Multiferroic magnetoelectric materials, which simultaneously exhibit ferroelectricity and ferromagnetism, have recently stimulated a sharply increasing number of research activities for their scientific interest and significant technological promise in the novel multifunctional devices. Natural multiferroic single-phase compounds are rare, and their magnetoelectric responses are either relatively weak or occurs at temperatures too low for practical applications. In contrast, multiferroic composites, which incorporate both ferroelectric and ferri-/ferromagnetic phases, typically yield giant magnetoelectric coupling response above room temperature, which makes them ready for technological applications. This review of mostly recent activities begins with a brief summary of the historical perspective of the multiferroic magnetoelectric composites since its appearance in 1972. In such composites the magnetoelectric effect is generated as a product property of a magnetostrictive and a piezoelectric substance. A...

Multiferroic magnetoelectric composites: Historical perspective, status, and future directions

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Artificial neural networks (ANNs) constitute a class of flexible nonlinear models designed to mimic biological neural systems. In this entry, we introduce ANN using familiar econometric terminology and provide an overview of ANN modeling approach and its implementation methods. † Correspondence: Chung-Ming Kuan, Institute of Economics, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 115, Taiwan; ckuan@econ.sinica.edu.tw. †† I would like to express my sincere gratitude to the editor, Professor Steven Durlauf, for his patience and constructive comments on early drafts of this entry. I also thank Shih-Hsun Hsu and Yu-Lieh Huang for very helpful suggestions. The remaining errors are all mine.

Artificial neural networks

Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films

The Structure of Turbulent Shear Flow By Dr. A. A. Townsend. Pp. xii + 315. 8¾ in. × 5½ in. (Cambridge: At the University Press.) 40s.

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The Structure of Turbulent Shear Flow

This paper presents an electromagnetic energy harvesting scheme by using a composite magnetoelectric (ME) transducer and a power management circuit. In the transducer, the vibrating wave induced from the magnetostrictive Terfenol-D plate in dynamic magnetic field is converged by using an ultrasonic horn. Consequently more vibrating energy can be converted into electricity by the piezoelectric element. A switching capacitor network for storing electricity is developed. The output of the transducer charges the storage capacitors in parallel until the voltage across the capacitors arrives at the threshold, and then the capacitors are automatically switched to being in series. More capacitors can be employed in the capacitor network to further raise the output voltage in discharging. For the weak magnetic field environment, an active magnetic generator and a magnetic coil antenna under ground are used for producing an ac magnetic field of 0.2–1 Oe at a distance of 25–50 m. In combination with the supply management circuit, the electromagnetic energy harvester with a rather weak power output (about 20 μW) under an ac magnetic field of 1 Oe can supply power for wireless sensor nodes with power consumption of 75 mW at a duration of 620 ms.

A magnetoelectric energy harvester and management circuit for wireless sensor network

The magnetostrictive/piezoelectric (MP) laminate composite has dramatically enhanced magnetoelectric (ME) effect when operating around resonance. The theoretical analysis of the resonant ME effect is investigated using the equivalent circuit method, in which the eddy current loss, the mechanical loss and the electric loss are all taken into account. The results indicate that, the mechanical loss plays a primary role in dissipations in resonant status, and a strong bias magnetic field is essential to restrain eddy current loss and improve the ME conversion efficiency.

Resonant magnetoelectric response of magnetostrictive/piezoelectric laminate composite in consideration of losses

A magnetoelectric (ME) composite consisting of a copper ultrasonic horn, a magnetostrictive Terfenol-D (TbxDy1−xFe2) plate, and multiple piezoelectric PZT [Pb(Zr1−xTix)O3] plates has been developed. The ultrasonic horn converges and amplifies the vibrating magnitude and drives PZT plates at wide bandwidth. The composite with multiple PZT plates electrically connected in series/parallel exhibits a 25 times higher ME voltage coefficient than the previous laminate composite of PZT and Terfenol-D plates. 100 times higher ME voltage coefficients can be obtained by using a silicon horn composite with a higher Q value of 104 and more PZT plates of ten electrically connected in series/parallel.

Enhanced magnetoelectric effects in composite of piezoelectric ceramics, rare-earth iron alloys, and ultrasonic horn

This paper proposes a ferro-nickel (Fe-Ni)/PZT H-type fork magnetoelectric (ME) composite structure and an energy management circuit for ME energy harvesting. The resonant fork composite structure with a high Q value shows a higher ME voltage coefficient and a stronger power coefficient compared with the conventional rectangular composite structure. The resonant fork composite structure can obtain an output power of 61.64 μW at an ac magnetic field of 0.2 Oe. The ME sensitivity of the fork structure reaches 11 V/Oe. For weak magnetic-field environment, an active magnetic generator and a magnetic coil antenna underground are used for producing an ac magnetic field of 0.2-1 Oe at a distance of 25-50 m. A management circuit of the power supply with matching circuit, energy-storage circuit, and instantaneous-discharge circuit is developed suitable for weak electromagnetic energy harvesting. The management circuit can continuously accumulate weak energy from the fork composite structure for a long period and provide a high-power output in a very short cycle. While the voltage across the storage supercapacitor is over 0.36 V, the instantaneous-discharge circuit can drive a wireless sensor network node with an output power of 75 mW at a distance of over 60 m.

Yumei Wen

Papers

A magnetoelectric energy harvester and management circuit for wireless sensor network

Resonant magnetoelectric response of magnetostrictive/piezoelectric laminate composite in consideration of losses

Enhanced magnetoelectric effects in composite of piezoelectric ceramics, rare-earth iron alloys, and ultrasonic horn

A Magnetoelectric Composite Energy Harvester and Power Management Circuit

Adaptive noise cancellation based on EMD in water-supply pipeline leak detection