Dielectric Objects Research Articles

Analysis of scattering from composite conductor and dielectric objects using single integral equation method and FG-FFT

A hybrid method of single integral equation and the electric/magnetic current combined field integral equation (JMCFIE) is proposed, abbreviated as SJMCFIE, for analyzing scattering from composite conductor and dielectric objects. Fitting Green’s function with fast Fourier transform (FG-FFT) is adopted to combine SJMCFIE to lastly formulate SJMCFIE-FG-FFT for reducing computation complexity of resultant matrix-vector multiplications further. Next, scattering from the composite hemisphere is computed to verify SJMCFIE-FG-FFT on memory storage, computation efficiency compared to SJMCFIE-MLFMA. Simultaneously, comparison of FG-FFT and the other FFT-based algorithms being combined with SJMCFIE shows that SJMCFIE-FG-FFT is insensitive to grid spacing, easy implementation, and high accuracy. Besides, SJMCFIE-FG-FFT also can be used for analyzing scattering from the coated structure.

Optical Trap-Mediated High-Sensitivity Nanohole Array Biosensors with Random Nanospikes.

We clarify an unconventional principle of the light-driven operation of a biosensor for enhanced sensitivity with the help of random nanospikes added to the surface of a nanohole array. Such a system is capable of optically guiding viruses and trapping them in the vicinity of a highly sensitive site by an anomalous light-induced force arising from random-nanospike-modulated extraordinary optical transmission and the plasmonic mirror image in a virus as a dielectric submicron object. In particular, after guiding the viruses near the apex of nanospikes, there are conditions where the spectral peak shift of extraordinary optical transmission can be greatly increased and reach several hundred nanometers in comparison with that of a conventional nanohole array without random nanospikes. These results will allow for the development of a simple, rapid, and highly sensitive virus detection method based on optical trapping with the help of random-nanospike-modulated extraordinary optical transmission, facilitating convenient medical diagnosis and food inspection.

Internally Combined Volume-Surface Integral Equation for a 3-D Electromagnetic Scattering Analysis of High-Contrast Media

An internally combined volume surface integral equation (ICVSIE) for analyzing three-dimensional (3-D) electromagnetic scattering from heterogeneous high-contrast (HC) dielectric objects is proposed. Iteratively solved (generalized) volume integral equations [(g)VIEs] often converge slowly when applied to the analysis of electromagnetic interactions involving dielectric objects with permittivities much higher than those of the surrounding medium [HC breakdown] or discretized using mesh elements much smaller than the wavelength [low-frequency (LF) breakdown]. The proposed ICVSIE hybridizes a VIE and a surface integral equation (SIE) in a manner that eliminates both breakdown phenomena. Just as in previous hybrid VIE–SIE approaches, the ICVSIE invokes Huygens surface equivalence principle to transform the original problem into coupled equivalent exterior and interior scenarios. In the exterior scenario, surface currents radiate in the original surrounding medium; in the interior problem, surface and volume polarization currents radiate in a medium with permittivity closer to that of the object. By judiciously combining integral equations pertinent to both scenarios, the ICVSIE system is assembled. Numerical results show that the proposed ICVSIE is both HC and LF stable when applied to the analysis of 3-D scattering problems.

Fast Solution of Electromagnetic Scattering From Homogeneous Dielectric Objects with Multiple-Traces EF/MFIE Method

In this letter, a novel multiple-traces electric field/magnetic field integral equation (MT-EF/MFIE) method is developed for solving electromagnetic (EM) scattering from dielectric objects. Different from the traditional Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) method, the nonconformal MT-EF/MFIE method can discretize the surface with two pairs of nonconformal meshes (exterior and interior). Meanwhile, the transmission conditions are enforced to ensure the continuity of currents, on the interface of the exterior domain and interior domain. Compared to the traditional PMCHWT method, this MT-EF/MFIE method leads to a better conditioned matrix and obviously interior memory and time consumption.

Design of a Wideband System for Measuring Dielectric Properties

A dielectric object placed in the near-field region of an antenna produces a scattered field, which alters the input impedance of the antenna. This property can be used to measure the electric parameters of dielectric materials. A wideband system for measuring the dielectric properties in the frequency range from 1.1 to 3.5 GHz is designed and prototyped. The system consists of a wideband directional antenna, a wideband radio frequency circuit, and a data processing unit and has been tested by using different dielectric samples across the frequency band, and good measurement results have been obtained.

Inverse Scattering for Monochromatic Phaseless Measurements

An inverse method and measurement setup for profile and constitutive parameters reconstruction from monochromatic phaseless information is presented. The method is based on the minimization of a cost function that relates the measured field with the one scattered by a model of the object under test (OUT), where the position, contour, and constitutive parameters are the unknowns. As a result, phaseless information is directly related to the inverse problem unknowns, thus avoiding the need of an intermediate phase retrieval step. Due to the nonlinear nature of the cost function, global optimization techniques, such as the particle swarm optimization and differential evolution algorithms, have been considered for cost function minimization. An exhaustive analysis of the cost function behavior as a function of the electric size of the OUT is presented, discussing the optimal OUT size where the proposed methodology provides accurate profile and constitutive parameters reconstruction. The proposed methodology is conceived to use it together with a simple, low-cost measurement setup for fast characterization of perfect electric conductor and dielectric objects. Measurement examples are presented aiming to prove the feasibility of the described measurement setup.

Discrete Quasi-Helmholtz Decomposition for 3-D High-Contrast Lossy Dielectric Problems

By applying Loop-Star decomposition of basis functions to form orthogonal transformation matrices, an efficient method for the analysis of electromagnetic scattering from three-dimensional dielectric and lossy objects, especially with high-contrast parameters to the background media, has been presented in this letter. The analysis of the diagonal blocks of the impedance matrix shows that the vector potential and scalar potential subspaces scale differently in relation to the material parameters, which may have a negative effect on the conditioning of the matrix and iteration efficiency. Therefore, new equations corresponding to the exterior and interior equations have been presented, respectively, by constructing discrete quasi-Helmholtz projection operators, based on the traditional dielectric integral formulations, i.e., Poggio–Miller–Chang–Harrington–Wu–Tsai. Numerical examples show that the proposed method is effective for high-contrast lossy dielectric objects by improving the condition number and decreasing the number of iterations.

On Characteristic Eigenvalues of Complex Media in Surface Integral Formulations

Although the surface integral equations (SIEs) have been extensively used in solving electromagnetic problems of penetrable objects, there are still open issues relating to their application to the Theory of Characteristic Modes (CMs). This letter demonstrates that when an SIE is used to solve for the CMs of a dielectric or magnetic object, the resulting eigenvalues are unrelated to the reactive power of the object, unlike the eigenvalues of perfect electric conductors. However, it is proposed that the classical eigenvalues, which provide useful physical insights, can be extracted from the SIE CM solution using Poynting's theorem. Large discrepancies between the SIE CM eigenvalues and the proposed eigenvalues, as well as the eigenvalue-derived characteristic quantities, are highlighted using a numerical example. The modal resonances, as predicted by the proposed eigenvalues, closely match those obtained for natural resonance modes.

A Multitasking Electrical Impedance Tomography System Using Titanium Alloy Electrode.

This paper presents a multitasking electrical impedance tomography (EIT) system designed to improve the flexibility and durability of an existing EIT system. The ability of the present EIT system to detect, locate, and reshape objects was evaluated by four different experiments. The results of the study show that the system can detect and locate an object with a diameter as small as 1.5 mm in a testing tank with a diameter of 134 mm. Moreover, the results demonstrate the ability of the current system to reconstruct an image of several dielectric object shapes. Based on the results of the experiments, the programmable EIT system can adapt the EIT system for different applications without the need to implement a new EIT system, which may help to save time and cost. The setup for all the experiments consisted of a testing tank with an attached 16-electrode array made of titanium alloy grade 2. The titanium alloy electrode was used to enhance EIT system's durability and lifespan.

Placement‐insensitive flexible RFID antenna for ‘peel‐and‐stick’ applications

Radio-frequency identification (RFID) systems with ‘peel-and-stick’ labels are currently limited to tracking items with nearly electromagnetically transparent material properties. This limitation stems from the antenna choice for these labels – a dipole variant. A ground plane edge treatment along with a feed slot with unique tuning capabilities is investigated as an alternative RFID antenna option. Ease of fabrication was maintained as a priority in all design decisions. The measured antenna displays true placement insensitivity with a constant impedance when attached to metal, lossy dielectric, or electromagnetically-transparent objects.

A 0.55 THz Near-Field Sensor With a $\mu \text{m}$ -Range Lateral Resolution Fully Integrated in 130 nm SiGe BiCMOS

This paper presents a room-temperature operating superresolution terahertz (THz) planar near-field solid-state sensor breaking the diffraction limit. Contrary to classical superresolution imagers implemented in the optical domain, the sensor features inbuilt illumination, evanescent-field sensing, and detection on a single chip, eliminating the need for any external optics. Both metallic and dielectric objects can be imaged with the sensor and mapped into a monotonic sensor response. It is operated around 533–555 GHz in 130 nm SiGe HBT technology and is capable of resolving structural details with a $\mu \text{m}$ -range resolution and a high response of up to 21.7 $\mu \text{A}$ with no amplification stages in the readout path. Here, the stop-band characteristic of a differentially driven 3-D split-ring resonator with high spatial confinement of evanescent surface fields is exploited as an object-tunable transmission modulator inserted in-plane between a tunable 3-push Colpitts oscillator and a broadband power detector. A separate antenna-coupled oscillator breakout provides a radiated power of up to 45 $\mu \text{W}$ (−13.4 dBm). This paper further demonstrates the 2-D scanned superresolution image with a remarkable SNR of up to 40 dB for the sensor operating at dc.

An Efficient Method for Analysis of EM Scattering from Objects Straddling the Interface of a Half-Space

An efficient method for the analysis of electromagnetic scattering from 3-D objects straddling the interface of a half-space has been presented in this letter. By truncating the interface, the analysis of scattering from an object within a half-space can be cast into that of a composite (high contrast) dielectric object in the free space. The conventional half-space Green’s function involves a Sommerfeld integral that is extremely time-consuming to evaluate, especially when objects get close to or straddle the interface. In this letter, the Green’s function of free space has been used to totally avoid the numerical evaluation of Sommerfeld integral. Moreover, fast algorithms, such as the multilevel fast multiple algorithm, can be incorporated easily without any restrictions, effectively compensating the cost due to the introduction of additional unknowns by the truncation. The factors affecting the accuracy and computational cost, such as the truncation radius and the angle of incident wave, have been investigated carefully through an example of a partially buried PEC sphere. A criterion for the truncation radius has been presented based on the coupling mechanism between the scatterer and the interface. Furthermore, the far-field response of the target in a half-space background should be expressed as a differential radar cross section. However, the high contrast problem of air/sea or air/ground requires efficient evaluations, and an integral formulation for modeling high-contrast dielectric objects has been employed to further expedite the computation. Numerical results have been presented to demonstrate the effectiveness and accuracy of the new method.

Interaction and charge transfer between dielectric spheres: Exact and approximate analytical solutions.

We present exact analytical solutions for charge transfer reactions between two arbitrarily charged hard dielectric spheres. These solutions, and the corresponding exact ones for sphere-sphere interaction energies, include sums that describe polarization effects to infinite orders in the inverse of the distance between the sphere centers. In addition, we show that these exact solutions may be approximated by much simpler analytical expressions that are useful for many practical applications. This is exemplified through calculations of Langevin type cross sections for forming a compound system of two colliding spheres and through calculations of electron transfer cross sections. We find that it is important to account for dielectric properties and finite sphere sizes in such calculations, which for example may be useful for describing the evolution, growth, and dynamics of nanometer sized dielectric objects such as molecular clusters or dust grains in different environments including astrophysical ones.

A Novel Single-Source Surface Integral Method to Compute Scattering From Dielectric Objects

Using the traditional surface integral methods, the computation of scattering from a dielectric object requires two equivalent current densities on the boundary of the dielectric. In this paper, we present an approach that requires only a single current density. Our method is based on a surface admittance operator and is applicable to dielectric bodies of arbitrary shape. The formulation results in four times lower memory consumption and up to eight times lower time to solve the linear system than the traditional PMCHWT formulation. Numerical results demonstrate that the proposed technique is as accurate as the PMCHWT formulation.

Introduction to Optical Tweezers.

Thirty years after their invention by Arthur Ashkin and colleagues at Bell Labs in 1986 [1], optical tweezers (or traps) have become a versatile tool to address numerous biological problems. Put simply, an optical trap is a highly focused laser beam that is capable of holding and applying forces to micron-sized dielectric objects. However, their development over the last few decades has converted these tools from boutique instruments into highly versatile instruments of molecular biophysics. This introductory chapter intends to give a brief overview of the field, highlight some important scientific achievements, and demonstrate why optical traps have become a powerful tool in the biological sciences. We introduce a typical optical setup, describe the basic theoretical concepts of how trapping forces arise, and present the quantitative position and force measurement techniques that are most widely used today.

Material-independent modes for electromagnetic scattering

In this Letter, we introduce a representation of the electromagnetic field for the analysis and synthesis of the full-wave scattering by a homogeneous dielectric object of arbitrary shape in terms of a set of eigenmodes independent of its permittivity. The expansion coefficients are rational functions of the permittivity. This approach naturally highlights the role of plasmonic and photonic modes in any scattering process and suggests a straightforward methodology to design the permittivity of the object to pursue a prescribed tailoring of the scattered field. We discuss in depth the application of the proposed approach to the analysis and design of the scattering properties of a dielectric sphere.

Lorentz force and the optical pulling of multiple rayleigh particles outside the dielectric cylindrical waveguides

The stimulating connection between the counter‐intuitive optical pulling effects and the Lorentz force has not been investigated in literature. This work demonstrates that multiple absorbing or non‐absorbing dielectric Rayleigh objects can be pulled locally with gradientless travelling waves outside a finite‐sized cylindrical nano or micro waveguide, if it is made up of a hollow core along with the cladding of at least two different dielectrics of appropriate refractive indices. Lorentz force analysis reveals that the bound surface charges of Rayleigh scatterer experience backward force, which overcomes the positive bulk force and ultimately results in the net pulling of the scatterer for several spatial regions outside the waveguide. Finally, in order to control the pulling of multiple Rayleigh particles based on scattering force and binding force, we have proposed a possible cylindrical coupler set‐up. This work may open a new window of optical pulling force due to the exclusion of conventional structured tractor beams along with the artificial exotic matters.

Microwave Measurement System for Detection of Dielectric Objects in Powders

Detection and removal of undesirable objects is an important issue in many material processing industries. This paper presents a microwave-based measurement technique for detection of dielectric objects in powder materials flowing through metal pipes. A nonintrusive microwave sensor is developed, which uses multiple resonant modes to obtain high sensitivity with respect to permittivity variations inside the pipe. Undesirable objects are detected based on the scattering parameters of the sensor, which are measured using a fast-sampling microwave transmitter and receiver unit. We present a detection algorithm derived from the likelihood-ratio test, which includes a parametric model of the local statistical distribution of the measured scattering parameter data. The model involves a set of Mobius transformations that map the measured scattering parameters to a domain where the data are Gaussian distributed. All unknown parameters in the model are estimated from data using maximum likelihood. Based on measurement results from a gravity-fall experimental setup, we conclude that small dielectric objects can be reliably detected in heterogeneous flows of dielectric powder.

Traveling Internal Plane-wave Synthesis (TIPS) for uniform B1 in high field MRI

A new target-field approach to generating uniform radio frequency (RF) fields within the human body for high field MRI is described. The method involves producing a set of external fields which, after interaction with a dielectric object, superimpose to produce a traveling plane wave, exposing all spins to the same RF amplitude (B1) over a cycle of the harmonic field. Conceptually this is similar to conventional RF shimming, but uses a different RF source design, input data, and objective function. The method requires a detailed knowledge of the coupling between exterior field modes, produced by an array of RF sources, and field modes within the body. Given an estimate of the coupling matrix, the linear superposition of external modes that produces a desired internal target field can be determined. The new method is termed Traveling Internal Plane-wave Synthesis (TIPS). A simple design of a coil array is described that can, in principle, generate the required field modes. Simulations demonstrate that radio frequency magnetic fields of nearly uniform (<1% variation) magnitude can be produced within dielectric objects larger than a wavelength in size. If the dielectric medium has non-zero conductivity, traveling waves are attenuated as they traverse the object, but field uniformity within planar slices is preserved. For general 3D imaging, a superposition of plane waves can provide field focusing to balance conductive losses, thereby achieving nearly uniform-magnitude B1+ magnetic fields over a volume of interest.

Dyadic Contrast Function for the Forward Model of Diffraction Tomography of Thin Cylindrical Objects

A forward model for diffraction tomography is derived for the case of thin cylindrical objects by introducing a dyadic contrast function that takes into account depolarization phenomena, which were not previously addressed. As a result, polarimetric measurements may be used to distinguish between dielectric or metallic thin cylindrical objects. In the case of metallic objects, it is also possible to reconstruct their direction.