This research investigates a passive wireless antenna sensor designed for strain and crack sensing. When the antenna experiences deformation, antenna shape changes, causing shift in electromagnetic resonance frequency of the antenna. A radio frequency identification (RFID) chip is adopted for antenna signal modulation, so that a wireless reader can easily distinguish backscattered sensor signal from unwanted environmental reflections. The RFID chip captures its operating power from interrogation electromagnetic wave emitted by the reader, which allows the antenna sensor to be passive (battery-free). This paper first reports the latest simulation results on radiation patterns, surface current density, and electromagnetic field distribution. The simulation results are followed with experimental results on the strain and crack sensing performance of the antenna sensor. Tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20 με, and can perform well at large strains higher than 10,000 με. With a high-gain reader antenna, the wireless interrogation distance can be increased up to 2.1 m. Furthermore, an array of antenna sensors is capable of measuring strain distribution in close proximity. During emulated crack and fatigue crack 2 tests, the antenna sensor is able to detect the growth of a small crack.
This paper describes a new approach using mobile sensor networks for structural health monitoring. Compared with static sensors, mobile sensor networks offer flexible system architectures with adaptive spatial resolutions. The paper first describes the design of a mobile sensing node that is capable of maneuvering on structures built with ferromagnetic materials. The mobile sensing node can also attach/detach an accelerometer onto/from the structural surface. The performance of the prototype mobile sensor network has been validated through laboratory experiments. Two mobile sensing nodes are adopted for navigating on a steel portal frame and providing dense acceleration measurements. Transmissibility function analysis is conducted to identify structural damage using data collected by the mobile sensing nodes. This preliminary work is expected to spawn transformative changes in the use of mobile sensors for future structural health monitoring.
An RFID-based folded patch antenna has been developed as a novel passive wireless sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 meters of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around -760 Hz/με, which is equivalent to a normalized strain sensitivity of -0.74 ppm/με. In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced "smart skin" antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics-electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model. Index Terms-Folded patch antenna, RFID sensor, structural health monitoring, smart skin, dielectric constant change, antenna sensor, wireless sensor, strain sensing.
In this paper and its sequel we report the results of Molecular Dynamics simulation of single component and binary gas mixtures in a porous medium with interconnected pores. The porous medium used in the study is a model pillared clay. In the present paper we study adsorption of binary gas mixtures, and investigate in detail the effect of various factors, such as the morphology of the pore space and the adsorbent-adsorbate interactions. A new mean-field statistical mechanical theory of adsorption is developed, and shown to provide very accurate predictions for the simulation results over wide ranges of the pressure, temperature and porosity of the system.
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