In-Pipe Wireless Communication for Underground Sampling and Testing

In this paper, we present an effective and low- cost wireless communication system for extremely long and narrow pipes that can replay the extant wire system in underground sensor network applications such as soil sampling and testing with the Cone Penetration Test (CPT), the most widely used underground sensor device. Different from existing in-pipe wireless techniques, we consider real-world pipelines that are very narrow and long. In particular, in our design data are first modulated at a commercial frequency and then converted to high frequency, between 14-15 GHz, to be transmitted along of the pipelines under the circular waveguide mode TM01. Especially, we design a cone-shaped antenna to overcome the aligning problem of feeds between the transmitter and receiver. To evaluate the applicability and efficiency of our design, we conduct realistic simulations as well as experiments with real prototypes. The results of experiments are consistent with our theoretical design and simulations and show that our proposed wireless system can transfer sensory data up to 20 m in narrow CPT pipes with a diameter of 17 mm when using the LoRa modulation with a transmitting power of 1 W, whereas existing underground radio techniques can transfer data from a depth of 2 m at maximum in the same condition. In our approach, it is also possible to add repeaters to extend the communication range when needed.