1 Early Development

The activity of the “Electromagnetic Fields” research team (simply ‘group’ hereinafter) started at the beginning of the 80s of the last century, when Prof. Roberto De Leo, full professor of “Electromagnetic Fields”, moved from Università di Bari to Università di Ancona. He immediately was aware of the development possibility offered by a new university and contacted Prof. Tullio Rozzi, full professor of “Microwaves” at the University of Bath (UK), who soon thereafter moved from England to Ancona. So, the development of the two main research lines that have always characterized the activity of the group can be dated back at the first half of the 80s.

One of the most important research topic investigated by Prof. De Leo group was the study of the environmental impact of the electromagnetic fields, a subject that allowed the Ancona research unit to become one of the most relevant at national level in this field, anticipating problems who would have gained the attention of the scientific community and common people many years later.

In the very general context of the environmental impact, we consider both the interaction between electromagnetic fields and human body, and the coexistence of electronic devices and equipments in the same space. The first topic concerns the safety aspects of the electromagnetic fields, the second electromagnetic compatibility (EMC) problems.

The dosimetry studies aimed to evaluate the power deposition into human tissues when exposed to electromagnetic fields allowed to develop original models and experimental techniques, that were progressively applied to investigate the problem of the therapeutic use of the electromagnetic fields. In particular, hyperthermia treatments, that is the possibility to nurse tumoral tissues with temperature enhancement through electromagnetic radiation, were intensively investigated. The key point was the design of the applicator, the antenna to be placed on the patient skin to radiate the cancer region. The challenging aspects were the design of the radiating structure in the very near field of the antenna, especially for the problem of the matching conditions varying from a patient to another, and the capability to focus radiation into the tumor, avoiding temperature increase of the healthy tissues. These studies led to cooperate with other academic institutions and with industrial partners: in the first case cooperation resulted in an European Project, and in the second one it gave rise to the realization of a device for hyperthermia treatment successfully tested in hospitals [1,2,3,4,5,6,7].

In the same time the group investigated the problem of the brain cortex stimulation with pulsed magnetic fields, showing a capability to anticipate forthcoming scenarios, because this technique is currently investigated as possible treatment of some neurological disorders as depression and Parkinson. In Ancona the research was essentially addressed to study the possibility of replacing the electrical brain stimulation, painful and uncomfortable for the patient, with the magnetic stimulation, without any inconvenience for the patient, aimed to check damages of the motor area of the brain cortex. Also in this case the research activity, in cooperation with some neurologists of the regional hospital, was at first directed to develop a realistic model to evaluate the interaction between a magnetic pulse and a human brain, in particular the current density distribution into the brain, and then to the design of applicators able to focus the currents in specific regions [8,9,10].

Ancona was also one of the first Italian university to deeply take care of the EMC aspects, both as a research topic and as an educational matter. In fact the University of Ancona was the first in Italy to insert a class of ‘Electromagnetic Compatibility’ in the degree course of ‘Electronic Engineering’, so fostering the change of philosophy in modern engineering design, in the sense that EMC should not be considered an accidental trouble, but an important aspect of the design constraints, because EMC phenomena have a rigorous electromagnetic support and can be accurately modelled. In the early 90s, on behalf of the Italian branch office of Hewlett Packard, the group gave many lectures in different Italian locations to engineers coming from Italian industries. From a research point of view the group investigated aspects concerning both external and internal compatibility. In the first case the focus was the shielding effectiveness of enclosures with particular concern to apertures and resonance effects, whereas, in second case, crosstalk effects among traces of PCBs were theoretically and experimentally characterized [11,12,13,14,15]. However the topic that had not been deeply studied yet in the literature, and that gave the group the maximum international visibility was the systematic approach to the study of fast and intense transient fields, mainly due to ESDs events or generated during EFT tests. Accurate models, experimentally validated, in the time and frequency domain, for linear and non-linear devices were developed, and allowed to show direct and indirect effects, excitation of dangerous resonances [16,17,18,19,20].

In early 90’s group headed by Prof. Rozzi started works on advanced electromagnetic models of several kind of waveguides, in particular planar structures. The research was aimed to obtain numerically efficient and accurate models of, e.g., microstrip and coplanar waveguide accounting for actual thickness and losses of conductors, in contrast to what available at the time, where finite thickness and losses were addressed by approximate perturbative approaches. This way a new technique was discovered, the so called “Generalized Transverse Diffraction Resonance” (GTRD) approach. At the end of 90’s this was applied not only passive waveguides but also to active devices, such as Field Effect Transistors, in order to model a new class of distributed amplifiers (Travelling Wave FET), and principles were discussed in-depth in a book [35] edited by the IEE (currently IET), London. While the approach was conceived for 2D, namely waveguide, in so called eigenvalue problems, there were initial ideas to extend it to a fully arbitrary 3D circuit (deterministic problem). As matter of fact this process was later accomplished between the end of 90’s and early years of the new millennium, and a software, called Electromagnetic 3D Simulation (EM3DS) was developed as result of such theories. EM3DS was among the very few general purpose simulation software available at that time—likely one out of 10 or slightly more- and gained popularity being used by many relevant institution and companies (e.g. NASA,Footnote 1 Intel,Footnote 2 L3 commFootnote 3 etc.), and integrated in commercial software by IntellisenseFootnote 4 (Corning) and Coventor,Footnote 5 while being able to work seamlessly with software like Microwave Office (AWR,Footnote 6 currently National Instruments). Further studies involved coupled acoustic waves and electromagnetic waves for integrated resonators like BAW and TFBAR.

2 From the Old to the New Millennium

We have to consider that in these years an extraordinary growth of the mobile telecommunication systems led to a dramatic increase of the number of base stations in urban areas: as a consequence the problem of the exposition of the population to electromagnetic fields became a matter of discussion on the media, in public meeting, at the central and local parliaments. As a consequence, the study of the electromagnetic environmental impact was the natural evolution of the previous studies concerning the interaction of the fields and the human body. A further motivation to approach the problem came from the continuous requests of many local governments to participate to the writing of the ‘antenna planning’ for cellular networks. The group decided to face the problem with a very general approach, consisting in an innovative philosophy, where the electromagnetic impact should have been a constraint of the network, as other telecommunication requests. More specifically, the problem concerns the choice of the RBS positions, antenna tilts and heights, and radiated powers for a specified number of RBSs serving the interested area. The proposed solution is based on an optimization procedure that carries out the following principal requirements: (1) minimization of the radiated electromagnetic field, (2) maximization of the C/I ratio, (3) minimization of the distance between RBSs and the area with more traffic, (4) maximization of the coverage percentage, and (5) maximization of the efficiency of the base station system. Original techniques based on artificial neural networks were developed to efficiently evaluate the path loss of the electromagnetic waves in urban environment, and, in the framework of a project of the national agency for environmental protection, a method was proposed to compare the environmental impact of different base stations [21,22,23,24].

In the EMC research domain, new topics specifically related to measurements were developed. In particular the characterization of field sensors in a wide frequency range allowed to perform measurements of fields generated by fast transient currents, and the study of the reverberating chambers allowed to characterize this particular measurement test site. In these years the group developed a new idea to stir the field inside the chamber, called source stirring, whose advantage with respect the more common mechanical stirring is the lack of heavy and bulky mechanical paddles. The technique and the array to perform the electronic stirring were patented [25,26,27,28,29,30,31]. It worth noting that in these years the plasma antenna was also theoretically studied [32] and experimentally characterized: this was the first self-consistent model of this kind of device, based on a multi-physic approach consisting in a mathematical system formed by the Maxwell and Boltzmann equations: the model allows to accurately describe the non-linear effects of the plasma ignition through an external field, describing all the transient behaviour of the physical quantities till steady state condition [33,34,35].

In the new millennium most of Rozzi’s group shifted toward nanotechnology, in both theoretical and experimental studies. Nanotechnology is a technological field covering all aspects of nanoscale science and technology from a multidisciplinary perspective. It characterizes the understanding and control of matter at nanoscale dimensions, that is from few hundreds nm down to atomic dimensions. Nanotechnology not only yields miniaturization of devices and enhancement of integration density, but also features unusual physical, chemical, and biological device properties. Since many nano-structured materials exhibit their most interesting properties in a wide spectrum, from the microwave up into the optical frequency range, the concept and realization of nanoelectronic devices is a challenge also for the microwave/RF engineering community. At the nanoscale, both the charged particles and electromagnetic fields must obey the laws of quantum mechanics, which leads to quantum electrodynamics. Therefore, by the theoretical point of view, intense work was devoted to exploit the machinery developed to solve Maxwell’s equations into the framework of quantum mechanics, and later using relativistic quantum mechanical equations (Dirac formulation) to express alternatively Maxwell’s equations [36, 37]. Starting from well-known numerical techniques (e.g. TLM, FEM, Scattering Matrix Method), full-wave solvers for the multiphysics modeling of the combined Maxwell-Schrödinger/Dirac problem have been developed [38, 39]. A core concept relies in the fact that the electromagnetic field provides source terms for the quantum transport equations, that, in turn, provide charges and currents for the electromagnetic field. The main research topics can be summarized as: (i) the modeling of nano-structures/devices/systems based on low-dimensional materials, e.g. carbon-nanotubes (CNT), graphene, 2D materials beyond graphene, nanoparticles; (ii) the analysis of complex systems, ranging from nano- to meso-scale, and including quantum transport, electromagnetics, opto-mechanics, thermal effects, opto-mechanics, opto-electronics.

On the experimental side, the group pioneered a new approach into the framework of Scanning Probe Microscopes (SPM), namely the Scanning Microwave Microscopy (SMM) [40]. In this approach a probe is brought in close proximity to the surface of a sample, and current scanning probe microscope are able to image single molecules; in SMM a microwave signal is injected in the probe, and scanned while detecting changes in the reflected microwave signal. Imaging resolution can be sub-nanometric or even atomic, in spite of centimetric wavelength, due to the behaviour of evanescent waves produced by the sharp tip. This way a map of differences in local electromagnetic properties (e.g. dielectric constant, conductivity) can be obtained; a set of calibration techniques was developed [41] enabling local quantitative measurements. SMM, with respect to other techniques, allows to obtain quantitative data (electromagnetic properties) and at the same time to probe below surfaces also samples that are optically opaque. At the same time it was discovered that some principle of Time Domain Reflectometry could be exploited to improve the quality of images [42] and to obtain further calibration approaches [43]. Incidentally, during a set of experiments on semiconductor polymers, a new phenomenon was discovered [44], that could lead to a new generation of mass storing devices, where the interaction between a probe and a semiconductor could permanently lower locally the polymer conductivity, by changing the degree of disorder at molecular scale (Fig. 1). Microwave microscopy could be also a new device to investigate non-invasively, without the need of labelling, biological samples, and as matter of fact the group is focusing in performing measurements on cells, mitochondria and small nanometric vesicles, called exosomes, that could be the mean by which some chemical signal spreads among cells; recent theories also suggest a role of exosomes in spreading of metastases in cancer. Mitochondria are on the other hand implied in a process, called apoptosis (cell suicide), whose role is being investigated for cancer, while being at the basis of cell metabolism and, consequently, potentially underlying degenerative diseases. Microwave microscopy could become a tool to compare electrical properties of organelles in both healthy and disrupted or ageing cells [45].

Fig. 1
figure 1

Comparison between current maps, lateral force and topographic images in scanning probe microscopy (conductive Atomic Force Microscopy). A square, 5 μm of side, was written; reading is performed in an area 7 μm × 7 μm in P3HT: [70] PCBM (1:1) annealed at 100 ℃ for 15 min. a Current map (0.5 V) b lateral force image: the written square appears as a region with increased molecular disorder c topography: no topographic change is visible. The above images were obtained simultaneously. Also, the acronym “UNIVPM” is written and represented in 3D: d current map, e Lateral force (inverted for clarity) and f topography (Reprinted from [44])

Full size image

Following the same concepts introduced in SMM, novel imaging techniques, based on scanning probe microscopy, were implemented in the range of optical frequencies by merging together in a lens-free system different methods, such as: Contrast-Phase Microscopy [46], Optical Tomography [47] and Synthetic Holography [48]. These systems exploit the principle of low temporal coherence combined with the high spatial coherence propriety of light confined inside a scanning optical micro-cavity. These approaches are well suitable to work in liquid environment, for biological applications, and integrable with the actual SPM systems to achieve nanometric resolution.

In the last years, some properties of the scattering matrix for non-uniform radial waveguides were analysed in order to simplify the evaluation of the e.m. fields in such structures [49]. The results were applied not only to e.m fields but also to acoustic applications. The analysis of the properties of the scattering matrix were used to define a new kind of equivalent circuit, able to represent N-ports microwave devices, in presence of guided and/or evanescent modes [50, 51]. The new circuit is based on a polygon with N sides, as the number of ports, and N(N − 3)/2 diagonals. Moreover, N transmission lines are connected to the N sides. Each side and diagonal are loaded with susceptances that represent the “kernel” of the microwave device. The circuital properties of the device (filter, coupler, multiplexer, …) are contained in the “kernel” of the circuit. The polygon equivalent network can be used for example in the measurement of N-port device [52] and in the synthesis of hybrid coupler [53].

3 Nowadays and Beyond

3.1 Reverberation Chamber

Reverberation chamber (RC) theory and applications remain hot topics in the current and future activity planning of the EMC group. This research activity led to international cooperation with other Universities as the University of Nottingham (UK), the College Park (USA), the Queen Mary of London (UK) [54]. From an industrial point of view, the RC finds application in traditional electromagnetic compatibility tests (immunity and emissions) and power electromagnetic applications, like the microwave heating processes. In all these fields of application, the Ancona activity was characterized by a strong interaction with industries (ELASIS-FIAT, Emitech, Tornati Forni, Unibind). The future trend in theoretical aspects will be focused on the necessity to properly combine deterministic and stochastic electromagnetic methods of analysis [55,56,57,58]. The necessity of stochastic methods becomes more evident when the RC is transformed into a chaotic environment [59, 60]. Another interesting RC application is the characterization of shielding materials in aerospace and building construction applications [61,62,63,64]. The advantage is the random field excitation of the material more adherent to real life situations, w.r.t traditional deterministic methods [65]. Recently, the application of RCs has been extended to the testing of wireless devices and systems [66]. In fact, the RC is able to provide a rich multipath propagation environment, very similar to real life situations where these devices (access points, smartphones, IoT devices, etc.) may operate in presence of strong reflections having random behavior. This last activity opened other research topics and led to the built-up of a joint laboratory TIMFootnote 7-UNIVPM for testing real live LTE base stations in 4G technology provided by NOKIAFootnote 8 [67,68,69,70]. Strong research and application activities are expected in the future for the extension to the emerging 5G technology.

3.2 Electromagnetic Sensors

European and national research policies have, among their priorities, initiatives that will contribute to build a healthy and active population for the future, as well to enhance inclusion of people with disabilities. In line with this topics, the research group also focused on the development of sensors to monitor vital parameters (breathing and heart rate) that can be used in domestic environments, as well as sensors that can be used by blind or visually impaired people both in everyday life (sensors for mobility) and in sport.

The monitoring of vital parameters through electromagnetic sensors developed by the team is non-contact and allows the subject to remain dressed and covered if the monitoring takes place during sleep [71]. This reduces the invasiveness of the system and increases its acceptance and ease of use.

This application activity has led the research team to work alongside companies that belong to the Marche territory with strong attitude to innovation. This collaboration leads to an exchange of know-how between companies and university that has allowed to address problems of implementation and design not common in daily academic activity. The realization of demonstration prototypes was the result of this synergy [72].

The activity on electronic travel aids for the autonomous walking of visually impaired person has turned to the planning and realization of a system based on a obstacle detection radar [73, 74]. The system has been miniaturized to allow the placement of the antenna on the white stick [75]. In parallel to this activity, two prototypes of systems have been designed and built to assist blind people in running: one to be inserted into an athletics track [76, 77], and another for road training [78], again for running. For these projects the group collaborated with a Paralympic champion who resides in our Region: Andrea Cionna, who offered his advice on the implementation of the systems, as well as tested them. Some short videos of the systems realized are available on [79].

3.3 Electromagnetics at Nanoscale

Nowadays, nanotechnology is one of the core research area of the group. The development of modern devices based on nanostructured materials and nanotechnologies, for a wide area of applications ranging from microwave to photonics, relies on an electromagnetic computational platform defined by new general modelling and simulation routes. Accordingly, programs and simulations are developed and optimized for specific issues and challenges. The latter are related to the low-dimensionality of novel materials and to the possible coexistence of multiphysics phenomena, e.g. electromagnetic (EM), charge propagation and quantum transport [80,81,82,83,84,85,86,87], In particular, quantum phenomena like ballistic transport, tunneling, many-body correlations, carrier confinement and interface effects overlap with classical physical effects, which make traditional circuit design unsuitable to nanoelectronics. To this purpose, we developed appropriated models based on the solution of coupled systems of equations dealing with combined electromagnetic-transport phenomena i.e. Schrödinger/Dirac, Maxwell-Boltzmann, etc. The above e.m. platform takes into account the different aspect-ratio between nano-structured materials and device environment, bridging from the atomistic to the continuum scale (extreme multi-scale analysis). The key-issue is the coupling of quantum models and electromagnetic models, that acts at discrete level, but, in some case, as for ballistic regime, also at continuum level [80]. Other physics can also include, e.g. coupling to phonons (thermal effects), in opto-mechanical cavities, [87, 88]. In order to support semiclassical modelling, ab initio methods for high-frequency simulations of atomic-thick materials/surfaces need to be considered, as the Density Functional Theory (DFT). A key development is that the aforementioned discrete, ab initio methods (atomistic level) transfer/integrate the results into/with the larger scale models by constitutive equations/relations [80], in order to incorporate all necessary physics towards the continuum, full-wave method (device/sub-module level).

Constitutive equations must result in constitutive relations, eventually in integral form, which are usually numerically easier to handle. Exploiting constitutive parameters extraction from models may also lead to a compact representation, like the one provided a by complex, dispersive: (i) electric permittivity/conductivity; (ii) magnetic permeability, possibly in tensorial form. Standard solvers usually can simulate either quantum transport or full-wave electromagnetics, but a simultaneous solution is very hard to be achieved at a large scale. There is therefore a strong need to link the atomistic scale up to the continuous world, in order to characterize practical macroscopic elements, like micro-antennas, terahertz and plasmonic devices, periodic and aperiodic metamaterials. The combined solution of quantum transport and electromagnetic wave propagation features: different partial differential equation systems (PDE-S); different propagation/diffusive nature of the PDE-S; non-linear coupling; large geometrical/electrical aspect ratios.

Nano-structured materials and electromagnetic (EM) smart surfaces are also the target for innovative industrial products for antenna, radar and sensing application at microwave frequencies and in photonics. These are micro- to nano- structured artificial surface materials (2D or 2.5D), where: (a) the working principles exploit extreme sub- wavelength features already for passive (linear) operation; (b) the material need to encompass an overall size of hundreds of wavelengths; (c) localized or distributed active non-linear micro- to nano-scale inclusions are deployed densely in the underlying textured surface. The latter include constructs comprising carbon nanotubes (CNT), metal nanowires and nanoparticles, graphene, or more conventional semiconductor-based devices.

The activities described above are now at a final stage, but new ideas and potential applications have arisen from them. Nowadays, studies are already underway to verify the feasibility of using the monitoring system of vital parameters to monitor the energy expenditure of a person at home, even in this case without the use of bulky and annoying electrodes connected to the person. At the same time, the experience of autonomous mobility of blind people could be borrowed for applications in the field of civil protection where there is a need to use drones with autonomous driving.