G. Roqueta

Analysis of the Electromagnetic Signature of Reinforced Concrete Structures for Nondestructive Evaluation of Corrosion Damage

This paper presents a nondestructive corrosion damage detection method for reinforced concrete structures based on the analysis of the electromagnetic signature of the steel rebar corrosion. The signature of the corrosion on the scattered field upon microwave illumination is first numerically analyzed. First-order quality factor parameters, the energy and the mean propagation delay, are proposed to quantify the corrosion amount in the structure. To validate the model, low-profile ultra-wide-band antennas (3-12 GHz) are fabricated and measured. Measurements on 12 reinforced concrete samples with induced corrosion are performed, using three different antenna setups. The experiments demonstrate a good correlation between an increase in the corrosion amount with a decrease in the energy and an increase in the time delay of the propagated signal.

Broadband Propagative Microwave Imaging of Steel Fiber Reinforced Concrete Wall Structures

In this paper, a system for the broadband microwave nondestructive testing of steel fiber reinforced concrete (SFRC) is presented. The system is able to produce a pixeled image of the fiber dosage in the concrete. The SFRC material is seen as a dielectric mixture formed by thin-wire metallic inclusions and a host medium. An electromagnetic model based on the Maxwell-Garnett approach for dielectric mixtures is used to relate the electromagnetic properties of the SFRC to the fiber dosage. A criterion to determine the practical upper frequency limit for the measurements is formulated. A measurement system based on two wideband waveguide antennas is designed for the analysis of two SFRC multiblock test structures. The electric capacitive host medium calibration is proposed in the cases where the concrete structures have parts fabricated with different processes. The laboratory measurements on the individual SFRC elements and on the SFRC multiblock structures are conducted to obtain the images of the fiber dosage in the SFRC. Good agreement between the real, simulated, and measured values is achieved.

Microwave Time-Domain Reflection Imaging of Steel Fiber Distribution on Reinforced Concrete

This paper presents a time-domain reflection electromagnetic analysis for nondestructive testing of the fiber dosage inside steel-fiber-reinforced concrete (SFRC). With the fibers treated as electrical dipoles, the Maxwell-Garnett mixing rule for dielectric mixtures is used to obtain an estimation of the density of fibers in the composite material from the time-domain measurement of the effective permittivity of the sample. First, a numerical electromagnetic modeling of the fiber polarizability is performed using a Method-of-Moments-based code and a simple frequency-dependent polarizability is obtained. Second, a robust and novel relationship between the mean propagation delay and the total stored energy with the effective permittivity of the medium is obtained. A wideband measurement system based on a time-domain setup in a reflection arrangement is used for the analysis of SFRC test structures. The fiber dosage in the SFRC structures is reconstructed, showing good agreement with the expected dosage figures.

Microwave dielectric properties inspection of fiber-reinforced civil structures

A non-destructive technique based on microwave frequency dispersion (or equivalently time-delay) measurements has been proved to perform an analysis of the density and spatial fiber distribution of the fiber-reinforced civil structures. This technique has a sensibility and dynamic range compatible with the actual needs of the civil structure measurements. In the range from 500 MHz to 3 GHz a kind of mathematical rule can be extracted in order to relate the steel fiber density in the material with the equivalent permittivity.

Electromagnetic modeling and characterization of steel fiber reinforced concrete during the pouring process

An accurate study of the variation of dielectric properties of SFRC has been analitically developed and experimentally tested in a fifteen days measurement campaign. The system is able to discriminate between pouring process of 0kg=m3 and 30kg=m3, which conclusion could be extensible to other standard dosage values. The high humidity content of the composite produces a variation of the ressonant frequency towards the lowest values, which will conditionate the suitable frequency range for future measurements. Under the resonance, the measured permittivity increasing behaviour is compliant with the behaviour of ∈reff described in the electromagnetical model, although the resonance point has decreased due to coupling effects that are not being considered in the model.

Fabrication and measurement of homemade standard antennas

Apprenticeship is linked to training. This paper is intended to be a tutorial on how to design, fabricate, and measure antennas in an economical and easy way, using recycled materials and common electronic devices such as a laptop and an access point. Several antenna designs built with household materials are proposed, giving practical design and fabrication guidelines. The use of the Wi-Fi band allows linking the experiment with daily-life devices, and proposing a simple and economical antenna-measurement system. The capacity to experiment with antennas from their design to measurement will defi nitely stimulate undergraduate or graduate students to get acquainted with the basic topics of antennas and propagation. The paper presented herein was awarded with the fi rst price in the IEEE AP-S Student Challenge 2010 [1, 2].