Overview of the RFID sensor

Radio Frequency Identification or RFID sensors “read” electrically stored data encrypted inside various tags, which is then reflected back to the sensor. The data is transferred to the sensor wirelessly, without the need for physical contact between sensor and tag, by means of electromagnetic fields.

Short-range tags, which are capable of transmitting data over a few metres at most, are read and powered by means of magnetic fields, but some are powered by electromagnetic radiation emitted from the RFID sensor while others are energised by means of batteries. The latter can be read from several hundred metres and a major advantage over other electronic reading technologies such as bar codes is that the tag need not be directly aligned with the sensor. By embedding such tags within various objects, they can be easily tracked at a distance with an RFID sensor.

Industrial applications of this electronic tag-wireless RFID sensor technology are now positively multifarious: minute tags can be embedded in medicines enabling them to be identified and located at the warehouse, car manufacturers use RFID tags to track the progress of vehicle assembly, and pets and farm animals can be tagged with miniscule chips injected under the skin to enable easy and immediate identification.

RFID tags are also now routinely issued to gas and oil industry personnel working on offshore rigs for safety purposes: the tags enable them to be located at all times as they go about their work and an individual can be swiftly pinpointed in the event of an emergency.



The precursors of the modern-day RFID sensor appeared during the Second World War, with IFF transponders capable of distinguishing whether the sound of an incoming aeroplane indicated enemy or friendly aircraft. These devices are still in use for aircraft identification in today’s aviation industry. Conceptually, a major step toward the development of contemporary RFID devices came in 1948, in the form of a seminal scientific paper by the radio engineer Harry Stockman. Stockman predicted a new generation of communication instruments based on “reflected power” – the core feature of contemporary RFID technology.

The first device to actually draw power from the interrogating radio signal, as today’s RFIDs do, was Mario Cardullo’s passive radio transponder of 1973, which he intended for use in several industries, largely because it was equipped with memory to make it highly versatile. Cardulo envisioned it being used to develop electronic licence plates, monitor the performance of vehicles, convey clinical data about patients in medicine, identify personnel and operate automatic gates in security systems, and create electronic credit cards and cheque books in banking, amongst a raft of other things.

Ten years later in 1983, the technology had advanced to become active as well as passive and the first patent bearing the moniker “RFID” went to the electrical engineer and inventor, Charles Walton.


Technical aspects

RFID technology employs a reader or ‘interrogator’ capable of transmitting a coded radio signal to “interrogate” a specially designed electro-active tag or label. As described earlier, this contains electronically stored data. The interrogator then “reads” or receives the reflected-back response from the tag. The information sent by the tag in response to the interrogating signal varies widely from model to model; some will simply yield a serial number but others can supply considerably more information, like the date of the tagged object’s production, data about the unique characteristics of the product as well as a batch or stock number.

Battery operated tags are generally “active”, transmitting their unique identification signals according to a pre-set schedule. Passive tags are activated by the signal coming from an RFID reader only; whereas battery assisted passive (BAP) tags are activated when the interrogator comes into proximity with them.

Readers can be “passive” (Passive Reader Active Tag devices, or PRAT) or “active” (Active Reader Passive Tag, or ARAT). As their names imply, PRAT readers do not interrogate the tag but instead are used with battery-powered active tags that actively transmit a signal to them. ARAT readers send out active signals to interrogate passive tags.

Low speed, short range RFID devices in the frequency range 120 – 150 kHz are typically used for collecting factory data or identifying animals, whereas at the opposite end of the spectrum, high data speed microwave RFID devices with ranges of up to 200m are in the frequency range 3.1-10 GHz. Tags in the Low and High Frequency bandwidths must be in close proximity to the reader to be interrogated, (they’re called “near field” devices as a result), chiefly because they are a tiny fraction of a wavelength away. Ultra High Frequency tags employ different reading and transmitting procedures and active versions can be configured to incorporate distinct and different receivers and transmitters. They also do not necessarily have to react at a frequency commensurate with the RFID reader’s signal.

Readers can excite responses from multiple tags (for example, similar products or components stored in a crate in a warehouse). Readers can be configured to “singulate” these multiple signals to pinpoint a specific tag.

Presently, much effort is underway to miniaturise RFIDs: biologists from Bristol University in 2009 successfully managed to glue tiny micro-transponders to living ants in order to track their in vivo behaviour. Chips are now being produced whose dimensions are no more than a speck of dust, with the smallest on record being developed by Hitachi: it measures a mere 0.05mm x 0.05 mm.


Product application - where the RFID sensor is used in manufacturing

RFID devices are today ubiquitous. In the form of microSD cards, they can be inserted into smartphones, electronically hooked up to the user’s bank account and used to make payments. Linked to portable laptop computers, RFID technology is today widely used in asset management, creating a paperless alternative and eliminating laborious manual data entry procedures. RFIDs can be attached to vehicles so that they can automatically pass through gated areas upon remote recognition without the driver having to stop and provide paper ID to security personnel. But the area in which they are most heavily deployed remains transportation and logistics, where they have revolutionised and simplified the intricacies of yard management, cross docking and the accuracy of pinpointing of multiple products in freight and distribution locations.


How the RFID sensor differs from other sensors

The hallmark feature of RFID technology is the efficient use of radio signals to transmit and receive coded data, which can then be used to identify and locate various items, manage company assets or to automatically activate gates and doors in secure access locations.


Current product advantages and limitations

The costs of RFID technology are relatively low and the efficiency gains they deliver are immense, slashing the number of goods lost during transportation and enabling much more efficient delivery routes for drivers. While increasing miniaturisation is undoubtedly expanding the technology’s versatility, the chief limitation at present with microscopic tags is the extreme difficulty of attaching antennae, which currently shrinks the “read range” for dust-sized particles to millimetres only.

Civil liberties groups have raised concerns that tags containing personal information about individuals can too easily be accessed by third parties, seriously compromising privacy.