Radio-frequency identification

Radio-frequency identification, known as RFID, is a method of automatic identification and data capture.

It uses electromagnetic fields to identify and track objects automatically. Unlike a traditional barcode, an RFID tag does not require a direct line of sight to be read. This allows the tag to be embedded deep within an object or hidden from view.

This technology is essential for modern logistics, security, and inventory management across many global industries.

An RFID system relies on the interaction between three main components: a tag, a reader, and a transmitter. The tag is a tiny radio transponder attached to an object. It consists of a microchip, which is an integrated circuit that stores and processes information, and an antenna for signal transmission.

The reader, also called an interrogator, sends out an electromagnetic interrogation pulse. When the tag receives this pulse, it responds by transmitting digital data back to the reader. This data is often a unique identifying number, such as an Electronic Product Code (EPC).

There are three primary types of tags categorized by how they receive power. Passive tags are small and inexpensive because they contain no battery. Instead, they harvest energy directly from the radio waves sent by the reader. However, they require a power level roughly a thousand times stronger than active tags to function.

Active tags include an on-board battery, allowing them to transmit signals over much greater distances, sometimes up to hundreds of meters.

Finally, battery-assisted passive (BAP) tags use a small battery to help power the tag's return signal when it is activated by a reader.

RFID technology has roots in several historical inventions. In 1945, Leon Theremin created "The Thing," a passive listening device that used reflected radio waves. While it was a covert device, its ability to be energized by an outside source makes it a predecessor to RFID. In 1973, Mario Cardullo patented the first true ancestor of modern RFID, which was a passive transponder with memory.

Later that year, researchers at Los Alamos National Laboratory demonstrated reflected-power RFID tags operating at 915 MHz. The first patent specifically using the term "RFID" was granted to Charles Walton in 1983.

Today, the RFID market is a massive global industry. In 2014, the market was valued at US$8.89 billion, growing from US$7.77 billion in 2013. This value is expected to rise from US$12.08 billion in 2020 to US$16.23 billion by 2029. The scale of production is immense; in 2024, approximately 50 billion tag chips were sold worldwide. These tags operate across various frequency bands, ranging from Low Frequency (LF) at 120–150 kHz to ultra-high frequencies used in specialized microwave applications.

Practical applications for RFID are found in nearly every sector. In manufacturing, tags can track an automobile's progress through an assembly line. In healthcare, they can track pharmaceuticals through warehouses. RFID is also used for animal identification through microchips implanted in livestock or pets.

In retail, tags help expedite checkouts and prevent theft. However, the ability to read personally linked information has raised significant privacy concerns, leading to the development of new security standards.

Managing multiple tags at once requires advanced technical protocols to prevent data errors. When many tags are in a reader's range, a "collision" can occur if they all respond at once. To solve this, systems use "singulation" methods. One method is the slotted Aloha system, where tags use a pseudo-random delay before responding. Another is the adaptive binary tree protocol, where the reader transmits data bit by bit to identify individual tags.

This ensures that even a pallet full of tagged items can be scanned accurately and efficiently.