, good selectivity, reliable reversibility, and relevant stability towards ethanol at low power consumption. The resulting superior sensing performances were attributed to the unique hierarchical structure. The internal void architecture of Pd/SnO 2 -HSs provided large specific surface areas, proper mesopore size distribution, large number of active adsorption/interaction sites, as well as promoted the chemisorption and dissociation of gas molecules due Pd-doping to yield superior gas response. In particular, the nano-sized SnO 2 particles ensured the uniform deposition of the materials to yield enhanced local conductivities, and possibly faster phase transfer reactions responsible for the extremely good response/recovery performance. This simple fabrication procedure combined with high sensing performances look promising for the development of hierarchical morphologies of novel materials for gas sensing applications.
Teng-Long Zhou,En-Kang Wu,Jia-Kang Wu,Tian Qiang,Xiao-Feng Gu,Ming-Yang Yan,Svetlana von Gratowski,Jun-Ge Liang
Traditional microwave gas sensors have been widely used for gas detection at room temperature due to the advantages of high sensitivity and multi-parameter detection. However, the detection results can be significantly affected by the change of humidity, which restricts their application in practical environments. To solve this problem, a microwave gas sensor based on SnO 2 /Co 3 O 4 composite nanofibers, a micro-heater and a dual-mode resonator was proposed, achieving high-precision measurement of acetone within the range of 10~500 ppm. The integration of micro-heater can reduce water molecule adsorption, leading to enhanced sensing stability under varying humidity levels. The results demonstrate that the construction of SnO 2 /Co 3 O 4 heterostructures can enhance the sensitivity due to increasing charge transfer capability. The maximum sensitivity reached 3.938 mdB/ppm at the optimal operating temperature of 150 ℃, which is approximately five times higher than that of room temperature conditions. Moreover, the sensitivity of the microwave gas sensor maintains almost unchanged under different humidity, which can be attributed to the integration of micro-heater. This work provides a novel strategy for the design of microwave gas sensors in practical environments.
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