Navy

Large area magnetic flux sensor

High sensitivity, dynamic range, and noise immunity in a device that detects normal static and dynamic flux through a large area

Electronics Sensors

The U.S. Navy has invented a large area magnetic flux sensor. The technology is available to qualified businesses who would make, use, or sell it.

During an Innovation Discovery Event at the Naval Surface Warfare Center, Carderock Division, panelist Peter Helfet, an independent business development consultant, measures the magnetic field value of the large-area magnetic field sensor, a new technology presented by Dr. John Miesner, an engineer in the Structural Acoustics and Target Strength Branch. (Dustin Q. Diaz/Navy)

Navy researchers developed a flux meter comprised of an electrically conductive member, a pair of piezoelectric members, a pair of tensioning mechanisms, and an electrical current generator.

The two piezoelectric members are positioned on either side of the conductive member. The two tensioning mechanisms put stress on the piezoelectric members in opposite directions away from the conductive member. Current flows through the conductive member and interacts with the magnetic field to produce transverse forces on the piezoelectric members causing relative voltage between their top and bottom electrodes. The voltages produced are indicative of a total magnetic flux through the conductive member. Demodulating the voltage provides an electrical signal with high sensitivity, dynamic range, and noise immunity.

The Navy invented the technology because there was no practical method to measure the total static and dynamic magnetic flux passing normally through a large area. Semiconductor Hall devices are commonly used in magnetic machines, but they are small and primarily sample a single point. Magnetoresistive devices are becoming more practical; however, they are small, and they sense flux down the device axis and not through the sensor thickness.

Many devices would benefit from a large area magnetic flux sensor. For example, an electrodynamic actuator produces forces proportional to the current through the coil conductors and the total flux perpendicular to the coil surface. Typically the coil is designed to be wider than optimum to keep the flux within the area of the coil as it moves and to thereby reduce force dependence on position. If the total flux perpendicular to the entire coil surface were known, then the conductor current could be controlled to eliminate the force dependence on position. This would allow the coil width to be optimized for more efficient actuator operation.

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