Mechano-Magnetic Telemetry for Underground Water Infrastructure Monitoring

Daniel Orfeo,Henry Mitchell,Ming Qin,Robert Farrell,Connie Ou,Tian Xia,Dylan Burns,Dryver R Huston

doi:10.3389/fbuil.2018.00029

Abstract

This study reports on the theory of operation, design principles, and results from laboratory and field tests of a magnetic telemetry system for communication with underground infrastructure sensors using rotating permanent magnets as the sources and compact magnetometers as the receivers. Many cities seek ways to monitor underground water pipes with centrally managed Internet of Things (IoT) systems. This requires the development of numerous reliable low-cost wireless sensors, such as moisture sensors and flow meters, which can transmit information from subterranean pipes to surface-mounted receivers. Traditional megahertz radio communication systems are often unable to penetrate through multiple feet of earthen and manmade materials and have impractically large energy requirements which preclude the use of long-life batteries, require complex (and expensive) built-in energy harvesting systems, or long leads that run antennas near to the surface. Low-power magnetic signaling systems do not suffer from this drawback: low-frequency electromagnetic waves readily penetrate through several feet of earth and water. Traditional magnetic telemetry systems that use energy-inefficient large induction coils and antennas as sources and receivers are not practical for underground IoT-type sensing applications. However, rotating a permanent magnet creates a completely reversing oscillating magnetic field. The recent proliferation of strong rare-earth permanent magnets and high-sensitivity magnetometers enables alternative magnetic telemetry system concepts with significantly more compact formats and lower energy consumption. The system used in this study represents a novel combination of megahertz radio and magnetic signaling techniques for the purposes of underground infrastructure monitoring. In this study, two subterranean infrastructure sensors exploit this phenomenon to transmit information to an aboveground radio-networked magnetometer receiver. A flow meter uses a propeller to directly rotate a diametrically magnetized neodymium magnet. A moisture sensor rotates a magnet with a low-power electric motor. Laboratory performance and field tests establish the capabilities of magnetic telemetry for IoT-linked leak-detection sensors. Remote datalogging with encryption demonstrates the viability of integrating sensors and surface receivers into a LoRa wireless IoT network.

Highlights

Buried infrastructure, such as water and sewer pipes, are often located in congested urban areas, in unknown locations, and in unknown condition
Section Signaling With Oscillating Magnetic Fields describes three initial tests undertaken to evaluate the capabilities of low frequency magnetic signaling for subterranean Internet of Things (IoT) applications
The rotating magnet produces an oscillating magnetic field, allowing information to be transmitted to an aboveground IoT-networked receiver, without the need for connecting wires, and with the potential to use less power than a radio-frequency transmitter

Summary

Introduction

Buried infrastructure, such as water and sewer pipes, are often located in congested urban areas, in unknown locations, and in unknown condition. Section Signaling With Oscillating Magnetic Fields describes three initial tests undertaken to evaluate the capabilities of low frequency magnetic signaling for subterranean IoT applications. This leads to the overall equipment design: the use of near-field magnetic signaling for short-range communication from subterranean sensors to surface receivers, and long-range LoRa wireless for aboveground data transmission.

Results

Conclusion