It shows a characteristic of the negative resistance coefficient against temperature (Wu et al. 2019). The purpose of accurate temperature measurement is to reduce detection errors, which can more accurately detect the current temperature status of the object, and these errors can be found and resolved in time, such as in medical care. Self-repairing yields from materials used in portable devices allow longer periods of use when scratches or cuts are generated. It has a high practical value in bionic robots, medical care and other domains.
We can obtain accurate signals from the flexible temperature sensors connected to the dielectric surface (Kun et al. 2014). The battery is an emergency power source that waits for the operation, control and communication of electrical equipment such as power plants and substations (Huda et al. 2013). These battery failures cause system failures, such as improper operation, control, communication and instructions, so it is very important to control the real-time temperature of the battery. Currently, the storage battery temperature monitoring method is mainly manual detection by an infrared temperature detector, which has little machining and high costs and cannot perform online monitoring. The flexible temperature sensor can be connected to a storage battery surface to measure the distributed temperature (Shin et al. 2013). This method is easy to perform and can follow faults and early warnings, reducing the safety risk of the electrical system.
In general, the cold bonding temperature is detected by a precision thermist in good thermal contact with the input connectors of the measuring instrument. The measuring instrument uses this second temperature measurement, together with the reading of the thermocouple itself, to calculate the actual temperature at the tip of the thermocouple. Understanding CJC is important, because any error in measuring the temperature of cold adhesion will lead to the same temperature error measured from the tip of the thermocouple.
Self-powered materials allow the equipment to extend the service period by collecting energy from body temperature and motion (Chen et al., 2017b; Cheng et al. 2018; Jayaweera et al. 2018; Liu et al. 2018). It is difficult to provide a durable, portable power supply for flexible temperature sensors. Apply these technologies to flexible temperature sensors and realize that self-sufficiency in energy is a major challenge.
Flexible thermocouples with thermocouple alloy films are manufactured on flexible IP or PDMS substrate, where thermocouple alloy films nickel-aluminum-silicon-manganese alloy film, nickel-aluminum alloy film, p-Sb2Te3, n-Bi3Te3 film, bi-te film, and so on. The electrodes of the temperature sensors of thermocouples are generally prepared from metal films. When the alloy films of two different components are combined in one circuit and the temperature of the two connection points is different, a thermoelectric potential is generated in the circuit (Trung et al. 2018). By measuring the temperature-dependent voltage at the intersection of two different alloy films, the flexible thermocouple can feel the temperature (Bell, 2008; Martin et al. 2010; Su and Shen, 2019). Resistance changes can be measured with flexible thermistors with high repeatability and precision and can be easily integrated on a platform. Flexible thermistors are flexible temperature sensors based on metallic film, semiconductor film and alloy film.
Most flexible temperature sensors using an individual material focus only on the unit state of mechanical stimuli or joints applied to multifunctional flexible temperature sensors. This approach will have higher production costs and a complicated production process. Therefore, most flexible temperature sensors are still in the laboratory phase and are individual and isolated devices, therefore they are not really used to serve human society. Existing flexible temperature matrix sensors are still struggling to achieve high elasticity and high flexibility. Flexible temperature sensors with a large surface area are poorly scalable, easy to cut and split and have a high sensitivity to electronic skin contact. The main research directions for flexible temperature sensors are high sensitivity and multifunctional, self-healing and self-cleaning, the source of self-nutrition and transparency (White et al. 2001; Rodríguez-Donate et al. 2011; Jie, 2012) .
The resistance of the thermal resistance film changes with increasing temperature. As described in Table 2, there is a comparison between different flexible thermistors. K-type thermocouples are designed to be used at a unique or gradually higher temperature. However, if they are to be used in a continuous temperature cycle, steps can be taken to reduce the risk of errors. For example, you must ensure that the thermocouple remains in optimal condition and regularly checks the equipment.
The temperature change is directly proportional to the resistance of the diode. While this can be challenging for many applications, it means that the sensor is designed for a specific application. In general, thermistors are built for temperatures below 500 degrees Fahrenheit and are best suited for very small temperature 208V ranges. For example, blood analyzers often use thermistors because the blood temperature can only fluctuate a small amount. Machine operators need a very sensitive sensor that can detect a slight temperature change very quickly. The wiring errors in Table 2 illustrate why temperature transmitters are used with IDT.
With thermistors, because they have certain device search curves, it is common to purchase sensors and combination instruments from the same manufacturer. The application of the temperature sensor in medical electronics is also common. For example, a contactless thermometer can measure the heat emitted by an external heat source from infrared radiation. A temperature sensor for the thermistor element can be used for a blood analyzer to control the temperature of the chambers, diffuser lamps and oil-cooled engines to prevent overheating.
Figure 6C shows that the dV / dT of the self-propelled flexible temperature sensor is 0.093 V K – 1 in a temperature range of 293–323 K . Oh group (Oh et al., 2018) reported a highly accurate flexible temperature sensor with a bio-inspirator adhesive that mimics the octopus. The highly accurate flexible temperature sensor consists of a CNT compound, poly (N-isopropyl acrylamide) temperature-sensitive hydrogel and poly (3,4-ethylenedioxydiphene) polystyrene sulfonate. The highly accurate flexible temperature sensor showed an ultra-high thermal sensitivity of 2.6% ° C – 1 to 25–40 ° C, therefore a change of 0.5 ° C in skin temperature can be accurately detected. At the same time, the pNIPAM-coated octopus that imitated the rim structure PDMS adhesive layer was manufactured by forming a single mold by applying an undermining phenomenon to photolithography. Without long-term skin irritation, the manufactured sensor showed reproducible and stable detection of the skin temperature with repeated fixation / detachment cycles on the skin.