How Does RFID Store And Transmit Data?

 

Slap an RFID tag on something and you can read it-anyone who's done warehouse inventory knows how convenient these things are. But convenience aside, if you ask most people to actually explain how data gets in and out, they can't. When I first got into this industry, I was completely lost too. It took getting burned by suppliers a few times before I figured things out.

 

The chip inside a tag is so small you can barely see it with the naked eye, but it does have storage space. How much depends on the chip model-cheap ones have just 96-bit EPC, expensive ones can go up to several kilobytes. 96 bits sounds small, but it's actually enough. Convert it to hexadecimal and you get 24 characters, more than enough to store a product code. I've seen clients insist on cramming production dates, batch numbers, and expiration dates all into the tag. After doing the math, tags with large user memory cost three times as much. They ended up just storing the ID and putting everything else in a database.

 

 

Some people ask how tags store data without batteries. I asked the same question back in the day. Turns out they use EEPROM, a storage medium that retains data without power. Unlike USB flash memory, EEPROM can be modified byte by byte, while flash needs to erase whole blocks. That's better suited for RFID where you're often changing individual records. Data written to it can last ten to twenty years-longer than the tag itself.

 

The data transmission principle is a bit convoluted. Tags don't have transmitters and don't actively send signals. The reader emits electromagnetic waves, the tag's antenna picks them up and generates an induced current, and the chip runs on that tiny bit of power. Then the chip does one thing: repeatedly switches the antenna's load impedance. When impedance changes, the strength of the reflected electromagnetic wave changes with it. The reader detects these variations in the reflected wave-high, low, high, low-that's your 0s and 1s.

 

 

This is called backscatter. When I explain it to clients, I usually skip that term-too academic. I just say the tag is like a shape-shifting mirror. The reader shines a flashlight at it, and the tag reflects the light back in its own rhythm by changing the mirror's angle. Not perfectly accurate, but easy to understand.

 

In real projects, the biggest headache isn't the theory-it's environmental interference. Metal reflects electromagnetic waves, water absorbs them, and warehouses are full of both. Last year I did a project at a distillery. Tags were on glass bottles. Empty bottles gave four to five meters read range. Filled with liquor, that dropped to under one meter. We eventually solved it by changing the tag placement. Metal is even worse. Once a client stuck tags directly on steel drums-couldn't read them at all. We ended up using anti-metal tags with a layer of wave-absorbing material underneath. Cost went up seven or eight times.

 

Frequency bands matter too. China's UHF uses 920-925 MHz, the US uses 902-928, Europe uses 865-868. When buying readers, check which bands they support, otherwise imported equipment might not work domestically. I've seen people buy used readers from the US to save money, only to find the frequency band was wrong and they couldn't even return it.

 

 

There are only a few chip manufacturers. Impinj's Monza series has the highest market share. NXP's UCODE is also common. Different chips have different memory configurations and sensitivities. Higher sensitivity means smaller power can activate the tag, which means longer read range. When selecting, look at the specific application-don't just look at price.

 

Write cycles are an easily overlooked parameter. EEPROM is rated for 100,000 cycles, which sounds like plenty, but some scenarios can actually hit that number. I worked on a returnable container management project where every inbound and outbound movement meant one write to the tag. Three or four cycles a day, over a thousand per year, use it for ten years and you can actually max it out. I recommended the client switch to read-only tags paired with a database-the tag just stores an ID, everything else gets updated in the cloud. Problem completely avoided.

 

Don't count on security. Regular tags have no password on the EPC area by default-anyone can read or write. You can set an access password to lock it down, but it's only 32 bits, hardly secure. Access control and payment applications use a completely different class of chips at a completely different price point. Tags used in logistics are basically running naked-but then again, they're not storing classified data anyway. As long as they're readable, that's good enough.