Volume 3, Issue 1 -

Self-biased magnetoelectric (ME) composites, defined as materials that enable large ME coupling under external AC magnetic field in the absence of DC magnetic field, are an interesting, challenging and practical field of research. In comparison to the conventional ME composites, eliminating the need of DC magnetic bias provides great potential towards device miniaturization and development of components for electronics and medical applications. In this review, the current state-of-the-art of the different self-biased structures, their working mechanisms, as well as their main characteristics are summarized. Further, the nature and requirement of the self-biased magnetoelectric response is discussed with respect to the specific applications. Lastly, the remaining challenges as well as future perspective of this research field are discussed.

We investigate a concept that can reduce the overall power requirement of a smart building through improvements in the real-time control of HVAC and indoor lighting based on the building occupancy. The increased number of embedded sensors necessary to realize the smart building concept results in a complex wiring and power structure. We demonstrate a floor tile energy harvester for creating a wireless and self-powered occupancy sensor. This sensor termed as “Smart Tile Energy Production Technology (STEP Tech)” can be used to control automation in smart buildings such as lighting and climate control based upon the real-time building occupancy mapping. The sensor comprises of piezoelectric transducer, energy harvesting circuit and wireless communication. Modeling and optimization procedure for the piezoelectric cymbal transducer is described within the framework of tiles. The design and selection of a packaging technique and construction of a durable floor tile enclosure aimed at protecting the bulk piezoceramic is discussed within the constraint that the deflection of the tile should be minimal such that it is not readily perceivable by humans, thus not disturbing their gait. Experimental results demonstrate that the piezoelectric tile could provide a promising solution for wireless occupancy sensing.

We fabricated piezoelectric vibration energy harvesters of c -axis-oriented epitaxial Pb(Zr,Ti)O 3 (PZT) thin films on stainless steel (SS304) cantilevers in an effort to improve their power-generation efficiency and toughness. Using radio-frequency magnetron sputtering, we deposited the epitaxial PZT thin films on the MgO substrates, and then transferred the PZT films onto microfabricated SS304 cantilevers using laser lift-off (LLO). LLO did not degrade the transferred epitaxial PZT thin films, which exhibited a high piezoelectric coefficient ( e 31, f =–4.8 C/m 2 ) and a low relative dielectric constant ( ε r =340), comparable to those of the original PZT thin film on MgO. At a resonance frequency of 143 Hz, the energy harvesters generated large output power of 1.8 μW at an acceleration of 1.0 m/s 2 , and the output power reached a maximum of 49 μW at an acceleration of 7.5 m/s 2 .

This paper outlines a mathematical framework to determine the upper bound on extractable power as a function of the forcing vibrations. In addition, the method described provides insight into the dynamic transducer forces required to attain the upper bound. The relationship between vibration parameters and transducer force gives a critical first step in determining the optimal transducer architecture for a given vibration source. The method developed is applied to three specific vibration inputs: a single sinusoid, the sum of two sinusoids, and a single sinusoid with a time-dependent frequency. As expected, for the single sinusoidal case, the optimal transducer force is found to be that produced by a resonant linear spring and a viscous damping force, with matched impedance to the mechanical damper. The resulting transducer force for the input described by a sum of two sinusoids is found to be inherently time dependent. The upper bound on power output is shown to be twice that obtainable from a linear harvester centered at the lower of the two frequencies. Finally, the optimal transducer force for a sinusoidal input with a time-dependent frequency is characterized by a viscous damping term and a linear spring with a time-dependent coefficient.

The effect of boundary conditions on a bistable device that buckles into an “S” shape and utilizes polyvinylidene fluoride is evaluated. Four permutations with different center constraints are the perfectly pinned circular steel, rigid glued circular steel, 3×1 and 5×1 3D printed rectangle polylactic acid prototypes. Using a load of 30 MΩ, which was close to the optimal load resistance, frequency sweeps in the forward and reverse directions indicated different nonlinearities depending on if the device is buckled or not. Peak resonant frequencies for the devices are around 18 to 30 Hz with bistable actuation occurring as low as 0.3 g rms . Damping was measured using logarithmic decrement, linear and nonlinear half-power methods. Results showed that the devices have an average damping ratio of 4.1%. The buckled 3×1 mm device with short compliance arms generated 12.6 μW at 21.1 Hz when swept forward at 0.4 g rms and had the highest figure-of-merit (FoM BW ) metric of all devices tested. Unbuckled devices tended to exhibit a spring stiffening nonlinearity while buckled devices obtained higher power outputs in the forward direction but could have their operating frequencies significantly lowered if swept backward. All buckled devices tested during a chirp input could be promoted to high-energy orbits for enhanced performance.

As we known, nanogenerator (NG) can be used in many fields, such as sensors, energy harvesting, biomedical application, and so on. Sometimes, the object that is a part of NG cannot be electrically connected to the load because it is a mobile object. To harvest energy from such a case and reduce the fabrication cost and achieve some new applications such as touch screen products, we need to find new method to fabricate NG. To attain the higher output current and output power, moreover, here we report a flexible and easy fabricated single electrode triboelectric nanogenerator (TENG) based on polydimethylsiloxane (PDMS) and silver (Ag) nanowires (NWs). Due to Ag NWs high specific surface area, the electrical conductivity of Ag NWs is better than the block of Ag, and PDMS is the transparent and flexible. The single electrode TENG not only can harvest energy from environment but also is a self-powered sensor for detecting acceleration from different angles. This TENG can attain an open-circuit voltage up to 330 V, a maximum short-circuit current of 15.5 μ A (2.6 μ A/cm 2 ) and a maximum power of 1.5 mW (0.25 mW/cm 2 ) on the load of 20 MΩ.

This work studies the modification of commercially available dispersions of intrinsically conductive polymer PEDOT:PSS with a strong base, KOH. It is concluded that addition of base derives a dedoping of the PEDOT chain and increase Seebeck coefficient from 15 µV/K to 90 µV/K. Supportive UV-Vis-NIR spectroscopy was used for tracking the doping level of the polymer. A surface morphology study of the dedoped PEDOT:PSS films was monitored by SEM. It was shown that if KOH is used in excess with respect to the acid component of PEDOT:PSS dispersions, it segregates at the surface forming crystallites. They, however could be easily removed by methanol rinsing without destroying the sample integrity. After material modification, a dispenser-printed polymer unileg-TEG with 61 unicouples was fabricated by printing. The TEG in form of 253 mm-long stripe shows a flexible behavior. At 90 K temperature difference a resulting power output of ~ 100 nW could be measured. We suggest that the low power output is due to a high internal generator resistance.