3-Axis Coil Sensor for Underwater Remote Sensing

This capstone project involves the design, fabrication, and testing of a compact, three-axis coil-based sensor capable of detecting and quantifying magnetic fields induced by a remote current-carrying conductor. The sensor will resolve the magnitude and phase of induced current independently along three orthogonal axes, allowing the system to determine both the amplitude and the directional (vector) characteristics of an alternating electromagnetic field originating from a linear transmitting conductor at a known or estimated standoff distance. The transmitting source will operate at defined and controllable power, frequency, and distance parameters, giving the team a repeatable test environment for calibration and performance validation.

Electromagnetic induction sensing is a well-established technique for locating buried or submerged conductors — pipelines, cables, rebar, and other ferrous or conductive infrastructure — that cannot be located visually. A single-axis receiver coil can detect field strength along one direction, but it cannot by itself disambiguate the orientation or bearing of the source conductor relative to the sensor. A three-axis coil array solves this by capturing the full vector components of the local magnetic field, enabling triangulation of direction and, with appropriate signal processing, estimation of depth or distance to the source. This capability underlies a wide range of geophysical and utility-locating instruments already on the market, but most commercial units are designed for handheld, land-based use. This project targets a smaller and lighter form factor intended for integration into constrained platforms — underwater enclosures and aerial drones — where existing solutions are typically too large, too heavy, or not adequately sealed and ruggedized. The completed sensor is intended to demonstrate feasibility for applications such as land-based buried pipe and utility locating, subsea power or communications cable tracking, underwater utility mapping, and general electromagnetic signal reception and direction finding — all of which share a need for a lightweight, direction-capable sensor that can be mounted on a mobile platform (a drone or an ROV/AUV) rather than carried by hand.

Objectives

Objectives

  • Design three mutually orthogonal receiver coils (or an equivalent tri-axial magnetic sensing element) tuned to respond to the induced field generated by a linear transmitting conductor at a specified frequency.
  • Develop the analog front end needed to condition each axis's induced signal, including amplification, filtering, and impedance matching as required.
  • Implement a digitization and processing stage that converts the raw per-axis signals into a usable output format (e.g., digital serial data, calculated vector magnitude and bearing, or logged/telemetered records).
  • Characterize how signal amplitude and phase vary with transmitter distance, frequency, and sensor orientation, and use that characterization to calibrate the sensor and inform a direction-finding approach.
  • Achieve a size, weight, and power profile compatible with integration into an aerial drone payload or a compact underwater enclosure.
  • Minimize noise, interference, and cross-talk between axes so that directional and amplitude measurements remain accurate across the intended operating range.

Design Requirements and Constraints

The sensor must satisfy the following requirements, which the team should refine into measurable specifications during the requirements-definition phase of the project:

  • Sense induced current/field independently on three orthogonal axes with sufficient sensitivity to detect signals at the power, frequency, and distance parameters provided.
  • Output data in a usable, well-documented format suitable for downstream processing or integration into a host platform.
  • Be small and lightweight enough for integration into an aerial drone payload bay or a compact underwater enclosure, with target size/weight budgets established early and validated against realistic host-platform constraints.
  • Tolerate the vibration, temperature range, and handling conditions typical deployment.
  • Maintain adequate sensitivity and dynamic range across the expected range of transmitter power levels and standoff distances, without saturating at close range or losing detectability at the maximum intended range.
  • Reject or minimize noise and interference from ambient EM sources, host-platform electronics (motors, ESCs, radios), and cross-talk between the three sensing axes.
  • Operate from a power budget compatible with battery-powered, untethered deployment on either host platform.

Deliverables

  • A working prototype sensor, including the three-axis coil assembly, signal-conditioning and digitization electronics, and a documented data output interface.
  • Design documentation covering the electrical design, coil specifications, and calibration procedure.
  • A test report characterizing detection performance — amplitude accuracy and directional accuracy — as a function of transmitter frequency, power, and distance.
  • An assessment of the design's suitability for underwater and aerial integration, addressing size, weight, power consumption.
  • (Stretch goal) A demonstration of direction-finding or source localization using the combined vector data from all three axes.

Motivations

DoC Mapping uses cutting edge technologies for underwater remote sensing applications. This sensor will be used as part of our new EM-Array remote sensing platform. The EM-Array is a hybrid sensor array that is used for advanced underwater cable and pipe tracking applications as well as unexploded ordinance surveys and marine archeology.

Qualifications

Minimum Qualifications:

Some suggested but not necessarily required skills the team will need to be successful in the project are below:

  • Circuits I/II and an electromagnetics/fields course covering magnetic induction and coil behavior — this is the core physics the sensor relies on.
  • Analog electronics: op-amp design, filter design, low-noise signal conditioning — needed to amplify the weak induced signals off each coil.
  • Embedded systems/microcontroller programming (C/C++) for digitization and the data output interface.
  • Signal processing familiarity — phase detection, lock-in/synchronous detection, or basic DSP — for pulling a known-frequency signal out of noise.
  • PCB design (KiCad, Altium, etc.) to fit everything into a compact, low-noise board.

Preferred Qualifications:
None Listed


Details

Project Partner:

Pete Weber

NDA/IPA:

No Agreement Required

Number Groups:

1

Project Status:

Accepting Applicants

Website:
www.docmapping.com
Keywords:
Magnetics Radio Coils Signal Processingunderwater remote sensing marine construction marine archaeology
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