A dielectric coating for improved performance of capacitive sensors in all- polymer microfluidic devices

Increasing the relative permittivity of dielectric materials can be useful in many applications, including capacitive sensing in microfluidics. In order to be able to efficiently integrate capacitive sensors with high sensitivity into all-polymer microfluidic devices, polymeric layers with high dielectric constants are required. In this contribution, a dielectric coating made from a polymeric base with mixed in ceramic particles, which exhibits enhanced dielectric properties compared to the polymer itself, is presented. Poly(methyl methacrylate) is chosen as a polymeric base material due to its processing properties. Its relative permittivity is increased by mixing in barium titanate particles at concentrations ranging from 0 vol% to 90 vol%. The dielectric properties of each fabricated mixture are investigated and the results are compared to theoretical values derived from standard mixing rules. To demonstrate the sensitivity enhancement of sensors due to the use of the fabricated dielectric coating, a microfluidic device is presented featuring a capacitive sensor for detection of fluids with different dielectric constants. It is shown that the sensitivity of the capacitive sensor is significantly increased by using the custom dielectric mixture when compared to pure poly(methyl methacrylate).