Modeling and Experimentation of short range communications for sensing and IoT

The thesis reports the mathematical models, experimental results and related activities for the development of wireless devices in short-range communication systems aimed at sensing and the Internet of Things. The work originates from the idea of Wireless Body Area Network where low-cost sensors and communicarion systems can be worn or integrated into clothes. Subsequently, the investigation was extended to devices external to the body to be used as laboratory sensors or as a communication device. The first part of the work dealt with the design and construction of wearable, fully textile and reconfigurable Ultra Wide Band (UWB) antennas for Wireless Body Area Network (WBAN) applications. These antennas have the ability to be used in two different configurations (monopole, microstrip), in order to change the topology of the short-range network and the type of communication (on-body communication and off-body communication). The obtained antennas are then used in the realization of a wearable radio-localization system on the principle of harmonic RADAR. A completely passive device, which allows to replicate the received signal in second harmonic, has been designed and built in order to be integrated into wearable UWB antennas. One envisaged use concerns the radio-localization of people whitin post-disaster scenarios or by connecting it to a transducer (for example of temperature) it can be used as a sensor. For the development of textile antennas, it has been envisaged the use of non-conventional dielectric materials, such as fabrics, paper, plastic and organic materials with the aim to use them in the design and construction of low cost and low environmental impact sensors and antennas in the microwave band. For that purpose, their dielectric characterization has been necessary. A permittivity measurement system has been designed based on the ring resonator principle which has elements of versatility and can also be used for the characterization of some types of liquid material. In this context, the research has been extended to the design and construction of low-cost microwave microfluidic sensors for the characterization of acqueous solutions and liquids in general. For what concerns the development of sensors to be used in laboratory, a completely passive RFId (Radio Frequency Identification) tag at 867 MHz has been designed and realized, in order to use it as a sensor in breaking test activities in the laboratory. The designed sensor exploits the variation of the input impedance of a twin line with variable parameters (tapered). Finally, in the context of reconfigurable beam antennas, a Low Noise Amplifier was designed and built to be replicated on the branches of the beam forming network of an antenna array operating at 5 GHz for Wi-Fi (Wi-Fi5) applications. The developed LNA has the peculiarity to work not only as a low-noise amplifier but also as a microwave switch which, when properly piloted, allows the reconfiguration of the antenna beam. This solution avoids the use of microwave switches or circulators and thus reduces the noise of the receiving chain and the overall dimensions.