Application of Nonredundant Sampling Representations of Electromagnetic Fields to NF-FF Transformation Techniques

An overview of the application of the band-limitation properties and nonredundant sampling representations of electromagnetic fields to NF-FF transformations is presented. The progresses achieved by applying them to data acquired on conventional NF scanning surfaces are discussed, outlining the remarkable reduction in the number of needed NF samples and measurement time. An optimal sampling interpolation expansion for reconstructing the probe response on a rotational scanning surface from a non-redundant number of its samples is also discussed. A unified theory of the NF-FF transformations with spiral scannings, which allow a remarkable reduction of the measurement time, is then reviewed by describing a sampling representation of the voltage on a quite arbitrary rotational surface from its nonredundant samples collected on a proper spiral wrapping it. Some numerical and experimental results assessing the effectiveness of the considered NF-FF transformations are shown too

An Effective Near-Field Far-Field Transformation Technique from Truncated and Inaccurate Amplitude-Only Data

Abstract-A general approach to the near-field far-field transformation from amplitude only near-field data is presented. The estimation of the far field is stated as an intersection finding problem and is solved by the minimization of a suitable functional. The difficulties related to the possible trapping of the algorithm by a false solution (common to any nonlinear inverse problem) are mitigated by setting the problem in the space of the squared field amplitudes (as already done in a number of existing papers) and by incorporating all the a priori knowledge concerning the system under test in the formulation of the problem. Accordingly, the a priori information concerning the far field, the near field outside the measurement region and the accuracy of the measurement setup and its dynamic range are properly taken into account in the objective functional. The intrinsic ill conditioning of the problem is managed by adopting a general, flexible, and nonredundant sampling representation of the field, which takes into account the geometrical characteristics of the source. As a consequence, the number of unknowns is minimized and a technique is obtained, which easily matches the available knowledge concerning the behavior of the field. The effectiveness of the approach is shown by reporting the main results of an extensive numerical analysis, as well as an experimental validation performed by using a very low cost nearfield facility available at the Electronic Engineering Department, University of Napoli, Italy. Index Terms-Near-field far-field transformation, only amplitude measurement

Magnetic Nanoparticle Hyperthermia

The synergic exploitation of electromagnetic fields and nano-components has led, in the last two decades, to the definition of new therapeutic tools for the treatment of cancer. One of these tools is the Magnetic Nanoparticle Hyperthermia, an emerging hyperthermic treatment where the tumor heating is achieved by accumulating into it magnetic nanoparticles and applying a low frequency magnetic field. Magnetic Nanoparticle Hyperthermia is very attractive thanks to the biocompatibility and low toxicity of the employed magnetic nanoparticles and the possibility of their selective accumulation into the tumor by means of minimally invasive administration routes. Moreover, they exhibit high dissipation capability and the transparency of the human tissues to low frequency magnetic fields allows treating tumors deeply located in the body. For these reasons, Magnetic Nanoparticle Hyperthermia has been extensively investigated, and clinical trials on human patients have been performed since 2003, with encouraging results and reduced side effects, especially concerning brain tumors. In this framework, an important topic is the characterization, both theoretical and experimental, of the properties, particularly the losses, of magnetic nanoparticles. The aim is to identify the nanoparticle parameters (size and shape) and the exposure conditions (magnetic field amplitude and frequency) that maximize the dissipation capability of the magnetic nanoparticles, in order to minimize their concentration in the tumor. However, maximizing the magnetic losses is only one face of the coin: one must also avoid overheating of the healthy tissue surrounding the tumor, due to the eddy currents induced by the applied field. Therefore, one should actually face a more complex constrained optimization problem. This explains in part why the setting of the operative parameters is still based on empirical, possibly over-restrictive, criteria, although the individuation of the actual optimal working conditions is a key point to extend its clinical effectiveness. In this chapter we will prevalently address this last aspect of Magnetic Nanoparticle Hyperthermia. We will begin with an overview of the main biological and physiological effects that are at the basis of the use of heating as an oncological treatment and of the main hyperthermia modalities. Next, we will introduce and discuss Magnetic Nanoparticle Hyperthermia, reporting the main results of its feasibility assessment and of the clinical trials performed up to now. Then, after revising the state of the art and current issues concerning the optimization of the magnetic nanoparticle losses, we will present a recently proposed criterion for the optimal choice of the working conditions in Magnetic Nanoparticle Hyperthermia, critically discussing the reliability of the analytical models on which it is based. Numerical results relative to the challenging and clinically relevant case of brain tumors, obtained by exploiting a 3D realistic model of the human head, will be presented, discussing their significance and practical relevance. Then, exploiting these results, the limits of clinical applicability of Magnetic Nanoparticle Hyperthermia for the treatment of brain tumors in adult patients will be estimated. A discussion on the possible future developments will conclude the chapter

On the Essential Dimensions of the Scattering Problems in Planar Layered Structures

The efficient analysis of large printed planar arrays with elements of arbitrary shapes and locations is a challenging complex problem, as it requires large memory storage and long computational times. Therefore different techniques are being developed in order to reduce this cost. Aim of this paper is to determine the minimum number of unknowns required to get a given accuracy, i. e., the problem size. To this end, we exploit the concept of degrees of freedom of the radiated field and the well-known representations of the stratified Green's functions. The obtained results can provide the basis for the development of computationally effective methods for the analysis of such kind of structures

Nanotechnology and Life: An Engineer's Perspective

Nanotechnology deals with the design, development, and manipulation of materials and devices with at least one dimension sized on a nanometer scale. It involves fields of science as diverse as surface science, organic chemistry, molecular biology, semiconductor physics, microfabrication, with a vast range of applications, such as in medicine, electronics, biomaterials, and energy production. Its ultimate goal is to be able to predictably design, construct, and control nanosystems, tailoring them to specified needs. This is the classical task of engineers, requiring a quantitative modeling of the problem of interest, detailed and accurate enough to make a reliable design possible. In the case of the applications to biology and medicine, living bodies are seen by nanotechnologists as the (essentially passive) environment in which the nanosystems perform their tasks. This modelization does not take into account the actual nature of living beings, which has been uncovered piece by piece in a long process, converging in the last 50 years to form a unified picture, which can be conveyed by a simple sentence: living organisms are hierarchically integrated sets of nanomachines. This may be clear to biologists, they lack reliable methodological and theoretical tools that allow the generalization of their findings into quantitative models, suited to a design procedure. Filling this gap would allow the engineering of biosystems at the nanometric scale, which has the potential of revolutionizing both nanotechnologies and biotechnologies. This article is an attempt to give an idea of this scenario from the engineering point of view, putting in perspective the problems and challenges, and giving an idea of the possible developments and their implications

A New Method to Avoid the Truncation Error in Near-Field Antennas Measurements

A new method to avoid the truncation error in antenna near-field measurements is presented. The approach relies on the concept of information content of the field. According to this point of view, the truncation problem is solved by picking up the information that is lost due to the finite size of scanning area, in points of the space reachable by the measurement system. The method can be applied to any scanning geometry, including the planar and cylindrical ones, whenever the set-up allows to vary the distance between the antenna under test and the probe during the scanning procedure. Application of the method to cylindrical near-field scanning is numerically investigated, assessing the effectiveness of the proposed technique