Resonance Frequency Tracking and Power Supply Adjusting Control for a High Frequency Ultrasonic Device Used to Oil-in-Water Microemulsion (Wastewater) Separation*

In the oil extraction and processing industry, ultrasonic technologies are increasingly used to treat water-in-oil and oil-in-water emulsions, offering an alternative to chemical, mechanical, electrostatic, and thermal methods. However, few studies focus on the control systems required to optimize piezo-electric operation transducers. A control system was developed that utilizes a function generator connected to a power amplifier and an oscilloscope with a current sensor to track and adjust the resonant operating frequency and power supply in response to emulsion properties variation. Initially, the system uses a sweep function to determine the initial state of the acoustic device by collecting data on frequency, voltage, current and phase difference and calculating the RMS power. Subsequently, a gradient function computes the power derivative as a frequency function and identify the resonance frequency. Experimental results showed a decline in power without ultrasound control and oscillations with unadjusted control. On the contrary, using the optimized control, power remained stable and the acoustic separation of a 3000 ppm oil-in-water microemulsion was successful achieved without chemical demulsifiers.