Anuja Shivaji Kangule
Bharati Vidyapeeth Deemed to be University
Nowadays, wireless sensor networks (WSNs) have become a powerful low-cost platform for connecting a large network of sensors. These networks have applications in health, military, commercial and industrial settings. Structural health monitoring (SHM) is one of the applications of WSNs in which sensors are distributed throughout a structure, it means wireless sensor networks are fixed in any device, instrument, or any construction, buildings, etc. to monitor the overall performance of that structure to sense or notify every small changes happened so simply WSNs are used to monitor the health of structure known as SHM.
SHM system is used with many structures to enhance public safety and reduce economic losses. For example high rise buildings, stadiums, bridges. SHM monitors critical infrastructures of high-rise buildings, stadiums, bridges and has the potential to improve structure life span & public safety. WSNs are an emerging technology that can be deployed with SHM applications. SHM is used to detect & locate damage to assess the structural integrity and predict the remaining lifetime of the subjected structure.
The use of WSNs is essential in the pharma industry to monitor pressure, humidity, temperature, etc. It plays important role in process control i.e. tablet granulation, tablet compression process, sterilization process in which temperature, %humidity, speed/rate is very essential to maintain. It is required to maintain this data on a 24×7 basis for FDA audit.
Wired sensor networks Vs Wireless sensor networks
It is designed using wired sensor networks, but due to high reliability, low installation & maintenance cost, WSNs have made SHM a compelling alternate platform.
|Wired sensor networks||Wireless sensor networks|
|Cost is very high ($10000 to $25000 real-world costing).||Cost is very low ($500 for each sensor node cost).|
|Very long deployment time.||Short deployment time.|
|Long lifespan & is typically limited by hardware lifespan.||Short lifespan & is typically limited by node battery lifespan.|
|The number of sensors is low.||The number of sensors is higher.|
|High bandwidth.||Limited bandwidth.|
|It has a high sensor data rate.||It has a low sensor data rate but higher than conventional WSNs.|
Where is it to be deployed?
Deployed at various locations throughout a structure, these sensors collect information about surroundings such as acceleration, ambient vibration, load & stress at sampling frequency upwards of 100 Hz. SHM is deployed in critical structures such as aerial vehicles, ships, high-rise buildings, dams, and bridges.
“One of the first SHM was installed on the Golden Gate Bridge in 2007 by a research team at the University of California in Berkeley”.
SHM using WSNs
There are two categories of SHM – 1) local 2) Global
Local SHM detects small defects, tiny cracks, or damage in the structure. Global SHM detects significant damage, which is large enough to change the entire structural integrity. In general, SHM requires the establishment of a large number of sensors throughout a structure capable of collecting sensed data. These collected data are processed such that decisions about the structure’s overall health can be made. In designing an SHM system, one of the most important considerations is the selection of sensors and sensor parameters. ‘Piezoelectric accelerometer‘ is the most commonly used sensor due to its low cost & ease of use.
Communication of WSNs
Data communication between Data Acquisition Unit (DAU) and Main Controller Room (MCR) is fixed, but it is mostly wired. Data communication between the sensor node and DAU is wireless, and it gains greater benefits for the lower-end communication and poses a new set of challenges for the researchers.
Damage detection and localization
The Primary role of SHM is to detect structural damage. It requires the collection of sensor data that can be used to extract parameters related to the overall health of structures.
For damage detection’s most commonly used parameter is the modal parameter. Estimation of this parameter can be performed in both the time & frequency domain. Once structural damage is detected, it is then necessary to determine the damage’s location. It requires the installation of sensors such that sufficient sensor coverage is provided to locate damage anywhere in the structure.
Techniques to detect damage and localization: frequency-based, stiffness matrix-based, model shape-based, support vector machine-based, flexibility matrix-based.
- The real-world implementation has been done to monitor the structural health of historical buildings. This is done when restoration work was carried out on them as a consequence of damage suffered after a light earthquake.
- For environment monitoring, robotics, security checkup & balance application, WSNs are used and researchers are also working on this.
- To monitor pressure, temperature, humidity, facilities, etc. In the manufacturing area in the pharmaceutical industry.
- Magneto Inductive Sensor to detect the passage of pills.
- Pharmaceutical facilities monitoring using a sensicast system.
- Cold chain management using WSNs.