Investigation of electrically isolated capacitive sensing skins on concrete to reduce structure/sensor capacitive coupling

Abstract

Damage to bridges can result in partial or complete structural failures, with fatal consequences. Cracks develop in concrete infrastructure from fatigue loading, vibrations, corrosion, or unforeseen structural displacement. Effective long-term monitoring of civil infrastructure can reduce the risk of structural failures and potentially reduce the cost and frequency of inspections. However, deploying structural health monitoring (SHM) technologies for crack detection on bridges is expensive, especially long-term, due to the density of sensors required to detect, localize, and quantify cracks. Previous research on soft elastomeric capacitors (SEC) has shown their viability for low-cost monitoring of cracks in transportation infrastructure. However, when deployed on concrete for strain monitoring, a structure/sensor capacitive coupling exists that may cause a significant amplification in the signal collected from the SEC sensor. This work provides a detailed experimental study of electrically isolating capacitive sensing skins for concrete structures to reduce the structure/sensor capacitive coupling of an electrically grounded sensor. The study illustrates that the use of rubber isolators effectively decreases the capacitive coupling between concrete, which inherently has capacitive properties, and sensors such as the SEC that utilize capacitance measurements. In addition, the required thickness of isolation for accurate strain monitoring using the SEC with geometry described in the paper is investigated and better strain correlation is observed between the rubber of isolation thickness 0.30 mm and 0.64 mm with rubber of isolation of approximately 0.40 mm having the best response. Tests were conducted on small-scale concrete beams, and results were validated on full-scale reinforced concrete bridge decks recently taken out of service. This study demonstrates that with proper isolation material, the SEC can accurately transduce strain from concrete within a 10 µε error for strain levels beyond 25 µε.

Soft elastomeric capacitors with an extended polymer matrix for strain sensing on concrete

“…Therefore, the strain measured by the SEC is overestimated compared to the actual strain in the concrete specimen; as discussed in detail in reference. 12 The strain on the SEC's surface bonded to the concrete was examined using digital image correlation for one sensor. The concrete specimen was loaded using the described cyclic loading method as part of the DIC investigation utilizing the experimental setup indicated in Figure 3(c).…”

“…The investigations by Ogunniyi et. al., 12 showed the need for electrical isolation of the concrete/sensor interface to prevent capacitive coupling between the SEC and the concrete; which leads to a capacitive signal that overestimates strain data. This is because concrete has innate capacitive properties while the SEC relies on capacitance measurements.…”

Performance evaluation of flexible capacitive sensors on non-uniform surfaces

“…Furthermore, the durability of the cSEC under various weather conditions has been established, 10 highlighting its suitability for long-term, cost-effective monitoring of medium-scale structures. A diagram of a cSEC used in this work is shown in Figure 1 A significant challenge in monitoring concrete using SECs is capacitive coupling between the SEC and the concrete, as detailed by Ogunniyi et al 8 For an SEC, capacitive coupling between a concrete structure and the SEC amplifies the measured capacitive signal for a given experienced strain. However, this amplification in signal and any significant structure/sensor capacitive coupling is not present when using the cSEC.…”

“…6 Their flexibility confers adaptability to monitor non-uniform surfaces. 7 However, previous evaluations have been constrained to smooth planer surfaces 8,9 or smooth surfaces with a single geometric change such as the motioning of welded flanged connections. The catalog of past investigations leaves a critical gap in our understanding of their performance on the more commonly encountered, irregular surface finishing of concrete structures.…”

A soft tactile sensing array with high sensitivity based on MWCNTs-PDMS composite of hierarchically porous structure

“…In general, the sensing mechanisms of pressure sensor can be classified into four typical categories: piezoelectricity [7][8][9], piezo-resistance [10][11][12], optics [13][14][15] and capacitance [16][17][18]. Among these mechanisms, extensive researches on capacitive implementation have been widely carried out due to its fast response time, considerable stability, durability and economic efficiency.…”