Decoupled Cantilever Arms for Highly Versatile and Sensitive Thermal Measurements

  • Authors: B. R. Burg, J. Tong, W.-C. Hsu, P. Sambegoro, A. Mavrokefalos, G. Chen
  • Sponsorship: National Research Fund, Luxembourg, cofunded by Marie Curie Actions under FP7 COFUND (893874); U. S. DoE, Office of Science, Office of Basic Energy Sciences, Division of Materials Science and Engineering (DE-FG02-02ER45977); Air Force Office of Scientific Research, Multidisciplinary University Research Initiative (MURI FA9550-08-1-0407)
Figure 1

Figure 1: The sample arm and probe arm on the cantilever are decoupled. The aim is to reduce the effective thermal conductance of the sample arm as much as possible by using a low conductivity material and avoid bending by using a single layer. The probe arm is attached to the sample arm and made up of a bi-material layer to enable temperature dependent deflection and allow for optical detection.

Microfabricated cantilever beams are used in microelectromechanical systems (MEMS) for a variety of sensor and actuator applications. Bimaterial cantilevers accurately measure temperature change and heat flux with resolutions several orders of magnitude higher than those of conventional sensors such as thermocouples, semiconductor diodes, as well as resistance and infrared thermometers and thus have allowed new applications to emerge where other techniques are unable to probe [1] [2] [3] [4] [5] . An important limitation in these systems, however, is the deflection of the measurement sample and sensitivity limitation due to inherent bimaterial design constraints [4] [5] [6] [7] [8] . To this end, a measurement platform based on the picowatt sensitivity of optomechanical microcantilever sensors was developed in which the probe- and sample section of the cantilever are separated [9] . The bending of a custom-designed bimorph cantilever accurately allows the absolute amount of transferred heat to be extracted and temperature to be determined based on the response from thermal inputs while the sample remains immobilized (Figure 1). Optimally tailoring the material properties for the different cantilever sections enhances the measurement sensitivity by over an order of magnitude with respect to current commercial systems. The rigid sample section offers measurement versatility ranging from thermal radiation and conduction measurements to the characterization of material thermal conductivities and absorptivities in nearly identical configurations. This measurement platform for fundamental heat transfer measurements will considerably improve the current understanding of nanoscale energy transport and conversion and material characterization. The platform will also lead to advanced design guidelines for energy capture and conversion devices, in particular thermophotovoltaic cells, (solar) thermoelectric generators, and waste heat recovery heat exchangers.

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