Search

In this paper a metrological assessment on the accuracy provided by a Time Domain Reflectometry (TDR)- based method for the estimation of moisture content of granular materials is proposed. In particular, comparative moisture content measurements are carried out through two different TDR instruments: an inexpensive portable unit and a high-performance unit. The main goals are first to assess a robust procedure for TDR moisture monitoring (in particular for sand-like materials), and second to provide a deep metrological analysis for minimizing and characterizing error contributions. This feature is particularly important when considering the proposed measurement procedures for industrial applications, where both accuracy and low cost must be guaranteed.

The need to correlate as accurately as possible Time to the power quality events pushes towards the necessity to develop circuits able to yield a time reference that is referable to International Time Standards. Moreover, the necessity to deploy distributed power quality monitoring systems requires these time references to be easy to disseminate, making them available on specific monitoring sites. In this paper, the possibility to obtain a time reference continuously traceable to a Cs133 atomic standard is proposed, by locking the Cesium-derived L1 GPS satellites carrier by means of a specifically designed GPS receiver. Such time reference would simply require visibility of one GPS satellite in order to be operative. In particular, the overall architecture of such receiver will be first outlined and then attention will be focused on the design and realization of the VCO which is one of its fundamental building blocks. Measurements carried out on a prototype of the proposed VCO show that its performances are adequate for the aim.

Soil moisture measurements are essential especially in the agricultural field, where it is crucial to guarantee that the optimal amount of water is provided to the cultivations. Most soil moisture measurement systems are local sensors; hence, a multitude of sensors must be distributed all over the field to obtain a comprehensive picture of the soil condition. Starting from these considerations, the present work addresses the feasibility of employing diffused sensing elements (in a wire-like configuration) for sensing soil moisture variations, based on capacitance measurements. To this purpose, for a preliminary validation of the proposed methodology, several experiments were carried out, thus identifying the suitable setup configurations and the potential of the method.

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.

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 work, the dielectric permittivity of four kinds of wood (Fir, Poplar, Oak, and Beech Tree), used in Italian Artworks and structures, was characterized at different humidity levels. Measurements were carried out using three different probes connected to a bench vector network analyzer: a standard WR90 X-band waveguide, a WR430 waveguide, and an open-ended coaxial probe. In particular, we investigated the dispersion model for the four wood species, showing how a log-fit model of the open-ended data presents a determination coefficient R2 > 0.990 in the 1–12 GHz frequency range. This result has proven helpful to fill the frequency gap between the measurements obtained at different water contents with the two waveguide probes showing an R2 > 0.93. Furthermore, correlating the log-fit vertical shift with the water content, it was possible to find a calibration curve with a linear characteristic. These experimental results will be helpful for on-site non-invasive water monitoring of wooden artworks or structures. Moreover, the final results show how the open-ended coaxial probe, with a measurement deviation lower than 7% from the waveguide measurements, may be used directly as a non-invasive sensor for on-site measurements.

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.

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.

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.

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.

Quality control of vegetable oils is becoming more stringent, and related laws are being enforced, especially for avoiding adulteration. As a result, there is a substantial need for methods of analysis that could provide real-time in-situ monitoring, especially for quality control purposes during production process. In this regard, the present paper investigates the possibility of monitoring qualitative characteristics of vegetable oils through microwave dielectric spectroscopy, which is a highly versatile investigative approach. In particular, the Cole & Cole frequency-domain dielectric parameters are known to be strongly related to the compositional characteristics of various substances. This way, starting from traditional Time Domain Reflectometry measurements performed on oils, the corresponding frequency domain information is retrieved. Successively, through a minimization routine, the Cole & Cole parameters of each considered oil are extrapolated. Results show that different dielectric characteristics can be associated with different oils. It is important to point out that the characteristics of the proposed procedure can be automated and, therefore, it may represent a promising solution for practical monitoring applications.

"Electromagnetic Band-Gap (EBG) materials can be successfully employed to improve the performances of antennas [1], [2]. When used as planar reflectors, as substrates, or as high-impedance ground-planes, they are able to eliminate the drawbacks of conducting ground-planes, to prevent the propagation of surface waves, also allowing a lowering of the antenna profile, and to improve the radiation efficiency. In EBG resonator antennas, instead, an EBG is employed as a superstrate on a primary radiator, backed with a ground plane, and its main effect is a considerable increase in the directivity [3]. It is also possible to obtain a highly-directive antenna by embedding a source in an EBG working near its band-gap edge, thanks to the limited angular propagation allowed."