A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things

Abstract

Flexible electronics, which can be distributed on any surface we need, are highly demanded in the development of Internet of Things (IoT), robot technology and electronic skins. Temperature is a fundamental physical parameter, and it is an important indicator in many applications. Therefore, a flexible temperature sensor is required. Here, we report a simple method to fabricate three lightweight, low-cost and flexible temperature sensors, whose sensitive materials are reduced graphene oxide (r-GO), single-walled carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). By comparing linearity, sensitive and repeatability, we found that the r-GO temperature sensor had the most balanced performance. Furthermore, the r-GO temperature sensor showed good mechanical properties and it could be bent in different angles with negligible resistance change. In addition, the performance of the r-GO temperature sensor remained stable under different kinds of pressure and was unaffected by surrounding environments, like humidity or other gases, because of the insulating layer on its sensitive layer. The easy-fabricated process and economy, together with the remarkable performance of the r-GO temperature sensor, suggest that it is suitable for use as a robot skin or used in the environment of IoT.

Flexible Sensors—From Materials to Applications

“…Nevertheless, these techniques require specialised equipment and are not easily scaled up to large area fabrication. Solution based processes such as spin coating [193], spray coating [337], electrospinning [147], roll-to-roll printing [338], inkjet printing [137,339,340], dispenser printing [341], and screen printing [337,342], offer an easier approach for the deposition of films on large area flexible substrates. In addition, these techniques are mostly applied at low temperatures, making them compatible with substrates that require a low thermal budget.…”

“…Electrical contact sensors change their electrical properties with respect to temperature. Most of the flexible temperature sensors fall into the electrical contact sensors category and they are either resistive [103,337,339,341,342,344,345,349,[437][438][439][440][441][442][443][444][445][446][447][448][449][450][451], pyroelectric [296,375,[452][453][454][455][456][457], capacitive [145,[458][459][460], thermoelectric [145,458,459], transistors [11,460], or diodes [441]. The performance of a temperature sensor is generally assessed by investigating its temperature sensitivity, temperature range, hysteresis and response time.…”

“…The resistance is then used to estimate the temperature of the metal. The sensitivity is often described using the sensors temperature coefficient of the resistance (TCR) [337].…”

“…In a NTC thermistor the resistance decreases with the increase in temperature, and the opposite occurs in the case of a PTC thermistor [461]. Thermistors were manufactured using graphene [337,448], CNTs [337,447], graphite [103,341], PEDOT:PSS [462], polyaniline nanofibre [451], polycarbonate/α -(BEDT -TTF)2I x Br 3-x [449], and hydrogels [450].…”

Wearable and Ultrasensitive Strain Sensor Based on High‐Quality GaN pn Junction Microwire Arrays

“…A great number of wearable and flexible sensors have been developed for various functions in recent years, such as temperature sensor, humidity sensor, strain sensor, and pH sensor. [ 1–6 ] Among these sensors, flexible strain sensors, which transduce mechanical stimuli into electrical counterparts, have been the major interest of many research teams because of the ubiquitous mechanical energy in the surroundings from human body motions even to air flow. [ 7–9 ] On the basis of different mechanisms, flexible strain sensors can be divided into several types including piezoresistivity, capacity, and piezoelectricity.…”