Nonlinear modal electromechanical coupling factor for piezoelectric structures containing nonlinearities

Within the linear framework,the Modal Electromechanical Coupling Factor(MEMCF)is an important indicator to quantify the dynamic conversion of mechanical energy and electrical energy of piezoelectric structures.It is also an important tool to guide the piezoelectric damping design of linear structures.Advanced aircraft often fly in maneuvers,and the variable working conditions induce drastic changes in the load level on structures.Geometric and contact nonlinearities of thin-walled structures and joint structures are often activated.To achieve a good vibration reduction effect covering all working conditions,one cannot directly use linear electromechanical coupling theory to instruct the piezoelectric damping design for nonlinear structures.Therefore,this paper defines the Nonlinear Modal Electromechanical Coupling Factor(NMEMCF)and proposes the corresponding numerical method for the first time to quantitatively evaluate the electromechanical coupling capability of nonlinear piezoelectric structures.Three candidate definitions of the NMEMCF are given,including two frequency definitions and one energy definition.The energy definition is the most promising one.It is not only applicable to both conservative and dissipative nonlinear structures but also compatible with the linear MEMCF.In addition,based on the energy formula,the NMEMCF can be obtained by only performing one nonlinear modal analysis in the open-circuit state.The analytical findings and the numerical tool are validated against two piezoelectric structures with different types of nonlinearities.A strong correlation among the NMEMCF,geometric parameters,and energy dissipation is observed.The results confirm that the proposed NMEMCF captures the physics of the electromechanical coupling phenomenon associated with nonlinear piezoelectric structures and can be used as an essential design indicator of piezoelectric damping,especially for variable working conditions.

Synthesis and Piezoelectric Properties of Lead-free (Bi_(0.5)Na_ (0.5))_ 1-x(Ba_aSr_b)_xTiO_3 Ceramics

A new group of lead-free piezoelectric ceramics,（Bi0.5 Na0.5）1-x（BaaSrb）xTiO3（abbreviated as BNBST[100x-100a/100b],0〈x〈1,a＋b=1）,was synthesized.The ceramics were prepared by conventional ceramic sintering technique,and the ceramics with density of 95% of the theoretical one can be sintered without the atmosphere control during the sintering process.The results of the X-ray diffraction（XRD） data show that the ceramics possess a single perovskite phase.The measurements of dielectric and piezoelectric properties reveal that the ceramics provide relatively high piezoelectric charge constant d33 and high planar electromechanical coupling factor kp.For the BNBST6-95/5 ceramics,d33 is equal to 170pC/N,and kp is equal to 32.0%.The fabrication technique for these ceramics is conventional and stable.

The Role of PZT in Flexible 1-3 Piezoelectric Composite for Smart Structure

Piezoelectric composite materials have the ability to perform both sensing and actuating functions.It is a viable candidate for smart actuation in underwater noise controlling with its higher coupling factor and lower acoustic impedance, when the piezoelectric rods are inclined to control its both the shear and the compression damping characteristics.In this paper, a simple physical model of 1-3 piezoelectric composite is advanced for maximizing the electromechanical coupling factor,the acoustic impedance,and the hydrophone figure of merit.

High Quality of Piezoelectric Response of Nano Ni Doped Pb1-xNixTiO3 Ceramic

A series of Pb1-xNixTiO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the general ceramic and co-precipitation method. The grain size decreased with increasing Ni contents. The piezoelectric modulus d33 increased with increasing Ni contents. It was observed also the d33 of the nanocomposite Pb1-xNixTiO3 prepared by co-precipitation method is higher than those of the prepared by general ceramic method. The coupling factor kp increased by the more doping of Ni. The ultrasonic wave velocity decreased also with increasing Ni contents. The polarized nano-sample of composition Pb0.5Ni0.5TiO3 is suitable for improving application of useful piezoelectric technology.

Lead-free 0-3-type composites:From piezoelectric sensitivity to modified figures of merit

Effective piezoelectric properties,electromechanical coupling factors(ECF)and figures of merit(FOM)are studied in leadfree 0-3-type composites based on novel ferroelectric 0.965(K_(0.48)Na_(0.52))(Nb_(0.96)Sb_(0.04))O_(3)-0.035Bi_(0.5)Na_(0.5)Zr_(0.15)Hf_(0.75)O_(3) ceramic.Systems of prolate ceramic inclusions are surrounded by a large polymer matrix that can be either monolithic(in the 0-3 composite)or porous(in the 0-3-0 composite).Non-monotonic volume-fraction dependences of the effective piezoelectric coefficients g_(3j)^(*),ECF k_(3j)^(*),squared FOM d_(3j)^(*)g_(3j)^(*)and their modified analogs for stress-driven systems are analysed,and examples of the high longitudinal piezoelectric sensitivity(g33^(*)>100 mV.m/N)are considered.A role of microgeometrical factors,that promote the large effective parameters and anisotropy of properties in the 0-3-type composites,is highlighted.New“aspect ratio-volume fraction”diagrams are first built to describe conditions for high piezoelectric sensitivity,large modified FOM and their anisotropy in the studied composites.These advanced materials can be of value for piezoelectric sensor,energy-harvesting and related applications.