Novel Principle for Flux Sensing in the Application of a DC + AC Current Sensor

This paper presents a new concept for measuring DC and AC magnetic flux densities within a ferromagnetic material. It is based on a measurement of the material's magnetostriction, which is its relative change in length due to the magnetic flux density inside the material. This dimensional change is converted to an electrical signal using a piezoelectric strain sensor. An additional sinusoidal AC excitation of the core material provides higher sensitivity of the length measurement and overcomes the inherent high-pass characteristic of the piezoelectric sensor. Therefore, flux density signals from DC to the kilohertz range can be measured. The concept's feasibility is demonstrated with the design and implementation of an isolated DC + AC current sensor with a measurement range of ±20 A and a bandwidth from DC to 20 MHz.