There is a growing interest in employing sub-soil sensing systems to support precision agriculture. This thesis presents the design of an RFID sub-soil sensing system which is based on integrating passive RFID technology and sub-soil sensing technology. The proposed RFID sub-soil system comprises of an above-ground RFID reader and a number of RFID sub-soil sensor nodes. The key feature of the system is that the sensor nodes do not require an on-board battery, as they are capable of harvesting energy from the ElectroMagnetic (EM) field generated by the RFID reader. The sensor nodes then transmit sensor measurements to the reader wirelessly through soil. With the proposed RFID sub-soil system, the high path loss of the sub-soil wireless channel is a significant problem which leads to the challenge for the system to achieve an acceptable Quality of Service (QoS). In this project, the path loss in soil has been characterised through CST simulations. In the simulations, the effect of the soil on the sensor node antenna has also been investigated. This thesis also presents the design and implementation of a programmable RFID reader platform and an embedded RFID sensor node prototype. The RFID reader platform is implemented using a National Instruments (NI) PXI system, and it is configured and controlled by NI LabVIEW software. The sensor node prototype is capable of harvesting RF energy and transmitting sensor measurements from a temperature sensor through backscatter communication. A series of sub-soil experiments have been carried out to evaluate the performance of the RFID sensor node prototype using the PXI-based RFID reader platform. The experimental results are presented and analysed in this thesis. Additionally, this work has explored trade-offs in the system design, and these design trade-offs are summarised and described.

Les réseaux de capteurs sans fils enfouis (RCSFE) sont des réseaux comportant des capteurs et leurs antennes enfouis dans la matière, en particulier enfouis dans le sol. Ils présentent un grand intérêt dans de nombreux domaines d’activités, comme le contrôle de l’environnement, l’agriculture de précision, la navigation et la sécurité. Les systèmes existants sont à bandes étroites et fonctionnent à des fréquences inférieures à 1 GHz. Ces systèmes impliquent l’utilisation d’antennes encombrantes, ce qui complique leur déploiement et peut conduire à des coûts élevés. De plus l’utilisation de largeurs de bandes étroites limite les débits de communications possibles et la résolution envisageables dans les applications de localisation. Enfin, les systèmes actuels sont gourmands en énergie, ce qui limite la durée de vie des éléments enfouis.Pour remédier à ces inconvénients pour certaines applications des RCSFE, on propose dans cette thèse d’utiliser la technique ultralarge bande (ULB) en bande normalisée 3,1 – 10,6 GHz dans les RCSFE. Cette technique permet l’utilisation d’antennes compactes, la simplification du déploiement, l’amélioration de la précision de localisation et l’augmentation du débit de communication et de la durée de vie des capteurs.Pour étudier la faisabilité des RCSFE ULB, nous avons conçu et réalisé trois antennes ULB compactes et en analyser l’effet du sol sur les performances de ces antennes ULB enfouies et sur les liens de communication ULB enfoui. En comparaison à un fonctionnement dans l’air, l’enfouissement dans le sol décale la bande passante de l’antenne vers les basses fréquences. Ce décalage augmente avec la teneur en eau du sol. L’atténuation apportée par le canal ULB enfoui augmente avec la fréquence de fonctionnement, la profondeur d’enfouissement et la teneur en eau du sol. Cependant, nous avons montré que des liaisons fiables sont possibles pour des distances de propagation dans le sol inférieures à 30 cm et des teneurs en eau inférieures à 20% / Wireless underground sensor networks (WUSN) consist of sensors which are buried in a medium with their antennas, in particular in soil. They attract a huge interest in different fields, like environment monitoring, precise agriculture, navigation and security. The existing narrowband systems operate at frequencies below 1 GHz. These systems imply the use of cumbersome antennas, which complicates the deployment and increases its cost. Furthermore, the use of narrow bandwidths limits the possible communication data rates and the potential resolution in localization applications. Finally, current systems are very energy consuming, which limits the lifetime of the underground elements.To overcome these drawbacks for certain applications of WUSN, we propose in this thesis the use of ultra wideband technology (UWB), in the normalized band 3.1 - 10.6 GHz, in WUSN. This technique allows the use of compact antennas, simplifying deployment, improving the localization accuracy and increasing communication data rates and the lifetime of the underground sensors.In order to assess the feasibility study of UWB WUSN, we have designed and realized three compact UWB antennas and analyzed the effect of soil on the performances of these underground UWB antennas and on the underground UWB communication links. Compared with operating in free space, burying the antenna shifts the antenna bandwidth towards low frequencies. This shift increases with soil water content. The attenuation introduced by the buried UWB channel, increases with the operating frequency, the burial depth and the soil moisture. However, we have shown that reliable communications are possible for distances of propagation in soil smaller than 30 cm and soil water contents below 20%