A Continuous, Impedimetric Parylene Flow Sensor

Abstract

A continuously recording, impedimetric thermal liquid flow sensor fabricated on a Parylene C thin film substrate is presented for the first time. The sensing concept, inspired by hot-film anemometry, includes an additional upstream unheated reference electrode pair which enabled attenuation of environmental drift in impedance by more than 5×. This sensor design and transduction approach was motivated by the need for an alternative to traditional hot-film anemometers for in vivo applications. An analytical model was developed to describe the axial fluid temperature surrounding the impedimetric sensor and its effect on solution conductivity. The impact of heater power was modeled and matched with experimental data; similar analysis was conducted for other parameters including channel height, ambient temperature, and electrolyte concentration. The sensor achieved a 2σ resolution of 17μ L/min over the range 43-200 μ L/min. The models and fabricated device significantly expand our understanding of thermal impedimetric flow sensing.