We present the design and characterization of a linear meta-transmission line (meta-TL) suitable for realizing hyper-compact Rotman lenses. Rotman lenses are true time delay beamforming networks that usually find applications in very-/ultra-high frequency systems such as satellite, radar, and unmanned aerial vehicle systems. The lenses designed using existing techniques tend to be at least $\mathbf{5}-\mathbf{6}\boldsymbol{\lambda}$ long making them infeasible for practical implementations. In this work, we propose a topology that achieves a very high degree of miniaturization by modifying the lumped element transmission line model. Specifically, by introducing mutual inductance terms between the first nearest neighbors in the lumped element model, we realize the meta-TL. The meta-TL can extend the linearity of the dispersion diagram by slowing down the wave within the line and lead to miniaturization. A 1D meta-TL has been designed, fabricated, and characterized demonstrating good transmission performance up to the cut-off frequency.

We present a novel approach for miniaturization of Rotman lenses used for versatile beamforming applications in satellite, radar, and unmanned aerial vehicle systems. Since these systems usually operate at very-/ultra-high frequencies (VHF/UHF), conventional techniques for Rotman lens design become impractical as they lead to bulky solutions ( > 5 − 6 λ long). To address this challenge, herein, we propose a modified lumped element transmission line (TL) model by introducing a mutual inductance term between the first nearest neighbors. Such a TL called the meta-transmission line can be used to extend the linearity of the dispersion diagram and reduce the overall size of the Rotman lens. A proof-of-concept 1D meta-TL is designed and analyzed to demonstrate the improvement in the linearity of the dispersion diagram by ~ 36%.

Optical systems that perform on-wafer measurement of particles have become one of the most important process control tools available to semiconductor man­ ufacturers and the IC industry. They give the process owner information neces­ sary to determine whether or not a specific process is under control, and so are ultimately significant contributors to yield-increasing strategies. It follows that the functional requirements of these systems depend on which process in the production cycle they support. Thus, during process development, a system with high throughput is not as important as a system with high-detection sensitivity and classification capability. On the other hand, a system employed to monitor a production line must have a throughput compatible with that line, without sacrificing sensitivity to those defects that are yield limiting [1]. The manner in which this trade-off between speed and sensitivity is accomplished is what dis­ tinguishes different commercial inspection systems from one another. However, regardless of the individual approaches, all such systems are based on the same physical principles. They are all concerned with the detection and classification of wavelength-or subwavelength-sized defects using light scattering in an envi­ ronment that includes a large scattering surface (the wafer) and possibly other light-scattering features intentionally incorporated onto the wafer surface (e.g., circuit patterns). In this chapter we focus on the physical foundations underlying the operation and design of a generic on-wafer inspection system.

A domain decomposition method for analyzing very large FDTD domains, tens of thousands of wavelengths long, is demonstrated by application to the problem of RADAR scattering in the maritime environment. Success depends on the elimination of artificial scattering from the “sky” boundary and this is ensured by an ultra-high performance absorbing termination that eliminates this reflection at angles of incidence from normal down to less than 0.2 degrees off grazing. The results are cross-validated at S-Band by comparison to Method of Moments over a 3.6 km flat conducting plane with an inhomogeneous atmosphere, and at X-Band by comparing to another parabolic equation method on propagation through an inhomogeneous atmosphere over a 4km long sea surface. Details of the method are given for the two-dimensional problem (2D). The same techniques used in 2D are being applied to three dimensions (3D).

A model of the input impedance of the toroidal permeable antenna, which is the dual of the conventional metal loop antenna, is derived, starting from Schelkunoff's transmission line description of the loop antenna instead of the electrically small limit model. The input impedance for the dipole mode is expressed in a form that has a frequency independent resistor terminating a reactive network which is called the Darlington form. Since such a circuit mimics the input impedance of the dipole modes of the spherical mode expansion, it works very well as we go beyond the electrically small limit even for magnetic antennas as large as multiple wavelengths. The realistic feed loop contribution is explicitly accounted for and results are compared with fullwave simulations of a typical toroidal antenna which shows good agreement well beyond the electrically small limit.

A model of the input impedance of the toroidal permeable antenna, which is the dual of the conventional metal loop antenna, is derived, starting from Schelkunoff’s transmission line description of the loop antenna instead of the electrically small limit model. This antenna operates in both the monopole mode and circularly polarized dipole mode and is constructed from a torus of high permeability material. Since the ultimate goal is to obtain an impedance model from which to derive the best matching network; the input impedance is expressed in a form that has a frequency independent resistor terminating a reactive network which is called the Darlington form. Because such a circuit mimics closely the input impedance of the dipole modes of the spherical mode expansion, it is a much better model of the antennas as we go beyond the electrically small limit. The feed loop contribution is explicitly accounted for and the results are compared with fullwave simulations of a typical toroidal antenna operating in both monopole and circularly polarized dipole modes which show a good agreement well beyond the electrically small limit.

A conformal permeable toroidal antenna operating in both a vertically polarized monopole mode and circularly polarized (CP) dipole mode in the UHF frequency range is designed based on theory of magneto-dielectric radiators. This antenna has been fabricated using a new advanced ferromagnetic laminate composite material whose high impedance and anisotropic properties enable an antenna that radiates via magnetic currents. The antenna, less than 0.5 m in diameter and less than 2 cm thick, was fabricated and tested. Including the imperfections of the feed network and a simple matching scheme, the antenna operates from 200 to 500 MHz with an input match of better than -10 dB, CP dipole realized gain as high as +2 dBi, and monopole mode vertically polarized gain as high as -1 dBi.

Recent experiments on high-efficiency permeable conformal antennas have drawn attention to a long-standing misconception on the theory of the ferrite rod antenna family. Deriving in closed form the radiation efficiency of these antennas and using full-wave simulations, we show that their radiation efficiency is not necessarily reduced by the loss tangent of the permeable material. It is shown that the key material parameter controlling the radiation efficiency of these antennas is not the loss tangent but the maximum of the Heaviside magnetic conductivity, a quantity proportional to Snoek's product. This yields the clear design rules for obtaining permeable antennas with maximized efficiency-bandwidth product (EBWP). Because the radiating currents of these antennas are the magnetic polarization currents in the material, they can be placed close to a metal ground plane or inside a low impedance medium without performance degradation while having an EBWP much higher than the metal-and-dielectric antennas having the same conformal volume, in spite of the presence of the magnetic loss. As an example, an antenna operating from HF to VHF can attain an EBWP 10 dB higher than the corresponding metal antenna. Similarly, using the Best-Yaghjian formalism, it is shown that these antennas are easier to match and can attain wider bandwidths than the equivalent conformal metal antennas.

In order to obtain the permeability of thin, rectangular, isotropic, and homogeneous substrates, we applied a correction to the effective (or apparent) permeability that is observed in resonant stripline cavity measurements. The correction was formulated as a single, closed form, analytic Morphology function. The Morphology function was applied for all measurement frequencies, and was parameterized in order to perform correction for a range of substrate cross-sectional sizes. Using both simulated and actual hardware measurements, comparisons were made to an existing correction method, which was shown to be a special case of the general Morphology function. In comparison, the Morphology function demonstrated a reduction in permeability inversion error, which was shown to be primarily bounded by sample cross-sectional size.

To detect and resolve sub-wavelength features at optical frequencies, beyond the diffraction limit, requires sensors that interact with the electromagnetic near-field of those features. Most instruments operating in this modality scan a single detector element across the surface under inspection because the scattered signals from a multiplicity of such elements would end up interfering with each other. However, an alternative massively parallelized configuration, capable of interrogating multiple adjacent areas of the surface at the same time, was proposed in 2002. Full physics simulations of the photonic antenna detector element that enables this instrument, show that using conventional red laser light (in the 600 nm range) the detector magnifies the signal from an 8 nm particle by up to 1.5 orders of magnitude. The antenna is a shaped slot element in a 60 nm silver film. The ability of this detector element to resolve λ/78 objects is confirmed experimentally at radio frequencies by fabricating an artificial material structure that mimics the optical permittivity of silver scaled to 2 GHz and “cutting” into it the slot antenna. The experimental set-up is also used to demonstrate the imaging of a patterned surface in which the critical dimensions of the pattern are λ/22 in size.

ABSTRACTA wideband surface‐scanning near‐field sensor in the form of a slot antenna, remotely interrogated by a wireless signal is reported. Perturbation of the antenna near‐field by subwavelength objects (λ/10) on the surface is detected in the far‐field as a change in the antenna signature, yielding image of the surface structure. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2677–2682, 2016

In a previous report it was shown that the channel capacity of an in vivo communication link using microscopic antennas at radiofrequency is severely limited by the requirement not to damage the tissue surrounding the antennas. For dipole-like antennas the strong electric field dissipates too much power into body tissues. Loop-type antennas have a strong magnetic near field and so dissipate much less power into the surrounding tissues but they require such a large current that the antenna temperature is raised to the thermal damage threshold of the tissue. The only solution was increasing the antenna size into hundreds of microns, which makes reporting on an individual neuron impossible. However, recently demonstrated true magnetic antennas offer an alternative not covered in the previous report. The near field of these antennas is dominated by the magnetic field yet they don’t require large currents. Thus they combine the best characteristics of dipoles and loops. By calculating the coupling between identical magnetic antennas inside a model of the body medium we show an increase in the power transfer of up to 8 orders of magnitude higher than could be realized with the loops and dipoles, making the microscopic RF in-vivo transmitting antenna possible.

This paper studies the challenging problem of detecting a low radar cross-section target in heavy sea clutter by proposing a physics-based sea clutter generation model. The model includes a process that generates random dynamic sea clutter based on the governing physics of water gravity and capillary waves and a finite-difference time-domain electromagnetics simulations process based on Maxwells equations propagating the radar signal. A subspace clutter suppression detector is considered to remove dominant clutter eigenmodes. The improved detection performance over matched filtering is demonstrated using sea clutter model simulations.

Under SBIR-funded contracts [1 & 2], researchers at JEM Engineering and Arizona State University have demonstrated the critical components of a new class of physically small antenna that utilizes a magneto-dielectric composite material having a high magnetic flux conductivity [3]. The magnetic material is placed into flux channels which are made from a metallo-dielectric substrate. The substrate can be placed directly onto a conducting platform skin and its thickness is on the order of one hundredth of a wavelength or less. This paper introduces a novel realization of such a flux channel antenna by winding a thin composite tape about a mandrel [4]. The number of turns is potentially several thousand as the composite tape thickness is only a half mil (13 microns). Measured gains (IEEE) for a magnetic loop, which is equivalent to an electric monopole, of -5 to +4 dBiL were demonstrated from 225 - 600 MHz by a prototype antenna that measured 0.25" high by 16" diameter.

A computational formulation is presented for the low frequency single-cell finite-difference time-domain (FDTD) modeling of nanospheres. The methodology is developed based on the observation that the electrostatic field inside a dielectric sphere is similar in nature to that of an FDTD cell, or equivalently by considering the electromagnetic correspondence between the single electric field component across an FDTD cell edge, and the electric dipole moment induced in an electrically small dielectric sphere when the latter is excited by a plane wave. By rigorously applying effective medium theory the physical existence of a subcell dielectric sphere in the FDTD grid is translated into an equivalent material, characterized by an effective permittivity that obeys the Clausius-Mossotti (CM) mixing rule, appropriately defined across the cell edge parallel to the excitation plane wave. A circuit based methodology is devised that allows to easily incorporate the effective medium representation of a subcell dispersive dielectric sphere into FDTD update equations. The theoretically derived results are supported by numerical experiments.

It is shown using full-wave simulations that several of the conventional assumptions made for extracting permeability data from a microstrip permeameter are not justified. In particular, the proportionality between the measured effective permeability in the device and the true permeability of the film is not a constant. It is a function of the permeability of the film, its geometry and the dimensions of the microstrip permeameter. A model exploiting the analyticity of the function relating effective to true permeability is used to derive this proportionality function for our device and the results are confirmed using full-wave simulations. The error incurred by not using this method and employing a reference sample for calibration or by using saturation magnetization “Ms” and anisotropy field “Ha” is shown to be anywhere between 5% and 40% and possibly even more. Our measurement set up is capable of measuring films as thin as 300 nm with a relative permeability as low as 10.