Bulk-micromachined circular foil type micro heat-flux sensor

A micro heat-flux sensor with high sensitivity under conditions of low heat flux has been designed, bulk-micromachined and tested in a convective environment. The sensor, which is based on the circular foil type heat-flux sensor, is composed of thermal paths and a thermopile. Thermal path layers of electroplated copper on both sides of a wafer are connected through a bulk-micromachined window. A thermopile consisting of a series of n thermocouples is used to get an n-fold output compared to a single couple. When the sensor is placed on a high temperature wall, heat flux from the wall flows through thermal paths and drains out to the environment, producing a temperature difference along these paths. The heat flux is obtained by measuring the temperature difference using a thermopile of Ni-Cr thermocouples. The calibrated sensitivity of the micro heat-flux sensor is 0.17-1.90 μV/(mW cm^-2) in the heat flux range 0-180 mW/cm².