Research On Self-powered Flexible Temperature Sensor:From Design,Preparation To Application

Flexible thermoelectric sensor systems based on environmental energy harvesting have garnered a lot of attention from researchers in the context of Io T and wearable health monitoring applications.Unlike traditional temperature sensors,self-powered flexible thermoelectric temperature sensors（FTES）could perform both environmental energy harvesting and temperature detection,laying the groundwork for passive Io T nodes and recharge-free wearable monitoring devices.Flexible thermoelectric sensor systems based on environmental energy harvesting have garnered a lot of attention from researchers in the context of Io T and wearable health monitoring applications.Unlike traditional temperature sensors,self-powered flexible thermoelectric temperature sensors（FTES）could perform both environmental energy harvesting and temperature detection,laying the groundwork for passive Io T nodes and recharge-free wearable monitoring devices.However,existing FTES research has primarily focused on thermoelectric power generation and temperature sensing as two separate units,and has rarely addressed self-powered temperature sensing technologies that combine these two functions.The goal of this research is to develop a two-parameter temperature measurement mechanism for thermoelectric devices using the temperature dependence of the Seebeck voltage and resistance of thermoelectric materials,and ultimately to design and prepare an integrated flexible thermoelectric device with both energy harvesting and temperature measurement functions.The majority of the research work and the conclusion are listed as follow:（1）A two-parameter temperature measurement mechanism from material to device has been developed,and the preferred pairing principle of Bi₂Te₃-based thermoelectric materials with both energy harvesting and temperature measurement functions has been analysed.The bismuth telluride based materials prepared by the combustion synthesis process and the hot extrusion process both have high linearity of resistance temperature dependence curves in the operating temperature range,while the materials prepared by the hot extrusion process have larger and more stable Seebeck coefficients and power factors,which are ideal thermoelectric materials with both energy harvesting and temperature measurement properties.The temperature dependence of the open circuit voltage V_oc and ACR of thermoelectric devices made from the above materials is highly linear and repeatable,and the upper and lower surface temperatures can be simultaneous monitored by detecting the V_oc and ACR of thermoelectric devices.The difference between the device detection temperature and the thermocouple test temperature is less than 1℃within the device operating temperature range.For complex heat-source surfaces in wearable devices and Io T scenarios,this paper propose a novel design and fabrication of a flexible Bi₂Te₃-based thermoelectric generator with substrate separation-material miniaturization strategy by micro-cut processing.The normalized power density reaches 5.26μW/cm²·K² for FTEG with a size of 2 mm×16 mm,which are among the best reported results for FTEGs,and the performance remains almost the same after 7400 bending cycles.Further,by combining the above structure with a strap-like the lower substrate,the FTES achieves three-dimensional flexibility in both transverse and longitudinal bending,with no significant change in ACR during 12,000 bends in the longitudinal direction and 4,000 bends in the transverse direction,providing high flexibility and reliability.（2）Using COMSOL finite element simulations,the effect of material geometry and convective heat transfer coefficients on the power generation performance of the device is explored,and the effects of different scenarios,wind speed,and material height are systematically investigated.The results show that the output performance of the device is proportional to the material height under single heat source conditions and inversely proportional under constant temperature difference conditions.When worn on the human wrist,the output voltage and power of the device after stabilization are proportional to the external convective heat transfer capability,and the 1.6 mm material height device can deliver an average of 57.9μW at 2 m/s wind speed,with a power density of 16.15μW/cm².On the simulated Io T grid switchgear contacts heat source,the FTES can continuously output 4.32 m W of milliwatt power under a wind speed of3.5 m/s and a environmental temperature difference of about 40 K.P（Vd F-HFP）HP radiation heat sink was utilized to increase the temperature difference between the hot and cold sides of the FTES to improve power production performance in windless settings.With the integrated heat sink,the FTES achieves a 63 m V increase in output voltage when worn on the wrist and achieves an output power of 0.312 m W at 75℃ on an analogue heat source.（3）Under various operating situations,the integrated“energy harvesting-temperature sensing”device exhibits very linear relationships between open-circuit voltage-temperature differential and ACR-average temperature.The temperature dependence curve of the device under simulated contact thermal resistance conditions remains highly linear with R² of 0.999,the resistive temperature dependence coefficient remains essentially unchanged and S_TEG is slightly reduced from the ideal fixed temperature difference at 27.11 m V/K.When the device is only in contact with the bottom heat source,it also shows a linear relationship between open circuit voltage,ACR,and different heat source temperatures,indicating that both parameters can be used to characterize the heat source temperature independently or to test the device’s hot and cold surface temperatures via a two-parameter coupling.In addition,the FTES has a fast,repeatable,multi-zone temperature response signal to external heat source stimuli,with a response rate of 2 s for fingertip touch,and different cells can sense temperature changes in different zones.The voltage temperature signal values of the FTES are in general agreement with the temperature dependence curves under simulated contact thermal resistance conditions in the previous section.The ACR of the device has a faster response for double-sided contact with the medium,with a response rate of about 2 s for fingertip stimulation,and a slightly slower response rate of about 5～12 s for single-sided lamination to a heat source,but is still higher than that of thermistor and other temperature measurement elements.The FTES also has a positive proportional relationship between output voltage and wind speed,as well as a regular correlation with the distance to the heat source,thus it can be used to detect elements like wind speed and excessive temperature warnings.By incorporating the STM32 microcontroller’s external temperature measurement circuitry,the device can display real-time test temperatures under single parameter conditions.Finally,by incorporating an STM32 microcontroller external temperature measurement circuit,the FTES enables the display of real-time test temperatures under single parameter conditions.