The selection of whether to use high, ultra-high or low-frequency (LF) radio frequency identification (RFID) technology for automated waste and recycling management usually comes down to the requirements of the application. Factors to consider when making the decision include how the RFID tag performs in the environment where it is being applied, its read-range, signal strength, and of course, the initial investment cost.
LF’s large radio frequency wavelength isn’t absorbed by moisture as much as HF’s and UHF’s small and compact waves, thereby making LF more resistant to moisture. Here are some additional reasons to consider LF.
It’s been around in the trenches: LF applications have been tried and tested. The animal tracking industry, rife with uncontrollable variables such as weather, unpredictable terrain and other obstacles, has been using LF technology for more than 15 years. It’s rugged, field-proven technology.
You can’t listen when you’re talking: Sure humans can, but in the case of RF communication between the tag and reader, the signal is lost. An LF air interface communication scheme called half duplex frequency modulation means the reader shuts down during the tag’s response, or simply, the reader and tag don’t talk to each other at the same time. Other LF products transmit and respond at the same time (a full duplex frequency system), thereby weakening the signal strength. Consider that the motor and the control lines of the garbage truck can also interfere with the reader and transponder, and the need for a strong signal becomes apparent.
Whatever UHF transmits bounces off metal: This creates an adverse effect on the ability to read the tag. UHF signals are electromagnetic and they bounce off the metal walls of the truck causing read holes that can make reading the tag inaccurate and inconsistent. LF signals are magnetic, small and direct, meaning they don’t bounce off the truck’s metal walls and they don’t interfere with the signal between the LF tag and reader.
One man’s trash is another man’s… trash?: In communities where trash disposal units are lined up in close quarters, the large read range of UHF can mean one can’s capacity could be measured while another is being identified, resulting in credits being allocated to the wrong residence. For example, if the Smith’s 50 pounds of recyclables are read as the Joneses, then the Jones family gets credit for it. It’s already hard enough to keep up with them without help from inaccurate trash readings.
If the tag fits, then use it: The form factor for LF transponders already exists with a rigid overmolded tag that is compatible with waste disposal units. The argument against LF solely rests on the initial investment cost. Some may opt for seemingly lower-cost UHF, although, by the time a new encapsulation is created for UHF’s larger antennae, the price is comparable.
Rafael Mena is with TI RFid Systems in Plano, Texas. contact Rafael at firstname.lastname@example.org