David Mascarenas

Development of an impedance-based wireless sensor node for structural health monitoring

This paper presents the development and application of a miniaturized impedance sensor node for structural health monitoring (SHM). A large amount of research has been focused on utilizing the impedance method for structural health monitoring. The vast majority of this research, however, has required the use of expensive and bulky impedance analyzers that are not suitable for field deployment. In this study, we developed a wireless impedance sensor node equipped with a low-cost integrated circuit chip that can measure and record the electrical impedance of a piezoelectric transducer, a microcontroller that performs local computing and a wireless telemetry module that transmits the structural information to a base station. The performance of this miniaturized and portable device has been compared to results obtained with a conventional impedance analyzer and its effectiveness has been demonstrated in an experiment to detect loss of preload in a bolted joint. Furthermore, for the first time, we also consider the problem of wireless powering of such SHM sensor nodes, where we use radio-frequency wireless energy transmission to deliver electrical energy to power the sensor node. In this way, the sensor node does not have to rely on an on-board power source, and the required energy can be wirelessly delivered as needed by human or a remotely controlled robotic device.

A mobile-agent-based wireless sensing network for structural monitoring applications

A new wireless sensing network paradigm is presented for structural monitoring applications. In this approach, both power and data interrogation commands are conveyed via a mobile agent that is sent to sensor nodes to perform intended interrogations, which can alleviate several limitations of the traditional sensing networks. Furthermore, the mobile agent provides computational power to make near real-time assessments on the structural conditions. This paper will discuss such prototype systems, which are used to interrogate impedance-based sensors for structural health monitoring applications. Our wireless sensor node is specifically designed to accept various energy sources, including wireless energy transmission, and to be wirelessly triggered on an as-needed basis by the mobile agent or other sensor nodes. The capabilities of this proposed sensing network paradigm are demonstrated in the laboratory and the field.

A miniaturized electromechanical impedance-based node for the wireless interrogation of structural health

This paper presents the development and applications of a miniaturized impedance sensor node for structural health monitoring. The principle behind the impedance-based structural health monitoring technique is to apply high frequency structural excitations (typically higher than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Although many proof-of-concept experiments have been performed using the impedance methods, the impedance-measuring device is bulky and impractical for field-use. Therefore, a recently developed, miniaturized, low-cost impedance measurement chip was used to measure and record the electric impedance of a piezoelectric transducer. The performance of this miniaturized and portable device has been compared to our previous results and its effectiveness has been demonstrated in detecting bolt preload changes in a bolted frame structure. Furthermore, the possibility of wireless communication and local signal processing at the sensor node has been investigated by integrating the device with a microprocessor and telemetry.

A low-power wireless sensing device for remote inspection of bolted joints

Abstract A new bolted-joint monitoring system is presented. This system consists of structural joint members equipped with piezoelectric (PZT) sensing elements and a wireless impedance device for data acquisition and communication. PZT enhanced washers are used to continuously monitor the condition of the joint by monitoring its dynamic characteristics. The mechanical impedance matching between the PZT enhanced devices and the joint connections is used as a key feature to monitor the preload changes and to prevent further failure. The dynamic response is readily measured using the electromechanical coupling property of the PZT patch, in which its electrical impedance is directly coupled with the mechanical impedance of the structure. A new miniaturized and portable impedance measuring device is implemented for the practical implementation of the proposed method. The proposed system can be used for the remote and rapid inspection of bolt tension and connection damage. Both theoretical modelling and experimental verification are presented to demonstrate the effectiveness of the proposed concept.

Wireless impedance device for electromechanical impedance sensing and low-frequency vibration data acquisition

This paper presents recent developments in an extremely compact, wireless impedance sensor node for combined use with both impedance method and low-frequency vibrational data acquisition. The sensor node, referred to as the WID3 (Wireless Impedance Device) integrates several components, including an impedance chip, 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 into one package to truly realize a self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency A/D and D/A converters so that the same device can measure low-frequency vibration data. The WID3 requires less than 60 mW of power to operate and is designed for the mobile-agent based wireless sensing network. The performance of this miniaturized device is compared to our previous results and its capabilities are demonstrated.

Full-field Structural Dynamics by Video Motion Manipulation

Structures with complex geometries, material properties, and boundary conditions, exhibit spatially local, temporally transient, dynamic behaviors. High spatial and temporal resolution vibration measurements and modeling are thus required for high-fidelity characterization, analysis, and prediction of the structure’s dynamic phenomena. For example, high spatial resolution mode shapes are needed for accurate vibration-based damage localization. Also, higher order vibration modes typically contain local structural features that are essential for highfidelity dynamic modeling of the structure. In addition, while it is possible to build a highlyrefined mathematical model (e.g., a finite element model) of the structure, it needs to be experimentally validated and updated with high-resolution vibration measurements. However, it is a significant challenge to obtain high-resolution vibration measurements using traditional techniques. For example, accelerometers and strain-gauge sensors provide low spatial resolution measurements. Laser vibrometers provide high-resolution measurements, but are expensive and make sequential measurements that are time-consuming. On the other hand, digital video cameras are relatively low-cost, agile, and provide high spatial resolution, simultaneous, measurements. A new framework is first developed for the blind extraction and visualization of the full-field, highresolution, dynamic parameters of an operating (output-only) structure from the digital video measurements using video motion manipulation and unsupervised machine learning techniques. See Fig. 1 for the experimental results of a vibrating cantilever beam and more video demos at http://www.lanl.gov/projects/national-security-educationcenter/engineering/research-projects/blind-modal-id.php.

Energy harvesting and wireless energy transmission for embedded sensor nodes

In this paper, we present experimental investigations using energy harvesting and wireless energy transmission to operate embedded structural health monitoring sensor nodes. The goal of this study is to develop sensing systems that can be permanently embedded within a host structure without the need for an on-board power source. With this approach the required energy will be harvested from the ambient environment, or periodically delivered by a RF energy source to supplement conventional harvesting approaches. This approach combines several transducer types to harvest energy from multiple sources, providing a more robust solution that does not rely on a single energy source. Both piezoelectric and thermoelectric transducers are considered as energy harvesters to extract the ambient energy commonly available on civil structures such as bridges. Methods of increasing the efficiency, energy storage medium, target applications and the integrated use of energy harvesting sources with wireless energy transmission will be discussed.

Online Electro-mechanical Impedance-based Structural Tamper Detection

Tools that provide evidence of whether or not the structure of a container have been tampered with are important for a number of applications. The problem of providing evidence of tamper has many similarities with the structural health monitoring (SHM) problem. As a result, techniques developed by the structural health monitoring community have potential to help address the problem of determining whether or not a structure has been tampered with by an adversary. The difference between SHM and detecting structural tampering is that the former deals with structures damaged by environmental and\or loads effects, while the latter deals with damage intentionally induced in a structure. Detecting structural tampering is complicated by the fact that a determined attacker can adopt a series of measures to recover the status ante quo. The challenge is to find unique features which are irreversibly modified during the attack despite attempts by the attacker to return the structure to its nominal initial condition. Furthermore, these features cannot be overly sensitive to benign environmental changes that cannot be accounted for. The authors explore the use of impedance-based online structure tampering detection technique. The variations of the impedance signature are monitored near one of the bolts used to seal a lid to the top of a box in order to assess if the structure has been tempered with. This study is performed by applying high-frequency structural excitations through surface-bonded piezoelectric transducers, and measuring the output impedances. For the specific problem under investigation, the challenge is represented by the need to separate a tampering attack not only from environmental modifications, but also from any damage’s onset and evolution which the structure can experience throughout its life. doi: 10.12783/SHM2015/93

A Remotely Readable, Self-authenticating Tamper Evident Seal Based on Graphene-based Materials and Compressive Sensing

Low-cost, high-precision patterning of flexible electrical components have gained special attention in many applications where multi-functional materials fuse structural support with electrical sensing. In particular, a number of structural health monitoring (SHM) applications call for the development of “sensing skin” technologies. One application that uses these technologies includes the development of next-generation tamper-evident seals (TES) that are capable of being read remotely. In our design, the state of the TES’s physical structure is monitored through an electrical circuit based on a conductive material. Electrical changes in the TES’s circuit correspond to material property changes induced by humidity, temperature, or chemical changes. Intrinsically unifying material and electrical properties, graphene and graphite derivatives promote simplistic manufacturing of flexible materials with unique electrical properties that are attractive for sensing skin applications. In addition to developing a functional graphenebased material, an encryption scheme to transmit the state of the material is devised utilizing compressive sensing. Our work focuses on the production of printable graphene-based materials and graphene-based/polymeric composites proficient for sensing environmental changes. Printing of functional complex graphene-based materials requires specific formulation while balancing electrical conductivity, formulation simplicity, solution viscosity, and printing compatibility. Production of electrically stable components on flexible substrates with programmable electrical properties will be key to using printed graphene-based materials in sensing skin applications. doi: 10.12783/SHM2015/269

A Multirotor-based Approach for Tap-testing Difficult-to-access Structures

Despite advances in structural health monitoring (SHM) technology, human-based inspections continue to remain dominate in practice when performing structural assessments. The reasons for this include the high costs associated with installing and maintaining current SHM, confidence decisions makers have in current SHM technology, and the familiarity the structural assessment community has with humanbased visual inspection. One of the major challenges and costs associated with human-based visual inspections is that structures are often difficult to access. They may be located high above waterways, thus requiring that an expensive crane or barge be rented to provide the inspectors a platform from which to conduct their inspection. In some cases inspectors may even need to rappel down the side of a structure in order to gain access, thus introducing additional safety concerns. Some research has been done to address these concerns by using emerging multirotor technology to facilitate visual structural inspections. Multirotors have shown great potential for maintaining state awareness of structures and construction sites, but one issue is that visual inspection is often hampered by mud, corrosion, vegetation, and other debris on the structure. A proper visual inspection often requires that this debris be removed. This limits the effectiveness of current multi-rotor based visual inspection technology. Furthermore, it is not uncommon for structural inspectors to enhance the quality of their inspection by using a conventional hammer to tap-test the structure of interest. The inspector will simply strike the structure and listen for differences in acoustic response that might indicate the presence of damage in structure. In this work we begin exploring the utility of adding a pneumatic hammer to a multi-rotor vehicle that can be used to facilitate structural inspections. The system features acoustic microphones and accelerometers that can be used to quantifiably document the results of the tap test. Perhaps more importantly though, this paradigm involves transmitting the acoustic response directly a remote structural inspector through earphones. The remote structural inspector can then use their expert judgment to select locations to perform additional tap tests. Furthermore, the pneumatic hammer could also be used to remove debris and corrosion from the structure in order to enhance visual inspection. One challenge associated with this technique is the need to remove acoustic noise caused by the multirotor propellers. Strategies for addressing this source of noise will be discussed. An additional question is how the dynamics of the multirotor will be affected when it is subjected to impact loads from the pneumatic hammers. The results of experimental tests will demonstrate the effect of the hammer impulse on the multicopter’s dynamics. doi: 10.12783/SHM2015/119