Chundong Xu

Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study

We numerically investigate the properties of coherent femtosecond single electron wave packets photoemitted from nanotips in view of their application in ultrafast electron diffraction and non-destructive imaging with low-energy electrons. For two different geometries, we analyze the temporal and spatial broadening during propagation from the needle emitter to an anode, identifying the experimental parameters and challenges for realizing femtosecond time resolution. The simple tip-anode geometry is most versatile and allows for electron pulses of several ten of femtosecond duration using a very compact experimental design, however, providing very limited control over the electron beam collimation. A more sophisticated geometry comprising a suppressor-extractor electrostatic unit and a lens, similar to typical field emission electron microscope optics, is also investigated, allowing full control over the beam parameters. Using such a design, we find ∼230 fs pulses feasible in a focused electron beam. The m...

Bi-stable energy harvesting based on a simply supported piezoelectric buckled beam

Bi-stable piezoelectric energy harvester has been found as a promising structure for vibration energy harvesting. This paper presents a high performance and simple structure bi-stable piezoelectric energy harvester based on simply supported piezoelectric buckled beam. The potential energy function is established theoretically, and electrical properties of the device under different axial compressive displacements, excitation frequencies, and accelerations are investigated systematically. Experimental results demonstrate that the output properties and bandwidth of the bi-stable nonlinear energy harvester under harmonic mechanical excitation are improved dramatically compared with the traditional linear energy harvester. The device demonstrates the potential in energy harvesting application to low-power portable electronics and wireless sensor nodes.

Cantilever driving low frequency piezoelectric energy harvester using single crystal material 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3

We present a high performance piezoelectric energy harvester CANtilever Driving Low frequency Energy harvester (CANDLE) consisting of cantilever beam and cymbal transducers based on piezoelectric single crystal 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3. Electrical properties of CANDLE under different proof masses, excitation frequencies, and load resistances are studied systematically. Under an acceleration of 3.2g (g = 9.8 m/s2), a peak voltage of 38 V, a maximum power of 3.7 mW were measured at 102 Hz with a proof mass of 4.2 g. Low resonance frequency and high power output performance demonstrate the promise of the device in energy harvesting for wireless sensors and low-power electronics.

Magnetoelectric effect of the multi-push-pull mode in 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3/Metglas magnetoelectric composite

This paper presents a model for the multi-push-pull configuration of magnetoelectric (ME) laminated composites which consist of magnetostrictive and piezoelectric layers with interdigitated ID electrodes encapsulated in Kapton. Analytical solutions for the ME voltage coefficient αV and charge coefficient αQ were derived. A ME composite has been made by magnetostrictive Metglas foils and piezoelectric 0.35Pb(In1/2Nb1/2)-0.35Pb(Mg1/3Nb2/3)-0.30PbTiO3 single crystal fibers, which exhibited a high ME charge coefficient αQ of 3756 pC/Oe at 1020 Hz. Besides showing a good linear relationship with AC magnetic field, the related ME sensor has a low noise equivalent magnetic induction of 10 pT/Hz1/2 at 1 Hz and 13 fT/Hz1/2 at resonant frequency.

An improved magnetic field detection unit based on length-magnetized Terfenol-D and width-polarized ternary 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3

A magnetoelectric laminate composite based on length-magnetized Terfenol-D alloy and width-polarized ternary 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal has been developed and exhibits a giant magnetoelectric voltage coefficient of 1.7 V/Oe at low frequencies and 20 V/Oe at resonance frequency 84 020 Hz besides showing good linearity range of response in the field range of 1 pT-10 μT. Due to its small capacitance of 43 pF, a specially designed low-noise voltage follower was used to match the impedance. Based on the circuit, the detection limit of composite has been reached 1.9 pT/Hz1/2 at 1020 Hz and 300 fT/Hz1/2 at 84 020 Hz, respectively.

Pressure effects on multiferroic LuFe2O4

This letter reports that both ac susceptibility and electronic transport measurements of the multiferroic compound LuFe2O4 under pressure show that the transition temperature from the paramagnetic state to the ferrimagnetic state decreases with increasing pressure, indicating that the pressure favors the paramagnetic state and suppresses the ferrimagnetic state. Moreover, the minimum of resistivity changes under pressure, which decreases with increasing pressure, appears at the magnetic phase transition temperature.

A low frequency and broadband piezoelectric energy harvester using asymmetrically serials connected double clamped-clamped beams

A novel structure of piezoelectric energy harvester was developed using double clamped–clamped beams serials connected by a rectangular frame, coupled with a proof mass and supporting mass near the center of upper and lower beams. The serials connection has a significant effect on reducing the resonance frequency, which is predicted by theoretical analysis and validated by experimental, and a reduction of 36.7% is achieved compared with the single clamped–clamped beam. More importantly, the bandwidth of the power spectrum is 36.4% wider, by introducing an asymmetry of 1 mm between the proof and supporting mass, than that of the symmetric setup. More than 0.8 mW ranging from 144 to 170 Hz is obtained near the two peaks of 0.992 mW at 150 Hz and 0.844 mW at 165 Hz, respectively. For its lower frequency, broader bandwidth and compact volume, the asymmetric harvester has promising application in wireless sensors networks.

Nonlinear output properties of cantilever driving low frequency piezoelectric energy harvester

Cantilever driving low frequency piezoelectric energy harvester (CANDLE) has been found as a promising structure for vibration energy harvesting. This paper presents the nonlinear output properties of the CANDLE to optimize the performance of the device. Simulation results of the finite element method illustrate that nonlinear contacts between the cymbal transducers and the cantilever beam are main reasons of the nonlinear output. However, high excitation acceleration of the nonlinear leap point limits the application of the device. Based on the simulation results and theory analysis, the excitation acceleration is reduced to 30 m/s2 by increasing the proof mass.