Health monitoring of pavement systems using smart sensing technologies

Pavement undergoes a process of deterioration resulting from repeated traffic and/or environmental loading. By detecting pavement distress and damage early enough, it is possible for transportation agencies to develop more effective pavement maintenance and rehabilitation programs and thereby produce significant cost and time saving. Structural Health Monitoring (SHM) has been conceived as a systematic method for assessing the structural state of pavement infrastructure systems and documenting their condition. Over the past several years, this process has traditionally been accomplished through the use of wired sensors embedded in bridge and highway pavement. However, the use of wired sensors has limitations for long-term SHM and presents other associated cost and safety concerns. Recently, Micro-Electromechanical Systems (MEMS) and Nano-Electromechanical Systems (NEMS) have emerged as advanced/smart-sensing technologies with potential for cost-effective and long-term SHM. To this effect, a study has thus been initiated to evaluate the off-the-shelf MEMS sensors and wireless sensors, identify their limitations, and demonstrate how the acquired sensor data can be utilized to monitor and assess concrete pavement behavior. The feasibility of implementing a wireless communication system into a MEMS sensor was also investigated. Off-the-shelf MEMS sensors and wireless sensors were deployed in a newly constructed concrete highway pavement. During the monitoring period, the temperature, moisture, and strain profiles were obtained and analyzed. The monitored data captured the effects of daily and seasonal weather changes on concrete pavement, especially, early-age curling and warping behavior of concrete pavement. These sensors, however, presented issues for long-term operation, so to improve performance, a ZigBee protocol-based wireless communication system was implemented for the MEMS sensors. By synthesizing knowledge and experience gained from literature review, field demonstrations, and implementation of wireless systems, issues associated with sensor selection, sensor installation, sensor packaging to prevent damage from road construction, and monitoring for concrete pavement SHM are summarized. The requirements for achieving Smart Pavement SHM are then explored to develop a conceptual design of smart health monitoring of both highway and airport pavement systems for next-generation pavement SHM. A cost evaluation was also performed for traditional as well as MEMS sensors and other potential smart technologies for SHM

Modeling And Development Of A MEMS Device For Pyroelectric Energy Scavenging

As the world faces an energy crisis with depleting fossil fuel reserves, alternate energy sources are being researched ever more seriously. In addition to renewable energy sources, energy recycling and energy scavenging technologies are also gaining importance. Technologies are being developed to scavenge energy from ambient sources such as vibration, radio frequency and low grade waste heat, etc. Waste heat is the most common form of wasted energy and is the greatest potential source of energy scavenging. Pyroelectricity is the property of some materials to change the surface charge distribution with the change in temperature. These materials produce current as temperature varies in them and can be utilized to convert thermal energy to electrical energy. In this work a novel approach to vary temperature in pyroelectric material to convert energy has been investigated. Microelectromechanical Systems or MEMS is the new technology trend that takes advantage of unique physical properties at micro scale to create mechanical systems with electrical interface using available microelectronic fabrication techniques. MEMS can accomplish functionalities that are otherwise impossible or inefficient with macroscale technologies. The energy harvesting device modeled and developed for this work takes full benefit of MEMS technology to cycle temperature in an embedded pyroelectric material to convert thermal energy from low grade waste heat to electrical energy. Use of MEMS enables improved performance and efficiency and overcomes problems plaguing previous attempts at pyroelectric energy conversion. A Numerical model provides accurate prediction of MEMS performance and sets design criteria, while physics based analytical model simplifies design steps. A SPICE model of the MEMS device incorporates electrical conversion and enables electrical interfacing for current extraction and energy storage. Experimental results provide practical implementation steps towards of the modeled device. Under ideal condition the proposed device promises to generate energy density of 400 W/L

MEMS Devices for Circumferential-scanned Optical Coherence Tomography Bio-imaging

Ph.DDOCTOR OF PHILOSOPH

Cascaded "Triple-Bent-Beam" MEMS Sensor for Contactless Temperature Measurements in Nonaccessible Environments

International audienceA microelectromechanical systems (MEMS) temperature sensor based on a cascade three-stage "bent-beam" structure is described in this paper. A suspended structure mechanically deforms in response to the change in ambient temperature, and then, a displacement is obtained; the structure is composed of three cascaded systems in order to enhance sensor sensitivity. The final conversion is made to an electrical signal that is obtained by using an interdigitated capacitor having one electrode fixed to the substrate and one electrode embedded into the moving tip of the MEMS sensor. The device has been conceived to operate passively in harsh environments where high temperatures could harm active electronic devices. The readout of the unknown temperature is therefore remotely performed by coupling the variable MEMS capacitor to a fixed inductor to compose a resonant LC circuit, which ismagnetically coupled to a reader circuit placed outside the environment where the measurement takes place. The temperature to be measured is therefore first converted into a displacement that, in turn, induces a change in a capacitor value; a variation in the resonant frequency of an LC circuit is finally observed through the remote readout circuit. This paper focuses on the analytical and numerical modeling of both the temperature-todisplacement and displacement-to-capacitance conversions, on the design and fabrication of an experimental prototype, on the experimental validation where results are extensively presented and commented, and, finally, on the design of the integrated resonant device for contactless measurements