Douglas J. Brown

Advanced sensing, degradation detection, diagnostic and prognostic capabilities for structural health management

This paper presents a micro-sized Linear Polarization Resistance (μLPR) corrosion sensor for Structural Health Management (SHM) applications. The μLPR sensor is based on conventional macro-sized Linear Polarization Resistance (LPR) sensors with the additional benefit of a reduced form factor making it a viable and economical candidate for remote corrosion monitoring of high value structures, such as buildings, bridges, or aircraft. An experiment was conducted with eight μLPR sensors and four test coupons to validate the performance of the sensor. The results demonstrate the effectiveness of the sensor as an efficient means to measure corrosion. The paper concludes with a brief description of a typical application where the μLPR is used in a bridge cable.

Corrosion Detection on Buried Transmission Pipelines with Micro-Linear Polarization Resistance Sensors

This paper presents an experiment adapting linear polarization resistance-based corrosion sensors, originally developed for aerospace applications, to measure the corrosion rate of API 5L ERW grade-B steel natural gas line pipe using micro-sized linear polarization resistance (µLPR) sensors made from the same alloy and grade steel. Sensors were installed under a 15 mil coating of fusion-bonded epoxy, at various proximities to a 1/8 inch defect introduced at a weld joint and along the pipe seam. After sensor installation the pipe was buried in an controlled environment with soil amended to a pH of five. This environment was held at a temperature above 35 °C while soil moisture content was modulated between wet and dry cycles, each lasting 7 days. LPR and environmental measurements were sampled at 5 min intervals. Post processing was performed to convert the LPR measurements to a surface-loss. Comparisons made in the data showed API 5L ERW grade-B steel natural gas pipelines were highly susceptible to corrosion along the seam, with all sensors showing activity in this region early in the experiment. Sensors adjacent to a weld joint began to display evidence of corrosion more slowly. These results verify the ability of µLPR sensors to measure corrosion activity under protective coatings in underground environments.

Optimizing ITO for incorporation into multilayer thin film stacks for visible and NIR applications

Indium Tin Oxide, ITO, is the industry standard for transparent conductive coatings. As such, the common metrics for characterizing ITO performance are its transmission and conductivity/resistivity (or sheet resistance). In spite of its recurrent use in a broad range of technological applications, the performance of ITO itself is highly variable, depending on the method of deposition and chamber conditions, and a single well defined set of properties does not exist. This poses particular challenges for the incorporation of ITO in complex optical multilayer stacks while trying to maintain electronic performance. Complicating matters further, ITO suffers increased absorption losses in the NIR – making the ability to incorporate ITO into anti-reflective stacks crucial to optimizing overall optical performance when ITO is used in real world applications. In this work, we discuss the use of ITO in multilayer thin film stacks for applications from the visible to the NIR. In the NIR, we discuss methods to analyze and fine tune the film properties to account for, and minimize, losses due to absorption and to optimize the overall transmission of the multilayer stacks. The ability to obtain high transmission while maintaining good electrical properties, specifically low resistivity, is demonstrated. Trade-offs between transmission and conductivity with variation of process parameters are discussed in light of optimizing the performance of the final optical stack and not just with consideration to the ITO film itself.