Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modelling and closed loop control of near-field acoustically levitated
  objects   The present paper introduces a novel approach for modelling the governing,
slow dynamics of near-field acoustically levitated objects. This model is
sufficiently simple and concise to enable designing a closed-loop controller,
capable of accurate vertical positioning of a carried object. The near-field
acoustic levitation phenomenon exploits the compressibility, the nonlinearity
and the viscosity of the gas trapped between a rapidly oscillating surface and
a freely suspended planar object, to elevate its time averaged pressure above
the ambient pressure. By these means, the vertical position of loads weighing
up to several kilograms can be varied between dozens and hundreds of
micrometers. The simplified model developed in this paper is a second order
ordinary differential equation where the height-dependent stiffness and damping
terms of the gas layer are derived explicitly. This simplified model replaces a
traditional model consisting of the equation of motion of the levitated object,
coupled to a nonlinear partial differential equation, accounting for the
behavior of the entrapped gas. Due to the relatively simple form of the model
developed here, it constitutes a convenient foundation for model based control
algorithms, governing the slow dynamics of near-field acoustically levitated
objects. Indeed, based on the former, a height dependent, gain scheduled PID
controller is developed and verified numerically and experimentally, both
providing satisfying results.

34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con