Why UHF RFID Struggles to Read Liquid Assets (and How to Fix it!)

By Times 7, Aug 17, 2020

Liquid assets can range from filled bottles of oils, sauces, and drinks to medicinal vials and pharmaceutical drugs. Even fruit, vegetables, meat, and seafood, both fresh and frozen, fall into the liquid asset category because of their water content.

The reason why UHF RFID struggles with liquid assets is due to the laws of physics.

Have you ever wondered how your food is heated in a microwave?

Microwave frequencies are 300 MHz to 300 GHz and liquids (especially water) absorb this energy. The absorption is used in the microwave to cook food. UHF RFID is part of the microwave spectrum and the same theory applies.

In UHF RFID, the radio frequency is absorbed by the liquid and only a little energy is left after the absorption to energize the tag, and even less energy is available for the tag to respond to the reader.

The Solution

With modern tag and reader antenna designs, a few challenges with tracking liquid assets can be mitigated.

1. Near-field emissions are magnetic rather than electric and therefore liquids do not absorb them.

2. Smaller loop tags are designed to create strong near-fields, large far-field inlay tags also incorporate a nearfield loop for these purposes.  

True NearField Antenna

Choosing the correct antenna is critical when it comes to reading liquid assets. The True NearField reader antennas’ intense surface fields can penetrate through liquids. A True NearField antenna will achieve stronger read results because of the close proximity to the tracked item, which means that minimal RF radiation will be absorbed by the liquid.

Times-7 has developed a UHF RFID True NearField Antenna Series. These are specifically designed to deal with tricky assets, such as liquids or metals. 

Image: Times-7 True NearField Antenna series: A1115, A1130 & A1163

Tag Selection

To create a close-proximity read zone of no more than 10 cm, we recommend pure near-field loop tags, such as the Smartrac Trap near-field tag. Or contact our expert team for further insights: sales@times-7.com. 

What to do in Real Life Applications

• Use a True NearField reader antenna to track individual or a batch of liquid medicinal vials at close distances

• Sparsely pack the tagged items. When stacked on top of each other, it is difficult to excite the blinded tags and the signal may not be powerful enough to be detected by the reader.

• You may not be able to detect a package of those vials pushed in a trolley through an RFID enabled portal, but you can read them when placed in the close proximity read zone.