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On the occasion of the 200th anniversary of Orsted's discovery of the magnetic effects of electric currents, this article summarizes the main stages of the development of electromagnetism before Maxwell, from Orsted's experiments through Ampere's development of electrodynamics and Faraday's discovery of electromagnetic induction, up to the development of Weber's electrodynamics. The emphasis is on the conceptual evolution that led, on the one hand, to unification under a coherent, mathematically sound theory for all known electromagnetic phenomena within the Newtonian paradigm of instantaneous action at distance, and on the other hand, to the foundations of Maxwell's revolution, which definitely changed that paradigm.

James Clerk Maxwel l (born in Edinburgh, United Kingdom, 13 June 1831; died in Cambridge, United Kingdom, 5 November 1879) is undoubtedly one of the preeminent scientists of all time (Figure 1). As Newton before him and Einstein after, he introduced new ways to look at physics, opening new conceptual horizons and modifying the body of accepted theories and physical conceptions. The modern vision of a physical world made of particles that interact through fields has a conceptual foundation in two of Maxwell's main contributions: the kinetic theory of gases and the theory of electromagnetic fields.

Magnetic nanoparticles-aided microwave imaging is an emerging modality for the diagnosis of early stage tumors. It exploits the possibility of modulating the response at microwaves of magnetic nanoparticles, employed as contrast agent selectively accumulated into the tumor. In this paper, we describe the results of an experimental study aimed at establishing the actual detection limits of the approach, namely the minimum amount of magnetic nanoparticles to be delivered for a reliable imaging. The assessment is carried out on breast phantoms made of ex-vivo minced pig tissues and using commercially available magnetic nanoparticles. The results show that it is possible to detect amounts of magnetic nanoparticles between 2 and 7 mg, dispersed in a volume of about one cubic centimeter, depending on the breast type. While such quantities are already consistent with those currently reachable via active selective targeting, an in-depth analysis of the results allows to identify strategies to further lower the detection limits up to four times, by refining the measurement set-up and setting the amplitude of the polarizing magnetic field modulating the nanoparticle response to a suitable value.

We address the synthesis of isophoric sparse ring arrays for full-Earth coverage from Geostationary Earth Orbit (GEO) satellites by means of steerable beams, switchable between two different widths. In particular, we pursue the desired beam zooming/shrinking through two interleaved sparse arrays deployed over the available circular aperture. To this aim, we propose two different antenna architectures. In one case, the two beams are radiated by two separate interleaved arrays; in the other case, the two beams are instead radiated by two interleaved arrays that share a common part of their layouts. Both the proposed architectures allow us to exploit a synthesis procedure that calculates the two interleaved arrays separately, through the cascade of two steps, both implemented with a (computationally) very efficient deterministic density-tapering approach. The proposed strategy allows to obtain isophoric sparse layouts, satisfying the required design constraints with a significant reduction of the control points with respect to the solution achievable exploiting noninterleaved isophoric sparse arrays.

Magnetic nanoparticles (MNP) enhanced microwave imaging could provide an effective approach for an early stage diagnosis of breast cancer, if encouraging results coming from accurate and realistic numerical studies are confirmed by an experimental proof of concept framework. To this end, an ad hoc laboratory setup has been designed and built up to verify the possibility of detecting the low signal scattered by MNP when embedded into a simplified but realistic breast phantom. This paper describes the developed measurement setup and the results coming from a first run of experiments, which confirm the possibility to detecting realistic amounts of accumulated nanoparticles. Moreover, the experimental results analysis allows addressing the future developments required to determine the ultimate detection limits of the technique, giving relevant information to plan the preclinical assessment.

This paper deals with the optimal synthesis of sum or difference patterns radiated by an array of fixed geometry. The aim is to establish the most general class of arrays for which such synthesis can be reduced to a linear programming problem, extending and completing previous results regarding uniformly spaced (linear and planar) arrays. It is shown that such a class consists of the centrosymmetric arrays, whose element patterns are either equal or Hermitian symmetric with respect to the center of symmetry. The optimal solutions are also Hermitian symmetric and the corresponding patterns are real. Furthermore, it is shown that the above class of arrays coincides with that of the arrays capable of radiating real patterns. Some numerical examples are provided to give an idea of the geometries and the synthesis problems to which the achieved result successfully applies and of the achievable computational advantage.

Magnetic nanoparticles have been recently proposed as a contrast agent for breast cancer microwave imaging. In this communication, we report on the ongoing activities aiming at the feasibility validation of magnetic nanoparticles enhanced microwave imaging. In particular, we discuss the results of some experiments, carried out to deal with the factors that influence the detection limits of the technique. Previous experiments have shown that a major limitation to the minimum amount of contrast agent that can be appreciated is due to the instrumental drift, which cannot be overcome by simply averaging the measurements. In addition, owing to the low level of the useful signal, possible magnetic effects arising from the system and the involved media can become relevant and impair the measurements. In the following, we deal with these aspects and present the results of a first set of experiments aimed at assessing the detection capabilities of the technique.

This contribution outlines the main stages of the path that in ten years led James Clerk Maxwell to the introduction of the concept of the electromagnetic field, to the formulation of the electromagnetic theory of light, and to the development of the equations we still adopt for the description of electromagnetic phenomena.

Discusses the technologies and applications supported by nanotechnology, considered one of the 21st century's most promising technologies. 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.

Non-periodic, sparse Direct Radiating Arrays employing equi-amplitude (isophoric) radiators represent an appealing solution to meet the requirements of next satellite services. In this work we address the synthesis of isophoric sparse arrays capable of radiating highly steerable pencil beams, in order to meet the requirement of full Earth coverage from GEO orbits. To this aim, we first of all perform an analytical study that allows assessing the geometrical constraints that the desired beam steerability puts on the design of the array layout. Starting from such results, in the second part of the work we address the actual synthesis of the sparse array. The proposed strategy consists in the synthesis of the optimal radiating feed followed by the synthesis of the array layout capable of taking into account the aforementioned geometrical constraints as well as the feeds' pattern, in such a way to guarantee satisfaction of the side lobe level constraint for every steered beam. Numerical examples demonstrate the effectiveness of the proposed synthesis strategy.

The problem of the optimal power-pattern synthesis of circularly symmetric shaped beams is addressed and solved. In particular, an existence criterion is provided to test a priori (i.e., without solving the overall synthesis problem) if a non-superdirective source of given size can radiate or not a circularly-symmetric power pattern lying in a given arbitrary mask. In the affirmative case, the proposed approach guarantees the achievement of the optimal solution, i.e., that of maximum directivity or minimum size, by using convex optimization techniques. In general, a number of equivalent source distributions (i.e., radiating the same power pattern) do exist, which can be explicitly determined in a deterministic way. Numerical examples concerning applications of actual interest support the given theory and confirm the effectiveness of the developed synthesis procedure.

The aim of this paper is to investigate the main aspects of the synthesis of plane wave generators (PWGs) i.e., arrays capable of emulating a plane wave, or a superposition of plane waves, in a given region. In particular, we introduce new figures of merit, particularly suitable for PWG synthesis procedures, and simple guidelines regarding size and shape of the PWG, as well as the number of radiating sources needed to synthesize the required plane waves. The performance limits of a PWG are analyzed, in terms of indexes related to the stability of the solution and to the level of the field amplitude on the lateral walls of the anechoic chamber in which the PWG is placed. Finally we present a synthesis method for PWGs, based on a planar sparse array architecture. Starting from the previously achieved results, a novel effective synthesis procedure is introduced. By means of such a procedure we are also able to take explicitly into account the mechanical and electrical tolerances in the PWG realization. In such a way we can assure the best performances, given the unavoidable errors in the positioning and excitation of the radiating elements.

This paper discusses some recent advances in the synthesis of isophoric sparse arrays, with reference to satellite communications. In particular, we first summarize some of the synthesis algorithm recently proposed, highlighting their advantages and drawbacks. Then, we show that, depending on the particular application scenario for which the sparse array must be designed, a better tailored algorithm exists. The presented analysis is aimed at providing a useful tool for antenna engineers involved in the overall design of sparse arrays for satellite communications.

A simple and effective nonuniform fast Fourier transform algorithm is presented. The algorithm is based on the interpolation of the exponential function in the Fourier transform using efficient truncated expansion algorithms for band-limited functions. Examples regarding the far-field evaluation of nonuniformly spaced antenna arrays are provided, and the behavior of the approximation error is analyzed, to confirm the effectiveness of the method.

This paper presents a novel approach to microwave hyperthermia exploiting magnetic nanoparticles as focusing agents, and reports the results of a 2D numerical study aimed at preliminarily assessing its effectiveness. The approach exploits magnetic nanoparticles, locally supplied to the tumor, to induce, through an external polarizing magnetic field, a detectable variation of its magnetic contrast. This variation is exploited to determine the excitations of the antenna array focusing the electromagnetic energy on the tumor. The advantage is that the synthesis of the excitations does not require any information neither on the geometry nor on the electromagnetic properties of the treated region, thus achieving totally blind field focusing. The magnetic nature of the magnetic nanoparticles contrast has required the development of an ad-hoc synthesis strategy, which, together with the use of magnetic nanoparticles, represents the novelty of the approach.

Microwave ablation is a cancer treatment based on the induction of coagulative necrosis of tumor cells by local heating. Recently, such a technique has progressed significantly in the clinical practice. However, its effectiveness would improve dramatically if paired with a system for the real-time monitoring of the evolving dimension and shape of the thermally ablated area. This paper explores the possibility of using microwave imaging as a convenient, non-invasive methodology to track the variation of the electromagnetic properties of ablated tissues and the surrounding region, so to monitor the overall treatment evolution in a non-invasive way. © 2016 European Association of Antennas and Propagation.

A generalized hybrid algorithm for the synthesis of uniform amplitude ring-arrays is introduced. The method exploits the analytical properties of the field radiated by a circular array in order to get advantages from the use of convex programming techniques. The method, aimed to the synthesis of circularly symmetric patterns, is very flexible and allows the use of different kind of feeds as well as stepped excitations. The synthesis procedure is demonstrated in the case of high-directivity pencil beam patterns.

Magnetic nanoparticles (MNP) enhanced microwave imaging has been recently proposed as a tool to pursue the diagnostics of breast cancer in an effective and reliable way. By means of a numerical analysis carried out under realistic conditions, this letter aims at assessing the measurement dynamic range (i.e., the measurement resolution), in terms of tumor size, nanoparticles concentration, and working frequency, required for an apparatus based on this diagnostic approach.

Uniform amplitude sparse arrays have recently gained a renewed interest and a number of synthesis techniques, mainly based on global optimization algorithms, have been presented. In this paper, after a discussion about the expected characteristics of such arrays, a simple deterministic approach for the case of pencil beams patterns is proposed and discussed. The approach, which outperforms previous synthesis techniques, takes inspiration from existing (not well-known) density taper procedures to develop a two stages synthesis where the first step is solved in a new closed analytical form, while the second one just requires local refinements or fast 1-D optimizations. As a consequence, the proposed approach avoids the need of multidimensional global optimization procedures and the inherent possibly prohibitive computational costs. Notably the first step, which also exhibits an improved flexibility with respect to other analytical techniques, already outperforms previous approaches in a number of cases of interest. Several numerical results confirm the effectiveness and usefulness of the proposed tools.

A suitable deterministic partitioning of large planar arrays in two kinds of properly shaped subarrays is shown to improve performances in terms of side-lobes peaks, directivity and aperture efficiency with respect to other existing solutions. The application of this simple idea to the case of large planar arrays with a reduced number of control points, useful in satellite applications, is demonstrated.

The problem of the optimal synthesis of circularly symmetric aperture distributions able to radiate pencil beams fulfilling well-defined requirements on the far-field and/or the directivity is addressed and solved. In particular, constraints concerning both the sidelobe level (SLL) and the directivity within a coverage zone are dealt with while being careful not to incur into the so called super-directive sources or into aperture fields actually difficult to be realized. The case wherein a constraint is enforced on the dynamics of the excitations is also considered. Numerical examples concerning cases of practical relevance are also shown in support to the given theory.

In the framework of medical applications of microwaves, magnetic nanoparticles enhanced microwave imaging represents a promising diagnostic modality. As a matter of fact, it merges the safety, low-cost and portability of microwave technology with the increased specificity enabled by the selective targeting capability of magnetic nanoparticles. In particular, a key ingredient of this technique is the possibility of modulating the response of nanoparticles in the microwave range by means of an external polarizing magnetic field. To this end, the amplitudes of the polarizing field have to be properly set, in order to achieve optimal performances. In this communication, we present an experimental study aimed at optimizing the working conditions in terms of field strength of a ultra-wide band radar system for detecting a magnetic nanoparticle induced contrast.

The use of contrast agents is gaining a huge interest in microwave imaging (MWI) of breast cancer [1]–[3] in order to discriminate the response of cancerous tissues from that of the surrounding healthy tissue, and so to reduce the occurrence of false negatives arising from the low contrast between the electric properties of cancerous and fibro-glandular tissues [4]. To this end, magnetic nanoparticles (MNPs) represent a viable and effective choice [5], [6]. Indeed, they are allowed for clinical use and can be functionalized with biological molecules able to selectively bind to cancerous cells. Moreover, the microwave magnetic response of the MNPs can be properly modulated by applying an external polarizing magnetic field (PMF), without significantly influencing the response of the surrounding healthy tissue. As a result, by exploiting a proper differential measurement strategy, one can separate the response of the background from that of the MNPs (i.e., the “useful” signal), which, if present, is unambiguously associated to the presence of a malignant lesion [5].

A new technique, exploiting magnetic nanoparticles as contrast agent, has been recently proposed for microwave breast cancer imaging. As human tissues are non magnetic, the adoption of a magnetic contrast agent, able to selectively target tumoral cells, represents an effective means to increase diagnostic reliability. Although the effectiveness of the new technique has been fully assessed through realistic and accurate numerical simulations, an experimental proof-of-concept is still needed to set the ground for a subsequent pre-clinical stage. In this communication, we present the first results of such an experimental validation, performed with an ad hoc designed laboratory set-up and exploiting a realistic (although simplified) breast phantom.

Purpose: This paper presents a numerical study aiming at assessing the effectiveness of a recently proposed optimisation criterion for determining the optimal operative conditions in magnetic nanoparticle hyperthermia applied to the clinically relevant case of brain tumours. Materials and methods: The study is carried out using the Zubal numerical phantom, and performing electromagnetic–thermal co-simulations. The Pennes model is used for thermal balance; the dissipation models for the magnetic nanoparticles are those available in the literature. The results concerning the optimal therapeutic concentration of nanoparticles, obtained through the analysis, are validated using experimental data on the specific absorption rate of iron oxide nanoparticles, available in the literature. Results: The numerical estimates obtained by applying the criterion to the treatment of brain tumours shows that the acceptable values for the product between the magnetic field amplitude and frequency may be two to four times larger than the safety threshold of 4.85 × 108A/m/s usually considered. This would allow the reduction of the dosage of nanoparticles required for an effective treatment. In particular, depending on the tumour depth, concentrations of nanoparticles smaller than 10 mg/mL of tumour may be sufficient for heating tumours smaller than 10 mm above 42 °C. Moreover, the study of the clinical scalability shows that, whatever the tumour position, lesions larger than 15 mm may be successfully treated with concentrations lower than 10 mg/mL. The criterion also allows the prediction of the temperature rise in healthy tissue, thus assuring safe treatment. Conclusions: The criterion can represent a helpful tool for planning and optimising an effective hyperthermia treatment.

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.

It has been recently shown that the Method of Auxiliary Sources is capable to solve the scattering problem for large smooth conductors, exploiting a number of unknowns substantially equal to the number of degrees of freedom of the scattered field. In this work, with reference with the 2D case, such MAS implementation is integrated with a Fast Multipole Method approach, thus achieving significant results in terms of memory savings and speed up of the impedance matrix inversion. Numerical examples are provided referring to PEC scatterers of elliptical shape.

An efficient near-field-far-field transformation technique with spherical spiral scanning, which uses a minimum number of data, is proposed. A nonredundant sampling representation of the electromagnetic field on the spiral and a fast, accurate and stable interpolation algorithm are developed to this end. By choosing the elevation step of the spiral coincident with the sample spacing needed to interpolate the field on a meridian, it is possible to reconstruct the field at any point on the spherical surface. This allows the evaluation of the data required by a spherical near-field-far-field transformation. Numerical examples assessing the effectiveness of the proposed technique are reported.

In this paper, we address the synthesis of isophoric sparse ring arrays for full Earth coverage from a GEO satellite by means of steerable beams, switchable between two different widths. We show that to achieve such a zooming capability, we cannot simply tailor the array geometry to one of the patterns and then obtaining the beam zooming/shrinking by means of a phase-only control. Hence, we propose a novel synthesis approach that, in order to obtain the required beam zooming/shrinking by means of a phase-only control, tailors the layout geometry simultaneously to both the beams. Numerical results are presented to demonstrate the effectiveness of the proposed approach. The analysis also shows that the required beam re-configurability cannot be achieved for free. In particular, to radiate simultaneously the narrow and wide beams, with a beam-width ratio 1:5, we have to employ a number of control point 80% greater than that necessary to transmit only the narrow beam.

An efficient probe-compensated near-field/far-field transformation technique with planar spiral scanning is proposed, which uses a minimum amount of data. A non-redundant sampling representation of the probe output voltage on a planar spiral and a fast, accurate and stable interpolation algorithm are developed. By choosing the angular step of the spiral coincident with the sample spacing needed to interpolate such a voltage on a radial line, it is possible to reconstruct the data required by the standard probe-compensated plane-rectangular near-field/far-field transformation technique. The use of an open-ended cylindrical waveguide as scanning probe allows probe co-rotation to be avoided. Numerical examples are reported, assessing the accuracy and the stability of the far-field reconstruction process.

Magnetic nanoparticle enhanced microwave imaging has been recently proposed as an effective strategy to monitor breast cancer. In this communication, we describe the ongoing activities concerned with a first experimental feasibility assessment of this technique. Such an activity aims at providing a proof-of-concept in realistic working conditions and it is obviously necessary to proceed towards the stage of pre-clinical trials.

A two-dimensional sampling interpolation algorithm to efficiently reconstruct the antenna far field is developed in this work. It is based on the recent theoretical results relevant to the nonredundant field representations over curves and surfaces. The use of an ellipsoid (prolate or oblate) as modeling of the source allows the reduction of the number of required samples with respect to a spherical source modeling, when considering antennas having one or two predominant dimensions. Numerical examples assessing the efficiency and stability of the algorithm are presented. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 181–185, 2001.

A new strategy to reduce the far-field reconstruction error due to the finite size of the measurement region in planar and cylindrical near-field/far-field transformation techniques is presented. The approach exploits the (spatial) band-limitation property of the radiated field in order to estimate the field outside the measurement area. A number of different estimation algorithms are investigated, with reference to both the accuracy of the estimation and the required computational effort. Numerical and experimental results show that with a small computational effort, it is possible to obtain a significant improvement of the reconstructed far-field pattern with respect to that obtained without near-field extrapolation.

In this paper, efficient sampling representations of the electromagnetic field, radiated by a centered parabolic antenna over a plane in the near-field region and over the far-field sphere, are presented. They use a. non-redundant number of samples, which remains finite even in the case of an unbounded planar observation domain. This result relies on a proper choice of the phase factor extracted from the field expression and of the coordinates used to parameterize the domain. By making explicit reference to the minimal convex domain enclosing the antenna, the number of needed data can be significantly reduced as compared with that required by modelling the antenna as enclosed in a ball. For the considered observation geometries, precise and fast sampling algorithms of central type have been developed. The reconstruction examples assess the effectiveness of the proposed representations. At last, the stability of the algorithms, with respect to random errors affecting the data, is proved by adding ...

It is shown that the electromagnetic (EM) field, radiated or scattered by bounded sources, can be accurately represented over a substantially arbitrary surface by a finite number of samples even when the observation domain is unbounded. The number of required samples is nonredundant and essentially coincident with the number of degrees of freedom of the field. This result relies on the extraction of a proper phase factor from the field expression and on the use of appropriate coordinates to parameterize the domain. It is demonstrated that the number of degrees of freedom is independent of the observation domain and depends only on the source geometry. The case of spheroidal sources and observation domains with rotational symmetry is analyzed in detail and the particular cases of spherical and planar sources are explicitly considered. For these geometries, precise and fast sampling algorithms of central type are presented, which allow an efficient recovery of EM fields from a nonredundant finite number of samples. Such algorithms are stable with respect to random errors affecting the data.