Interrogation unit and SAW RDL sensor design for automatic measurement of temperature and stress

Technology advances towards the concept of IoT (Internet of Things), which is the idea of a global network that integrates electronics and computer-based systems on physical devices continuously sharing data, resulting in efficiency improvements and other benefits. Another branch of engineering developments is directed towards automation and artificial intelligence, which are being increasingly implemented in today’s world, and predictably will play a very important role in the years to come. What all these concepts have in common is the necessity gathering information of their surroundings, or in other words, the incorporation of sensors. The monitorization of physical parameters such as temperature or the concentration of a certain substance in the air are of vital importance, because they may trigger actions that need to be taken to avert dangerous situations. A sensor is a device that transforms a physical parameter into an electrical variable, which can be measured and quantified. Throughout the years, many sensing devices have been studied and developed; however, Surface Acoustic Waves (SAW) technology specifically presents various attractive qualities for the current sensor market. SAW sensors are solid state devices based in piezoelectric materials, which transform electrical energy into mechanical waves. These are affected by multiple physical parameters, like temperature, pressure, stress, concentration of a gas, etc., which modify the waveform traveling through the material substrate (its amplitude, its frequency and / or its transversal speed). These changes can be measured by a radio-frequency unit, and the information about the physical parameters affecting the sensor can be extracted. An interesting benefit of these devices is that they are passive, and as such don’t need any kind of power supply. Adding the fact that they can be interrogated wirelessly, offer higher protection against electromagnetic interference and their small size and low cost, SAW devices are a very interesting alternative for IoT applications. The available computerized units in the market needed to extract the information acquired by these sensors, however, are still expensive and specialized. This is the motivation for this project: the development of a low-cost, multi-purpose, automatic interrogation unit, based in software-designed radio (SDR), that can extract information from SAW devices response to an excitation signal. It is also a goal to accomplish this task in real-time. The focus will be put on reflective delay line (RDL) SAW devices. To this end, the software toolkit GNU Radio will be used, in conjunction with an Ettus B200 board that enables the implementation of an SDR.Outgoin