Inductively coupled nanocomposite wireless strain and pH sensors

Loh, Kenneth J.,Lynch, Jerome P.,Kotov, Nicholas A. Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.5

Recently, dense sensor instrumentation for structural health monitoring has motivated the need for novel passive wireless sensors that do not require a portable power source, such as batteries. Using a layer-by-layer self-assembly process, nano-structured multifunctional carbon nanotube-based thin film sensors of controlled morphology are fabricated. Through judicious selection of polyelectrolytic constituents, specific sensing transduction mechanisms can be encoded within these homogenous thin films. In this study, the thin films are specifically designed to change electrical properties to strain and pH stimulus. Validation of wireless communications is performed using traditional magnetic coil antennas of various turns for passive RFID (radio frequency identification) applications. Preliminary experimental results shown in this study have identified characteristic frequency and bandwidth changes in tandem with varying strain and pH, respectively. Finally, ongoing research is presented on the use of gold nanocolloids and carbon nanotubes during layer-by-layer assembly to fabricate highly conductive coil antennas for wireless communications.

A distributed piezo-polymer scour net for bridge scour hole topography monitoring

Loh, Kenneth J.,Tom, Caroline,Benassini, Joseph L.,Bombardelli, Fabian A. Techno-Press 2014 Structural monitoring and maintenance Vol.1 No.2

Scour is one of the leading causes of overwater bridge failures worldwide. While monitoring systems have already been implemented or are still being developed, they suffer from limitations such as high costs, inaccuracies, and low reliability, among others. Also, most sensors only measure scour depth at one location and near the pier. Thus, the objective is to design a simple, low cost, scour hole topography monitoring system that could better characterize the entire depth, shape, and size of bridge scour holes. The design is based on burying a robust, waterproofed, piezoelectric sensor strip in the streambed. When scour erodes sediments to expose the sensor, flowing water excites it to cause the generation of time-varying voltage signals. An algorithm then takes the time-domain data and maps it to the frequency-domain for identifying the sensor's resonant frequency, which is used for calculating the exposed sensor length or scour depth. Here, three different sets of tests were conducted to validate this new technique. First, a single sensor was tested in ambient air, and its exposed length was varied. Upon verifying the sensing concept, a waterproofed prototype was buried in soil and tested in a tank filled with water. Sensor performance was characterized as soil was manually eroded away, which simulated various scour depths. The results confirmed that sensor resonant frequencies decreased with increasing scour depths. Finally, a network of 11 sensors was configured to form a distributed monitoring system in the lab. Their exposed lengths were adjusted to simulate scour hole formation and evolution. Results showed promise that the proposed sensing system could be scaled up and used for bridge scour topography monitoring.

Vibration-based identification of rotating blades using Rodrigues' rotation formula from a 3-D measurement

Loh, Chin-Hsiung,Huang, Yu-Ting,Hsiung, Wan-Ying,Yang, Yuan-Sen,Loh, Kenneth J. Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.6

In this study, the geometrical setup of a turbine blade is tracked. A research-scale rotating turbine blade system is setup with a single 3-axes accelerometer mounted on one of the blades. The turbine system is rotated by a controlled motor. The tilt and rolling angles of the rotating blade under operating conditions are determined from the response measurement of the single accelerometer. Data acquisition is achieved using a prototype wireless sensing system. First, the Rodrigues' rotation formula and an optimization algorithm are used to track the blade rolling angle and pitching angles of the turbine blade system. In addition, the blade flapwise natural frequency is identified by removing the rotation-related response induced by gravity and centrifuge force. To verify the result of calculations, a covariance-driven stochastic subspace identification method (SSI-COV) is applied to the vibration measurements of the blades to determine the system natural frequencies. It is thus proven that by using a single sensor and through a series of coordinate transformations and the Rodrigues' rotation formula, the geometrical setup of the blade can be tracked and the blade flapwise vibration frequency can be determined successfully.

Eff ect of Structural Change on Temperature Behavior of a Long-Span Suspension Bridge Pylon

이정휘,Kenneth J. Loh,최현성,안호현 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.6

The eff ect of structural changes on the temperature behavior of a long-span bridge pylon was examined using fi eld-measured data and fi nite element (FE) analysis. Temperature behavior of the pylon could be modeled using two characteristic parameters, α and β, which refl ect the infl uence of the variation in the ambient temperature and the sectional temperature diff erence, respectively. Two major structural changes namely, decrease in stiff ness in the lower region of the pylon and decrease in area of the main cable were considered in the FE analyses, which showed that both α and β were aff ected by the structural changes. Furthermore, the two characteristic parameters could be extracted with suffi cient accuracy from fi eld-measured temperatures and tilting angle data using a system-identifi cation technique. Consequently, the feasibility of identifi cation of structural changes by continuous observation of temperature parameters was demonstrated. However, the tilting angle of the pylon is infl uenced by other loads than the temperature and therefore future studies on eliminating other loading eff ects (such as that owing to wind or traffi c) are necessary.

Vibration-based identification of rotating blades using Rodrigues’ rotation formula from a 3-D measurement

Chin-Hsiung Loh,Yu-Ting Huang,Wan-Ying Hsiung,Yuan-Sen Yang,Kenneth J. Loh 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.6

In this study, the geometrical setup of a turbine blade is tracked. A research-scale rotating turbine blade system is setup with a single 3-axes accelerometer mounted on one of the blades. The turbine system is rotated by a controlled motor. The tilt and rolling angles of the rotating blade under operating conditions are determined from the response measurement of the single accelerometer. Data acquisition is achieved using a prototype wireless sensing system. First, the Rodrigues' rotation formula and an optimization algorithm are used to track the blade rolling angle and pitching angles of the turbine blade system. In addition, the blade flapwise natural frequency is identified by removing the rotation-related response induced by gravity and centrifuge force. To verify the result of calculations, a covariance-driven stochastic subspace identification method (SSI-COV) is applied to the vibration measurements of the blades to determine the system natural frequencies. It is thus proven that by using a single sensor and through a series of coordinate transformations and the Rodrigues' rotation formula, the geometrical setup of the blade can be tracked and the blade flapwise vibration frequency can be determined successfully.

In situ reduction of gold nanoparticles in PDMS matrices and applications for large strain sensing

Donghyeon Ryu,Kenneth J. Loh,Robert Ireland,Mohammad Karimzada,Frank Yaghmaie,Andrea M. Gusman 국제구조공학회 2011 Smart Structures and Systems, An International Jou Vol.8 No.5

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite’s strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

A wireless impedance analyzer for automated tomographic mapping of a nanoengineered sensing skin

Pyo, Sukhoon,Loh, Kenneth J.,Hou, Tsung-Chin,Jarva, Erik,Lynch, Jerome P. Techno-Press 2011 Smart Structures and Systems, An International Jou Vol.8 No.1

Polymeric thin-film assemblies whose bulk electrical conductivity and mechanical performance have been enhanced by single-walled carbon nanotubes are proposed for measuring strain and corrosion activity in metallic structural systems. Similar to the dermatological system found in animals, the proposed self-sensing thin-film assembly supports spatial strain and pH sensing via localized changes in electrical conductivity. Specifically, electrical impedance tomography (EIT) is used to create detailed mappings of film conductivity over its complete surface area using electrical measurements taken at the film boundary. While EIT is a powerful means of mapping the sensing skin's spatial response, it requires a data acquisition system capable of taking electrical impedance measurements on a large number of electrodes. A low-cost wireless impedance analyzer is proposed to fully automate EIT data acquisition. The key attribute of the device is a flexible sinusoidal waveform generator capable of generating regulated current signals with frequencies from near-DC to 20 MHz. Furthermore, a multiplexed sensing interface offers 32 addressable channels from which voltage measurements can be made. A wireless interface is included to eliminate the cumbersome wiring often required for data acquisition in a structure. The functionality of the wireless impedance analyzer is illustrated on an experimental setup with the system used for automated acquisition of electrical impedance measurements taken on the boundary of a bio-inspired sensing skin recently proposed for structural health monitoring.

Sensing and actuation technologies for smart socket prostheses

Sumit Gupta,Kenneth J. Loh,Andrew Pedtke 대한의용생체공학회 2020 Biomedical Engineering Letters (BMEL) Vol.10 No.1

The socket is the most critical part of every lower-limb prosthetic system, since it serves as the interfacial component thatconnects the residual limb with the artifi cial system. However, many amputees abandon their socket prostheses due to thehigh-level of discomfort caused by the poor interaction between the socket and residual limb. In general, socket prosthesisperformance is determined by three main factors, namely, residual limb-socket interfacial stress, volume fl uctuation of theresidual limb, and temperature. This review paper summarizes the various sensing and actuation solutions that have beenproposed for improving socket performance and for realizing next-generation socket prostheses. The working principles ofdiff erent sensors and how they have been tested or used for monitoring the socket interface are discussed. Furthermore, variousactuation methods that have been proposed for actively modifying and improving the socket interface are also reviewed. Through the continued development and integration of these sensing and actuation technologies, the long-term vision is torealize smart socket prostheses. Such smart socket systems will not only function as a socket prosthesis but will also be ableto sense parameters that cause amputee discomfort and self-adjust to optimize its fi t, function, and performance.

In situ reduction of gold nanoparticles in PDMS matrices and applications for large strain sensing

Ryu, Donghyeon,Loh, Kenneth J.,Ireland, Robert,Karimzada, Mohammad,Yaghmaie, Frank,Gusman, Andrea M. Techno-Press 2011 Smart Structures and Systems, An International Jou Vol.8 No.5

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.

Monitoring Osseointegrated Prosthesis Loosening and Fracture using Electrical Capacitance Tomography

Sumit Gupta,Kenneth J. Loh 대한의용생체공학회 2018 Biomedical Engineering Letters (BMEL) Vol.8 No.3

A noncontact, noninvasive, electrical permittivity imaging technique is proposed for monitoring loosening of osseointegratedprostheses and bone fracture. The proposed method utilizes electrical capacitance tomography (ECT), whichemploys a set of noncontact electrodes, arranged in a circular fashion around the imaging area, for electrical excitations andmeasurements. An inverse reconstruction algorithm was developed and implemented to reconstruct the electrical permittivitydistribution of the interrogated region from boundary capacitance measurements. In this study, osseointegratedprosthesis phantoms were prepared using plastic rods and Sawbone femur specimens, which were subjected to prosthesisloosening and fracture monitoring tests. The results demonstrated that the spatial location and extent of prosthesis looseningand bone fracture could be estimated from the ECT reconstructed permittivity maps. The resolution of the reconstructedimages was further enhanced by a limited region tomography algorithm, and its accuracy in terms of identifyingthe severity, location, and shape of bone fracture was also investigated and compared with conventional full regiontomography.