Office for Technology Commercialization

Magnetic Position Sensor

Technology #20130174

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Magnetic Field ModelingFree PistonHydraulic Applications
Rajesh Rajamani, PhD
Professor, Mechanical Engineering Department,College of Science and Engineering
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Kevin Nickels
Technology Licensing Officer 612-625-7289
Patent Protection

PCT Patent Application Filed

Oscillating and Linear Motion Measuring Device

A position sensor system has been designed that models the movement of an object based on the fluctuations in the magnetic field surrounding it. Based upon the distance between the sensor and the object, the magnetic field strength and direction will be unique. For example, in a free-piston engine the piston can be modeled and calibrated magnetically with this measuring device. The sensor, placed non-intrusively on the external face of the cylinder, is able to provide highly accurate position measurements along the entire stroke length by analyzing the change in the magnetic field produced as the piston oscillates. The magnetic sensing device has been tested and shown to give a piston position in a free-piston engine within 0.4 mm accuracy.

Note: This magnetic position sensor technology has been licensed to Innotronics. If you have questions, please contact the University of Minnesota's Office for Technology Commercialization.

Free-Piston, Pneumatic and Hydraulic Applications

In order to obtain accurate position measurements of devices with parts that move linearly or oscillate, control systems such as pneumatic systems, hydraulic systems and free-piston engines rely upon sensors. Current technologies for measuring linear motion include potentiometers, lasers, and LED systems that are often intrusive, requiring either a mechanical connection or a direct line-of-sight between the sensor and the moving part. These specifications require that the sensor be embedded directly into the device being measured, which is often costly and can impede the action of the moving member.

Position Based on Magnetic Field Modeling

This technology has a wide range of possible applications for which exact measurements of position based on magnetic field modeling can be achieved. Any ferromagnetic material can be calibrated with the sensor, or a separate, additional magnet may be mounted on the object to provide a measurable magnetic field. Significant cost reduction can be achieved based on properties of the system to provide non-intrusive, non-contact, accurate measurements in a small package.


  • Magnetic sensing allows for accurate positioning information of any calibrated magnetic object based on inherent magnetic fields.
  • Can be placed external to the object to be measured, so that the system would neither require redesign to accommodate the sensor within the system nor expose the sensor to potentially harsh environments.
  • Does not require direct contact or line-of-sight, which simplifies installation of sensors for objects that are isolated, such as a piston within a cylinder.
  • Sensor can accommodate a large measurement range and does not scale with the measurement range.

Phase of Development Prototype Developed