Logistics and supply chain management are increasingly turning to radio frequency identification (RFID) technology to provide real-time visibility into the locations and quantities of materials and items. The use of RFID tags can speed the inventory management process, reduce opportunities for human error and help reduce inventory shrinkage. RFID tags do not necessarily need to be visible to be read and can be read while the tag is inside a box or other enclosure. In addition, one person can read hundreds of RFID tags at once from a distance.
Designers need to select between RFID tag power architectures and data formats, and they need compact and accurate RFID readers. Tags and readers may also need to meet the requirements of the Electronic product code (EPC) UHF Gen2v2 technology standard and the RAIN RFID data format.
This article reviews RFID technologies, including active and passive tags, and the possibility of enhancing passive tag performance with the addition of energy harvesting. It summarizes the various industry standards that designers need to be aware of when deploying RFID-based logistics tracking systems and closes by presenting RFID tags and reader choices from STMicroelectronics, Murata Electronics, and Melexis Technologies, along with evaluation platforms to speed the design of RFID logistics solutions.
RFID platforms can be categized in several ways; by operating frequency bands, powering architecture, and data communications formats. There are three primary operating frequency bands, low frequency (LF), high-frequency (HF), and ultra-high frequency (UHF). The LF band covers 30 to 300 kiloHertz (kHz), with most LF tags operating at 125 kHz. LF tags have a shorter read range of about 10 to 30 centimeters (cm) and slower read speeds than higher frequency tags but are relatively less sensitive to electromagnetic interference (EMI). They are used for cable identification, surgical instrument, medical equipment tracking, and maintaining tool inventories.
Near field communication (NFC) tags are a subset of HF RFID. All NFC tags operate in the HF band, but not all tags in the HF band use NFC protocols (Figure 1). NFC tags are generally limited to a few centimeters (cm) of transmission distance, while other HF tag designs can transmit up to 30 cm. In addition, NFC tags are only specified for operation at 13.56 Megahertz (MHz). While all RFID tag frequencies are used in logistics applications, UHF RFID tags are sometimes referred to as ‘supply chain’ tags due to their combination of longer read ranges, faster read rates, and the availability of data formats optimized for logistics applications.
technology” alt=”How to Deploy the Latest RFID Advances in Logistics Tracking Applications”>Figure 1: NFC tags are a subset of LF RFID technology and typically operate at 125 kHz. (Image source: STMicroelectronics)
RFID tags can be categorized according to their power architectures:
- Active tags have a battery and can transmit periodically, without being polled, and can have read ranges up to 100 meters.
- Passive tags must be polled by a reader. The energy from the reader’s RF signal turns on and powers the tag, reflecting information back to the reader.
- Energy harvesting tags are a form of passive tag that can capture the RF energy transmitted by the reader and use the harvested energy to power additional system components.
- Semi-passive tags, also called battery-assisted tags, include a battery but operate like a passive tag and only transmit data when polled by a reader.
Passive tags, including UHF and NFC designs, are the most common forms of RFID in logistics solutions. Active tags are much more expensive and are typically used to track high-value assets in the construction, transportation, and healthcare industries. Semi-passive tags, especially those using NFC technology, are only found in specific applications such as cell phones.
The ISO/IEC 14443 and ISO/IEC 15693 standards ensure interoperability of NFC-enabled devices. NFC operation is based on inductive coupling and is sensitive to antenna orientation (Figure 2). An NFC device can be a passive design powered by the RF field generated of another NFC device or a semi-passive design with a battery power source. Because of their short transmission ranges, NFC tags are inherently more secure. In addition, NFC tags must be read one at a time, while other RFID technologies such as UHF tags support the simultaneous reading of large numbers of tags. Compared with other LF RFID technologies, NFC tags can store and transmit larger quantities of information, enhancing their utility in logistics applications. A dynamic NFC RFID tag is a dual interface, fast transfer, energy harvesting tag with configurable interrupts, RF management, and low power operating modes.
Figure 2: Proper antenna orientation is needed to enable the inductive coupling required by NFC devices. (Image source: STMicroelectronics)
RAIN and EPC for logistics management
The use of the ISO/IEC 18000-63 GS1 UHF Gen2 protocol is promoted by the RAIN (RAdio frequency Identification) RFID alliance. RAIN technology was developed to link UHF RFID tags to the cloud using the internet. RAIN’s EPC gen 2v2 is a protocol for passive RFID tags and supports security and privacy by authenticating tags and readers. RAIN has modified the ISO numbering system to simplify the use of company identification numbers.
The EPC universal identifier standard for physical objects was developed by EPCglobal, a joint venture between GS1 US (formerly the Uniform Code Council, Inc.) and GS1 (formerly EAN International). EPC has been adopted as the ISO 18000-6C standard. It standardizes how readers and tags communicate and how EPC data is shared between users. EPC is an identifier and data format, while RFID is the RF carrier technology.
Dynamic NFC tags
For logistics solutions that can benefit from dynamic NFC tags, designers can turn to the ST25DVxxKC family from STMicroelectronics. Devices in this family offer 4 kilobits (Kbit), 16 Kbit, and 64 Kbit of electrically erasable programmable memory (EEPROM). For example, the ST25DV04KC is a 4 Kbit device. All ST25DVxxKC devices use the ISO/IEC 15693 NFC protocol and have two interfaces. The I2C serial link can be operated from a dc power source such as a battery. The RF link activates when the received carrier’s RF energy is powering the device. These tags also include an energy harvesting capability to power external components (Figure 3). This analog output (V_EH) delivers the analog voltage V_EH available when the energy harvesting mode is enabled and when the RF field strength is sufficient. The energy harvesting voltage output is not regulated.
Figure 3: ST25DVxxKC devices use the ISO/IEC 15693 NFC protocol (center block), an I2C interface (lower right), and energy harvesting capability (in the Analog Front End and Digital Unit Control blocks). (Image source: STMicroelectronics)
NFC reader eval board
The X-NUCLEO-NFC03A1 from STMicroelectronics is an NFC card reader evaluation board based on the ST25R95-VMD5T that can speed the development of RFID solutions (Figure 4). The ST25R95-VMD5T manages frame coding and decoding for standard applications, such as NFC. The X-NUCLEO-NFC03A1 supports ISO/IEC 14443 Type A and B, ISO/IEC 18092, and ISO/IEC 15693 (single or double subcarrier) protocols. It can detect, read, and write using NFC Forum Type 1, 2, 3, and 4 tags. In addition, this eval board is compatible with the ST Arduino™ UNO R3 connector pin assignment.
Figure 4: The X-NUCLEO-NFC03A1 card reader eval board enables expansion of the STM32 Nucleo boards for NFC with support for proximity, and vicinity standards. (Image source: STMicroelectronics)
RFID on metal surfaces
Designed for use on surgical instruments and tools, Murata’s LXTBKZMCMG-010 on-metal UHF RAIN RFID tag uses the metal surface as a booster antenna to increase the read range up to 150 cm. The LXTBKZMCMG-010 operates over the entire UHF frequency band, measures only 6.0 x 2.0 x 2.3 millimeters (mm), and has an operating temperature range of -40 to +85 °C. It complies with the EPC global Gen2 (v2) and the RAIN RFID protocols.
US regulations require a unique device identifier (UDI) to be placed on each surgical tool. Like EPCs, UDI regulations are designed to support medical equipment’s safe use and storage. UDI systems apply to many types of medical equipment but are especially important with surgical instruments where there is a significant risk of preparing incorrect instruments for a procedure. Europe is also expected to require UDIs on surgical tools in the future. In addition to the logistics challenges related to surgical tools, the setup of surgical tools is time-consuming and prone to error, even by experienced individuals.
Figure 5: The metal surfaces of surgical instruments and tools are used by Murata’s LXTBKZMCMG-010 on-metal UHF RAIN RFID tag as a booster antenna to increase the read range. (Image source: Murata)
LF RFID transceiver IC and eval board
Logistics solutions that can benefit from an LF RFID transceiver can turn to the MLX90109 single-chip 125 kHz RFID transceiver from Melexis. The MLX90109 combines minimum system cost and power consumption in a highly flexible device. The reader’s carrier frequency and oscillator frequency are determined with an external coil and capacitor connected as a parallel resonant circuit, eliminating the need for an external oscillator and preventing zero modulation effects with perfect antenna tuning. The non-decoded transponder signal can be transmitted on a single wire interface for the simplest implementation. Optionally, the MLX90109 can decode the transponder signal on-chip and share the decoded signal through a 2-wire interface with the clock and data. Features of the MLKX90109 include:
- Highly integrated solution in an SO8 package
- External quartz reference not needed; only two resistors plus antenna
- On-chip decoding supports ease of use and fast system design
- Clock and open-drain data outputs enable 2-wire serial communication
Melexis’ EVB90109 allows designers to evaluate the performance of the MLX90109 IC (Figure 6). It also speeds the development of compact and cost-effective RFID applications. All pins of the MLX90109 eval board are available on a dual in-line (DIL) socket for easy connection to an external microcontroller. The EVB90109 can be used to read data from a transponder, or it can be used to send information to a transponder using On/Off keying modulation. The ‘fast decay’ circuit of an external transistor and diode in parallel on the antenna supports fast protocol operation.
Figure 6: Designers can gauge the performance of the MLX90109 IC using the EVB90109 eval board. (Image source: Melexis)
RFID tags are increasingly being used in logistics tracking applications. The variety of available RFID tag technologies, including various frequency bands, powering architectures, and communications and data protocols, means that there are tags available that can meet a wide range of logistics tracking needs. With some RFID technologies, one person can read hundreds of RFID tags at once from a distance, speeding up the inventory management process. In the case of surgical instruments, the use of RFID tags can eliminate one source of human error and make surgeries safer. UHF and NFC RFID tags are the most common forms of RFID in logistics solutions, but LF 125 kHz tags can support low-cost and simple designs with a minimum of external components.