Acoustic tweezers allow for manipulation of small objects like elastic spheres with a force generated by the radiation pressure which arises from the nonlinear interaction between the incident and scattered waves by the object. The accurate control of the object by acoustic tweezers requires the study of the components of the three-dimensional (3D) force. If the physical properties of the elastic sphere are known, then the 3D components of the force can be calculated thanks to a decomposition of the incident acoustic field in the spherical functions basis. This study proposes evaluating the expansion coefficients. Three methods are used and compared. The first one consists of measuring the acoustic field on a spherical surface centered on the theoretical position of the object and to calculate the spherical functions decomposition by Lebedev quadratures. The second method is based on the measurement of the acoustic field at random points in a spherical volume and on the resolution of the inverse problem by a sparse method called the orthogonal matching pursuit. In the third method, the incident beam is measured on a transverse plane, decomposed into a sum of plane waves, and then the expansion coefficients are calculated. The results of the three methods will be presented and compared.

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Abstract-In this paper, a novel double-band integrated antenna for applications in WLAN is presented and studied. Based on the mature dipole theory, radiation elements are printed on the two faces of a low cost FR4 substrate. The two dipoles are designed on the sides of the feedline, which can reduce the impact of each other availably. The distance between the two arms and the width of the arms plays an important role in improving the impedance matching. Furthermore, by folding the arms efficiently, the current distribution of the proposed antenna is extended, and the dimensions of the proposed antenna can be reduced. The size of the designed antenna is just 34 mm × 24 mm × 1 mm (about 0.27λ × 0.19λ × 0.008λ, λ is the wavelength relative to the frequency 2.4 GHz). Moreover, the prototype of the antenna is constructed and tested, which shows a good agreement with simulated result. The measured bandwidths, ranging from 2.35 GHz to 2.61 GHz and from 4.7 GHz to 6.0 GHz respectively, are obtained with return loss less than −9.54 dB (about 2 : 1 VSWR). The proposed antenna covers 2.4/5 GHz WLAN bands, and radiation patterns with good omni-directional radiation in the operating frequency are observed.

Recent studies have shown the possibility to manipulate small elastic spheres in 3D with a single-sided beam. Acoustical tweezers are very appealing because they provide a fine spatial control of the motion of a single particle in space. Their main limitations are due to the weak restoring axial force and improving this force is still a challenge. We show theoretically that the spherical vortex beams can trap large particles and enhance the axial force. Indeed, the special features of these unusual beams look like the bottle beams in optics. Nevertheless, their spatial complexity presupposes that they can be produced with sufficient precision. Therefore, attention is paid to the synthesis of the spherical vortices. A method based on the inverse filter method is proposed. It allows to synthesize them with a very good precision since the theoretical force is recovered experimentally with an error smaller that than 10%. Then, the spherical vortices are used to trap polyethylene beads with radii between 500 and 590 µm. Experiments show that the radial trap is working while no beads have been trapped in the axial direction. This failure is analyzed in detail and is shown to be mainly due to sensitivity to the properties of the materials which influences the resonance modes of the elastic sphere. This study paves the way to the optimization of acoustical tweezers for the manipulation of large objects.