Investigation of the Near-Carrier Noise for Strain-Driven ME Laminates by Using Cross-Correlation Techniques

The near-carrier noise around the longitudinal mechanical resonance of a magnetoelectric laminated composite has been investigated. By simultaneously applying a high-frequency electric field across the piezoelectric phase, the sensor response to low-frequency magnetic signals can be shifted around the “carrier” frequency as side band modulation signals. This magnetoelectric response can appear either as an electric charge via piezoelectric-to-piezoelectric (PP) modulation effects or as a magnetic signal via piezoelectric-to-magnetic (PM) modulation effects. These two signals are detected either with a charge preamplifier or with a coil surrounding the sample and the low-frequency sensor response to the applied magnetic field can be recovered by using two independent synchronous detectors. We have designed an experimental setup to observe the direct (passive) low-frequency noise and the noise corresponding to the two above modulations. Noise cross-correlating measurements were also carried out to investigate the origin of the near-carrier noise. No noise coherence was found between the direct low-frequency noise and the noise resulting from either the PP or the PM modulations. However, a noise coherence factor of more than 50% has been found between the signals recovered from the two modulation techniques. A simple model has been used to explain this effect. The magnetoelectric sensor is considered as a nonlinear forced vibration system. Noise sources passing through such a system can be amplified and distributed around the carriers as side band noise where it hampers the equivalent magnetic noise performance. Electronic–thermal noise caused by dielectric dissipations in the piezoelectric phase can be considered as a noise source with a negligible contribution to the total noise floor. Mechanical–thermal low-frequency excess noise is found to be the only intrinsic noise source which is filtered by the nonlinear ME system and is present as an output near-carrier noise which dominates the noise level after the demodulation processes.