Development of ring-type magnetoelectric composites for electric current sensor and transducer applications

Abstract

This thesis explores design, modeling, finite-element analysis, fabrication and evaluation of novel ring-type magnetoelectric (ME) composites for electric current sensor, dual-mode transducer, and bidirectional current-voltage (I-V) converter applications. Original contributions from this research include: (1) This study proposes a novel class of ring-type ME laminated composites to compensate shortcomings of existing rectangular ME composites for electric current sensor application for the first time. The novel composites not only exhibit features of power supply-free, high-sensitive, and wide-frequency bandwidth, but also have capabilities of detecting vortex magnetic fields and self magnetically biasing. Thus auxiliary means to channel vortex magnetic fields and external magnetic bias methods used for the rectangular ME composites are not required for the novel composites, which greatly simplifies designs of ME current sensors. (2) One contribution is establishment of a new quasistatic theoretical model, based on a static force equilibrium equation, to predict non-resonance characteristics of the ring-type ME laminates at low frequency (far below resonance frequency). In addition, three dynamic models based on a new analytical method (generalized Hamilton principle) are built to predict the resonance characteristics of the ring-type ME composites near resonance frequencies for different deformation modes (radial, thickness, and radial thickness coupled modes). These models are more precise and convenience for the novel ring-type composites than the traditional approaches. The results reveal that an optimal performance of the ring-type composites can be achieved for vf=0.5, P8 PZT, and ratio tm/tp=1. From the quasistatic model, a guide of tailoring constituent material properties is also developed to further enhance performance of the ring-type laminates for applications, and a mode-coupling effect, which greatly enhances resonance SI and useful for transducer application, is discovered in the coupled-mode model. (3) A sample of the novel ring-type ME composites, fabricated according to the optimal results from the theoretical analyses, is found to have a high non-resonance SI of ~15 mV/A over a wide frequency range of 1-20 kHz with excellent linearity, high repeatability, and extremely low hysteresis. It also shows a large resonance SI of ~180 mV/A at the radial mode of 62 kHz and ~150 mV/A at the thickness mode of 224 kHz. Furthermore, the sample is able to keep high performance under disturbance from a magnetic field as strong as 100 A/m and temperature up to 80 C. (4) An innovative dual-mode transducer without need of power supply is developed. It consists of a ring-type ME laminate with output port connected to input port of a Rosen-type piezoelectric transformer and the transformer is purposely designed to have the same resonance frequency with the ring-type laminate. The dual-mode transducer possesses two concurrent operational modes: current sensing (CS) mode and current transduction (CT) mode. In CS mode its performance is the same as a single ring-type ME laminate, providing a large SI of ~12 mV/A over a wide bandwidth up to 20 kHz, while in CT mode, due to voltage amplification effect of the piezoelectric transformer, it plays just as a current transducer with large resonance sensitivity of 1.1 V/A, ~5-times larger than a single ring-type laminate, near resonance frequency. (5) To address disadvantages (unidirectional and energy consuming) of conventional I-V and V-I converters, we generate a passive bidirectional I-V converter, which is a coil-wound ring-type laminate. It exhibits both good I-V and V-I conversion abilities, including high linear relation between input and output signals, large conversion factors and wide frequency range up to 80 kHz.