Optimising a modified free-space permittivity characterisation method for civil engineering applications

Muller, Wayne; Scheuermann, Alexander

doi:10.1088/1742-2132/13/2/s9

Cited by 5 publications

(5 citation statements)

References 16 publications

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“…Because of limitations with existing methods, an alternative characterization approach using a modified free-space (MFS) technique was previously investigated (31), validated (34), and further optimized (35). The approach involves measuring the magnitude and phase of sinusoidal electromagnetic signals passing between a fixed pair of antennas conducted initially without-and then later with-a sample of known thickness placed in between.…”

Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

“…Because the antennas limit the operational bandwidth of both devices, the MFS measurements occur over the same frequency range as the NM-GPR. Sample edges, thickness, aspect ratio, antenna spacing and other aspects can also influence the results and have previously been investigated and optimized (34,35). The antennas are vertically aligned to measure through a boxed material sample.…”

Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

“…To remove the influence of the floor of the sample box, the initial reference measurement is collected through a ply sheet, representing the base of the box. A ply sheet is used instead of an empty box to avoid reflections from the sides of the box (35). Figure 1 illustrates the antenna arrangement during ply sheet calibration and sample measurement and also shows an image of the VNA connected to the antennas during measurement of a boxed material sample.…”

Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

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Permittivity Characterization of Unbound Granular Pavement Materials with a Modified Free-Space Approach

Muller

2016

Transportation Research Record: Journal of the Transportation R

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Moisture has a considerable influence on the structural performance of unbound granular (UBG) pavements. Multioffset ground-penetrating radar has the potential to quantify moisture within these materials by measuring the permittivity of pavement layers. To enable moisture estimates from these field measurements, relationships between permittivity and volumetric moisture are required. This paper describes the use of a modified free-space (MFS) laboratory approach to measure the permittivity of compacted UBG material samples and to develop these relationships. Material samples were compacted within form ply boxes; various density and moisture conditions were targeted. A vector network analyzer was used to measure the phase shift between a fixed pair of ground-coupled dipole antennas as a result of sample insertion and an initial ply sheet reference measurement. Frequency-dependent permittivity values for the samples were then determined over the range of 1.0 to 2.0 GHz on the basis of these measurements. Mean values over this range were then related to the volumetric moisture content of the samples. An indicative moisture–permittivity relationship was proposed on the basis of MFS measurements of samples from several quarries. Overall, the permittivity results from the MFS approach showed reasonably good agreement for samples at higher moisture contents compared with relationships in the literature that are based on time domain reflectometry. However, for drier samples, the MFS permittivity values were higher than the literature predictions. Possible reasons for these differences are discussed, and an overview of the advantages and limitations of using the technique for characterizing UBG materials is given.

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Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

Section: Methodology Modified Free-space Approachmentioning

confidence: 99%

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Permittivity Characterization of Unbound Granular Pavement Materials with a Modified Free-Space Approach

Muller

2016

Transportation Research Record: Journal of the Transportation R

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“…Ideally frequency-dependent measurements of pavement permittivity would be used, to better account for the varying influence of water at different frequencies. A suitable frequency-dependent permittivity measurement approach was identified from agricultural applications [45]. The approach involves measuring the relative phase-shift and signal attenuation due to the insertion of a dielectric sample of known thickness between two antennas.…”

Section: Moisture-permittivity Relationsmentioning

confidence: 99%

“…Prior to equipment completion, semi-automated implementations of conventional [42] and two selfcorrecting geophysical methods [43] were investigated using numerical simulations. A modified free-space (MFS) permittivity characterisation approach was also developed to calibrate petro-physical relations for UBG pavement materials to enable field moisture predictions [42,[44][45][46]. In this paper an improved semi-automated analysis method is The second half was constructed in three layers -base, upper sub-base and lower sub-base.…”

Section: Introductionmentioning

confidence: 99%

Characterising moisture within unbound granular pavements using multi-offset Ground Penetrating Radar

Muller¹

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Moisture has a significant influence on the performance and durability of unbound granular (UBG) pavements with thin bituminous surfacings, which form the vast majority of all-weather Australian roads. Techniques for measuring pavement moisture content are therefore important to quantify its influence on structural performance, enable early detection of problem areas, and to assess the condition of flood-affected pavements.Conventional techniques, however, require invasive probes or physical sampling which are impractical for large-scale investigations. Ground Penetrating Radar (GPR) techniques show promise, yet existing methods achieve only qualitative estimates, involve simplifications that limit accuracy or require complicated or laborious data analysis. The aim of this research was to develop a semi-automated approach using multi-offset GPR to quantitatively estimate the moisture content and depth of UBG pavement layers while maintaining data analysis simplicity.The research made use of a new type of 3-dimensional (3D) GPR technology able to continuously collect ground-coupled multi-offset gathers across the road while travelling at up to traffic speeds. To enable development of analysis methods prior to equipment completion, numerical simulations were used to model the expected response for typical pavement configurations. These data were used to test a semi-automated approach using interface tracking and conventional multi-offset geophysical analysis methods.They were also used to develop two novel self-correcting analysis techniques, Interface Matching (IM) and Ray-path Modelling (RM), which use migration and tomographic approaches, respectively.A permittivity characterisation approach, later called modified free-space (MFS), was also adapted for laboratory characterisation of UBG materials. It was used to calibrate petro-physical relations for these materials that enable pavement moisture estimates from the GPR measurements. As the MFS approach departs from conventional freespace methods, numerical modelling and a series of laboratory experiments were used to assess measurement accuracy and to determine the influence of sample edges, aspect ratio, and depth and antenna separation on the measurements. These investigations demonstrated that the MFS approach was suitable using the proposed equipment, sample sizes and for the range of relative permittivity values likely to be encountered. It also produced results that compared well with established apparatus over the frequency range relevant to pavement GPR.iii Measurements using this approach were also compared with conventional time-domain reflectometry (TDR) and common-offset GPR measurements of moisture-varying and density-varying UBG samples. The comparison showed similar results for most samples, although TDR reported lower relative permittivity values for drier and lowerdensity materials.Upon completion of the 3D GPR equipment, a revised analysis approach called Raypath Modelling-Semblance (RM-S) was developed. It was used to analyse multi-off...

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Semi-automatic determination of layer depth, permittivity and moisture content for unbound granular pavements using multi-offset 3-D GPR

Muller

2018

International Journal of Pavement Engineering

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Optimising a modified free-space permittivity characterisation method for civil engineering applications

Cited by 5 publications

References 16 publications

Permittivity Characterization of Unbound Granular Pavement Materials with a Modified Free-Space Approach

Permittivity Characterization of Unbound Granular Pavement Materials with a Modified Free-Space Approach

Characterising moisture within unbound granular pavements using multi-offset Ground Penetrating Radar

Semi-automatic determination of layer depth, permittivity and moisture content for unbound granular pavements using multi-offset 3-D GPR

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