Near-field acoustic levitation generated by dual-frequency ultrasound

Near-field acoustic levitation (NFAL) offers many advantages over traditional non-contact methods, particularly in the fields of microelectromechanical systems and semiconductor processing. However, its application is limited by small levitation heights where maintaining a stable microscale gas film presents challenges. To address this issue, this paper investigates enhancing the load-carrying capacity (LCC) of NFAL systems through dual-frequency ultrasound (DFUS) technology. We first introduce the basic principles of NFAL, and theoretical modal based on the Reynolds equation, followed by a numerical solution using the Finite Difference Method (FDM). A multimodal coupled piezoelectric transducer operating in dual frequencies is proposed. Frequency compensation is achieved by altering the electrical boundaries of passive piezoelectric ceramics, overcoming the resonance frequency drift problem during high-power operation, and stable DFUS is generated. Experimental results demonstrate the impact of the second harmonic phase on levitation heights, revealing that optimized phase adjustments can significantly influence levitation height, with the optimal phase around 280°. With a radius of the acoustic radiation surface of 5 mm, and a gravitational load of 0.909 N, the results indicate that when a fundamental vibration with an amplitude of 3 μm is superimposed with a second harmonic of the same amplitude, DFUS at the optimal phase enhances levitation performance compared to single-frequency ultrasound (SFUS), with the increment rate of the levitation height reaching up to 78.5 % in the experiments. This study confirms the feasibility of DFUS for improving the performance of NFAL systems and lays the groundwork for future applications of dual-frequency ultrasound levitation. • Near field acoustic levitation with dual-frequency ultrasound is investigated for the first time. • Pressure distribution under dual-frequency vibration was theoretically analyzed with FDM. • Stable dual-frequency ultrasound was generated by a multimodal coupled transducer system. • Experimental investigations confirmed the feasibility of acoustic levitation with dual-frequency ultrasound. • The phase of the second harmonic ultrasound significantly influences the levitation performance.