Sensor Monitoring with RFID
Introduction
Sensor Monitoring can be a vital ability in certain applications, such as logistics and healthcare. Combining sensor monitoring with RFID allows for the observation of uniquely identifiable items at short and long ranges. Whether using battery power or collected RF energy, sensors can collect relevant data pertaining to:
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- Temperature
- Humidity
- Moisture
- Motion/Movement
Sensor Monitoring has been operative in both battery-assisted passive and active RFID tags for quite some time. With advancements in technology, especially in energy collection and impedance, sensor monitoring can now be accomplished using passive RFID tags without a decrease in read range. Sensor monitoring RFID tags must be read by readers that have interfaced with specific application software in order for the sensor data to be interpreted correctly. If the sensor information is collected by an RFID reader without the appropriate software, the information will be unintelligible.
To fully understand the abilities and characteristics of sensor monitoring and RFID, it is easier to examine how each type of tag works with the addition of a sensor.
Active Sensor Monitoring RFID Tags
Active RFID tags are grouped into two distinct classes: beacons and transponders.
Transponders only send information when interrogated first by an RFID reader. With the addition of a sensor, when interrogated, these tags can be asked to only send a unique ID, or can be asked to send the sensor data as well. When transponders are interrogated by the reader and asked for pertinent sensor information, the tag powers on, powers the sensor, and then modulates the signal with the information and sends it back to the reader.
Beaconing RFID tags are consistently sending information out at predetermined intervals. Beacon tags with sensors can be programmed to send their sensor information either every time they beacon or send the data on a pre-programmed schedule. Programming beacons to only send their sensor data at a specific time conserves battery power and ultimately enables the battery to last longer. Sensor data typically contains a large amount of information and requires more energy to be sent, which is an important factor to consider when working with sensor monitoring applications.
BAP Sensor Monitoring RFID Tags
Battery- Assisted Passive RFID tags must be interrogated by an RFID reader first in order for them to send a signal, similar to active transponder and passive RFID tags. BAP sensor tags do not have the extreme read ranges that are usually expected with battery-enabled tags; however, BAP tags still have much greater range than passive RFID tags. Sensors in these tags are powered by the internal battery and can function in two ways: either by sending the real-time sensor data upon request by the RFID reader, or by storing the sensor information over time by using data logging capabilities and sending the collected data when requested by the RFID reader.
BAP sensor tags can have data logging capabilities and provide the ability to take scheduled sensor measurements like active beaconing tags. The internal battery allows the sensor to turn on, take a measurement, store the data, and then turn back off. Because the tag is not constantly sending that information to the reader, it does not consume as much battery power as a beaconing active tag. When the data logging BAP sensor tag is read by the reader, all the information collected over a predetermined period of time will be transferred to the reader for observation.
Passive Sensor Monitoring RFID Tags
Recently, manufacturers have figured out a way to incorporate sensors into passive RFID tags withoutgreatly affecting read range. Because passive tags do not have an internal battery to power the sensors, passive tags use RF energy to power the IC/sensor and to send the relevant information back to the reader.
Currently, passive RFID sensor tags can be used to detect temperature and humidity or moisture because of a newly designed integrated circuit (IC). The IC is designed with a bank of capacitors that is able to detect the presence of moisture based on how the moisture affects the tuning of the antenna. That information is then backscattered back to the RFID reader for observation.
Conclusion
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