SAW RFID Devices Using Connected IDTs as an Alternative to Conventional Reflectors for Harsh Environments

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 67; no. 6; pp. 1267 - 1274
• Main Authors: Floer, Cecile, Hage-Ali, Sami, Nicolay, Pascal, Chambon, Hugo, Zhgoon, Sergei, Shvetsov, Alexander, Streque, Jeremy, M'Jahed, Hamid, Elmazria, Omar
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.06.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers
• Subjects: Amplitudes; Configurations; Coupling coefficients; Electrodes; Engineering Sciences; Frequency control; High temperature; High temperature environments; Interrogation; Lithium niobate; Lithium niobates; Micro and nanotechnologies; Microelectronics; Propagation; Questioning; Radio frequency identification; radio frequency identification (RFID); Reflection; Reflectors; Substrates; surface acoustic wave (SAW); Surface acoustic waves; Tags; Temperature measurement
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2019.2943310

Remote interrogation of surface acoustic wave identification tag (ID-tags) imposes a high signal amplitude which is related to a high coupling coefficient value (<inline-formula> <tex-math notation="LaTeX">K^{2} </tex-math></inline-formula>) and low propagation losses (<inline-formula> <tex-math notation="LaTeX">\alpha </tex-math></inline-formula>). In this article, we propose and discuss an alternative configuration to the standard one. Here, we replaced the conventional configuration, i.e., one interdigital transducer (IDT) and several reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the detected signal using direct transmission between IDTs instead of the reflection from passive reflectors. This concept can, therefore, increase the interrogation scope of ID-tags made on a conventional substrate with high <inline-formula> <tex-math notation="LaTeX">K^{2} </tex-math></inline-formula> value. Moreover, it can also be extended to suitable substrates for harsh environments, such as high-temperature environments: the materials used exhibit limited performances (low <inline-formula> <tex-math notation="LaTeX">K^{2} </tex-math></inline-formula> value and relatively high propagation losses) and are, therefore, rarely used for identification applications. The concept was first tested and validated using the lithium niobate 128° Y-X cut substrate, which is commonly used in ID-tags. A good agreement between experimental and numerical results was obtained for the promising concept of connected IDTs. The interesting features of the structure were also validated using a langasite substrate, which is well-known to operate at very high temperatures. Performances of both substrates (lithium niobate and langasite) were tested with an in situ RF characterization up to 600 °C. Unexpected results regarding the resilience of devices based on congruent lithium niobate were obtained.