Near-field acoustic levitation and applications to bearings: a critical review

Abstract

The importance to industry of non-contact bearings is growing rapidly as the demand for high-speed and high-precision manufacturing equipment increases. As a recently developed non-contact technology, near-field acoustic levitation (NFAL) has drawn much attention for the advantages it offers, including no requirement for an external pressurized air supply, its compact structure, and its ability to adapt to its environment. In this paper, the working mechanism of NFAL is introduced in detail and compared to all existing non-contact technologies to demonstrate its versatility and potential for practical applications in industry. The fundamental theory of NFAL, including gas film lubrication theory and acoustic radiation pressure theory is presented. Then, the current state-of-the-art of the design and development of squeeze film air bearings based on NFAL is reviewed. Finally, future trends and obstacles to more widespread use are discussed.

Viscoacoustic squeeze-film force on a rigid disk undergoing small axial oscillations

“…Practical applicability of the present analysis is limited by the possibility of elastic deformations in the oscillating body that may be non-negligible in the analysis of the induced flow (see Shi et al 2019). Of particular interest beyond this study is the characterization of axisymmetric squeeze-film systems involving radially non-uniform driving oscillations h = h(r, t).…”

“…where h o a is the mean separation distance, ω is the angular frequency and εh o is the oscillation amplitude, with ε 1 in our study. Such slender-flow systems, commonly referred to as squeeze films, are of great interest in the context of gas lubricated bearings present in high-speed rotary machinery and also in acoustic levitation devices used in assembly line transport of microelectronics (see Shi et al 2019). In the former case of squeeze-film air bearings, there is great demand for predicting the load capacity, while in the latter, referred to as near-field acoustic levitation, the sensitivity of transported items additionally warrants comprehension of radial pressure departures p − p a from the outer ambient value p a .…”

“…The limit of large Stokes numbers α 2 1, where the flow is nearly inviscid outside thin near-wall boundary layers, has been the subject of widespread interest in the context of acoustic levitation, which typically concerns the suspension of light objects in the antinodes of standing pressure waves between a vibrating piston and a reflector plate separated by an integral multiple of the half-wavelength of sound (see Shi et al 2019). In 1902, Lord Rayleigh presented a foundational formulation of acoustic radiation inside a cylindrical piston of air undergoing transverse vibrations, expressing the overpressure in terms of the volumetric energy density (see Rayleigh 1902).…”

The performance evaluation of a surface-textured ultrasonic levitation bearing under multi-operation mode

“…Near-field acoustic levitation (NFAL) is the phenomenon that occurs when the levitated plate is suspended by the force caused by the squeeze motion of the vibrator. NFAL has been applied in several industrial components such as bearing, 12 motor, 13 non-contact transportation system, 14,15 because of its compact structure, no requirements for materials and stable levitation. Ultrasonic levitation bearing based on NFAL has been studied by researchers from various aspects.…”

A simplified FEM analysis on the static performance of aerostatic journal bearings with orifice restrictor

“…The accuracy and efficiency of numerical solution is the key part of bearing performance analysis and optimal design. 2,3 In the reported literatures related to numerical method for calculating the lubrication equation of aerostatic bearings with orifice restrictor, many researches concentrate on the computational fluid dynamics (CFD) method such as finite element method (FEM), finite difference method (FDM) and finite volume method (FVM). [4][5][6] Based on the powerful commercial software, such as FLUENT and CFX, CFD method has great advantages in modeling convenience, calculation accuracy and micro flow visualization.…”