Yumei Wen

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

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.

A Magnetoelectric Composite Energy Harvester and Power Management Circuit

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.

A two-dimensional broadband vibration energy harvester using magnetoelectric transducer

In this study, a magnetoelectric vibration energy harvester was demonstrated, which aims at addressing the limitations of the existing approaches in single dimensional operation with narrow working bandwidth. A circular cross-section cantilever rod, not a conventional thin cantilever beam, was adopted to extract vibration energy in arbitrary in-plane motion directions. The magnetic interaction not only resulted in a nonlinear motion of the rod with increased frequency bandwidth, but also contributed to a multi-mode motion to exhibit double power peaks. In energy harvesting with in-plane directions, it showed a maximum bandwidth of 4.4 Hz and power of 0.59 mW, with acceleration of 0.6 g (with g = 9.8 m s−2).

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.

An Upconversion Management Circuit for Low-Frequency Vibrating Energy Harvesting

This paper proposes a high-efficiency small-size upconversion management circuit for low-frequency vibrating energy harvesting. Due to low vibrating frequency (32 Hz), the transformer of a traditional matching circuit has a large inductance (9171 H) and a large size (> 50 × 50 × 50 mm3). An upconversion matching circuit with a smaller inductance (25.3 H) and a smaller size (<; 20 × 20 × 20 mm3) is developed. By using the smaller size upconversion matching circuit, higher charging power and ultimate charging voltage can be obtained at a higher frequency (3.28 kHz). The matching circuit can efficiently work at a wide vibrating frequency range. In order to drive the wireless sensor with a higher consumption power (110 mW), an instantaneous discharging circuit is developed that is suitable for weak vibrating energy harvesting (406 μW). The instantaneous discharging circuit can accumulate weak energy from the vibrating transducer during a long period, and it can provide a higher power output in a very short time. While the voltage across the storing capacitor is over 0.36 V, the instantaneous discharge circuit can drive a wireless sensor with an output power of 110 mW at a distance of over 80 m. The small-size high-efficiency upconversion management circuit can be used in many other low-frequency energy harvesters.

A magnetoelectric energy harvester with the magnetic coupling to enhance the output performance

In this research an energy harvester employing the magnetoelectric (ME) transducer to convert mechanical vibration energy into electrical energy is presented, and it is demonstrated that the use of a magnetically coupled cantilever beam can achieve to enhance the output performances of the harvester in terms of improving the electric output and tuning the resonant frequency efficiently. Under the acceleration of 0.2 g (with g = 9.8 ms−2), the resonant frequency is successfully tuned range from 16.1 to 27.9 Hz, and the output power is obviously improved from 42.3 to 151.4 μW with the effect of magnetic coupling.

Detecting and evaluating the signals of wirelessly interrogational passive SAW resonator sensors

The wireless sensing signal of a passive surface acoustic wave (SAW) resonator sensor is the response of the SAW resonator in a passive circuit to wireless radio frequency interrogation. The response is produced only in the case that the interrogation covers the operational frequency band of the resonator. The wireless response is transient and can only be detectable in a proximity after switching off the interrogation. Due to the fact that, while used as a sensor, the resonant frequency of the resonator is related to and varying with the measurand, the interrogation to a passive SAW resonator sensor has to trace and follow the correspondent variation of the frequency band of the device. The energy evaluation of the response is applied to detect the availability of the sensing response and is used as a feedback argument to roughly localize the operational frequency range of the sensor. A modified frequency estimation is employed to estimate the sensing characteristic frequency in the transient wireless sensing signal with a low signal-to-noise ratio. The estimation is used to further adjust the interrogation frequency to follow the frequency variation of the sensor until the response becomes optimal. The evaluation of signal energy along with the statistical quantity of frequency estimation gives a reference for the confidence of the estimated frequency.

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.