# Wearable Sensors for Vital Signs Measurement: A Survey
## 2 Classification of Wearable Medical Sensors
### Classification and Application of Wearable Medical Sensors
#### 2.2.3 Wearable Medical Sensors for Detecting Body Temperature  
Body temperature is one of the important indicators that reflect the health of the human body. Accuracy of monitoring also directly affects the health of the human body. Knowing the specific value of the human body temperature can indirectly obtain the health information of the human body. This is of great significance to the prevention, infiltration and treatment of diseases, especially the prevention and control of influenza during the new coronavirus epidemic. Many scholars have conducted related research on body temperature detection with medical sensors (Table 3). [PERSON] et al. (2017) demonstrated ultra-fast detection and a reversible MoS\({}_{2}\) gas sensor at room temperature. By measuring body temperature, it was found that under light excitation, MoS\({}_{2}\) exhibits enhanced sensitivity, ultra-fast response time (29 s), and excellent recovery rate of NO\({}_{2}\) (100 ppm) at room temperature. This is a significant improvement in sensitivity, and the sensor has reliable selectivity to NO\({}_{2}\) and various other gases [30]. [PERSON] et al. (2018) proposed and developed a resistive flexible NH\({}_{3}\) sensor, which was prepared by depositing polyaniline-cerium dioxide (PANI-CeO\({}_{2}\)) nanocomposite film on a flexible polyimide (PI) substrate by an in situ self-assembly method. By comparing the morphology, structure and chemical characteristics of pure PANI and PANI-CeO\({}_{2}\) nanocomposites, and their effects on temperature detection, it was found that the PANI-CeO\({}_{2}\) thin-film sensor enhanced the response; shortened recovery time; produced a perfect response concentration linearity; had good reproducibility, excellent selectivity, remarkable long-term stability, ultra-low detection concentration (16 ppb) and theoretical detection limit (0.274 ppb); and had excellent flexibility, with no significant reduction in response after 500 bending/extension cycles [31]. By analyzing the tissue-like mechanical compliance and good biocompatibility of a self-healing hydrogel-bioelectronic device, [PERSON] et al. (2019) proposed a self-healing, durable, heat-resistant and dual-sensing hydrogel sensor. They found that the hydrogel-bioelectronic device had superior mechanical and thermal sensitivity, and could realize a flexible touch keyboard for feature recognition and a \"heat indicator\" for human forehead temperature detection [32]. [PERSON] et al. (2019) prepared a flexible hybrid film composed of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) for use as a multi-functional temperature and liquid leakage monitoring sensor, based on piezoresistive effect. The experimental results showed that with the increase in SNP content, the hardness and Young's modulus of the hybrid film decreased, but the thermal conductivity showed the opposite trend. The resistance of the hybrid film decreased linearly with the increase in temperature. As the amount of solvent adsorbed increased, the resistance change increased linearly. These characteristics prove the potential applications of hybrid membranes in detecting temperature and liquid leakage [33]. [PERSON] et al. (2020) reported a multi-functional sensor composed of a hydrophobic membrane and graphene/polydimethylsiloxane sponge. It was found that in the case of temperature stimulation, the sensor displayed a temperature-sensing resolution of 1 Kelvin through the pyroelectric effect. The sensor could generate output voltage signals after physical contact with different flat materials, following the principle of contact induction charging, and the corresponding signals could be used to infer material properties in turn. Therefore, this multi-functional sensor performed well in terms of low cost and material recognition, and provided a design concept to meet the challenges of functional electronics [34].