An effective approach for road asset management through the FDTD simulation of the GPR signal

Ground-penetrating radar is a non-destructive tool widely used in many fields of application including pavement engineering surveys. Over the last decade, the need for further breakthroughs capable to assist end-users and practitioners as decision-support systems in more effective road asset management is increasing. In more details and despite the high potential and the consolidated results obtained over years by this non-destructive tool, pavement distress manuals are still based on visual inspections, so that only the effects and not the causes of faults are generally taken into account. In this framework, the use of simulation can represent an effective solution for supporting engineers and decision-makers in understanding the deep responses of both revealed and unrevealed damages. In this study, the potential of using finite-difference time-domain simulation of the ground-penetrating radar signal is analyzed by simulating several types of flexible pavement at different center frequencies of investigation typically used for road surveys. For these purposes, the numerical simulator GprMax2D, implementing the finite-difference time-domain method, was used, proving to be a highly effective tool for detecting road faults. In more details, comparisons with simplified undisturbed modelled pavement sections were carried out showing promising agreements with theoretical expectations, and good chances for detecting the shape of damages are demonstrated. Therefore, electromagnetic modelling has proved to represent a valuable support system in diagnosing the causes of damages, even for early or unrevealed faults. Further perspectives of this research will be focused on the modelling of more complex scenarios capable to represent more accurately the real boundary conditions of road cross-sections. Acknowledgements - This work has benefited from networking activities carried out within the EU funded COST Action TU1208 “Civil Engineering Applications of Ground Penetrating Radar”

Antennas for GPR Systems

Antennas are a critical hardware component of a radar system, dictating its performance in terms of capability to detect targets. In this Chapter, a wide review on Ground-Penetrating Radar (GPR) antennas is given. Firstly, the general characteristics of GPR antennas are resumed and the requirements they have to satisfy are listed: these are somehow unique and very different than in conventional radar antennas, since GPR antennas operate in a strongly demanding environment, in close proximity to or at a limited distance from the natural or manmade investigated area. Subsequently, an overview on the most frequently used GPR antennas, for both pulsed and stepped-frequency radar systems, is provided; recent studies concerning innovative solutions are presented and information on antenna arrays for GPR applications is included, as well. The Chapter continues with a census of commercial antennas of a number of GPR manufacturers, where the centre frequencies and general characteristics of the antennas available on the market are schematically organised in tables. Aided by measurements and powerful computer modelling techniques, GPR antenna designers are increasingly able to predict and understand the performance of proposed design in realistic electromagnetic environments: the Chapter includes two sections reviewing techniques for the experimental characterisation and numerical modelling of GPR antennas. Finally, conclusions are drawn and research perspectives in the field of GPR antennas are discussed

FDTD simulation of the GPR signal for effective inspection of pavement damages

Ground-penetrating radar (GPR) is a wide ranging non-destructive tool used in many fields of application including effective pavement engineering surveys. Despite the high potential and the consolidated results obtained over the past decades, pavement distress manuals based on visual inspections are still widely used, so that only the effects and not the causes of faults are generally considered. In such context, simulation can represent an effective solution for supporting engineers and decision-makers in understanding the deep responses of both revealed and unrevealed damages. In this study, the use of FDTD simulation of the GPR signal is analyzed by simulating three different types of flexible pavement at two different center frequencies of investigation commonly used for road surveys. Comparisons with the undisturbed modelled pavement sections are carried out showing promising agreements with theoretical expectations, and good chances for detecting the shape of damages are demonstrated

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020