A metal-dielectric (M-D) multilayer has been applied as a subwavelength structure to exhibit the negative index of refraction. Periodic MD multilayer or symmetrical five layered MDMDM multilayer has been arranged to exhibit an equivalent complex refractive index with negative real part. As the extinction coefficient is much smaller than the index of refraction, the wave vector and Poynting vector are in opposite directions. How to reduce the extinction coefficient and raise the transmittance becomes an issue. In this work, the metal films within the multilayer are not arranged with the same thickness as well as dielectric films. The thickness of each layer is tuned to increase the transmittance. The previous example of a five layered MDMDM as a negative index metamaterial at a wavelength of 363.8nm is adopted here to do the improvement of loss. The near field simulation is also adopted here to observe the backward wave propagation as a negative refraction phenomenon.
The objective of this paper is to upgrade a wireless sensing unit which can meet the following requirements: 1)
Improvement of system powering and analog signal processing 2) Enhancement of signal resolution and provide reliable
wireless communication data, 3) Enhance capability for continuous long-term monitoring. Based on the prototype of the
wireless sensing unit developed by Prof. Lynch at the Stanford University, the following upgrading steps are
summarized:
1. Reduce system noise by using SMD passive elements and preventing the coupling digital and analog circuits, and
increasing the capacity of power.
2. Improve the ADC sampling resolution and accuracy with a higher resolution Analog-to-Digital Converter (ADC): a
24bits ADC with programmable gain amplifier.
3. Improve wireless communication by using the wireless radio 9XTend which supported by the router (Digi MESH)
communication function using 900MHz frequency band.
Based on the upgrade wireless sensing unit, verification of the new wireless sensing unit was conducted from the
ambient vibration survey of a base-isolated building. This new upgrade wireless sensing unit can provide more reliable
data for continuous structural health monitoring. Incorporated with the identification software (modified stochastic
subspace identification method) the smart sensing system for SHM is developed.
The objective of this paper is to develop a novel sensing system which can conduct continuous monitoring of a building
structure and generate a monitoring report. The building monitoring data will focus on the ambient vibration responses.
Two servers are used in this SHM system: 1) wireless measurement server which takes care of measuring and archiving
all the structural responses and environmental situation, and 2) analysis server which conducts the signal processing on
the received signals. The measurement server is in charge of the collection of signals and broadcast wirelessly from all
sensors to the analysis server. Dominant frequencies and mode shapes of the building will be estimated in the analysis
server from the continuous monitoring of the ambient vibration data (velocity) of the building by using AR-Model,
Frequency Domain Decomposition and Stochastic Subspace Identification methods. The proposed continuous
monitoring system can effectively identify the building current health condition and generate a report to the owner.
This paper presents the structural control results of shaking table tests for a steel frame structure in order to evaluate
the performance of a number of proposed semi-active control algorithms using multiple magnetorheological (MR) dampers. The test structure is a six-story steel frame equipped with MR-dampers. Four different cases of damper arrangement in the structure are selected for the control study. In experimental tests, an EL Centro earthquake, a Kobe earthquake and a Chi-Chi earthquake (station TCU067) are used as ground excitations. Various control algorithms are used for this semi-active control studies, including the Decentralized Sliding Mode Control (DSMC), LQR control and passive-on and passive-off control. Each algorithm is formulated specifically for the use of MR-dampers. Additionally, each algorithm uses measurements of the absolute acceleration and the device velocity for the determination of the control action to ensure that the algorithm can be implemented on a physical structure. The performance of each algorithm is evaluated based on the results of shaking table tests, and the advantages of each algorithm is compared and discussed. The reduction of the story drift and acceleration throughout the structure is examined.
This study examines the potential use of wireless communication and embedded computing technologies within realtime
structural control applications. Based on the implementation of the prototype WiSSCon system in a three story steel
test structure with significant eccentricity, the centralized control architecture is implemented to mitigate the lateral and
torsional response of the test structure using two MR dampers installed in the first story. During the test, a large
earthquake time history is applied (El Centro earthquake) at the structure base using a shaking table. Three major
performance attributes of the wireless control system were examined: (1) validation of the reliability of wireless
communications for real-time structural control applications, (2) validation of a modified exponential damper model
embedded in the wireless sensors to operate the MR dampers, and (3) exploration of control effectiveness when using
WiSSCon in a centralized architectural configuration.
An extensive program of full-scale ambient vibration testing has been conducted to measure the dynamic response of a 240 meter cable-stayed bridge - Gi-Lu Bridge in Nan-Tou County, Taiwan. A MEMS-based wireless sensor system and a traditional microcomputer-based system were used to collect and analyze ambient vibration data. A total of four bridge modal frequencies and associated mode shapes were identified for cables and the deck structure within the frequency range of 0~2Hz. The experimental data clearly indicated the occurrence of many closely spaced modal frequencies. Most of the deck modes were found to be associated with the cable modes, implying a considerable interaction between the deck and cables. The results of the ambient vibration survey were compared to modal frequencies and mode shapes computed using three-dimensional finite element modeling of the bridge. For most modes, the analytical and the experimental modal frequencies and mode shapes compare quite well. Based on the findings of this study, a linear elastic finite element model for deck structures and beam element with P-Delta effect for the cables appear to be capable of capturing much of the complex dynamic behavior of the bridge with good accuracy.
In recent years, substantial research has been conducted to advance structural control as a direct means of mitigating the
dynamic response of civil structures. In parallel to these efforts, the structural engineering field is currently exploring
low-cost wireless sensors for use in structural monitoring systems. To reduce the labor and costs associated with
installing extensive lengths of coaxial wires in today's structural control systems, wireless sensors are being considered
as building blocks of future systems. In the proposed system, wireless sensors are designed to perform three major tasks
in the control system; wireless sensors are responsible for the collection of structural response data, calculation of
control forces, and issuing commands to actuators. In this study, a wireless sensor is designed to fulfill these tasks
explicitly. However, the demands of the control system, namely the need to respond in real-time, push the limits of
current wireless sensor technology. The wireless channel can introduce delay in the communication of data between
wireless sensors; in some rare instances, outright data loss can be experienced. Such issues are considered an intricate
part of this feasibility study. A prototype Wireless Structural Sensing and Control (WiSSCon) system is presented
herein. To validate the performance of this prototype system, shaking table experiments are carried out on a half-scale
three story steel structure in which a magnetorheological (MR) damper is installed for real-time control. In comparison
to a cable-based control system installed in the same structure, the performance of the WiSSCon system is shown to be
effective and reliable.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.