Modeling Heater Electrodes on Sheet Metal for Arbitrary Temperature Distributions

We present a method for the design of heater electrodes on substrates with high thermal conductivity such as sheet metal. The substrate is covered with a thin polymer insulation layer on both faces, which are, in turn, carrying screen printed, electrically conductive heater electrodes and another protective polymer overlayer. The temperature inside a predetermined optimization area is required to be as uniform as possible, which is desirable for various high-precision heating applications. We alternatively also aim to design a heater structure to create non-uniform temperature distributions such as a temperature dip, a peak or a gradient. These temperature distributions are required for droplet operations like splitting, merging, and moving droplets, subsequently realizing a newly proposed “lab on metal” approach in microfluidics. For this purpose, an optimization algorithm yields the required distances between linear heater electrodes. The resulting electrode distribution was numerically obtained for different optimization areas. Finally we describe the fabrication of a test device and show infrared measurements of the FEM modeled temperature distributions on the experimental realized heaters. We describe the design of heater electrodes, capable of triggering droplet motion on a “Lab-On-Metal”, as an alternative technology in Lab-On-a-Chip applications.