Fully Printed Flexible Heat Flow Sensors and their Utilization toward Heat Generation Monitoring for People and Machineries

Abstract A flexible and highly sensitive heat flow sensor, which can be attached to the human body and to various types of machinery for measuring their heat generation, is an ideal device for monitoring human health and the operational conditions of machinery. These sensors may be of great value for the implementation of sophisticated cyber physical systems. However, the fabrication of flexible and highly sensitive heat flow sensors is challenging because it is difficult to fabricate efficient heat–voltage conversion materials on flexible film substrates. In this study, a fully printed flexible heat flow sensor with high sensitivity is examined, which allows the detection of minute quantities of heat flow with the magnitude of several tens of milliwatts. The sensor features a device structure, wherein thermoelectric layers comprising carbon nanotube and polymethyl methacrylate coating are placed on the top and bottom surfaces of the flexible substrate and are connected by through‐holes. Due to the resultant flexibility and high sensitivity, the sensor can be attached to a human arm and detect the heat emanating from it. Additionally, it is demonstrated that changes in the load of a machine under operation can be monitored by attaching the flexible heat flow sensor to the machine.