This is Heat Flux MF-180M Sensors (MTI.AWS.EK.MF.180M). A heat flux sensor is a thermopile, an electronic device that translates thermal energy into an electrical voltage proportional to the temperature gradient across its thermocouples' hot and cold junctions. 
EKO Instruments offers a selection of thin substrate heat-flux sensors in a range of different sizes and thicknesses, an ideal option for research and engineering applications as well as manufacturing control and monitoring processes.
As small as 4 x 2 cm², with a thin 0.9 mm plate, the MF-180 is a flexible option for a variety of applications with a measurement range from -30°C to 120°C. Light and easy to install, multiple units of the MF-180 are a great alternative to the HF-30S for large areas with an irregular surface.