Microwave Interferometry Measurements for Railway-Specific Applications

Abstract

Abstract. The microwave interferometry is a rather new measurement method, whose functioning principle allows the non-contact synchronous acquisition of structural displacements for several points along a structure, with accuracy in sub-millimetre range at a sampling rate of up to 4 kHz. Due to the high sampling rate, the acquisition of dynamic responses is also possible. Hence, main modal structural parameters such as natural frequencies and damping ratios can be straightforwardly identified. Furthermore, the synchronous measurement of several points along the targeted object, achieved due to a range resolution of about 0.75 m, may allow the direct determination of modal shapes. Under consideration of its novel character and a lack of previous experience with respect to railway-specific tasks, the measurement method had to be subjected to a systematic and comprehensive validation process prior to a reliable implementation in everyday practice. The validation process included several parallel measurements and comparisons with conventional measurement techniques. Besides the direct verification of the quality of the results, it was used as well for defining boundary conditions and limitations of the measurement method with respect to railway-specific applications. As a result, an evaluation matrix was created, which illustrates the applicability of the microwave interferometry for different types of structures. This paper gives a brief introduction of the microwave interferometry and presents some aspects and selected results of the validation process, which was performed within a cooperation project between the TU Darmstadt (Germany) and the German Railways (Deutsche Bahn AG).

Contactless Deformation Monitoring of Bridges with Spatio-Temporal Resolution: Profile Scanning and Microwave Interferometry

“…For the application of microwave interferometry, good overviews are given by Gentile and Bernardini [ 12 ], Bernardini et al [ 13 ], Rödelsperger et al [ 24 ]. Microwave interferometry has also been applied to various types of structures in recent years: bridges [ 8 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ], wind power plants [ 21 ], telecommunication towers [ 32 , 33 ], chimneys [ 24 ] or urban buildings [ 34 , 35 , 36 ]. Publications dealing with the performance evaluation through comparisons with conventional sensors are, for example, [ 8 , 35 , 37 , 38 ].…”

“…Microwave interferometry has also been applied to various types of structures in recent years: bridges [ 8 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ], wind power plants [ 21 ], telecommunication towers [ 32 , 33 ], chimneys [ 24 ] or urban buildings [ 34 , 35 , 36 ]. Publications dealing with the performance evaluation through comparisons with conventional sensors are, for example, [ 8 , 35 , 37 , 38 ]. In summary, microwave interferometry shows excellent performance in determining the natural frequencies of the structures under investigation, while the derivation of absolute displacements often shows large systematic errors even though additional reflectors were attached to the structures in almost all studies.…”

“…However, the direct measurement of absolute displacements using classical LVDTs is usually very complex or even impossible due to the lack of fixed reference points [ 3 ]. In order to fill this gap, remarkable advances in the field of contactless displacement measurement methods have been made in recent years [ 7 , 8 ]. They allow the measurement of structural displacements without the need for installing any sensors on the structure.…”

“…Moreover, the extension of the investigation to a railway bridge in operation provides indications of further limitations in the application that clearly go beyond the results of the conceptual comparison. For example, systematic errors of microwave interferometry with respect to the derivation of absolute displacement values, which has already been discussed in the literature [ 8 ], cannot only be quantified but also corrected by using both systems simultaneously.…”

Advancing Ground-Based Radar Processing for Bridge Infrastructure Monitoring

“…The precision is evaluated in laboratory environments [ 3 , 28 ]. Additionally, comparisons to other sensors such as accelerometers [ 15 ], terrestrial laser scanners [ 29 ], and displacement transducers [ 30 ] are performed.…”