Printed Miniature Magnetic Probes

Project Overview & My Contribution

This project was aimed at developing a line of inductive pickup coils for measuring magnetic fields that could be easily manufactured in large quantities. Most coils are wound by hand in small quantities and at great time-cost. By designing a probe that can be printed with existing flexible printed circuit board technology, cost and time to produce such probes could be reduced dramatically. My work began with the theoretical design of these probes to optimize for desired functionality, such as rise time, signal strength, etc., within the restrictions of manufacturing capabilities. I then created CAD models and PCB designs using Solidworks and NI Ultiboard. I then worked in conjunction with SF Circuits (flexible PCBs) and Quest Integrated (AJD 3D-printing) to manufacture the models. At the conclusion of the Phase I grant, I successfully tested the designs with known magnetic fields.

Skills Demonstrated / Gained

- B-dot (Magnetic) probe theory: Rise times

considerations (inductance, capacitance, resistance), Signal-to-Noise ratios

- PCB Design within restraint of flexible PCB manufacturing

- CAD Design for Aerosol Jet Deposition Printing (surface energy, material interactions, etc)

- Interaction with PCB company design teams to push the manufacturing limits

- Familiarity with Aerosol Jet Deposition printing


Poster from 2013 APS DPP in Denver, CO

Funded under SBIR Phase I

In modern fusion concepts, inductive pickup loops are one of the primary magnetic diagnostics in tokamaks and small-scale concept exploration experiments. They are used in industries and laboratories that utilize and study low-temperature plasmas. Inductive pickup loops are capable of extremely high bandwidths, allowing for the measurements of both high frequency magnetic perturbations (requires microsecond type resolution) as well as slower field profiles associated with the more steady confinement fields (requires second type resolution).

Even the most sophisticated fusion devices employ inductive pick up loops, with multiple versions planned for measurements in long-pulse burning plasma devices and experiments such as ITER. In theory, all of these probes are simple in their basic concept and construction; however, complexities arise during implementation that makes careful design important for precision measurements and probe longevity. For example, the Redmond Plasma Physics Laboratory invested more than $1 million and four man years to construct a 96 channel probe.

Eagle Harbor Technologies, Inc. (EHT) is developing a technique to significantly reduce the cost and development time of producing magnetic field diagnostics. EHT is designing probes that can be printed on flexible PCBs thereby allowing for extremely small coils to be produced while essentially eliminating the time to wind the coils. The coil size can be extremely small when coupled with the EHT Hybrid Integrator, which is capable of high bandwidth measurements over short and long pulse durations. This integrator is currently being commercialized with the support of a DOE SBIR. Additionally, the flexible PCBs allow probes to be attached to complex surface and/or probes that have a complex 3D structure to be designed and fabricated. During the Phase I, EHT will design and construct magnetic field probes on flexible PCBs, which will be tested at the University of Washingtons HIT-SI experiment and in EHTs material science plasma reactor.

Commercial Applications and Other Benefits:

There are a large number of scientific and industrial applications that could benefit from the production of magnetic field probes printed on flexible PCBs. The small-scale concept exploration experiments routinely use inductive pickup loops both as internal probes and as surface probes. As new experiments are built or existing ones upgraded, flexible magnetic field probes can be used to make more complex internal and surface probes. ITER, a large tokamak under construction, will utilize about 2000 channels of magnetic field probes. Additionally, the flexible printed probes could be used anywhere a time varying magnetic field is measured, including medical devices, geophysical sensors, and aerospace applications.

3-Axis Surface Probe

Printed using a flexible PCB

Toroidal Field "Rogowski" Coil

Printed using a flexible PCB

3-Axis Magnetic Probe

Printed using Aerosol Jet Deposition (AJD)

Macro image of 3-Axis Probe

AJD-Printed pads and traces (Pads are ~ 2 mm square)