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A woodpile Electromagnetic Bandgap (EBG) material has been designed, by using an in-house code that implements the Fourier Modal Method (FMM). A couple of alumina-woodpile samples have been fabricated. Several results have been collected for the transmission behaviour of the woodpile and of resonators with woodpile mirrors, in a shielded anechoic chamber, by using a vector network analyzer, in the 8–12 GHz range. These new experimental data highlight interesting properties of 3D EBG resonators and suggest possible innovative applications. Comparisons of the collected results with FMM show a satisfactory agreement. An application of the EBG resonator has been considered, for gain enhancement of a microstrip antenna: an increase of about 10 dB in the broadside gain has been measured; experimental data and numerical results obtained with the commercial software HFSS show a good agreement. A comparison is presented between EBG resonator antennas and two-dimensional uniform arrays. Finally, HFSS results are provided for EBG resonator antennas working at higher frequencies or with a more selective superstrate: a gain enhancement of more than 18 dB is achieved by such antennas.

In spite of the technological advancement of the healthcare system, monitoring skin hydration still remains a challenging task. The solutions currently available in the literature are inadequate to obtain continuous real-monitoring, especially in a wearable perspective. Starting from these considerations, this paper addresses the implementation of an innovative wearable device that can monitor skin hydration through microwave reflectometry technique. In particular, a preliminary validation was carried out through time-domain reflectometry (TDR) in-vivo measurements, from which the corresponding frequency-domain (FD) data were extrapolated. Successively, an in-depth study on the frequency response of the sensing element designed with respect to different skin hydration levels was carried out through full-wave simulations on human phantoms. This strategy allowed to consider different reference skin hydration levels and to obtain specific calibration curves relating the dielectric permittivity of skin to the FD-response of the monitoring system. The obtained results have thus led to the implementation of a system based on microwave reflectometry, with large potential for real-time, continuous monitoring of skin hydration.

Quality control is of great importance in food industry, both for the evaluation of product characteristics and to avoid the occurrence of foreign bodies contamination in packaged items. With respect to the inspections against possible contaminants inside the product, different technologies are currently adopted along production chain lines. However, the number of accidents involving low density objects remains very large. To overcome this limitation, the use of electromagnetic technologies has been recently proposed. In this work, the synergic use of terahertz and microwaves technologies is proposed, so to provide high resolution images and in-depth inspections of different scenarios, including low density materials. A focus study on sugar samples is considered, reporting both its broadband characterization at microwaves and preliminary terahertz imaging to evaluate the integrity of the packaging. Ongoing research is devoted to the development and validation of a microwave device for monitoring food products along the production line.

Traditional wireless communication methods tend to saturate in terms of data rate, frequency spectrum and reliability. Visible Light Communication (VLC) integrated with the emerging technology of Internet-of-Things (IoT) opens up to a wide range of indoor applications. In this work we will describe the potential of an optical wireless communication infrastructure and we will make a comparison with the emerging 5G and 6G Wi-Fi (RF) technologies.

In this work, an innovative system for structural health monitoring of metallic pipes is presented. The proposed system relies on exploiting the pipeline as a waveguide for the propagation of an electromagnetic (EM) signal. By analyzing the reflected signal, it is possible to assess the possible presence of anomalies or damage in the pipe.The innovative aspect of the proposed monitoring system is that the EM test signal is injected in the pipeline/waveguide through a coaxial/waveguide transition that is made on the surface of the pipe. In practical applications, this strategy would allow to connect more easily to operating, buried pipes.To characterize the propagation of the EM signal in such conditions and to verify the changes on the reflected signal provoked by variation of the conditions of the pipe, experimental tests were carried out and a dedicated processing strategy was developed. The obtained results, although preliminary, confirmed that the proposed method holds unexplored potential to be used as a structural health monitoring solution.

In this paper, a time domain reflectometry (TDR)-based system for measuring water content of raw construction materials is presented. The proposed system relies on the fact that the presence of water leads to an increase of the dielectric permittivity of materials; therefore, from TDR-based permittivity measurements, it is possible to infer the water content value. In practical applications, the proposed system could be used for assessing the intrinsic water content of construction materials before they are poured into the concrete mixture. Knowing the intrinsic water content of the raw materials, in fact, would allow to evaluate the optimal amount of water that should be added to the mixture in order to achieve the desired waterto- cement ratio. This, in turn, would permit to fine-tune and control the mechanical properties of the final concrete structures. For assessing the feasibility of using the proposed system for the intended purpose, water content measurements were carried out on three construction materials, namely, sand, gray cement, and white portland cement. For each of these materials, a calibration curve relating water content to the apparent dielectric permittivity was derived; additionally, through repeated measurements, also a confidence interval was associated with the calibration curves.

Dielectric permittivity-based measurement techniques are establishing themselves as attractive solutions for assessing moisture content of historic masonry materials. The relative simplicity of the measurement principle and the inherent adaptability to diverse operating conditions are two of the most notable features of these techniques. In spite of these specific advantages, however, there are still some aspects that hinder the widespread use of permittivity-based moisture content measurement systems, and make their standardization difficult. In particular, the density of the sample under test may affect the estimation of permittivity, thus possibly leading to inaccurate moisture content measurements. As a result, the measurement system should be re-calibrated even when the same type of material is being investigated (e.g., two samples of the same type of stone, but extracted from different quarries).To circumvent this problem and to fully exploit the potential of permittivity-based moisture content measurements, in this work, a strategy for compensating for the effect of density is addressed. In order to verify the suitability of this strategy, moisture content measurements were carried out on samples of two type of stones typical of historic masonry, namely gentile stone and red-clay brick.

In this work, the assessment of water content of building materials, to be used for moisture content monitoring of Cultural Heritage structures is addressed. To this purpose, different methods and probes were comparatively used to infer, noninvasively, the relationship between the water content of stone materials and the reflection properties at microwave frequency of the material. In particular, three types of probes were used: an open-ended coaxial probe; a patch resonator; and an open-ended waveguide. In addition, two different measurement instruments were compared; namely, a vector network analyzer and a time-domain reflectometer. Experimental tests were carried out on two types of stone materials ( gentile and leccese stone), which are typically found in Cultural Heritage structures of Southern Italy. For each of the considered measurement systems, the experimental results and the related uncertainty evaluation are reported.

A transmission line simulator for applications to TDR measurements and TDR-based sensors is presented. The proposed simulator, fully developed in MATLAB environment, is designed to be a fast, efficient and easily customizable tool, and its performance are compared with commercial simulation software packages. The simulator is intended for measuring arbitrary profiles of primary parameters (R, C, G, L) of a transmission line, by matching simulated TDR waveform with experimental TDR data. In the paper, this use is demonstrated by measuring the parameter profiles of actual coaxial cables. The simulator can be used in any kind of TDR measurement, e.g. leak detection in pipes, distributed moisture measurements in soil, health monitoring in building concrete, etc.

In this work, a time domain reflectometry (TDR)-based system for measuring water content of construction materials is presented. The proposed system relies on the fact that the presence of water leads to an increase of the effective dielectric permittivity of materials (being the relative dielectric permittivity of construction materials in the order of 3–7, and that of water approximately 78). Therefore, through TDR measurements of the apparent permittivity of the material, it is possible to obtain calibration curves that allow retrieving the water content. Starting from these considerations, in this paper, the results related to moisture content measurements of three construction materials (namely, plaster mortar, portland cement and pozzolan cement) are reported. The advantage of the proposed system is that it can allow to monitor in real time the water content of construction materials inline, so as to assess their quality throughout the production process.

In this work, the validation and the practical implementation of a methodology exploiting a time domain reflectometry (TDR)-system for monitoring rising damp in building structures are described in detail. The proposed system employs wire-like, passive, diffused sensing elements (SEs) that are embedded, at the time of construction or renovation, inside the walls of the building to be monitored. The SEs remain permanently inside the wall, ready to be interrogated when necessary. Experimental and simulation results are reported, which demonstrate the possibility of practical implementation and the associated performance in terms of sensitivity.

Olive oil production represents a big part of the Mediterranean economy, and as such it must be protected from frauds. For this reason, it is necessary to develop alternative low-cost techniques, applicable on large scale, for checking the quality of the product and for detecting adulteration. On such bases, the present work deals with the possibility of adopting microwave reflectometry for obtaining a 'spectral signature' of vegetable oils. For this purpose, time domain reflectometry (TDR) measurements, in combination with specific data processing, are first used for the dielectric characterization of several oil types. Successively, the acquired data are processed through the principal component analysis (for identifying clusters of oil types that exhibit common features) and through the partial least square analysis (for identifying a predictive model for detecting oil adulteration). Results confirm that the proposed procedure holds considerable potential for quality and anti-adulteration control purposes, especially in view of practical applications. © 2012 Elsevier Ltd. All rights reserved.

The design and the experimental characterization of a waveguide system for complex permittivity measurements on both solid and granular materials are presented. The proposed system is intended for the dielectric characterization of asphalt concrete and of its components at frequencies around 2.45 GHz. Therefore, the system provides measurements on granular materials, such as mineral aggregates found in the asphalt concrete. A series of experimental tests on reference materials shows, via comparison with a standard measurement system, errors within 1%. A theoretical analysis of uncertainty contributions confirms a predicted expanded uncertainty lower than 2%. Furthermore, to test the proposed system for dielectric spectroscopy on materials typical of the asphalt industry, measurements were also performed on calcareous and basaltic materials, which are typically used for the production of asphalt. Finally, three different dielectric models (namely, $\alpha $ model, Ansoult’s model, and Topp’s equation) were comparatively assessed to identify the most suitable ones in describing the water content and dielectric permittivity relationship for the considered materials.

The design and preliminary metrological characterization of a waveguide system for complex permittivity measurement on both compact and granular materials is presented. The proposed system is intended for the dielectric characterization of asphalt concrete and of its components at frequencies around 2.45 GHz. Therefore, the system easily allows performing measurements on granular materials, such as mineral aggregates found in the asphalt concrete. A series of experimental tests on reference materials shows, via comparison with a standard measurement system, errors within 1%. A theoretical analysis of uncertainty contributions confirms a predicted expanded uncertainty lower than 5%.

In this work, an accuracy analysis of the estimation of the time of flight (ToF) for time domain reflectometry (TDR) signals is carried out. For this purpose, three different criteria (referred to as ‘maximum derivative’, ‘zero derivative’, and ‘tangents crossing’) were comparatively applied for the evaluation of the ToF of a TDR signal propagating along a set of RG-58 coaxial cables (with different known length and with known electric parameters). Successively, as a further experimental test, the same criteria were applied on bi-wire cables with unknown electric parameters. Results show that, among the tested criteria, the ‘zero derivative’ criterion provided the best accuracy in the estimation of the ToF.

In this paper, a performance analysis, in terms of accuracy, linearity, and repeatability, of three criteria to estimate the time of flight in time-domain reflectometry (TDR) signals is carried out. In a first set of experiments, the three criteria [referred to as maximum derivative (MD), zero derivative, and tangent crossing (TC)] are applied to TDR signals propagating along a set of coaxial cables, with different known lengths and known electrical parameters. In a second set of experiments, the same criteria are applied to biwire cables in air, with different known lengths and unknown electrical parameters. Finally, in the last set of experiments, the criteria are applied in a more complex situation, i.e., on a biwire used as a sensing element for water-level measurement. The results show that, among the tested criteria, TC appears to provide a very good performance in terms of systematic errors and superior performance in terms of repeatability. The popular MD criterion appears to be more prone to random errors due to noise and TDR artifacts. The results of this paper are relevant to many practical applications of TDR, ranging from fault location in cables to media interface sensing.

In this paper, a time-domain reflectometry (TDR) based system for monitoring liquid level inside tanks is presented. The proposed system resorts to a flexible, two-wire probe, which can be attached to the walls of containers and adapted to their shape. The proposed system is particularly useful for industrial applications; in fact, after a preliminary calibration, it can measure automatically and in real time the level of liquids inside containers (even tens of meters tall). The proposed system was tested on metallic and on nonmetallic containers. In the latter case, as the probe is positioned on the outside wall of the container, a totally noninvasive monitoring of liquids is achieved. The obtained results show that the system has considerable potential for being easily and effectively employed in practical, industrial applications. Finally, simulations were carried out, thus providing useful information for optimizing the system performance and for predicting its limitations.

In the present work, an alternative probe configuration to be used for time domain reflectometry (TDR)-based monitoring of liquid level inside tanks is presented. The proposed probe, which resorts to a bifilar transmission line configuration, is flexible and adaptable to the surface of the containers to be monitored. This feature, along with the other advantageous characteristics of TDR, makes this probe configuration particularly attractive for industrial applications. In this paper, to test the applicability of the method, two different scenarios are considered: monitoring of liquids contained in metallic tanks and non-invasive monitoring of liquids in non-metallic tanks. Results show that, in both cases, the proposed system has considerable potential for being easily and effectively employed in practical, industrial applications.

In this paper, different customized systems for microwave permittivity measurements on liquid samples, based on reflectometric measurements, are presented and analyzed. Their performance is compared against the one deriving from the most widely adopted commercial measurement setup. The systems are designed with the aim of providing less expensive solutions without compromising measurement accuracy. The purpose of the first proposed solution is to replace the commercial measurement software exploiting a reformulation of the classical theory. Based on this alternative formulation, a 'homemade' probe is built by properly modifying an N-type coaxial connector, thus providing a system requiring a lower quantity of liquid under test. Moreover, a different experimental approach which uses time-domain reflectometry (TDR) instrumentation is presented. Such solution is by far the least expensive, as it allows avoiding the use of costly instrumentation (such as a vector network analyzer). In order to metrologically characterize the proposed solutions, a series of repeated measurements is performed on a set of well-referenced liquids. After extracting the Cole-Cole parameters through each of the considered measurement methods, the resulting type A uncertainty is evaluated. Finally, comparison with literature data allows the estimation of measurement bias. The analysis evidences that custom solutions generally exhibit an accuracy comparable to the one of the commercial solution, with a slight degradation of performance for the TDR-based setup, which, however, compensates for this drawback with its appealing low cost. © 1963-2012 IEEE.

In this work, a dielectric permittivity measurement system, to be used for quality control of edible oils, is presented. The proposed system relies both on low-frequency and high-frequency measurements (performed through and LCR meter and through a time-domain reflectometer, respectively), thus allowing a "broadband" investigation of the dielectric behavior of edible oils. The adoption of a single, specifically-designed probe (used for all the measurements), along with the possibility of using portable instrumentation, makes the proposed system an appealing candidate for the realization of a continuous, on-site system for quality monitoring of edible oils. The proposed system was first validated on materials with well-known dielectric characteristics. Successively, it was used to investigate the dielectric behavior of some autochthonous varieties of olive oils and of seed oils. The ultimate goal of this work is to pave the way for the development of an alternative method of analysis that could be able to distinguish among different kinds of oils, to certify oil quality and origin, and to detect the possible presence of adulterants. © 2011 IEEE.

Quality control of vegetable oils is becoming more stringent, and strict laws are being enforced, especially for avoiding adulteration. The public bodies that are responsible for the prevention of the adulteration of foodstuffs necessitate methods of analysis that could facilitate large-scale in situ controls. Similarly, oil producers constantly strive to speed up internal quality control. As a direct consequence, there is an increasing demand for innovative methods of analysis that could guarantee real-time in situ monitoring and provide adequate accuracy. On such bases, the present work addresses the possibility of monitoring qualitative characteristics of vegetable oils through microwave dielectric spectroscopy. To this purpose, the Cole-Cole dielectric parameters of different vegetable oils are evaluated through an innovative automatable procedure that suitably combines traditional TDR measurements, SOL calibration, frequency domain processing, TL modelling and, finally, a minimization routine. The proposed procedure is carried out first on different "pure" oils and, secondly, on some oil mixtures. The obtained results confirm that different dielectric characteristics are associated with different oils, thus confirming the considerable potential of dielectric spectroscopy for quality and anti-adulteration control purposes, especially in view of practical applications. © 2010 Elsevier Ltd. All rights reserved.

Measurement and control of the fluid parameters play a very important role in industry applications such as in the petrochemical industrial processing, where there is an increasing demand for real-time determination of dielectric parameters in relation to the product quality. Furthermore, in such a context, additional stringent requirements frequently deal with the spatial localization of non-miscible-layered liquids, like water layers often present in the bottom of tanks during the refinery industrial processing. Recently, reflectometry has become a very attractive method for monitoring applications, thanks to its accuracy and flexibility performance. In this paper, the design of a suitable probe configuration and an associated calibration structure, both leading to an optimal experimental set-up for practical reflectometry measurements in petrochemical industrial applications, are illustrated. Moreover, starting from frequency-domain reflectometry data, a robust optimization procedure is implemented and experimentally tested, thus allowing the accurate evaluation of the frequency-dependent dielectric properties and of multiple levels in different stratified liquids. Results derived through the simple time-domain technique are compared with those achieved through two different frequency-domain approaches, involving the Fast Fourier Transformation (FFT) of time-domain reflectometry (TDR) data and direct vector network analyzer (VNA) measurements, respectively. It is demonstrated that the frequency-domain approaches can significantly enhance the measurement accuracy, allowing the estimation of fuel level with an uncertainty lower than 0.5 mm. Furthermore, it is also shown that a low-cost TDR system, combined with an appropriate FFT-based algorithm, can be successfully adopted for the simultaneous measurement of permittivity and levels, without substantially affecting the measurement accuracy performance when compared to the direct frequency-domain VNA measurements.

The need to deploy distributed power quality monitoring systems requires the development of circuits able to yield an accurate time reference that is easy to disseminate on specific monitoring sites. In this paper, the design and initial realization of a time reference continuously traceable to a Cs133 atomic standard is proposed. Such reference is based on the locking of the Cesium-derived L1 GPS satellites carrier and would simply require visibility of one GPS satellite in order to be operative. In particular, attention is focused on the hybrid design and realization of the carrier tracking section, with particular emphasis on its fundamental building blocks, such as the voltage controlled oscillator, mixers, and power dividers. The design procedure for the different blocks and some prototypes are discussed and preliminary measurements showing their functionality are presented.