The importance to industry of non-contact bearings is growing rapidly as the demand for highspeed 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 stateof- 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.

运用数字全息测量技术对声悬浮场中煤粉颗粒的冷态、热态现象进行了实验研究。通过电荷耦合器件(CCD)记录煤粉颗粒的冷热态全息图，应用小波变换对图像进行重建，获得同一煤粉颗粒在不同投影面下的粒径以及空间位置。重点分析了煤粉在CO2激光器照射下，挥发分析出及颗粒破碎现象，挥发分只在竖直方向析出，且主要集中在尖角处。破碎形成的颗粒大小不一，位置比较随机，z轴方向距离较大。通过分析热态时颗粒粒径随时间的变化，获得了颗粒的燃烧速度，同时给出了颗粒z轴位置随时间的变化。实验结果表明数字全息技术可以应用于声悬浮场中煤粉颗粒燃烧时的测量，是研究煤粉燃烧的有力工具。

基于二次曝光全息干涉测量原理，采用四倍相位倍增光路对声悬浮声压场分布进行了可视化研究.拍摄了给定模式的超声悬浮场在不同超声换能器激励电流时的光学全息图并进行光学再现，由再现光波的全息干涉条纹图样得到了反映声压场分布的光波波前相位变化，并进行了对比分析.结果表明，与无相位倍增光路相比，采用四倍相位倍增光路可使同一声压场的全息干涉条纹数目大大增加，测量灵敏度明显提高，为进一步研究声悬浮场声压分布提供了一种有效方法.