Wireless Underground Sensor Networks (WUSN) is an emerging area of research. They are used in many applications from intelligent irrigation to security and assisted navigation. WUSN mainly use narrowband systems working in the frequency range below 1 GHz and, therefore, suffer from a poor localization capability and large-sized antennas. The use of Impulse Radio Ultra Wideband (IR-UWB) technique allows alleviating these drawbacks. In this letter, the impact of soil on UWB underground to aboveground communication link is studied experimentally. More specifically, the effects of the orientation of the buried antenna, of the burial depth and soil moisture are investigated. The experimental results show that, at 7 GHz, additional attenuations of 10, 34 and 40 dB are noted for depointing the underground antenna by 90°, increasing the depth from 0 to 30 cm and rising the soil moisture from 0% to 20%, respectively. Burial depth lower than 30 cm or soil moisture lower than 20% allow getting acceptable received signal strength (superior to -100 dBm) for communication and localization, particularly in the UWB low band (3.1 to 5 GHz). The obtained results bring out the feasibility of UWB WUSN.Index Terms-buried antenna, underground communication, UWB, WUSN.

Abstract-A compact printed dipole antenna using fractal shape for Radio Frequency IDentification (RFID) is presented. The proposed antenna consists of a third iteration fractal tree structure with the aim of reducing the antenna size. It occupies a volume of 78×30×1.58 mm 3 and the radiator is composed of two arms. The antenna has been designed and optimized to cover the bi-band for passive RFID tag at 915 MHz and 2.4 GHz. A parametric study of the proposed antenna was carried out in order to optimize the main parameters. Details of the proposed antenna design and measurement results are presented and discussed.

No abstract

Ultra-wideband (UWB) wireless underground sensor networks consist of wirelessly connected underground sensor nodes that communicate through the soil. Performances of buried antennas and of the communication link depend on the soil dielectric characteristics. The effects of soil moisture and depth, in the frequency band of 3.1-10.6 GHz, on an UWB antenna return loss and bandwidth are presented. The measurements are conducted in two different types of soil: sandy soil and railway pebbles. The experimental results show that burying antenna shifts down its bandwidth. This phenomenon is accentuated by the increase of soil moisture and not impacted by the burial depth variations. In a dry sandy soil, the shift of the bandwidth low-end is of 0.75 GHz, while it is 1 and 1.5 GHz at 5 and 20% soil moisture, respectively. This fact has allowed us to further miniaturise the used antenna.