Ebook: Pulsed Electromagnetic Fields: Their Potentialities, Computation and Evaluation

Exploiting the potentialities of electromagnetic (EM) fields with high pulse rates is at the core of the Computer Science's challenging demand for designing ultra-fast integrated circuits that are capable of handling the digital signals involved, next to exploiting the possibilities of wireless (i.e., pulsed EM fields supported) digital information transfer.

To address this challenge, the Workshop Pulsed Electromagnetic Fields: Their Potentialities, Computation and Evaluation collects state-of-the-art contributions on the computational modeling of pulsed EM fields in configurations that are representative for road mapping future developments. Furthermore, it sets itself the task to accommodate relevant interaction as to in which direction these developments are to be pursued. The included works cover a very broad range, from the physical and mathematical foundations up to operational systems making use of the potentialities arising from the use of pulsed EM fields.

The workshop will set the course for an intensified and formalized cooperation on fundamental research between the Delft University of Technology and the University of Hong Kong. Two aspects are here primarily envisaged: the impact of pulsed EM fields with ultra-high pulse rates on the methods for designing integrated circuits and systems for inter- and intra-device wireless transfer of information, and the evaluation of the possible impact of such fields on the ‘Electromagnetic environment’, in particular their Electromagnetic Interference with ‘living and inert matter’.

The organizers express their gratitude to the Netherlands Organisation for Scientific Research (NWO) and Research Grants Council of Hong Kong (RGC) / University Grants Committee of Hong Kong that provided the financial means for the workshop's organization via their “Collaboration Hong Kong – Joint Research Scheme”. They also extend their gratitude to the specialized Delft University of Technology departments that provided the logistic support for this event.

Ioan E. Lager

Li Jun Jiang

Delft and Hong Kong, January 25, 2013

The Airy beam (AiB) has attracted a lot of attention recently because of its intriguing features. We have previously provided a cogent physical explanation for these properties by showing that the AiB is, in fact, a caustic of rays that radiate from the tail of the Airy function aperture distribution. We have also introduced a class of ultra wide band (UWB) Airy pulsed beams (AiPB), where a key step has been the use of a proper frequency scaling of the initial aperture field that ensures that all the frequency components propagate along the same curved trajectory so that the wavepacket of the AiPB does not disperse. An exact closed form solution for the AiPB has been derived using the spectral theory of transients (STT) which is an extension of the well know Cagniard–de Hoop (CdH) method. In this paper we discuss the properties of the AiB and AiPB, and use the present problem to discuss the relation between the CdH method and the STT.

An array-structure theory of Maxwell wavefields in affine (3 + 1)-spacetime is presented. The structure is designed to supersede the conventional Gibbs vector calculus and Heaviside vectorial Maxwell equations formulations, deviates from the Einstein view on spacetime as having a metrical structure (with the, non-definite, Lorentz metric), and adheres to the Weyl view where spacetime is conceived as being affine in nature. In the theory, the electric field and source quantities are introduced as one-dimensional arrays and the magnetic field and source quantities as antisymmetrical two-dimensional arrays. Time-convolution and time-correlation field/source reciprocity are discussed, and expressions for the wavefield radiated by sources in an unbounded, homogeneous, isotropic, lossless embedding are derived. These expressions clearly exhibit their structure as convolutions in spacetime. The bookkeeping of the array structure smoothly fits the input requirements of computational software packages. An interesting result of fundamental physical importance is that the ‘magnetic charge’ appears as a completely antisymmetrical three-dimensional array rather than as a number (as in the Dirac quantum theory of the magnetic monopole). The generalization of the array structure to affine (N + 1)-spacetime with N > 3 is straightforward and is conjectured to serve a purpose in theoretical cosmology. No particular ‘orientation’ of the observer's spatial reference frame (like the ‘right-handedness’ in conventional vector calculus) is required.

In this paper, we propose a frequency independent approach, the numerical steepest descent path method, for computing the physical optics scattered electromagnetic field on the quadratic parabolic and saddle surfaces. Due to the highly oscillatory nature of the physical optics integral in the high frequency regime, the proposed method relies on deforming the integration path of the integral into the numerical steepest descent path on the complex plane. Furthermore, critical-point contributions which contain the stationary phase point, boundary resonance points, and vertex points, are comprehensively studied in terms of the numerical steepest descent path method. To illustrate the efficiency of the proposed method, some extensive numerical results for the physical optics integral defined on arbitrary lines, triangles and polygonal domains are demonstrated. Finally, numerical results on these quadratic surfaces illustrate that the proposed numerical steepest descent path method is frequency independent in computational cost and error controllable in accuracy.

Many system-level electromagnetic design problems are multiscale and very challenging to solve. They remain a significant barrier to system design optimization for a foreseeable future. Such multiscale problems often contain three electrical scales, i.e., the fine scale (geometrical feature size much smaller than a wavelength), the coarse scale (geometrical feature size greater than a wavelength), and the intermediate scale between the two extremes. Existing computational tools are based on single methodologies (such as finite element method or finite-difference time-domain method), and are unable to solve large multiscale problems. We will present our recent progress in solving realistic multiscale system-level EM design simulation problems in time domain. The discontinuous Galerkin time domain method is used as the fundamental framework for interfacing multiple scales with finite-element method, spectral element method, and finite difference method. Numerical results demonstrate significant advantages of our multiscale method. A more detail discussion of the method is given in [1].

The concept of generalized complex inductance for the partial element equivalent circuit (PEEC) technique is introduced to model microstrip radiation problems. Using the semi-analytical Greens functions for microstrip substrates, the imaginary part of this generalized complex inductance can be shown to represent a frequency-dependent resistance containing information about the losses from spatial radiations (spherical and lateral) and surface waves (cylindrical). Hence, different radiation components can be derived separately, providing a useful and unique feature for representing high-speed/high frequency microstrip structures and antennas in the network domain.

Generalized-ray theory for time-domain electromagnetic fields in a horizontally layered medium is developed. After introducing appropriate integral transformations and source-type field representations in vertically inhomogeneous media, the solution is written out in terms of generalized ray constituents whose space-time counterparts are constructed with the aid of the Cagniard-DeHoop technique. The formulation lays the foundation to rigorously study time domain field behavior in numerous practical topologies where a stratified multilayer is involved, such as planar antennas and circuits, but also EMC and propagation problems.

A hybrid electromagnetics (EM)-circuit simulation method employing the discontinuous Galerkin finite element time domain method (DGFETD) is developed to model single lumped port networks comprised of both linear and non-linear elements. The whole computational domain is split into two subsystems. One is the EM subsystem that is analyzed by the DGFETDwhile another is the circuit circuit subsystem that is modeled by the Modified Nodal Analysis method (MNA) to generate a circuit subsystem. The coupling between the EM and circuit subsystems is achieved through a lumped port. Due to the local properties of DGFETD operations, only small coupling matrix equation systems are involved. To solve non-linear devices, the standard Newton-Raphson method is applied to solve the established non-linear system equations. Numerical examples are presented to validate the proposed algorithm.

Variational data assimilation, also sometimes simply called the ‘adjoint method’, is used very often for large scale model calibration problems. Using the available data, the uncertain parameters in the model are identified by minimizing a certain cost function that measures the difference between the model results and the data. A variational scheme requires the implementation of the adjoint of (the tangent linear approximation of) the original model which is a tremendous programming effort, that hampers new applications of the method. Recently a new ensemble approach to variational inverse modelling using Proper Orthogonal Decomposition (POD) model reduction has been proposed that does not require the implementation of the adjoint model. Using an ensemble of forward model simulations an approximation of the covariance matrix of the model variability is determined. A limited number of leading eigenvectors of this matrix are selected to define a model sub space. By projecting the original model onto this subspace an approximate linear model is obtained. Once this reduced model is available the minimization process can be solved completely in reduced space with negligible computational costs.

Schemes based on the well-known Kalman filtering algorithm are also used recently for inverse modeling. The last years a number of ensemble based algorithms have been proposed, e.g., the Ensemble Kalman filter (EnKF), the Reduced Rank Square Root filter (RRSQRT) and the Ensemble Square Root filter (ESRF). Although introduced for linear state estimation, these new algorithms 102 Ensemble methods for large scale inverse problems are able to handle nonlinear models accurately and, therefore, are very attractive for solving combined state and parameter estimation problems. It has been shown recently that the so-called symmetric version of the ESRF introduces the smallest increments and, therefore, is in most applications more accurate then the original version of this algorithm.

This contribution presents the fabrication and measurements of the leaky lens antenna integrated with a cryogenically cooled Kinetic Inductance Detector, in order to achieve an ultra sensitive THz receivers over a bandwidth ranging from 0.15GHz to 1.5 THz. The system has been manufactured and characterized in terms of power efficiency, and radiation pattern properties. The agreement between the expectations and the measurements is excellent already at this first attempt. These measurements demonstrate the manufacturability and repeatability at THz frequencies of the properties of the leaky lens antenna concept.

The loop-to-loop pulsed electromagnetic field wireless signal transfer is investigated with a view on its application in wireless digital information transfer. Closed-form expressions are derived for the emitted magnetic field and for the open-circuit voltage of the receiving loop in dependence on the mutual orientation of the loops and the characteristics of the feeding pulse. Numerical results are given for some configurations that are representative for microelectronic wireless signal transfer. In them, the transmitting loop is excited with a monocycle pulse electric current and with a propitious, causal, ultra wide-band pulse. The results are indicative for the potentialities of the pulsed-field wireless signal transfer concerning the received signal characteristics and the system's compliance with regulatory specifications on ElectroMagnetic Emission.