A MEMS Variable Reluctance Sensor for Contactless Detection of a Ferrous Rotating Target

Area of Science:

• Sensor Technology
• Microelectromechanical Systems (MEMS)

Background:

• Variable reluctance sensors are crucial for robust, contactless motion detection in challenging environments.
• Existing sensors often face limitations in space-constrained or harsh conditions.

Purpose of the Study:

• To present a novel MEMS-based variable reluctance induction sensor for characterizing rotating ferromagnetic targets.
• To investigate the sensor's capability for noncontact measurement of rotational speed, proximity, and target geometry.

Main Methods:

• Development of a MEMS sensor featuring a micromachined planar micro-coil and an external permanent magnet.
• Utilized lumped-element modeling and finite-element magnetostatic simulations to analyze sensor operation.
• Experimental validation using rotating drill bits and a high-gain amplification circuit.

Main Results:

• The sensor generates a voltage signal modulated by the target's rotation, encoding speed, proximity, and shape information.
• Demonstrated reliable detection up to 1500 rpm for targets as small as 5 mm in diameter and at distances up to 8 mm.
• Measured voltage waveforms varied consistently with target geometry, proximity, and speed.

Conclusions:

• MEMS variable reluctance induction sensors offer a promising solution for compact and noncontact speed sensing.
• The developed sensor technology shows potential for effective target shape detection in various applications.