Non-contact detection of free flying nanoliter droplets

In this paper we present a non-contact droplet sensor that allows for the detection of free flying liquid droplets with diameters in the range of 200-400 mu m. The working principle is based on capacitive detection. The detector was fabricated cost-effectively in standard PCB-technology (printed circuit board) and characterized by experiments: Due to its small dimensions (18 x 56 x 1.6 mm) it can easily be placed into the flight-path of the liquid droplet when the distance between the dispenser and the target is at least 3 mm. The proposed sensor is able to detect any irregularity such as velocity, shape or volume variations in the droplet dispensing process by comparing the actual sensor signal with an average liquid specific "fingerprint". Therefore it is especially suited for online process monitoring in its present form.