Construction is one of the prominent sources of employment and essentially the life force behind all the infra projects, be it roads and highways and bridges and tunnels, office buildings, residential buildings, etc. You can’t do without it. This is one such field that has benefitted the most from technological advancements and unorganized, unskilled laborers.
While technology has allowed for new machines and tools that allow for faster construction work, various kinds of sensors can also be used to monitor the integrity and health of structures. Most of these IoT sensors are battery operated and can detect temperature, humidity, strain, and stress pretty accurately and share this data to a cloud-backed data storing and processing system.
Passive RFID sensors offer an alternative to battery-operated sensors and can be embedded in structures and materials, creating smart structures and smart materials. As embedded sensors (ESs), RFID labels can be inserted into the materials or attached to the structure, measuring and monitoring changes in strain, stress, temperature, etc.
Radiofrequency identification is a wireless technology that uses small electronic devices known as RFID tags. RFID tags come with silicon memory that can be encoded with data and this data is transmitted from the tag to the RFID reader, as RF signals, when an RFID reader sends an interrogating signal.
These RFID tags can also be used as RFID sensors by reconfiguring their antenna design to respond to environmental changes, be it temperature, moisture, humidity, strain, etc.
RFID Strain Sensors
RFID Strain Sensors are designed with chipped RFID tags by adding a strain sensor to the RFID integrated circuit in the RFID tag. In the case of chipless RFID tags, the fabrication of strain sensors is done using sensing materials as substrate and with the use of resonators and reflectors.
The passive (battery-free) RFID strain sensors can be used in SHM (Structural Health Monitoring) systems to detect bend or strain directly on the chip. Therefore, it can detect and monitor any strain and stress changes in the structure the sensors are directly attached to, allowing for predictive maintenance, safety, and longevity of various infrastructure assets. The data, however, is collected using RFID antennas and RFID readers, strategically installed at various locations to ensure continuous data collection.
Recently researchers at MIT also came up with an idea to turn RFID tags into sensors by configuring the Integrated circuit (IC) in such a way that it works as a fully passive RFID tag but also switches to a semi-passive RFID tag connected to a external power source when it detects some changes in the environment such as humidity, temperature, etc. These sensors can be deployed to monitor temperature in retail cold chains and mines, humidity, fill levels in dustbins, etc.
Features of passive RFID sensors
1. Passive RFID sensors are small, wireless devices that utilize radio-frequency signals to transmit and receive data. Being wireless, the data can be transmitted via radio frequency signals, when interrogated by an RFID reader.
2. These sensors do not require a power source of their own and instead rely on the energy emitted by the RFID reader to function.
3. Passive RFID sensors are capable of measuring and monitoring various parameters such as temperature, strain, humidity, and vibration.
Benefits of Passive RFID Sensors for Structural Health Monitoring
1. A Cost-effective Solution
Passive RFID sensors are relatively inexpensive compared to traditional wired sensors, making them a cost-effective choice for large-scale monitoring projects. Chipless RFID sensors are in development that cost the least of all sensors and provide the same efficiency. Chipless RFID tags cost around 1 US cents.
Their affordability allows for the deployment of a higher number of sensors, resulting in improved monitoring accuracy and coverage.
2. Passive RFID Sensors are Wireless and Non-Intrusive
Passive RFID sensors are non-intrusive and eliminate the need for extensive wiring, reducing installation time and complexity. Their wireless nature makes them ideal for retrofitting existing structures without disrupting their functionality. These sensors can be easily embedded or attached to structural components without causing damage or altering the original design.
3. Offer Real-time Monitoring
Passive RFID sensors provide real-time data, enabling continuous monitoring of structural health. The ability to detect and transmit data wirelessly allows for immediate analysis and response to any deviations or anomalies. Real-time monitoring helps identify potential structural issues, preventing catastrophic failures and minimizing maintenance costs.
4. Longevity and Durability
Passive RFID sensors are designed to withstand harsh environmental conditions, ensuring their longevity and reliability. These sensors are resistant to moisture, corrosion, and other external factors that might compromise their performance. Their durability allows for long-term monitoring, making them suitable for structures with extended service life.
Need for Structural Health Monitoring in Construction
Once any of the structure is constructed, it is common practice to maintain the same. Following are the reasons for that:
1. Early Detection of Structural Issues
Structural failures can lead to significant economic losses, human casualties, and environmental damage. Passive RFID sensors enable the early detection of structural issues such as cracks, deformations, and material degradation, preventing potential disasters.
2. Improved Maintenance Planning
Continuous monitoring of structural health by passive RFID sensors provides valuable data for proactive maintenance planning. Timely maintenance interventions based on accurate sensor data can extend the lifespan of structures and reduce maintenance costs in the long run. Moreover, it can also save valuable lives by preventing unforeseen collapse of the structure.
3. Enhanced Structural Performance
Real-time monitoring allows for a better understanding of structural behavior under various loads and environmental conditions. Structural Engineers can analyze the collected data by passive RFID sensors and optimize structural designs, leading to improved performance and safety.
To summarize, the need for early detection of structural issues, improved maintenance planning, and enhanced structural performance further emphasizes the significance of passive RFID sensors in ensuring the safety and longevity of our built environment. These sensors can be designed with chipped RFID as well as Chipless RFID tags.
Passive RFID strain sensor tags offer numerous benefits for monitoring the structural health of various infrastructure assets. Their cost-effectiveness, wireless nature, real-time monitoring capabilities, and durability make them an ideal choice for SHM applications.
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