Investigation of bimaterial cantilever beam for heat sensing in liquid

This paper presents the theoretical and experimental temperature profiles along a microcantilever beam operated in liquid and employed in this research as a temperature sensor. The main application of this cantilever beam is for sensing temperature variations of mammalian cells. The cantilever beam was microprocessed as a composite structure fabricated from thin layers of silicon nitride and gold. In order to achieve high sensitivity the cantilever beam was conceived with the length at microscale and the thickness at nanoscale dimensions. Very small temperature variations generated the deflection of the cantilever beam free end due to different values of the thermal expansion coefficients of silicon nitride and gold. The paper is focused on the temperature calibration of the cantilever beam temperature sensor when it is operated in liquid. In the paper a microwire heater was used as a localized heat source to generate the heat required for calibration purposes. The cantilever beam was immersed in the liquid and the heater temperature was varied from 27.5 °C to 71.8 °C. In analogy with the situation when temperature variations are sensed at certain distance from a cell in suspension the heater was located at 15 μm distance from the cantilever beam. The experimental deflection values were compared with the theoretical deflection values and the heat transfer coefficient h of the system was calculated. At low temperatures the heat transfer coefficient value was 381 W/m²K and at higher temperatures 642 W/m²K. The experimental measurements illustrate that the cantilever beam deflection has the largest values when the heater was located near the midpoint of the cantilever beam. A systematic investigation of the cantilever beam deflection in liquid as a function of the applied heat is important for chemical and biological applications.