Ultrastable and highly sensitive eddy current displacement sensor using self-temperature compensation

• A self-temperature compensation method for eddy current displacement sensor is proposed.
• A simple AC bridge is designed to separate the resistive and inductive part of the coil.
• The eddy current sensor (ECS) has sub-nanometer resolution.
• The temperature coefficient of this self-compensation ECS is only about 2.6 nm/°C.
• This self-compensation method does not need any additional hardware of probe.

This paper proposes a new method to reduce the thermal drift of eddy-current sensors (ECSs) by two orders of magnitude. Theoretical analysis shows that a well-designed bridge will help to decouple two vectors related to the resistance and inductance variations of the sensing coil of ECSs. Experiments show resistance variation has a considerably larger coefficient with temperature change compared to that of inductance variation. Other than being neglected, resistance variation compensates for the influence of temperature on inductance variation, which is used to derive true displacement information. A prototype ECS with high-resolution of sub-nanometer and ultrahigh thermal stability is manufactured and tested. Results show that the thermal drift of the prototype ECS is approximately 2.6 nm/°C, equivalent to 9.7 ppm/°C of the coil's inductance change. This self-temperature compensation method for ECS is simple, low cost, universal, very effective, and has competitive advantages in most applications.