Understand why read vs write read range changes significantly and how to take that into account in your specific application.
Previous posts discussed about how read range works in UHF RFID systems. As an extra fact, it is important to note how a higher power consumption on the tag impacts the read range of the system.
Read vs write range
A direct example of this is the differentiation between reading an RFID tag and writing on an RFID tag. While reading only takes the tag to access a specific memory block inside the RFID chip, writing on the memory requires the RFID chip to use more power during longer times.
Remember that the RFID chip had a very important specification called sensitivity – the lowest energy required for it to function. You will now understand why some tag manufacturers share two different values: read range and write range.
Write range will be generally much shorter than the read range but it may be equally important – and thus, the limitation – for some applications. Those RFID solutions relying only on reading EPC numbers will be OK with good read ranges.
However, some solutions will require not only reading but writing on tags – data from specific processes, dates, etc. The limitation for these solutions will not be the read range but the write range – and time required, by the way.
Adding sensors to RFID tags
You can probably guess by now what happens to read range when you are working with UHF RFID systems incorporating battery-free sensors.
Adding external sensors of any kind in UHF RFID tags is possible. Sensors such as ambient light, temperature, pressure, strain gages, accelerometers, magnetometers, soil moisture, and many more can work battery-free as RFID sensor tags.
RFID sensor tags are limited by the power transfer in the reader to tag side. Sensitivity of the RFID chips that are optimized for battery-free sensors is generally lower than those designed only for ID communication. On top of that, these tags should show:
- Tag ID read sensitivity. Directly linked to chip read sensitivity
- Tag write sensitivity. Directly linked to chip write sensitivity
- Sensor read sensitivity. Depends on the electronics and sensors deployed on the specific sensor tag. More power consumption means shorter read range to this is a value that should be given with the tag, not the RFID IC itself
It is important to note that sensor tags may be read at a specific distance but, once read, you may not be able to power up the sensor. That’s why you will need to focus on the sensor read range more than the standard ID read range when using passive RFID sensor tags.
For more information on read range of UHF RFID systems download the free eBook ‘The secrets of read range in UHF RFID sensor systems‘.