Radio Frequency Identification Tag for Tracking and Tracing Applications: A Step by Step Design Workflow
Radio Frequency Identification (RFID) is a well-established infrastructure for tracking and tracing applications across multiple industrial supply chains such as pharmaceutical, cosmetics, automobiles, textiles, logistics and other internet of things (IoT) applications. A typical RFID system consists of an RFID interrogator and an RFID tag. The interrogator sends the query signal and the tags within the range of the interrogator receives the query signal and responds by backscattering the identification information. A typical RFID tag consists of an antenna for transmitting and receiving and an RFID chip that contains the identification information. The role of the chip is to ensure that the backscattered signal carries this identification information in terms of bits to the interrogator. There are many commercial RFID chips available in the market that can be used for creating an RFID tag. The following procedure enables a successful simulation of a new antenna design for matching an RFID chip.
Step 1: Identify the RFID chip and obtain the input impedance of the chip at the frequency of operation from the data sheet. For example, In this case, Higgs 3 RFID chip with an input impedance of 39.5 – j70 Ω at 915 MHz is chosen.
Step 2: Identify the substrate for designing the RFID tag. In most cases, typically RFID are screen printed and always has a polyethylene substrate (plastic). For example, in this case, the chosen substrate has properties of the following: dielectric constant of 3.5 and loss tangent of 0.017 with a thickness of 1.52 mm.
Step 3: Identify the area available for the tag and the type of antenna. Typically, since the frequency is in MHz, the size of the antenna is huge and hence miniaturization techniques such as meandered dipole is commonly used. For example, in this case, a meandered dipole is chosen as the antenna type.
Step 4: Identify the impedance matching circuit. Since the input impedance of the microchip is not a standard 50 Ω, it is essential to create a passive impedance matching circuit to conjugate match the input chip impedance. For example, in this case, the port impedance for the antenna is chosen as 39.5 + j70 Ω.
Step 5: Design the antenna with maximum gain using inductance loops for impedance matching and produce a new design as shown in Fig 1 with a good gain at 915 MHz. Standard tricks for designing a simple dipole antenna applies. The solver used for this design is Method of Moments (MoM) and the file is attached to the article (see RFID.cfx).
Fig 1: Schematic of the RFID tag matched to Higgs3.
The reflection coefficient for the above tag is shown in Fig 2 and the 3D gain is shown in Fig 3.
Fig 2. Reflection coefficient of the simulated RFID tag.
Fig 3. 3D Radiation pattern for the RFID tag.