Studies of Electrohydrodynamic Ejection by Induced Current Measurement and Optical Particle Counting

The droplet ejection technology based on electrohydrodynamic (EHD) method can produce micro-droplets smaller than the diameter of the nozzle, which is a technical option to improve the resolution of inkjet printing and alleviate the risk of nozzle blockage. However, EHD ejection is affected by many parameters including the flow rate, the voltage between the nozzle and the collector electrode. It is of practical value to monitor the state of the EHD ejection in real-time. In this paper, an EHD ejection device is built, which include a high-speed camera, a current amplifier for the induced current at the collector electrode, and an optical particle counter. Through high-speed photography and image processing, detailed information of the ejection process can be obtained. But the equipment is expensive, and real-time processing of large amount of images are impossible. Combined with the measurement of the induced current at the collector electrode and the scattered light of the micro-droplet, a rather complete description of the ejection state can be obtained. This approach is expected to be used for the monitoring and control of the EHD ejection.