Ground Penetrating Radar (GPR) is an established technology for detecting anomalies beneath the surface of the ground. GPR systems currently in use tend to be hand held or trolley mounted devices that can be moved smoothly over the surface with little or no stand off from the ground and normally have a single transmit/receive antenna pair. However, these properties are quite different from the requirements of a vehicle mounted system such as track width coverage, variable ground clearance and a noisier environment. This paper, based on Countermine research carried out by the UK Defence Science and Technology Laboratory (Dstl), details the development and application of a military, vehicle mounted GPR system. Requirements of a vehicle mounted system are outlined and research towards creating a multi-antenna, vehicle mounted technology demonstrator is discussed. The paper also examines methods of data representation for GPR systems and the advantages that can be gained in this area using a multi-antenna array such as enhanced imagery and three dimensional reconstruction of objects beneath the surface.
There has been considerable discussion in the technical community on a number of questions concerned with smart materials and structures, such as what they are, whether smart materials can be considered a subset of smart structures, whether a smart structure and an intelligent structure are the same thing, etc. This discussion is both fueled and confused by the technical community due to the truly multidisciplinary nature of this new field. Smart materials and structures research involves so many technically diverse fields that it is quite common for one field to completely misunderstand the terminology and state-of-the-art in other fields. In order to ascertain whether a consensus is emerging on a number of these questions, the technical community was surveyed in a number of ways including via the Internet and by direct contact. The purpose of this survey in the final analysis was to better define the smart materials and structures field, its current status and its potential benefits. Results of the survey are presented and discussed.
The concept of the smart structure integrates structural engineering, sensing, control systems and actuation to provide a mechanical assembly which is capable of responding to its environment and/or loading conditions. The realization of the smart structure requires integration of skills in a variety of scientific and engineering disciplines ranging from mechanical engineering through materials science into signal processing, data analysis, sensing and actuation. The sensing technology must have a number of key features of which the ability to take distributed measurements of various parameters throughout the structure is paramount. Fiber optics technology therefore promises to have a significant role to play in the evolution of the smart structures concept. This paper analyses this role in detail, presents an assessment of the current state-of-the art in fiber optic technology related to smart structures and presents a scenario for future developments.
This paper reports on the basic design and preliminary evaluation of an entirely novel cable configuration which enables the detection of water, pH or similar variables as a function of position along the length of an optical fibre. This sensing capability is realised through a combination of Optical Time Domain Reflectometry (OTDR) and a microbend transducer activated by chemically sensitive water swellable polymers (hydrogels). Experiments with a water sensor prototype have demonstrated the detection of wetted sections of less than 25 cm length in cables longer than 100 m and indicate that interrogation of sensors several kilometres long is possible. The present experiments have demonstrated the principal of measurement through the development of a distributed water detector. However the technique can be used to monitor various chemical parameters such as pH or ionic concentration by selecting the appropriate gel as the responsive medium.
We report on preliminary experimental trials aimed at assessing the suitability of a distributed water monitor as a means of determining the presence of grout in reinforced tendon ducts of civil engineering structures. This sensing capability is realized through a combination of Optical Time Domain Reflectometry (OTDR) and chemically sensitive water swellable polymers (hydrogels). This form of sensor cable can detect water as a function of linear position along its length with a spatial resolution of a few centimeters<SUP>1,2</SUP>. The experiments carried out here indicate that this approach has considerable potential as a means of providing quality assurance during the grouting procedure.
Smart Structures and Materials technology will undoubtedly yield a wide range of new materials plus new sensing and actuation technologies and this will have a radical effect on current approaches to structural design. To meet the multi-disciplinary research challenge posed by this technology, the Smart Structures Research Institute (SSRI) has been established at the University of Strathclyde, Glasgow. This paper describes the background, current and planned activities and progress made in developing this new and very promising technology.
It is inevitable that Fibre Optics for data transmission and sensing will play a key role in future control systems for aerospace mobile platforms. It is important that the practical requirements for sensing/instrumentation in aerospace systems are well understood. Displacement sensing is a primary parameter and Wavelength Division Multiplex (WDM) digital optical encoding schemes offer a very attractive design solution.