Caijiang Lu

High-resolution current sensor utilizing nanocrystalline alloy and magnetoelectric laminate composite

A self-powered current sensor consisting of the magnetostrictive/piezoelectric laminate composite and the high-permeability nanocrystalline alloys is presented. The induced vortex magnetic flux is concentrated and amplified by using an optimized-shape nanocrystalline alloy of FeCuNbSiB into the magnetoelectric laminate composite; this optimization allows improving the sensitivity significantly as well as increasing the saturation of the current sensor. The main advantages of this current sensor are its large dynamic range and ability to measure currents accurately. An analytical expression for the relationship between current and voltage is derived by using the magnetic circuit principle, which predicts the measured sensitivity well. The experimental results exhibit an approximately linear relationship between the electric current and the induced voltage. The dynamic range of this sensor is from 0.01 A to 150 A, and a small electric current step-change of 0.01 A can be clearly distinguished at the power-line frequency of 50 Hz. We demonstrate that the current sensor has a flat operational frequency in the range of 1 Hz-20 kHz relative to a conventional induction coil. The current sensor indicates great potentials for monitoring conditions of electrical facilities in practical applications due to the large dynamic range, linear sensitivity, wide bandwidth frequency response, and good time stability.

Enhancement of resonant magnetoelectric effect in magnetostrictive/piezoelectric heterostructure by end bonding

We report large magnetoelectric (ME) effects in heterostructures (HSs) by attaching Metglas at the free ends of piezoelectric Pb(Zr1−x,Tix)O3 (PZT) plates. With this configuration, the influences of non-magnetic interfacial layer decrease and the cantilever structural Metglas with free vibrations generate large magnetic forces to drive PZT mechanically, instead of shear forces. Consequently, the heterostructure exhibits a ∼3.6 times larger magnetoelectric voltage coefficient (αME) than that of previous bilayer laminate structure. The largest αME is 535 (V/cm Oe) when the length and the thickness of Metglas are 18 mm and 75 μm, respectively. This heterostructure is of interest for high-sensitive dc magnetic field sensors.

Giant self-biased magnetoelectric response with obvious hysteresis in layered homogeneous composites of negative magnetostrictive material Samfenol and piezoelectric ceramics

Giant self-biased magnetoelectric (ME) response and obvious hysteresis are observed in trilayer homogenous ME laminate composite consisting of negative magnetostrictive Samfenol (SmFe2) plates and piezoelectric ceramic PZT (Pb(Zr,Ti)O3) plates. The large anisotropic field of SmFe2 oriented the direction [111] of easy magnetization results in an enhanced internal bias due to its huge intrinsic anisotropic constant. The experimental results demonstrate that this composite exhibits ∼30 times higher ME voltage coefficient than that of composite FeNi/PZT/FeNi with weak ME coupling at zero bias. These results provide the possibility of this homogeneous ME composite for ultra-sensitive magnetic field sensing without bias.

Enhanced Acoustic Energy Harvesting Using Coupled Resonance Structure of Sonic Crystal and Helmholtz Resonator

An acoustic energy harvester using a coupled resonance structure of a sonic crystal resonator and an electromechanical Helmholtz resonator with a piezoelectric composite diaphragm is proposed to enhance energy harvesting. Due to acoustic resonance coupling between the sonic crystal resonator and the Helmholtz resonator, the coupled resonance structure has a larger acoustic pressure magnification than each individual resonator structure. Consequently, the stronger vibration of the diaphragm and the higher harvesting efficiency are obtained. Experimental results show that the proposed harvester exhibits ~23 and ~262 times higher maximum harvesting efficiencies than the sonic crystal resonator and the Helmholtz resonator structure, respectively.

Note: High-efficiency broadband acoustic energy harvesting using Helmholtz resonator and dual piezoelectric cantilever beams

A high-efficiency broadband acoustic energy harvester consisting of a compliant-top-plate Helmholtz resonator (HR) and dual piezoelectric cantilever beams is proposed. Due to the high mechanical quality factor of beams and the strong multimode coupling of HR cavity, top plate and beams, the high efficiency in a broad bandwidth is obtained. Experiment exhibits that the proposed harvester at 170-206 Hz has 28-188 times higher efficiency than the conventional harvester using a HR with a piezoelectric composite diaphragm. For input acoustic pressure of 2.0 Pa, the proposed harvester exhibits 0.137-1.43 mW output power corresponding to 0.035-0.36 μW cm(-3) volume power density at 170-206 Hz.

Energy harvesting from electric power lines employing the Halbach arrays

This paper proposes non-invasive energy harvesters to scavenge alternating magnetic field energy from electric power lines. The core body of a non-invasive energy harvester is a linear Halbach array, which is mounted on the free end of a piezoelectric cantilever beam. The Halbach array augments the magnetic flux density on the side of the array where the power line is placed and significantly lowers the magnetic field on the other side. Consequently, the magnetic coupling strength is enhanced and more alternating magnetic field energy from the current-carrying power line is converted into electrical energy. An analytical model is developed and the theoretical results verify the experimental results. A power of 566 μW across a 196 kΩ resistor is generated from a single wire, and a power of 897 μW across a 212 kΩ resistor is produced from a two-wire power cord carrying opposite currents at 10 A. The harvesters employing Halbach arrays for a single wire and a two-wire power cord, respectively, exhibit 3.9 and 3.2 times higher power densities than those of the harvesters employing conventional layouts of magnets. The proposed devices with strong response to the alternating currents are promising to be applied to electricity end-use environment in electric power systems.

Energy Harvesting From Two-Wire Power Cords Using Magnetoelectric Transduction

This paper presents an energy harvester using a Terfenol-D/PMNT/Terfenol-D magnetoelectric (ME) transducer for scavenging ac magnetic field energy from two-wire power cords connected to household and commercial appliances. The harvester uses a magnetic circuit consisting of six NdFeB magnets mounted on the free end of a cantilever beam. The magnets produce concentrated flux gradient on the ME transducer, and the vertical Ampere forces acting on the two conductors of the power cord are superimposed. An enhanced movement is then induced on the magnetic circuit. The ME transducer undergoes magnetic field variations and generates power output. A prototype is fabricated and tested. Because of the high magnetomechanical coupling effect of the magnetostrictive material and the large flux gradient on the ME transducer, the harvester can generate a maximum power of 671.2 Ω W with a matching load resistance of 991 kΩ at 6 A. The results demonstrate the potential of the proposed device applied to electricity end-use environment in electric power systems.

Dynamic magnetostrictive properties of magnetization-graded ferromagnetic material and application in magnetoelectric composite

This paper investigates the dynamic magnetostrictive properties in a laminate ferromagnetic material FeCuNbSiB/Ni (FN) consisting of a Nickel (Ni) plate and the Fe-based nanocrystalline alloy (FeCuNbSiB) foils. The resonant dynamic piezomagnetic coefficient (d33,m) is studied particularly in experiments. The experimental results demonstrate that the d33,m versus DC bias magnetic field data of FN show strong hysteretic and remanent behaviors. The zero-biased d33,m ranges from 5.14 to 42.7 (nm/A), depending on the numbers of FeCuNbSiB layer L. The maximum zero-biased d33,m of FN is 42.7 nm/A for FN with L = 4, which is ∼24.1 times larger than that of Ni. By combining FN with piezoelectric Pb(Zr0.52,Ti0.48)O3 (PZT), a giant zero-biased magnetoelectric voltage coefficient αME of ∼89.2 (V/cm Oe) is observed in composite FN/PZT/FN. Thus, the laminate magnetostrictive layer FN can be used for obtaining a self-biased magnetoelectric composite.

Magnetoelectric Composite Metglas/PZT-Based Current Sensor

This paper presents an electric current sensor employing an unsymmetrical magnetoelectric composite Metglas/Pb(Zr,Ti)O3 (PZT) consisting of magnetostrictive Metglas and piezoelectric PZT. As the Metglas foils with excellent magnetic characteristics induce the magnetic field around a current-carrying cable, an output voltage is generated in Metglas/PZT. The influence of the numbers of Metglas foil (L) on resonance output voltage (Vo, r) is experimentally investigated in detail. The results demonstrate that the maximum Vo, r is 223 mV for Metglas/PZT with L = 4 under 190.2 Hz frequency and dc biased magnetic field Hdc = 16 Oe. By adding a 1.3 g tip mass at the free end of Metglas/PZT, the resonant frequency of Metglas/PZT with L = 4 can be adjusted to 50 Hz, where the Vo, r is 211 mV at Hdc = 16 Oe. With the excellent linearity and large current sensitivity (114.2 mV/A) when measuring low-frequency alternating magnetic fields of 50 Hz, this sensor is ideally suited for power-line current measurement.

Packaged current-sensing device with self-biased magnetoelectric laminate for low-frequency weak-current detection

A packaged current sensor consisting of a SmFe2/PZT/SmFe2 self-biased magnetoelectric (ME) laminate and a Fe73.5Cu1Nb3Si13.5B9 nanocrystalline flux concentrator for weak-current detection at the power-line frequency is fabricated and characterized. The giant magnetostrictive material of the SmFe2 plate with its large anisotropic constant provides a huge internal anisotropic field to bias the ME transducer in a closed magnetic loop. Consequently, the additional magnetomotive force induced by the internal field and the corresponding increased effective permeability contribute to an improvement in sensitivity. Experimental results demonstrate that the presented sensor has a higher sensitivity of 152 mV A?1 at 50 Hz with a slight nonlinearity of ?0.01% FS and matches well with the predicted value. This current-sensing device exhibits approximately 2.3 times higher sensitivity than does conventional ME composite with PZT and Terfenol-D plates serving as the key sensitive component. In addition, the packaged sensor is evaluated for a long period of 72 h to determine stability over time, and the results are analyzed by means of a mathematical statistics method; favorable stability with an uncertainty of 0.5 ?V is obtained in continuous 1 h testing. These results represent a significant advancement in the development of promising applications of tri-layer self-biased ME laminate for monitoring power-line electric cords.