Embedded Real-Time Sensor Network for Smart Structure

INTERNATIONAL JOURNAL
OF PROFESSIONAL ENGINEERING STUDIES
Volume I/Issue 2/DEC 2013
Embedded Real-Time Sensor Network for Smart
Structure Health Monitoring
R. Venkateshwara Rao1, B. A. Sarath Manohar Babu 2
M.Tech Student, Dept of ECE, G. Pullaiah College of Engineering & Technology, Nandikotkur Road, Kurnool Dist, ap, India
2
Assistant Professor, Dept of ECE, G. Pullaiah College of Engineering & Technology, Nandikotkur Road, Kurnool Dist, ap, India
1
Abstract- The present paper proposes structural
health monitoring with wireless sensor network to
check the vibration levels of a building. The
wireless sensor network mainly checks the
vibrations of a certain building if they may cause
any damage or it checks the health and state of
buildings. These vibration levels are compared
with some fixed threshold values of the sensors.
Measurements obtained are executed in two
modes; in first step we need to measure the results
with obtained measurements of each sensor node
in order to verify the overcoming of fixed
threshold values. In the second step, node has to
detect the possible error sensors on the basis of
measurement data obtained nearby sensors. The
sensor networks used for structural monitoring
correspond to standard wired data acquisition
system. In other words we are using ZIGBEE
technology for wireless communication for more
flexibility and capability of the wireless sensor
network. In this we are using a wireless cam to
view the position and health of the building; we
can view this in PC. MEMS are used to check the
vibrations or any tilt in the building.
Keywords - structural health monitoring, wireless
sensor network, decision-making, measurement
uncertainty.
I.
INTRODUCTION
The main source to the preservation of the buildings
structural health, of degradation and decay are due to
improper maintenance, negligence for long time, and
in addition we can add natural causes such as
earthquakes or weather conditions. In some critical
cases, the structural stability can be compromised
because of wrong evaluation of safety levels. Among
the various causes of degradation of building
structural integrity, the attention has been focused on
the vibrations effect. The problem of vibration
transmitted to buildings has taken, in recent years,
increasing importance both in relation to the different
structural types of the modern buildings and in
relation to the proliferation of vibration sources. In
some, man activities, road and rail traffic, the
operation of factories close to residential areas can
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sometimes cause damages and this may lead to the
need to verify if the vibrations are such as to induce
or less damages to the building, especially where
there are architectural damages generated by other
causes. In general, structural damages to the building,
attributable to this type of phenomena, are always
derived from the contribution of other causes.
Important structural damages can be caused only by
vibrations of certain intensity, for example,
earthquakes. But other forms of damage are frequent
and, without compromising the structural safety of
buildings, can worsen its state.
These are the so-called “damage thresholds” that may
occur in the form of cracks in the plaster,
enhancements of existing cracks, damage to
architectural elements. The problem becomes
particularly relevant in the conservation of
monumental buildings, [1].
The measurement of vibration in buildings can be
aimed at different objectives:
a) recognition of the problem; in order to check
whether the vibration levels may cause any
damage to buildings and need further study;
b) verification and control; in order to compare the
vibration levels with the limits suggested by
specific regulations;
c) characterization for purpose of diagnostics; in
order to verify the occurrence of structural
changes due to peculiar phenomena such as
earthquakes, or degradation of materials;
d) Characterization for purposes of forecasting; in
order to obtain information on the building
structural properties through the estimation of its
dynamic parameters.
The monitoring of vibrations can be used to
verify the performances of structures. So it is an
useful tool for the characterization of on- going
phenomena by using mathematical interpretative
models. It can be used to identify the model
properties of a structure and to point out the existence
of damages by measuring its response to forced
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OF PROFESSIONAL ENGINEERING STUDIES
stimuli. The solution for this is to use appropriate
distributed monitoring networks in order to perform a
control of building state and stability by means of a
remote data management. In this way, it is possible to
guarantee a timely diagnosis of the structural
condition and to characterize possible states of alarm.
Currently, structural engineers use wired data
acquisition systems in order to acquire vibration data
in the building, but these systems are expensive, are
cumbersome to install and manage. The wireless
sensor networks represent an optimal solution for
systems of structural health monitoring because they
simplify the connection to the measurement
instrumentation and allow realizing low-cost
measurement systems, [2].
With some limitations on the processing
power, storage and data transmission they can
overcome the problems of the current acquision
systems. Therefore the wireless architecture permits
to achieve a more flexible and dynamic monitoring
due to the easy displacement of the nodes. The
identification of network devices and their activation
state from sleeping proceeds much faster than for the
other standards (identification 30 ms, activation 15
ms) the Zigbee standard has been chosen in
particular. ZigBee allows a greater number of nodes
(up to 255) consuming less energy with wider
coverage(up to 100 m) and its stack requires less
memory space of the other standards so that it can be
used more easily on microcontroller board. Causes of
damage
to
structures
experiences
about
environmental impact induced by vibrations have
helped to identify threshold limit values and, security
criteria.
The different parameters identified
considering limits such as the range of frequency and
amplitude of vibration, the characteristic time of the
phenomenon (continuous or transient), the number of
transient events, the time of exposure, the influence
of soil, the type and condition of the structures. The
ISO 4866 and UNI 9916 are the relevant Standard
regulations to the effects of vibrations on buildings.
The limited effects of vibrations that can lead to the
emergence of architectural damage, “damage
threshold” is provided by these rules for the structural
response of buildings. It is good to highlight that the
response of a building to a dynamic excitation and
the damage that this can produce depend on the
spectral content of the excitement and on dynamic
characteristics of the building. It is possible to assess
the risk of harm associated with the vibratory
phenomenon in question, by measuring the vibration
levels, knowing the natural frequencies of the
building and integrating these data with information
on the structural characteristics of the building and its
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Volume I/Issue 2/DEC 2013
condition. It proposes a measurement methodology
which provides guidelines for the choice of the
transducers (accelerometers) and their locations with
these standards.
The transducers can be chosen according to
the position and vibration mode of the structure. The
multiple channels which are connected to different
sensors use acquisition systems and are connected to
central computer unit. Such architectures are very
expensive, and limit the analysis of the structure
because of the use of wired connections. The
Wireless Sensor Networks, can overcome the
problems of the previous acquisition systems, and
have limitations on the processing power, storage and
transmission. The present paper shows the design of a
wireless sensor network with ZigBee technology for
monitoring vibrations in the buildings. In this project
the main attention has been focused on the
measurement reliability. The vibrations transmitted to
the buildings are measured by each sensor node by
extern fonts and alerts if the fixed thresholds are
exceeded taking into account the consequences of a
wrong decision and the measurement uncertainty. In
order to verify the possible occurrence of wrong
decisions a procedure has been implemented
considering the historical calibration information of
each sensor of the network.
II.
THE SENSOR NETWORK DESIGN
The following sensor network consists of N sensor
nodes connected in a star configuration to the
coordinator node or main node. The main node
receives the measurement results from the nodes and
can transmit them directly to a central processing
unit.
Fig.1. sensor network block diagram.
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Through ZigBee wireless technology the nodes of
multi functional network devices are able to
communicate with each other. Each sensor node
consists of four basic units: the unit composed by
acceleration sensor; the Computational Unit which
performs the A/D conversion and processes and
stores data; the Communication Unit that connects
the node to the network and allows the transfer of
data; and the unit responsible of the energy supply for
the node. The sensing unit consists of accelerometers
(MMA7660FC) with measurement range 5 g pk,
sensitivity 1 V/g and frequency range 0.6-450 Hz.
The Controller (Arm7LPC2148) has been used for
controlling the acquisition and storage of data. It is
equipped with 32 kB RAM and 512 kB program
memory, the processor operates with a clock
frequency of 60 MHZ. The computational unit which
performs the A/D conversion (MCP3901), has a dual
channel analog front end (AFE) containing two
synchronous sampling delta-sigma Analog-to-Digital
Converters (ADC) 16/24-bit.
The transfer of data is performed by the
Microchip ZigBee Stack mounting aboard an 32bit
Arm7TDMI which communicates via SPI bus with
the Zigbee transceiver. The coordinator node is able
to communicate directly with the PC by serial
interface for wireless data transmission to a remote
client. For simplicity, the realized sensor is composed
by only two single-axis accelerometers being able to
measure acceleration along the x and y axes.
Volume I/Issue 2/DEC 2013
Fig. 3.Control section
On the request of the operator, the nodes of
the network begin the measurement, sampling the
signal acquired by the accelerometers with a
frequency rate of 250 S/s. If the measured values are
exceeded then compared with the threshold limits ,
the nodes transmit an alert signal to the master node
and then to the central station which verifies the
reliability of results. The recorded data are
transmitted to the central processing unit if the results
are reliable, where a Virtual Instrument (VI) has the
task to process the available information.
THE DECISION MAKING APPROACH
Micro Electro Mechanical Systems
Introduction: Micro-Electro-Mechanical Systems
(MEMS) is the integration of mechanical elements,
sensors, actuators, and electronics on a common
silicon substrate through micro fabrication
technology. While the electronics are fabricated using
integrated circuit (IC) process sequences (e.g.,
CMOS, Bipolar, or BICMOS processes), the
micromechanical components are fabricated using
compatible "micromachining" processes that
selectively etch away parts of the silicon wafer or add
new structural layers to form the mechanical and
electromechanical devices.
Fig. 2.Transmitter section
During the acquisition process, the
coordinator node is always active, whereas the other
nodes remain in a state of low power consumption
until they must make the data transmission.
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MEMS promises to revolutionize nearly every
product category by bringing together silicon-based
microelectronics with micromachining technology,
making possible the realization of complete systemson-a-chip. MEMS is an enabling technology
allowing the development of smart products,
augmenting
the
computational
ability
of
microelectronics with the perception and control
capabilities of micro sensors and micro actuators and
expanding the space of possible designs and
applications.
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Microelectronic integrated circuits can be thought of
as the "brains" of a system and MEMS augments this
decision-making capability with "eyes" and "arms",
to allow micro systems to sense and control the
environment. Sensors gather information from the
environment through measuring mechanical, thermal,
biological, chemical, optical, and magnetic
phenomena. The electronics then process the
information derived from the sensors and through
some decision making capability direct the actuators
to respond by moving, positioning, regulating,
pumping, and filtering, thereby controlling the
environment for some desired outcome or purpose.
Because MEMS devices are manufactured using
batch fabrication techniques similar to those used for
integrated circuits, unprecedented levels of
functionality, reliability, and sophistication can be
placed on a small silicon chip at a relatively low cost.
Microelectromechanical systems (MEMS) (also
written
as
micro-electro-mechanical,
or
MicroElectroMechanical) is the technology of the
very small, and merges at the nano-scale into nano
electromechanical
systems
(NEMS)
and
nanotechnology. MEMS are also referred to as micro
machines (in Japan), or Micro Systems Technology MST (in Europe). MEMS are separate and distinct
from the hypothetical vision of molecular
nanotechnology or molecular electronics. MEMS are
made up of components between 1 to 100
micrometers in size (i.e. 0.001 to 0.1 mm) and
MEMS devices generally range in size from 20
micrometers (20 millionths of a meter) to a
millimeter. They usually consist of a central unit that
processes data, the microprocessor and several
components that interact with the outside such as
micro sensors[1]. At these size scales, the standard
constructs of classical physics are not always useful.
Due to MEMS' large surface area to volume ratio,
surface effects such as electrostatics and wetting
dominate volume effects such as inertia or thermal
mass.
The potential of very small machines was
appreciated long before the technology existed that
could make them—see, for example, Richard
Feynman's famous 1959 lecture There's Plenty of
Room at the Bottom. MEMS became practical once
they could be fabricated using modified
semiconductor device fabrication technologies,
normally used to make electronics. These include
molding and plating, wet etching (KOH, TMAH) and
dry etching (RIE and DRIE), electro discharge
machining (EDM), and other technologies capable of
manufacturing very small devices.
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MEMS description MEMS technology can be
implemented using a number of different materials
and manufacturing techniques; the choice of which
will depend on the device being created and the
market sector in which it has to operate.
PRINCIPLE OF OPERATION
The Free scale Accelerometer consists of a
MEMS capacitive sensing g-cell and a signal
conditioning ASIC contained in a single package.
The sensing element is sealed hermetically at the
wafer level using a bulk micro machined cap wafer.
The g-cell is a mechanical structure formed from
semiconductor materials (polysilicon) using masking
and etching processes. The sensor can be modeled as
a movable beam that moves between two
mechanically fixed beams. Two gaps are formed; one
being between the movable beam and the first
stationary beam and the second between the movable
beam and the second stationary beam.
The ASIC uses switched capacitor techniques to
measure the g-cell capacitors and extract the
acceleration data from the difference between the two
capacitors. The ASIC also signal conditions and
filters (switched capacitor) the signal, providing a
digital output that is proportional to acceleration.
Applications
Fig.5.Microlectromechanical systems chip, sometimes called "lab
on a chip
In another view point mems applications are
categorized by the field of application(Commercial
applications include):

Inkjet printers, which use piezoelectric or
thermal bubble ejection to deposit ink on
paper.
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
Accelerometers in modern cars for a large
number of purposes including airbag
deployment in collisions.
standard, Bluetooth, microwaves and some other
devices. It is capable of connecting 255 devices per
network.

Accelerometers in consumer electronics
devices such as game controllers (Nintendo
Wii), personal media players / cell phones
(Apple iPhone, various Nokia mobile phone
models, various HTC PDA models)[9] and a
number of Digital Cameras (various Canon
Digital IXUS models). Also used in PCs to
park the hard disk head when free-fall is
detected, to prevent damage and data loss.
The specification supports data transmission rates of
up to 250 Kbps at a range of up to 30 meters.
ZIGBEE's technology is slower than 802.11b (11
Mbps) and Bluetooth (1 Mbps) but it consumes
significantly less power.

MEMS gyroscopes used in modern cars and
other applications to detect yaw; e.g. to
deploy a roll over bar or trigger dynamic
stability control.

Silicon pressure sensors e.g. car tire pressure
sensors, and disposable blood pressure
sensors.

Displays e.g. the DMD chip in a projector
based on DLP technology has on its surface
several hundred thousand micro mirrors.

Optical switching technology which is used
for switching technology and alignment for
data communications.

Bio-MEMS applications in medical and
health related technologies from Lab-OnChip to MicroTotalAnalysis (biosensor,
chemosensor).

Interferometric modulator display (IMOD)
applications in consumer electronics
(primarily displays for mobile devices).
Used to create interferometric modulation reflective display technology as found in
mirasol displays.
III.
ZIGBEE Technology
ZIGBEE is a new wireless technology guided by the
IEEE 802.15.4 Personal Area Networks standard. It
is primarily designed for the wide ranging automation
applications and to replace the existing non-standard
technologies. It currently operates in the 868MHz
band at a data rate of 20Kbps in Europe, 914MHz
band at 40Kbps in the USA, and the 2.4GHz ISM
bands Worldwide at a maximum data-rate of
250Kbps. The ZIGBEE specification is a
combination of Home RF Late and the 802.15.4
specification. The specification operates in the
2.4GHz (ISM) radio band - the same band as 802.11b
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Fig.6. Pin diagram of X-Bee Transceiver
System data flow
Fig .7. Serial data flow
The X-Bee RF Modules interface to a host
device through a logic-level asynchronous Serial
port. Through its serial port, the module can
communicate with any logic and voltage Compatible
UART; or through a level translator to any serial
device. Data is presented to the X-Bee module
through its DIN pin, and it must be in the
asynchronous serial format, which consists of a start
bit, 8 data bits, and a stop bit. Because the input data
goes directly into the input of a UART within the XBee module, no bit inversions are necessary within
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the asynchronous serial data stream. All of the
required timing and parity checking is automatically
taken care of by the X-Bee’s UART. If the
microcontroller wants to send data to transceiver, it
will send RTS (Request to Send) signal. If the
transceiver is idle it sends CTS (Clear to Send)
signal. The RTS and CTS signals are active low.
When microcontroller receives CTS command it will
send data to the transceiver through DIN pin. The
transceiver will send the data to microcontroller
through DOUT pin. The communication between
transceiver and the microcontroller at the transmitter
and receiver is similar. The communication between
transmitter
and receiver
is
through
RF
communication.
Applications of ZIGBEE Technology:
1
ZIGBEE Home Automation
2
ZIGBEE Smart Energy 1.0
3
ZIGBEE Telecommunication Services
4
ZIGBEE Health Care
5
ZIGBEE RF4CE - Remote Control
6
ZIGBEE Industrial Plant Monitoring
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IV.
Webcam
"Webcam" refers to the technology generally; the
first part of the term ("web-") is often replaced with a
word describing what can be viewed with the camera,
such as a net cam or street cam. Webcams are video
capturing devices connected to computers or
computer networks, often using USB or, if they
connect to networks, Ethernet or Wi-Fi. They are
well-known for low manufacturing costs and flexible
applications. Video capture is the process of
converting an analog video signal—such as that
produced by a video camera or DVD player—to
digital form. The resulting digital data are referred to
as a digital video stream, or more often, simply video
stream. This is in contrast with screen casting, in
which previously digitized video is captured while
displayed on a digital monitor.
Webcams typically include a lens, an image sensor,
and some support electronics. Various lenses are
available, the most common being a plastic lens that
can be screwed in and out to set the camera's focus.
Fixed focus lenses, which have no provision for
adjustment, are also available. Image sensors can be
CMOS or CCD, the former being dominant for lowcost cameras, but CCD cameras do not necessarily
outperform CMOS-based cameras in the low cost
price range. Consumer webcams are usually VGA
resolution with a frame rate of 30 frames per second.
Higher resolutions, in mega pixels, are available and
higher frame rates are starting to appear.
Fig.9. Webcam
Fig. 8.The Virtual Instrument
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The video capture process involves several
processing steps. First the analog video signal is
digitized by an analog-to-digital converter to produce
a raw, digital data stream. In the case of composite
video, the luminance and chrominance are then
separated. Next, the chrominance is demodulated to
produce color difference video data. At this point, the
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data may be modified so as to adjust brightness,
contrast, saturation and hue. Finally, the data is
transformed by a color space converter to generate
data in conformance with any of several color space
standards, such as RGB and YCbCr. Together, these
steps constituted video decoding, because they
"decode" an analog video format such as NTSC
orPAL.
VII.
Support electronics are present to read the image
from the sensor and transmit it to the host computer.
The camera pictured to the right, for example, uses a
Sonix SN9C101 to transmit its image over USB.
Some cameras - such as mobile phone cameras - use
a CMOS sensor with supporting electronics.
[2] “Handbook of Sensor Networks: Compact
Wireless and Wired Sensing Systems”, edited
Ilyas Mahgoub, 2005.
FEATURES:
 Smallest wireless video & audio camera
 Wireless transmission and reception
 High sensitivity
 Easy installation & operation
 Easy to conceat
 Light weight
 Low power consumption
 Small size
VI.
CONCLUSIONS
A remote monitoring structural building network
using ZigBee Technology has been designed in order
to monitor the health and preservation state of
buildings. The system verifies if the vibration levels
overcome the fixed thresholds in order to characterize
risky situations. In order to improve the reliability of
the decisions made, two modes of algorithms have
been implemented. A first mode of algorithm has
been implemented on each sensor in order to decide
if the fixed acceleration threshold is exceeded taking
into account the consequences of a wrong decision
and the measurement uncertainty. The second mode
of algorithm is implemented in order to verify the
reliability of each sensor results taking into account
the historical calibration information of sensors of the
network.
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REFERENCES
[1] A. Ioannis, T. Ioannis, E. Anaxarogas,
“Intelligent Seismic Acceleration Signal
Processing for Damage Classification in
Buildings”,
IEEE
Transactions
on
Instrumentation and Measurement, Vol. 56,
2007.
[3] Sa-aat Niwitpong, Hung T. Nguyen, Vladik
Kreinovich and Ingo Neumann, “Hypothesis
Testing with Interval Data: Case of Regulatory
Constraints”, International Journal of Intelligent
Technology and Ap-plied Statistics Vol.1, No.2
(2008) pp.19-41.
[4] B. Krishnamachari, S. Iyengar, “Distribuited
Bayesian Algorithms for Fault-Tolerant Event
Detection in Wireless Sensor Networks”, IEEE
Transactions on Computers, vol.53, no.3, 2004.
[5] Robert B. Abernethy, “The New Weibull
Handbook, Reliability & Statistical Analysis for
Predicting Life, Safety Survivability, Risk, Cost
and Warranty Claims”, Fifth Edition 2006.
R. Venkateshwara Rao pursuing his M.Tech in
Embedded systems from G. Pullaiah college of
engineering and technology, Nandikotkur Road,
Kurnool Dist, AP, India.
B. A. Sarath Manohar Babu, his Qualification is
M.tech, currently working as an Associate Professor,
in the Department of Electronics and communication
Engineering, G. Pullaiah College of engineering and
technology, Nandikotkur Road, Kurnool Dist, AP,
India. Approved by AICTE, New Delhi, Affiliated to
JNTU Anantapur
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