A major challenge impeding the deployment of wireless sensor networks for structural health monitoring (SHM) is developing a means to supply power to the sensor nodes in an efficient manner. In this paper, we explore possible solutions to this challenge by using a mobile-host based wireless energy transmission system to provide both power and data interrogation commands to sensor nodes. The mobile host features the capability of wirelessly transmitting energy to sensor nodes on an as-needed basis. In addition, it serves as a central data repository and processing center for the data collected from the sensing network. The wirelessly transmitted microwave energy is captured by a receiving antenna, transformed into DC power by a rectifying circuit, and stored in a storage medium to provide the required energy to the sensor node. The application of wireless energy transmission is targeted toward SHM sensor nodes that have been recently developed by the authors, which can be used to collect peak mechanical displacements or piezoelectric impedance measurements. This paper will describe considerations needed to design such energy transmission systems, experimental procedure and results, method of increasing the efficiency, energy conditioning circuits and storage medium, and target applications. Experimental results from a field test on the Alamosa Canyon Bridge in southern New Mexico will also be presented.

A field demonstration of a new and hybrid wireless sensing network paradigm for structural health monitoring (SHM) is presented. In this paradigm, both power and data interrogation commands are conveyed via a mobile agent that is sent to each sensor node to perform individual interrogations, which can alleviate several limitations of traditional sensing networks. This paper will discuss such prototype systems, which will be used to interrogate capacitive-based and impedance-based sensors for SHM applications. The capacitive-based wireless sensor node is specifically built to collect peak displacement measurements. In addition, a wireless sensor node for collecting electromechanical impedance data has also been developed. Both sensor nodes are specifically designed to accept various power sources and to be wirelessly triggered on an as-needed basis so that they can be used for the hybrid sensing network approach. The capabilities of these miniaturized and portable devices are demonstrated in the laboratory and the field, which was performed at the Alamosa Canyon Bridge in southern New Mexico.

This paper presents recent developments in an extremely compact, wireless impedance sensor node for use in structural health monitoring (SHM). The sensor node uses a low-cost integrated circuit that can measure and record the electric impedance of a piezoelectric active-sensor. The sensor node also integrates several components, including a microcontroller for local computing, telemetry for wireless data transmission, multiplexers for managing up to seven piezoelectric transducers per node, energy storage mediums, and several triggering options including a wireless triggering circuit into one package to truly realize a comprehensive, self-contained wireless active-sensor node for SHM applications. It is estimated that this sensor node requires less than 75 mW of total power to operate measurement, computation and data transmission. In addition, the sensor node can also be used for the active-sensor self-diagnostic process that can monitor the operational condition of piezoelectric transducers used in SHM applications. The performance of this miniaturized and portable device is compared to our previous results and its broader capabilities are demonstrated.

This paper presents a signal processing tool that efficiently performs piezoelectric (PZT) sensor diagnostic and validation. Validation of the sensor/actuator functionality during structural health monitoring (SHM) operation is a critical component to successfully implement a complete and robust SHM system, especially with an array of PZT active-sensors involved. The basis of this method is to track the capacitive value of PZT transducers, which manifests in the imaginary part of the measured electrical admittance. Both degradation of the mechanical/electrical properties of a PZT transducer and the bonding defects between a PZT patch and a host structure can be identified by the proposed process. However, it is found that the temperature variations in sensor boundary conditions manifest themselves in similar ways in the measured electrical admittances. Therefore, we examine the effects of temperature variation on the sensor diagnostic process and develop an efficient signal processing tool that enables the identification of a sensor validation feature that can be obtained instantaneously without relying on prestored baselines. This paper concludes with experimental results to demonstrate the effectiveness of the proposed technique.

This paper describes the development of the next generation of an extremely compact, wireless impedance sensor node for use in structural health monitoring (SHM) and piezoelectric active-sensor self-diagnostics. The sensor node uses a recently developed, low-cost integrated circuit that can measure and record the electrical impedance of a piezoelectric transducer. The sensor node also integrates several components, including a microcontroller for local computing, telemetry for wirelessly transmitting data, multiplexers for managing up to seven piezoelectric transducers per node, energy harvesting and storage mediums, and a wireless triggering circuit into one package to truly realize a comprehensive, self-contained wireless active-sensor node for various SHM applications. It is estimated that the developed sensor node requires less than 60 mW of total power for measurement, computation, and transmission. In addition, the sensor node is equipped with active-sensor self-diagnostic capabilities that can monitor the condition of piezoelectric transducers used in SHM applications. The performance of this miniaturized device is compared to our previous results and its broader capabilities are demonstrated.

Sensor networking is an important first-line component in any structural health monitoring (SHM) application. We present how an interdisciplinary team of structural, mechanical, electrical, and computer engineers are tackling a large-scale civil infrastructure SHM application by proposing a new variant on sensor networking. Most sensor arrays are typically interrogated via conventional wired networks, which require centralized processing and powering. Conversely, recent technology advances in embedded architectures and power harvesting have allowed! wireless networks to be developed, where each individual sensor is individually powered and communicates with neighboring sensors or substations via hopping, protocols. This work will present a hybrid approach to sensor array interrogation,, where both power and data interrogation commands are conveyed via an autonomous: aerial vehicle that is sent (via remote piloting or GPS autopilot programming) to each sensor or node to perform the individual interrogation. Power does not have to reside at the sensor node, relaxing battery or other such powering requirements. This work will discuss such a prototype system, which will be used to interrogate impedance-based and capacitive-based preload sensors on a full-scale bridge.

Structural Health Monitoring (SHM) promises to deliver great benefits to many industries. Primarily among them is a potential for large cost savings in maintenance of complex structures such as aircraft and civil infrastructure. However, several large obstacles remain before widespread use on structures can be accomplished. The development of three components would address many of these obstacles: a robust sensor validation procedure, a low-cost active-sensing hardware and an integrated software package for transition to field deployment. The research performed in this thesis directly addresses these three needs and facilitates the adoption of SHM on a larger scale, particularly in the realm of SHM based on piezoelectric (PZT) materials. The first obstacle addressed in this thesis is the validation of the SHM sensor network. PZT materials are used for sensor/actuators because of their unique properties, but their functionality also needs to be validated for meaningful measurements to be recorded. To allow for a robust sensor validation algorithm, the effect of temperature change on sensor diagnostics and the effect of sensor failure on SHM measurements were classified. This classification allowed for the development of a sensor diagnostic algorithm that is temperature invariant and can indicate the amount and type of sensor failure. Secondly, the absence of a suitable commercially-available active-sensing measurement node is addressed in this thesis. A node is a small compact measurement device used in a complete system. Many measurement nodes exist for conventional passive sensing, which does not actively excite the structure, but there are no measurement nodes available that both meet the active-sensing requirements and are useable outside the laboratory. This thesis develops hardware that is low-power, active-sensing and field-deployable. This node uses the impedance method for SHM measurements, and can run the sensor diagnostic algorithm also developed here. Finally, the need for an integrated system for SHM is of primary consideration in this thesis. Without such a system the widespread adoption of SHM will not take place, and this thesis addresses the issue by developing an integrated SHM solution. The solution incorporates active-sensing impedance-measurement based hardware and software with a combination of existing damage-detection algorithms. The result is an integrated system for in-field measurement, validation and analysis of structures. The system specifically incorporates the sensor validation procedure and sensor node also developed in this thesis. In conclusion, recommendations for the future direction of this research topic are made.

This paper presents a piezoelectric sensor diagnostic and validation procedure that performs in-situ monitoring of the operational status of piezoelectric (PZT) sensor/actuator arrays used in structural health monitoring (SHM) applications. The validation of the proper function of a sensor/actuator array during operation, is a critical component to a complete and robust SHM system, especially with the large number of active sensors typically involved. The method of this technique used to obtain the health of the PZT transducers is to track their capacitive value, this value manifests in the imaginary part of measured electrical admittance. Degradation of the mechanical/electrical properties of a PZT sensor/actuator as well as bonding defects between a PZT patch and a host structure can be identified with the proposed procedure. However, it was found that temperature variations and changes in sensor boundary conditions manifest themselves in similar ways in the measured electrical admittances. Therefore, we examined the effects of temperature variation and sensor boundary conditions on the sensor diagnostic process. The objective of this study is to quantify and classify several key characteristics of temperature change and to develop efficient signal processing techniques to account for those variations in the sensor diagnosis process. In addition, we developed hardware capable of making the necessary measurements to perform the sensor diagnostics and to make impedance-based SHM measurements. The paper concludes with experimental results to demonstrate the effectiveness of the proposed technique.

Damage assessment is often done through correlating changes in a system's modal properties. In this research, the modal space is expanded through adding known virtual changes to the system dynamics at discrete points. This is the control feedback process is similar in principle to the Perturbed Boundary Condition methods that were proposed in the previous decade but more expansive through choice of controller parameters. By assembling these perturbed systems in concert with the baseline model the system space is expanded and changes in modal properties can be more readily observed. From these changes, inferences about physical alterations of the system can be deduced. Specifically, this project will assess the degree to which the technique proposed in (3) is applicable to a real structure, with the ultimate goal of identifying the location and level of structural change to a cantilever beam. NOMENCLATURE a C Controller acceleration influence matrix v C Controller velocity influence matrix d C Controller displacement influence matrix n Number of natural frequencies r Number of damage variables m Number of controller gains