The Magic of Inventory Tracking – Demystified by IMaR Gateway
Companies in Ireland, across the retail, agritech, supply chain, healthcare and manufacturing sectors, have many technology needs. Applications to meet those needs include wearable prototypes, Track & Trace solutions, inventory management, patient safety, asset tracking, authentication and Real Time Location Systems (RTLS).
RTLS is the name generally used to describe systems for tracking and locating indoors although it is not exclusive to indoor systems. It is implemented using a range of technologies and algorithms and these are discussed below. Radio frequency identification has its origins in Radar and the creation of its extension Identification Friend or Foe (IFF) in which a radio signal impinging on a transponder caused it to emit its identification signal.
Developed as an identification technology and an asset tracking mechanism, its use was extended to location using a number of different techniques. The identification principle is where an impinging radio frequency is modulated by the transponder, commonly called a tag, to include the transponder’s identifier and through coupling either by magnetic flux or electromagnetic wave some portion of the energy is sent back towards the RFID reader where it is interpreted. Low frequency (LF) and high frequency (HF) tags use near-field or magnetic-field (inductive)coupling to the reader, while ultra-high frequency (UHF) tags use far-field or electromagnetic wave coupling to the reader. LF RFID systems operate at 125 kHz or 134 kHz and are predominantly used for animal identification or access systems.
HF RFID systems operate at 13.56 MHz. HF systems are primarily used in tickets systems or more recently in payment systems. The most common HF RFID system is called NFC which stands for Near Field Communications. It is essentially a subset of HF RFID with the peculiarity that NFC readers can communicate with one another, exclusive to it alone among RFID systems. This is exploited in payment systems using mobile phones where the NFC reader on the phone communicates with the checkout NFC reader. Additionally several companies and organisations use NFC based identity cards for their employees that can control access to different areas based on employee authorisations. These systems tend to have lower unit costs, in part due to the wide deployment and their inherent ergonomics. LF and HF systems’ range is quite limited and the user needs to actuate the read mechanism by bringing the tag or reader, in the case of a smart phone, close to the reading device. For animal tracking, the animals are funnelled through a narrow gap to allow their tags to be read. Ultra-high frequency, (UHF), signals propagate using the far field and thus have a greater range and can be further divided into passive systems and active systems. Passive systems include both tags containing integrated circuits (IC) or chips (the classic passive tags) and tags where the identifier is a consequence of a physical arrangement of the tag such as in Surface Acoustic Wave (SAW) tags. The chip-less tags use resonant structures, different resonant combinations being used to form tag identifications. The passive tags reflect back a portion of the energy they receive from the reader transmitting antenna. In the case of a SAW tag, the RF wave is converted to an acoustic wave by virtue of the antenna being bonded to a crystal structure that converts the energy from an electromagnetic wave to a physical wave using the piezoelectric electric effect.
There are many other mechanisms to engineer chip-less tags such as Time-domain reflectometry, a form of printable tag, nanometricmaterial ink-tatoos, a form of chemical etched tags and others. For active RFID systems, the tag periodically transmits its identification without the need for the tag to be impacted by a transmitted signal, consequentially requiring a power source. Active tags have an advantage of a greater read range but are more expensive than their passive counterparts and use proprietary protocols.
A hybrid UHF version exists, called semi-passive, whereby the power source is used to power the tag logic circuitry only and does not actively transmit its identifier giving a much longer battery life but also providing a greater range. UHF tags found a ready use in the logistics environment where shipments entering or leaving choke points, such as loading bay doors, could be easily read. The usage evolved from tracking assets to tracking humans although other applications such as contact-free toll charging also arose.
An RFID system has as its basic components, an antenna, a modulator-demodulator and a controller. The antenna is the air interface that converts an electrical signal from the modulator to a radio wave in the case of a UHF system or an extending magnetic flux in the case of a HF or LF system. It also operates in the reverse direction converting the received EM wave or magnetic flux and converting it back to an electrical signal. The modulator-demodulator converts the electrical signal to a binary signal and vice-versa. It also provides an impedance matching element to the antenna. The binary signal comes from or is passed to the controller. The controller will perform any encryption or decryption of the signal to be passed to the tag. For UHF readers there will be additional functionality and complexity to handle the potentially large volume of tags to be managed where a hundred or more tags can be read per second creating complex issues surrounding signal recovery. Additionally, UHF readers can have multiple antennae which adds further complexity.
That’s where IMaR comes in. IMaR has experience of a wide range of sensing, mechatronic and tagging technologies. IMaR can also now support companies’ own initiatives, by measuring performance of RFID devices and application setups, verifying conformance, supporting the development of readers, tags and ICs, measuring tag frequency sensitivity, communication range and backscatter measurements. To that end, IMaR has acquired a state-of-the-art radio frequency identification (RFID) test and development suite, funded by Enterprise Ireland. Wherever humanly possible, IMaR will deploy and test of RFID equipment on-site in industrial environment. The development suite includes a full complement of RFID readers, antennas, RF test equipment and a large catalogue of RFID tags of varying properties which satisfy many different use cases. The facility’s RFID readers cover a wide range of applications: high frequency (HF, for ticketing, payment, and data transfer applications), low frequency (LF, good for livestock tracking), RAIN (passive tags), near-field communication (NFC, for contactless payment etc.), ultra-wideband (UWB, for track-and-trace) plus associated antenna arrays/multiplexers and a series of RFID test units.
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