“Logistics and supply chain management are increasingly turning to radio frequency identification (RFID) technology to enable real-time visibility into the location and quantity of materials and goods. Using RFID tags can speed up inventory management, reduce human error, and help reduce inventory drawdowns. RFID tags don’t have to be seen to be read, and can be read when the tag is inside a box or other enclosure. Additionally, a single person can read hundreds of RFID tags at once from a distance.
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Author: Jeff Shepard
Logistics and supply chain management are increasingly turning to radio frequency identification (RFID) technology to enable real-time visibility into the location and quantity of materials and goods. Using RFID tags can speed up inventory management, reduce human error, and help reduce inventory drawdowns. RFID tags don’t have to be seen to be read, and can be read when the tag is inside a box or other enclosure. Additionally, a single person can read hundreds of RFID tags at once from a distance.
Designers need to choose between power architectures and data formats for RFID tags, as well as compact, accurate RFID readers. Tags and readers may also need to meet the requirements of the Electronic Product Code (EPC) UHF Gen2v2 technical standard and the RAIN RFID data format.
This paper reviews RFID technologies, including active and passive tags, and the possibility of improving passive tag performance by adding energy harvesting capabilities. This article summarizes the various industry standards that designers need to be aware of when deploying RFID-based logistics tracking systems, and concludes with an introduction to RFID tag and reader selection from STMicroelectronics, Murata Electronics, and Melexis Technologies, which are used to accelerate RFID logistics solution design evaluation platform.
RFID platforms can be divided into several forms by operating frequency band, power supply architecture and data communication format. There are three main operating frequency bands, Low Frequency (LF), High Frequency (HF) and Ultra High Frequency (UHF). The low frequency band is 30 – 300 kHz, and most low frequency tags operate at 125 kHz. Low-frequency tags have shorter read distances, around 10 – 30 cm, and are slower to read than high-frequency tags, but are relatively less susceptible to electromagnetic interference (EMI). These labels are used for cable identification, surgical instruments, medical equipment tracking, and maintaining tool inventory.
Near Field Communication (NFC) tags are a subset of high-frequency RFID. All NFC tags work in high frequency bands, but not all high frequency tags use the NFC protocol (Figure 1). The transmission distance of NFC tags is generally limited to a few centimeters, while other high-frequency tags are designed to transmit 30 cm. In addition, the operating frequency of NFC tags is specified at 13.56 MHz. While all RFID tag frequencies are used in logistics applications, UHF RFID tags are sometimes referred to as “supply chain” tags because of their combination of greater read range, faster read rates, and better readability for logistics applications. optimized data format.
Figure 1: NFC tags are a subset of low-frequency RFID technology, typically operating at 125 kHz. (Image credit: STMicroelectronics)
RFID tags can be classified according to their power architecture:
・ Active tags contain batteries, can transmit periodically, without polling, and have a read range of up to 100 m.
• Passive tags must be polled by the reader. The energy of the RF signal emitted by the reader turns ON and powers the tag, reflecting the information back to the reader.
・ An energy harvesting tag is a passive tag that captures radio frequency energy emitted by a reader and uses the harvested energy to power other system components.
• Semi-passive tags (also known as battery-assisted tags) include a battery, but operate like passive tags, transmitting data only when polled by a reader.
Passive tags (including UHF and NFC designs) are the most common form of RFID in logistics solutions. Active tags are expensive and are often used to track high-value assets in the construction, transportation, and medical industries. Semi-passive tags, especially those using NFC technology, are limited to specific applications such as cell phones.
The ISO/IEC 14443 and ISO/IEC 15693 standards ensure interoperability between NFC-enabled devices. The operation of NFC is based on inductive coupling and is sensitive to antenna orientation (Figure 2). An NFC device can be a passive design powered by an RF field generated by another NFC device, or a semi-passive design with battery power. Due to their short transmission distance, NFC tags are inherently more secure. In addition, NFC tags must read only one tag at a time, while other RFID technologies such as UHF tags support the simultaneous reading of a large number of tags. Compared to other low-frequency RFID technologies, NFC tags can store and transmit more information because of their improved utilization in logistics applications. The Dynamic NFC RFID Tag is a dual interface, fast transmission, energy harvesting tag with configurable interrupts, radio frequency management and low power operating modes.
Figure 2: To achieve the inductive coupling required by an NFC device, the antenna needs to be placed in the proper orientation. (Image credit: STMicroelectronics)
RAIN and EPC for Logistics Management
The ISO/IEC 18000-63 GS1 UHF Gen2 protocol is driven by the RAIN (RAdio Frequency Identification) RFID consortium. RAIN technology is used to connect UHF RFID tags to the cloud using the Internet. RAIN’s EPC gen 2v2 is a passive RFID tag protocol that enables security and privacy by authenticating tags and readers. RAIN modifies ISO’s numbering system to simplify the use of company identification numbers.
The EPC Universal Identifier Standard for Physical Objects was developed by EPCglobal. EPCglobal is a joint venture between GS1 US (formerly Uniform Code Council, Inc.) and GS1 (formerly EAN International). EPC has been adopted as an ISO 18000-6C standard. EPC specifies how readers and tags communicate and how EPC data is shared between users. EPC is an identifier and data format, while RFID is a radio frequency carrier technology.
Dynamic NFC tags
For logistics solutions that can benefit from dynamic NFC tags, designers can use STMicroelectronics’ ST25DVxxKC series. This family of devices offers 4 Kb, 16 Kb and 64 Kb of electrically erasable programmable memory (EEPROM). For example, the ST25DV04KC is a 4Kb device. All ST25DVxxKC devices use the ISO/IEC 15693 NFC protocol, which provides two interfaces. The I2C serial link can be powered by a DC power source such as a battery. The RF link is activated when the received RF energy from the carrier powers the device. These tags also have energy harvesting capabilities to power external components (Figure 3). This analog output (V_EH) provides the effective analog voltage V_EH when energy harvesting mode is enabled and the RF field strength is large enough. The Voltage output of the energy harvesting is unregulated.
Figure 3: ST25DVxxKC devices use ISO/IEC 15693 NFC protocol (middle block), I2C interface (bottom right), energy harvesting capability (analog front end and digital unit control block). (Image credit: STMicroelectronics)
NFC Reader Evaluation Board
STMicroelectronics’ X-NUCLEO-NFC03A1 is an ST25R95-VMD5T-based NFC reader evaluation board that can accelerate the development of RFID solutions (Figure 4). The ST25R95-VMD5T manages frame encoding and frame 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 dual carrier) protocols. It can detect, read and write using NFC Forum Types 1, 2, 3 and 4 tags. In addition, the evaluation board is compatible with ST Arduino™ UNO R3 connector pinout.
Figure 4: The X-NUCLEO-NFC03A1 reader evaluation board enables the STM32 Nucleo board to extend NFC to support proximity and proximity standards. (Image credit: STMicroelectronics)
RFID on metal surfaces
Designed for surgical instruments and tools, Murata’s LXTBKZMCMG-010 UHF RAIN RFID tag on metal utilizes the metal surface as an enhanced antenna, extending the read range to 150 cm. The LXTBKZMCMG-010 operates over the entire UHF band, measures only 6.0 x 2.0 x 2.3 mm, and has an operating temperature range of -40 to +85°C. The tag is compliant with EPC global Gen2 (v2) and RAIN RFID protocols.
U.S. regulations require that a Unique Device Identification (UDI) be placed on each surgical tool. Like EPCs, UDI regulations are designed to regulate the safe use and storage of medical devices. UDI systems are suitable for many types of medical devices, but are especially important for surgical instruments, where improper instrument preparation during surgery can pose significant risks. Europe is also expected to require UDI on surgical tools in the future. In addition to the logistical challenges associated with surgical tools, the setup of surgical tools can be time-consuming and error-prone, even for those with experience.
Figure 5: The metal surfaces of surgical instruments and tools are used as enhanced antennas by Murata’s LXTBKZMCMG-010 UHF RAIN RFID tags on metal to extend the read range. (Image credit: Murata)
LF RFID Transceiver ICs and Evaluation Boards
Logistics solutions that can benefit from LF RFID transceivers can use Melexis’ MLX90109 single-chip 125 kHz RFID transceiver. The MLX90109 device is highly flexible while achieving the lowest system cost and power consumption. The reader’s carrier frequency and oscillator frequency are determined by external coils and Capacitors that act as parallel resonant circuits, so no external oscillators are required, preventing zero modulation effects for perfect antenna tuning. Non-decoded transponder signals are transmitted over a single-wire interface for simple implementation. Optionally, the MLX90109 can decode the transponder signal on-chip and share the decoded signal with clock and data over a 2-wire interface. Features of the MLKX90109 include:
・ Highly integrated solution in SO8 package
・ No external quartz reference required; only two resistors and 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 was used to evaluate the performance of the MLX90109 IC (Figure 6). It also accelerates the development of compact, cost-effective RFID applications. All pins of the MLX90109 evaluation board are located on dual in-line (DIL) sockets for easy connection to an external microcontroller. The EVB90109 can be used to read data from a transponder or to send information to a transponder using on/off keying modulation. A “fast decay” circuit of external transistors and diodes in parallel with the antenna supports fast protocol operation.
Figure 6: Designers can use the EVB90109 evaluation board to measure the performance of the MLX90109 integrated circuit. (Image credit: Melexis)
Summarize
RFID tags are increasingly being used in logistics tracking applications. Currently, the variety of RFID tag technologies, including various frequency bands, power supply architectures, and communication and data protocols, means that there are many tags that can meet a wide range of logistics tracking needs. With some RFID technologies, hundreds of RFID tags can be read remotely at the same time, thereby speeding up inventory management. In the case of surgical instruments, the use of RFID tags can eliminate sources of human error and improve surgical safety. UHF and NFC RFID tags are the most common forms of RFID in logistics solutions, but LF 125 kHz tags can support low-cost, simple designs that require few external components.