Coplanar capacitance sensors for detecting water intrusion in composite structures

Abstract

Composite materials are becoming more affordable and widely used for retrofitting, rehabilitating and repairing reinforced concrete structures designed and constructed under older specifications. However, the mechanical properties and long-term durability of composite materials may degrade severely in the presence of water intrusion. This study presents a new non-destructive evaluation (NDE) technique for detecting the water intrusion in composite structures by evaluating the dielectric properties of different composite system constituent materials. The variation in the dielectric signatures was employed to design a coplanar capacitance sensor with high sensitivity to detect such defects. An analytical model was used to study the effect of the sensor geometry on the output signal and to optimize sensor design. A finite element model was developed to validate analytical results and to evaluate other sensor design-related parameters. Experimental testing of a concrete specimen wrapped with composite laminate and containing a series of pre-induced water intrusion defects was conducted in order to validate the concept of the new technique. Experimental data showed excellent agreement with the finite element model predictions and confirmed sensor performance.

Optimization of the coplanar interdigital capacitive sensor

“…For imaging applications, the effect of sensor geometry on sensor performance is analyzed and the optimum balance of penetration depth and signal strength is proposed. In [10], a coplanar capacitive sensor is developed for detecting water intrusion into composite structures. A Maxwell 2D model is utilized to study the relationship between the capacitance across the sensors and the geometrical parameters of the sensors.…”

Parallel double-plate capacitive proximity sensor modelling based on effective theory

“…In civil engineering field, T. Bore et al 9 have used the capacitive probe based on fringe effect principle to detect the both voids and white paste in ducts of bridges without having to open them and achieve good performance. Amr A Nassr et al 10 have designed a capacitive proximity sensor to detect the water intrusion in composite structures by evaluating the dielectric properties of different composite system constituent materials, a This research was performed while Nan Li was at Research Center for Non-destructive Testing and Evaluation, Beijing, 100124. b Electronic mail: nan.li@bjut.edu.cn 2158-3226/2014/4(2)/027119/9 C Author(s) 2014 4, 027119-1 and in his another paper, 11 a capacitive proximity sensors to detect air voids, water intrusion, and glue infiltration damages in fiber-reinforced polymers-strengthened concrete structures has been introduced. For simplest proximity sensor structure, Morgan 12 has presented an analytical model of the basic SAW (Surface acoustic wave) transducers, and later, Engan, 13 Datta and Hunsinger 14 have calculated the admittance of the basic SAW (Surface acoustic wave) transducers, and these models are available for capacitive proximity sensor structures, However, these mathematical models and analytical equations is also too complicate to be applied for sensor design directly.…”

Positive and negative variations in capacitive images for given defects under varying experimental conditions

“…In previous work, the feasibility of the CI technique on various materials and structures, e.g., concrete [3,4] composite [5][6][7][8][9], Corrosion under Insulation (CUI) [10,11], and adhesive layer [12] has been demonstrated. Normally, a decreased overall permittivity (e.g., presence of air void in glass fiber composite) within the volume of influence of the CI probe at a given scanning position will result in a decreased capacitance value and produce a "darker point" in the capacitive image.…”