Biomedical subjects
Publications and source records attributed to Tomasz M Grzegorczyk.
We demonstrate the possibility of serially guiding and sorting nanometer-sized particles without the use of any external control. The working principle is based on an equilibrium between scattering and binding forces, the latter depending on the properties of the particles. A configuration is proposed that utilizes this property and is shown to efficiently sort small particles as function of their size.
Finite-size left-handed material (LHM) slabs are studied both analytically and numerically. The analytical method is based on Huygens' principles using truncated current sheets that cover only the apertures of the slabs. It is shown that the main effects on the images' spectra due to the size of the slabs can be predicted by the proposed analytical method, which can, therefore, be used as a fast alternative to the numerical simulations. Furthermore, the property of negative-energy streams at the image plane is explained. This unique property is found to be due to the interactions between propagating and evanescent waves and can only occur with LHM slabs, both finite size and infinite.
The momentum transfer to absorbing particles is derived from the Lorentz force density without prior assumption of the momentum of light in media. We develop a view of momentum conservation rooted in the stress tensor formalism that is based on the separation of momentum contributions to bound and free currents and charges consistent with the Lorentz force density. This is in contrast with the usual separation of material and field contributions. The theory is applied to predict a decrease in optical momentum transfer to Mie particles due to absorption, which contrasts the common intuition based on the scattering and absorption by Rayleigh particles.
Various trapping configurations have been realized so far, either based on the scattering force or the gradient force. In this Letter, we propose a new trapping regime based on the equilibrium between a scattering force and optical binding forces only. The trap is realized from the interaction between a single plane wave and a series of fixed small particles, and is efficient at trapping multiple free particles. The effects are demonstrated analytically upon computing the exact scattering from a collection of cylindrical particles and calculating the Lorentz force on each free particle via the Maxwell stress tensor.
The Mie theory and the Foldy-Lax multiple-scattering equations are applied to compute the scattered field of an arbitrary number of infinite dielectric cylinders of arbitrary size, subject to in-plane incidences. The Maxwell stress tensor is then used to compute the force on each cylinder. Trapping and binding forces are studied as a function of particle size, number, permittivity, and separation. Finally, the formulation is applied to a system of 20 particles, and the results show clear similarities with known experimental reports. The formulation presented here extends the capabilities of modeling particle interaction and optical matter beyond the simple cases of the Rayleigh regime and two-particle systems.
We propose a method to retrieve the effective constitutive parameters of a slab of bianisotropic metamaterial composed of split-ring resonators from the measurement of the S parameters. Analytical inversion equations are derived for homogeneous loss-less bianisotropic media, and a numerical retrieval approach is presented for the case of lossy bianisotropic media. The method is verified both analytically and numerically, and it is shown that the results for various split-ring resonator metamaterials qualitatively corroborate the conclusions found in published papers. The proposed retrieval method can be used as a valuable tool for the study of anisotropic and bianisotropic properties of metamaterials.
We analyze an S-shaped inclusion for the realization of metamaterials exhibiting left-handed properties. Unlike most of the conventional inclusions used so far that are composed of two separate geometries-typically a split ring and a rod-the inclusion proposed in this paper is made of only one S-shaped element which yields an overlapping negative permittivity and negative permeability response over a frequency band of about 2.6 GHz. By adopting this geometry, we manage to lower the negative permittivity frequency band down to the level of the negative permeability frequency band, thus allowing the overlapping to occur. Therefore, the structure works as a stand alone and does not require the use of an additional rod. A theoretical analysis is carried out to study this inclusion and numerical simulations, as well as a Snell refraction experiment, clearly show that the material indeed exhibits a negative index of refraction at some frequencies. The simple pattern of the inclusion, the wide left-handed frequency band exhibited, and the low losses measured indicate the superiority of this inclusion in the realization of left-handed metamaterials.
We propose an improved method to retrieve the effective constitutive parameters (permittivity and permeability) of a slab of metamaterial from the measurement of S parameters. Improvements over existing methods include the determination of the first boundary and the thickness of the effective slab, the selection of the correct sign of effective impedance, and a mathematical method to choose the correct branch of the real part of the refractive index. The sensitivity of the effective constitutive parameters to the accuracy of the S parameters is also discussed. The method has been applied to various metamaterials and the successful retrieval results prove its effectiveness and robustness.