Kailiang Ren

Single crystal PMN-PT/Epoxy 1-3 composite for energy-harvesting application

One key parameter in using electroactive materials to harvest electric energy from mechanical sources is the energy conversion efficiency. Recently, it was shown that, in the relaxor ferroelectric PMN-PT single crystals, a very high longitudinal electromechanical coupling factor (>90%) can be obtained. This paper investigates energy harvesting using 1-3 composites of PMN-PT single crystals in a soft epoxy matrix. It is shown that 1-3 composites enable the single crystals operating in the longitudinal mode to achieve high efficiency for energy harvesting, and the soft-polymer, matrix-supported single-crystal rods maintain high mechanical integrity under different external loads. For comparison, 1-3 composites with piezoceramic PZT also are investigated in energy-harvesting applications, and the results show that the high coupling factor of single crystal PMN-PT 1-3 composites leads to much higher electric energy output for similar mechanical energy input. The harvested energy density of 1-3 composite with single crystal (22.1 mW/cm/sup 3/ under a stress of 40.4 MPa) is about twice of that harvested with PZT ceramic 1-3 composite (12 mW/cm/sup 3/ under a stress of 39 MPa). At a higher stress level, the harvested-energy density of 1-3 PMN-PT single crystal composite can reach 96 mW/cm/sup 3/.

An active energy harvesting scheme with an electroactive polymer

We investigate the energy harvesting with an electrostrictive polymer, possessing high electromechanical response and elastic energy density, which make it possible to generate high electric energy density and attractive for the active energy harvesting scheme. It is shown that combining the active energy harvesting scheme and high electromechanical response of the polymer yields a harvested electric energy density of ∼40mJ∕cm3 with a 10% efficiency.

Permanent Polarity and Piezoelectricity of Electrospun α‐Helical Poly(α‐Amino Acid) Fibers

Electrospinning is a versatile and cost-effective method for the fabrication of polymeric fi bers with sub-micrometer diameter. [ 1 ] Although several patents and recent publications have discussed the production of piezoelectric fi bers via electrospinning, to date, a direct evidence of poled molecular dipoles and their correlation to fi ber piezoelectricity have not been demonstrated. [ 2 , 3 ] Here we show for the fi rst time that electrospinning can be used as a one-step method to produce polar polymer fi bers with electric dipoles permanently poled in the direction of the fi ber axis, resulting in high non-linear optical (NLO) activity and thermally stable piezoelectricity. This was achieved by electrospinning poly( γ -benzyl α , L -glutamate) (PBLG), a liquid crystalline, α -helical poly( α -amino acid) with macroscopic dipoles prealigned in the direction of helical axis, which can couple synergistically with external electric fi eld and shear force. [ 4 ] The electrospun fi bers exhibited a d 33 piezoelectric coeffi cient of 25 pC N − 1 , which did not deteriorate even after 100 ° C thermal treatment for over 24 h. To the best of our knowledge, this is one of the highest thermally stable piezoelectric coeffi cients reported for poled polymers. [ 5 ] The piezoelectric PBLG fi bers could be used in fl exible and light transducers, which are ideal for integration into small sensing and energy harvesting devices. [ 6 ]

Application of Micromachined

This paper presents the design, fabrication, and characterization of thermal infrared (IR) imaging arrays operating at room temperature which are based on Y-cut-quartz bulk acoustic wave resonators. A novel method of tracking the resonance frequency based upon the measurement of impedance is presented. High-frequency (240-MHz) micromachined resonators from Y-cut-quartz crystal cuts were fabricated using heterogeneous integration techniques on a silicon wafer. A temperature sensitivity of 22.16 kHz/°C was experimentally measured. IR measurements on the resonator pixel resulted in a noise equivalent power of 3.90 nW/Hz1/2, a detectivity D* of 1 × 105 cm · Hz1/2/W, and a noise equivalent temperature difference of 4 mK in the 8- to 14-μm wavelength range. The thermal frequency response of the resonator was determined to be faster than 33 Hz, demonstrating its applicability in video-rate uncooled IR imaging. This work represents the first comprehensive thermal characterization of micromachined F-cut-quartz resonators and their IR sensing response.

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Ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-1,1-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer with VDF/TrFE/CFE composition of 59.2∕34.6∕7.2 (mole %) exhibits a high dielectric constant (∼50) around room temperature and strong electromechanical response. It can form miscible blends with poly(methyl methacrylate) (PMMA). This paper reports the results of a systematic investigation of the influence of PMMA on the microstructure and electromechanical responses of the terpolymer blends with PMMA content up to 10wt%. It was found that the crystallinity of the blends decreases nearly linearly with increased PMMA content. Since the dielectric constant and polarization response of P(VDF-TrFE-CFE) terpolymer are mainly from the crystalline region, these properties accordingly exhibit proportional reduction with increased PMMA concentration. Nevertheless, a small amount (∼5wt%, for instance) of PMMA can raise the elastic modulus of the blend quite markedly while the field-induced strain le...

-Cut-Quartz Bulk Acoustic Wave Resonator for Infrared Sensing

We show that the nonlinear piezoelectric response of polyvinylidene fluoride (PVDF) exhibits quite different behavior compared with the piezoceramics. Instead of increasing linearly with the stress amplitude Tac, d31 coefficient raises with Tac2. Furthermore, the nonlinear effect does not set in until the strain increases beyond 0.3%, indicating very strong barriers to the domain wall motions in PVDF. The electromechanical coupling factor k31 also exhibits an increase with stress. Furthermore, the piezopolymer can withstand more than 3% strain without degrading the piezoelectric responses.

Microstructure and electromechanical responses in semicrystalline ferroelectric relaxor polymer blends

The authors show that a high transverse piezoelectric response with both high piezoelectric d31 (d31=43.1pm∕V) and electromechanical coupling k31 coefficients (k31=0.187), much higher than those in the piezoelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) copolymers, can be obtained in poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] 10wt% copolymers under quasistatic condition. Furthermore, the copolymers also display a higher d31 coefficient compared to the d33 coefficient, which seems to be unusual compared with most other piezopolymers. The experimental data suggest that the origin of the unusual piezoelectric response in these P(VDF-HFP) copolymers originates from a reversible change between a poled α-like structure and β-like structure. The phase change nature also results in a large frequency dispersion of the piezoelectric response and a smaller d31 (=20.5pm∕V) at 50kHz.

Direct piezoelectric response of piezopolymer polyvinylidene fluoride under high mechanical strain and stress

Extremely large, lightweight, in-space deployable active and passive microwave antennas are demanded by future space missions. This paper investigates the development of PVDF based piezopolymer actuators for controlling the surface accuracy of a membrane reflector. Uniaxially stretched PVDF films were poled using an electrodeless method which yielded high quality poled piezofilms required for this applications. To further improve the piezoperformance of piezopolymers, several PVDF based copolymers were examined. It was found that one of them exhibits nearly three times improvement in the in-plane piezoresponse compared with PVDF and P(VDF-TrFE) piezopolymers. Preliminary experimental results indicate that these flexible actuators are very promising in controlling precisely the shape of the space reflectors. To evaluate quantitatively the effectiveness of these PVDF based piezopolymer actuators for space reflector applications, an analytical approach has been established to study the performance of the coupled actuator-reflector-control system. This approach includes the integration of a membrane reflector model, PVDF piezopolymer actuator model, solution method, and shape control law. The reflective Newton method was employed to determine the optimal electric field for a given actuator configuration and loading/shape error.

Piezoelectric responses in poly(vinylidene fluoride/hexafluoropropylene) copolymers

Ferroelectric relaxor P(VDF-TrFE-CFE) terpolymer can generate a hysteresis-free polarization of 47mC∕m2 at an electric field of 100MV∕m and is attractive for many potential actuating and sensing applications. Fourier transform infrared spectra under electric field reveal that this large polarization originates from the field-induced crystalline phase transformation. The nonpolar TGTG′ chain conformation in P(VDF-TrFE-CFE) can be converted into polar trans (Tm>4 and T3G) conformation under high electric field and the latter can be effectively aligned to the applied field direction. Furthermore, this conformation transformation is completely reversible and no hysteresis can be observed during the switching of applied electric field. In contrast, normal ferroelectric polymer P(VDF-TrFE) exhibits square polarization loop with very small reversible polarization.

Piezoelectric Polymers Actuators for Precise Shape Control of Large Scale Space Antennas

We present recent studies in the fundamentals and applications of the relaxor ferroelectric polymers, i.e., Poly(vinylidene fluoride-trifluroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE) terpolymers and high energy electron irradiated P(VDF-TrFE) copolymers. We show that the dynamic processes in these relaxor ferroelectric polymers are very similar to these observed in various polar-glasses. We further show that the large and reversible polarization change in these polymers leads to giant electrostriction and large electro-optic effect. By employing active electric boundary conditions, we demonstrate that the large electromechanical responses in these electroactive polymers can be made use of effectively for energy harvesting with high harvested electric energy density and efficiency. Terpolymer composites with ZnS nanoparticles provide an advanced E-O polymer which refractive index can be varied widely by small amount of ZnS in the composites while maintaining the large E-O effect of the matrix.