A mechanical pencil lead-supported carbon nanotube/Au nanodendrite structure as an electrochemical sensor for As(<small>III</small>) detection

Duy, Pham Khac,Sohn, Jong-Ryeul,Chung, Hoeil The Royal Society of Chemistry 2016 The Analyst Vol.141 No.20

<P>A mechanical pencil lead (MPL), an easily obtainable carbon-based material with a consistent size, was used as a frame to construct an MPL-supported carbon nanotube/Au nanodendrite (MPL-CNT/AuND) sensor through simple electrodeposition of Au onto the MPL in the presence of CNTs. A nanodendrite structure was adopted to ensure large numbers of active electrochemical sites because of its hierarchical structure with well-aligned terraces; the CNTs were used to firmly adhere the fabricated Au nanodendrites to the MPL surface to ensure ruggedness. The MPL-CNT/AuND structure was used to measure As3+ samples in a concentration range from 0.5 to 80 ppb using anodic stripping voltammetry (ASV). The variation in peak intensities was linear (R-2: 0.997), and the limit of detection (LOD) was 0.4 ppb. The average relative standard deviation (RSD) of the peak intensities from the voltammograms of each sample collected using three separately prepared MPL-CNT/AuNDs was 8.7%, thereby demonstrating good sensor-to-sensor reproducibility. Furthermore, when three As3+ samples prepared in tap water were measured, the accuracy was maintained without noticeable degradation and the response was steady up to 50-cycle measurements.</P>

Vibration-Based Monitoring of Stay-Cable Force Using Wireless Piezoelectric-Based Strain Sensor Nodes

Khac-Duy Nguyen,Jeong-Tae Kim 한국비파괴검사학회 2012 한국비파괴검사학회지 Vol.32 No.6

This study presents a method to monitor cable force using wireless sensor nodes and piezoelectric sensors. The following approaches are carried out to achieve the objective. Firstly, the principle of piezoelectric materials (e.g., PZT) as strain sensors is reviewed. A cable force estimation method using dynamic features of cables measured by piezoelectric materials is presented. Secondly, the design of an automated cable force monitoring system using the data acquisition sensor-node Imote2/SHM-DAQ is described. The sensor node is originally developed by University of Illinois at Urbana-Champaign and is adopted in this study to monitor strain-induced voltage from PZT sensors. The advantages of the system are cheap, and eligible for wireless communication and automated operation. Finally, the feasibility of the proposed monitoring system is evaluated on a lab-scaled cable.

Wireless Impedance Sensor with PZT-Interface for Prestress-Loss Monitoring in Prestressed Concrete Girder

Khac-Duy Nguyen,So-Young Lee,Jeong-Tae Kim 한국비파괴검사학회 2011 한국비파괴검사학회지 Vol.31 No.6

Ensuring the designed prestress force is very important for the safety of prestressed concrete bridge. The loss of prestress force in tendon could significantly reduce load carrying capacity of the structure. In this study, an automated prestress-loss monitoring system for prestressed concrete girder using PZT-interface and wireless impedance sensor node is presented. The following approaches are carried out to achieve the objective. Firstly, wireless impedance sensor nodes are designed for automated impedance-based monitoring technique. The sensor node is mounted on the high-performance Imote2 sensor platform to fulfill high operating speed, low power requirement and large storage memory. Secondly, a smart PZT-interface designed for monitoring prestress force is described. A linear regression model is established to predict prestress-loss. Finally, a system of the PZT-interface interacted with the wireless sensor node is evaluated from a lab-scale tendon-anchorage connection of a prestressed concrete girder.

Wireless Impedance-Based SHM for Bolted Connections via Multiple PZT -Interfaces

Khac-Duy Nguyen,Jeong-Tae Kim 한국비파괴검사학회 2011 한국비파괴검사학회지 Vol.31 No.3

This study presents a structural health monitoring (SHM) method for bolted connections by using multi-channel wireless impedance sensor nodes and multiple PZT-interfaces. To achieve the objective, the following approaches are implemented. Firstly, a PZT-interface is designed to monitor bolt loosening in bolted connection based on variation of electro-mechanical(EM) impedance signatures. Secondly, a wireless impedance sensor node is designed for autonomous, cost-efficient and multi-channel monitoring. For the sensor platform, Imote2 is selected on the basis of its high operating speed, low power requirement and large storage memory. Finally, the performance of the wireless sensor node and the PZT-interfaces is experimentally evaluated for a bolt-connection model. Damage monitoring method using root mean square deviation(RMSD) index of EM impedance signatures is utilized to estimate the strength of the bolted joint.

Damage detection in beam-type structures via PZT’s dual piezoelectric responses

Khac-Duy Nguyen,김정태,Duc-Duy Ho 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.11 No.2

In this paper, practical methods to utilize PZT’s dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material’s dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.

Numerical Simulation of Electro-Mechanical Impedance Response in Cable-Anchor Connection Interlace

Khac-Duy Nguyen,Jeong-Tae Kim 한국비파괴검사학회 2011 한국비파괴검사학회지 Vol.31 No.1

In this study, a finite element(FE) analysis on electro-mechanical impedance response of cable-anchor connection interface under various anchor force is presented. In order to achieve the objective, the following approaches are implemented. Firstly, an interface washer coupled with piezoelectric(PZT) material is designed for monitoring cable-force loss. The interface washer is a small aluminum plate on which a PZT patch is surface-bonded. Cable-force loss could be monitored by installing the interface washer between the anchor plate and the anchorage of cable-anchor connection and examining the changes of impedance of the interface washer. Secondly, a FE model for cable-anchor connection is established to examine the effect of cable-force on impedance response of interface washer. Also, the effects of geometrical and material properties of the interface washer on impedance responses under various cable-forces are investigated. Finally, validation of the FE analysis is experimentally evaluated by a lab-scale cable-anchor connection.

Smart PZT-interface for wireless impedance-based prestress-loss monitoring in tendon-anchorage connection

Khac-Duy Nguyen,김정태 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.9 No.6

For the safety of prestressed structures such as cable-stayed bridges and prestressed concrete bridges, it is very important to ensure the prestress force of cable or tendon. The loss of prestress force could significantly reduce load carrying capacity of the structure and even result in structural collapse. The objective of this study is to present a smart PZT-interface for wireless impedance-based prestress-loss monitoring in tendon-anchorage connection. Firstly, a smart PZT-interface is newly designed for sensitively monitoring of electro-mechanical impedance changes in tendon-anchorage subsystem. To analyze the effect of prestress force, an analytical model of tendon-anchorage is described regarding to the relationship between prestress force and structural parameters of the anchorage contact region. Based on the analytical model, an impedance-based method for monitoring of prestress-loss is conducted using the impedance-sensitive PZT-interface. Secondly,wireless impedance sensor node working on Imote2 platforms, which is interacted with the smart PZTinterface, is outlined. Finally, experiment on a lab-scale tendon-anchorage of a prestressed concrete girder is conducted to evaluate the performance of the smart PZT-interface along with the wireless impedance sensor node on prestress-loss detection. Frequency shift and cross correlation deviation of impedance signature are utilized to estimate impedance variation due to prestress-loss.

EM Impedance-based Tension Monitoring of Cable-Anchorage in Mooring System of Offshore Structure

Khac-Duy Nguyen,Po-Young Lee,Jeong-Tae Kim 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

For offshore structure moored by cable system, the stability of the structure is dependent on tensile force of the cables. The loss of cable force may result in large displacement and unbalance of the structure. This study presents an electromechanical impedance-based method for tension monitoring of cable-anchorage in mooring system of offshore structure. In order to achieve the objective, the following approaches are implemented. Firstly, an PZT-Interface is introduced to monitor tensile force of cable. Once installed into the cable-anchorage, the PZT-interface works like a cantilever plate with imperfectly fixed boundary. The loss of cable force is represented by the weakness of the fixed boundary. Secondly, the variations of electromechanical (EM) impedance of the PZT-interface due to the variations of cable force are investigated. Several index like root mean square deviation, correlation coefficient deviation and frequency shift are utilized to capture these changes. Finally, the feasibility of the method is evaluated on a lab-scale cable-anchorage model.

Wireless Impedance Sensor with PZT-Interface for Prestress-Loss Monitoring in Prestressed Concrete Girder

Nguyen, Khac-Duy,Lee, So-Young,Kim, Jeong-Tae The Korean Society for Nondestructive Testing 2011 한국비파괴검사학회지 Vol.31 No.6

Ensuring the designed prestress force is very important for the safety of prestressed concrete bridge. The loss of prestress force in tendon could significantly reduce load carrying capacity of the structure. In this study, an automated prestress-loss monitoring system for prestressed concrete girder using PZT-interface and wireless impedance sensor node is presented. The following approaches are carried out to achieve the objective. Firstly, wireless impedance sensor nodes are designed for automated impedance-based monitoring technique. The sensor node is mounted on the high-performance Imote2 sensor platform to fulfill high operating speed, low power requirement and large storage memory. Secondly, a smart PZT-interface designed for monitoring prestress force is described. A linear regression model is established to predict prestress-loss. Finally, a system of the PZT-interface interacted with the wireless sensor node is evaluated from a lab-scale tendon-anchorage connection of a prestressed concrete girder.

Innovative cable force monitoring of stay cables using piezoelectric dynamic strain responses

Nguyen Khac Duy,Huynh Thanh Canh,Ji-Yong Lee(이지용),Sung Woo Shin(신성우),Jeong-Tae Kim(김정태) 한국소음진동공학회 2013 한국소음진동공학회 학술대회논문집 Vol.2013 No.4

This study presents a method to monitor cable force of a long-span cable-stayed bridge using a smart piezoelectric sensor system. The following approaches are implemented in order to achieve the objective. Firstly, the method to utilize piezoelectric materials for the health monitoring of stay cables is presented. For strain measurement of a stay cable, a PZT-embedded smart skin is designed to overcome the difficulties of bonding PZT sensors directly on stay cables. Secondly, a piezoelectric strain monitoring system for stay cables is designed. For the operation of the sensor board, the Imote2 sensor platform is used to provide the computation, wireless communication and power supply units. The feasibility of the proposed monitoring system is then evaluated on a full-scale cable of a cable-stayed bridge.