THE past few years have witnessed a growing interest in the measurement of unsteady heat transfer phenomena. This increase in interest is due to the need and desire to understand the heat transfer process that occurs in inherently unsteady environments and to support the numerical modeling of unsteady heat transfer phenomena in suitable validating experiments. Research has been conducted on a number of topics involving both natural and forced unsteadiness, including turbine blade heat transfer, boundary-layer transition, turbulent boundary layer, etc. Despite the vast progress made in the field of optical measurement techniques for determining global heat-flux distribution on the surface using various methods, including the liquid crystal technique, infrared and phosphor thermography, and temperaturesensitive paint, there is still an urgent need for a single-point heat transfer measurement technique of high temporal resolution. This is primarily due to the lack of temporal resolution of all optical methods to capture real high-frequency fluctuations of heat flux at the wall. Situations such as these might occur in conjunction with flow phenomena that are present in the transitional process of a hypersonic boundary layer from the very beginning of transition till downstream to the turbulent state. In such a high-speed flow, two gauge parameters are therefore of importance: the gauge sensitivity (voltage output and heat-flux density) and the time response should be as high as possible to achieve a large signal/noise ratio even at high frequencies.

A wide range of well-established single-point heat-flux gauges is available for various applications in thermodynamics and fluid mechanics with different characteristics. Conventional gauges may be categorized as gauges based on the following: 1) the dissipation of electric power from a heater mounted on the substrate surface, 2) transient surface-temperature measurement using various techniques such as those involving coaxial thermocouples and thin-film assistance elements, and 3) temperature-difference measurements that include the well-established Gardon-type gauges, Schmidt–Boelter gauges, and standard layered gauges, which have achieved a very high level of perfection and performance in the form of microsensors.