The best choice for simple, inexpensive tracking without batteries is a passive RFID tag. Because they are light and easy to maintain, they are used in many sectors like retail, logistics and access control.

This article will explain how passive RFID tags operate, explain when to use them, talk about the available frequency types and discuss their advantages and disadvantages.

What Are Passive RFID Tags

A passive RFID tag does not include its own source of energy. It only works when it receives energy from an RFID reader. RFID tags are particularly helpful when you manage a big inventory of assets.

Keep these things in mind:

• Passive RFID tags do not include any internal battery.
• RFID tags are activated by signals coming from the readers.
• Most tags are available for as little as $0.08 per tag.
• They can work for a longer period than battery-powered devices.
• They can send signals only over a short distance which is usually 30 feet or less.

How Do Passive RFID Tags Work

Think of passive RFID tags as gathering energy from their environment. They do not start work until a reader emits a radio-frequency (RF) signal. After that, the tag starts to gain power and sends out its data.

Here’s what you need to do each step of the way:

1. Radio Wave Emission – A radio wave is sent out by the RFID reader.
2. Energy Harvesting –While in the wave field, the tag harvests energy from the waves with its antenna.
3. Chip Activation – The energy turns on the chip inside the tag.
4. Data Reaction– The chip responds to a signal by sending data (for example, a serial number). It does this by reflecting the signal and modulating it which is called backscatter.
5. Reaction of Readers– The reader detects the changes in the voice and interprets the message.

Because this exchange is so fast, you get instant and smooth tracking.

When to Use RFID Tags That Are Passive

Choose passive RFID tags if you don’t require constant updates or a very long range. Because they do not transmit data by themselves, you only see data after a reader activates them. Because of this, they are both economical and easy to take care of.

Passive RFID tags should be used for:

• You are labeling thousands of items that are low-cost.
• There is no need for real-time GPS tracking.
• You are working in a place that is indoors or just slightly rugged.
• Pick a thin design that sticks well to the adhesive.

Kinds of passive tags include:

• Inlays:Inlays are thin, flexible and inexpensive; they are ideal for putting labels on packages or clothes.
• Hard tags:Durable plastic or metal hard tags are perfect for outdoor locations and places where harsh weather and temperatures are usual.

Passive RFID Tags Frequency Types

The communication between an RFID tag and a reader depends on matching the used frequency. The most common frequencies for passive RFID tags are LF, HF and UHF.

1. Low Frequency (LF) uses either 125 kHz or 134 kHz.

• Range:3 inches
• Best for:Tracking of Animals, managing access
• Pros:Works effectively next to metal or water
• Cons:The distance you can send information is quite limited

2. High Frequency (HF) – 13.56 MHz

• Range:Up to 1 foot
• Best for:Library systems, NFC payments and transit cards
• Pros:Data is sent stably and this technology is popular
• Cons:It needs you to be closer to the antenna than UHF does.

3. Ultra High Frequency (UHF) – 860–960 MHz

• Range:Up to 30 feet (depending on the size of the tag and how strong the reader is)
• Best for:Managing inventory, following assets, tolling
• Pros:Passive tags can be read from long distances and data can be written and read very quickly.
• Cons:Might be affected by metal and liquid substances nearby

Note that how UHF is handled can vary by country, so double-check the local regulations.

Passive RFID Tags Advantages

Passive RFID tags are useful for a number of reasons.

• Affordable:They cost a lot less than active or battery-powered tags.
• Lasts for years: There is no battery to run out, so you can keep using it for a long time.
• Small size: You can easily place them where you want because they are compact.
• Few interferences: Passive tags are not as easily disrupted by electromagnetic noise.
• Simple to scale:Tagging large numbers of items is easy with passive RFID.

Passive RFID Tags Disadvantages

• Reduced reading range:Range is limited to about 30 feet for most, but it depends on the frequency used.
• Absence of current information:Since tags only send data when scanned, you can’t continuously observe the movement.
• Reliant on readers:If readers are not placed in the right way or are not well-covered where you have tags, the results will be poor.
• Storage space is limited: Most passive tags can only store a little, for example, an ID number.

Applications of Passive RFID Tags

Most Popular Applications

• Access Control (HF/NFC):Tag-based entry systems for allowing access to buildings, events or parking areas
• Animal ID (LF):Using microchips for pets and tracking systems for livestock
• Retail Inventory (UHF):Stock counts, handling losses and automated stock replenishment for retailers (UHF).
• UHF (Toll Collection): The vehicle’s ID makes toll payments effortless.
  

 Semi-Popular Applications

• Race Timing (UHF): Monitor the times when runners or cyclists cross the start/finish lines
• Library Management (HF/NFC): Let the system process checkouts and catalog entries automatically
• Product Authentication (HF/NFC): Defend branded products against being counterfeited
• Asset Tracking (UHF): Manage high-value items that are kept in warehouses or factories

Emerging Applications

• Work-in-Process (UHF): Monitor every item as it goes through production
• Logistics (UHF): Keep track of all shipments from the beginning to the end of the supply chain
• Food Inventory (HF/UHF):In grocery or restaurant environments, use Food Inventory (HF/UHF) to oversee perishable items.
• Pharmaceuticals (HF/UHF):For pharmaceuticals (HF/UHF), verify and follow the movement of medicine from where it is made to where it is sold

Important Information Regarding Battery-Assisted Passive RFID Tags

Battery-assisted passive (BAP) RFID tags are also referred to as semi-passive or semi-active tags and they are not as advanced as active tags but more advanced than passive tags. Even though readers are needed to activate transmission, these tags have a battery inside which improves the strength of the signal and the reliability of reading.

The reasons this matters to you:

• You experience better results than traditional passive tags.
• They are still cheaper than the full-function tags.
• They work properly in cool areas and when there is metal around.

But since the battery will eventually run out, you lose some of the very long lifespan that pure passive RFID tags can have.

Conclusion

Now you understand the operation of passive RFID tags, the types of frequencies involved and their strengths and weaknesses. Choose the correct tags and update them as often as needed for your situation.