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

Remote interrogation of SAW ID-tags imposes a high coupling coefficient value ($\text{K}^{\mathbf {2}}$), which many of the most promising substrates for high temperature applications do not possess. In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the standard configuration, i.e. one interdigital transducer (IDT) and several disconnected reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the reflected signals, using direct transmission between IDTs instead of the reflection on passive reflectors. Numerical simulations show promising results. A test structure was also characterized experimentally. As a first step, the test structure was based on the well-known lithium niobate $128 ^{\circ}\mathrm {Y} -\mathrm {X}-$cut substrate. This concept will be extended to other substrates with lower $\text{K}^{\mathbf {2}}$ value, which should prove especially interesting for high temperature applications.