Poly(vinylidene fluoride), PVDF, as one of important polymeric materials with extensively scientific interests and technological applications, shows five crystalline polymorphs with α, β, γ, δ and e phases obtained by different processing methods. Among them, β phase PVDF presents outstanding electrical characteristics including piezo-, pyro-and ferroelectric properties. These electroactive properties are increasingly important in applications such as energy storage, spin valve devices, biomedicine, sensors and smart scaffolds. This article discusses the basic knowledge and character methods for PVDF fabrication and provides an overview of recent advances on the phase modification and recent applications of the β phase PVDF are reported. This study may provide an insight for the development and utilization for β phase PVDF nanofilms in future electronics.

https://www.mdpi.com/2073-4360/10/3/228/pdf

Properties and Applications of the β Phase Poly(vinylidene fluoride).

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053002/pdf

Piezoelectric thin films: an integrated review of transducers and energy harvesting

Nonlinear vibration isolation for fluid-conveying pipes using quasi-zero stiffness characteristics

In this paper, we present a review of the experimental identification of dynamic parameters of bearings in a rotating machine. Major emphasis is given to vibration-based identification methods and the review encompasses descriptions of experimental measurement techniques, mathematical modeling, parameter extraction algorithms and uncertainty in the estimates applied to a variety of bearings. The parameter extraction algorithms include the descriptions of governing equations of the rotor-bearing system and identification methods in both time and frequency domains. The identification techniques have been classified based on methods used to excite the system. The review includes a variety of bearings and similar components, which play an active link between the rotating and stationary parts of a machine. Based on the state of the art in bearing identification, conclusions are made and future directions are suggested.

Identification of Dynamic Bearing Parameters: A Review

Vibration and noise control using shunted piezoelectric transducers: A review

Analytical study of a quasi-zero stiffness coupling using a torsion magnetic spring with negative stiffness

The traditional tuned mass absorber is widely employed to control the vibration of a primary structure by transferring the vibrating energy to the absorber. However, the working band of the absorber is very narrow, which limits the application of broadband vibration control. This study presents a novel broadband electromagnetic absorber by first introducing two negative impedance shunts to improve broadband damping of the absorber. The electromagnetic absorber is modeled, and the corresponding electromagnetic coupling coefficient is tested. A cantilever beam is employed to verify the broadband vibration absorption of the negative resistance (NR) shunted electromagnetic absorber (NR absorber) and the negative inductance NR shunted electromagnetic absorber (NINR absorber). The governing equations of the beam with two absorbers are derived, and the experiments are set up. The results point out that the NR and NINR absorbers can attenuate the broadband vibration. The proposed absorbers do not need the feedback system and the real-time controller compared to the active absorber; hence, they have great application potential in aerospace and in submarine applications, as well as in civil and mechanical engineering.

https://iopscience.iop.org/article/10.1088/0964-1726/23/12/125044/pdf

Negative impedance shunted electromagnetic absorber for broadband absorbing: experimental investigation

Active vibration control of a cylindrical shell partially covered by a laminated PVDF actuator (LPA) is studied. The electromechanically coupled equations of the system are derived considering the influences of the bonding layers. The analytical expressions of the control forces induced by the LPA are obtained and thereafter a parametric study is conducted to evaluate the effects of the physical properties of the actuator on the control forces. The active vibration control of a clamped–free cylindrical shell using an LPA with different layer numbers is simulated and carried out experimentally. It shows that the control forces of the actuator can be significantly enhanced by increasing the PVDF layer number while keeping the driving voltage unchanged. As a result, the modal vibrations of the shell are suppressed quite well (the vibration amplitude is cut by 64.08%) under a relatively low control voltage (40 V) with a five-layer LPA whose area is only 0.21% of that of the shell. Additionally, as the LPA partially covers the shell surface along the circumferential direction, it can exert a radial actuating force on the structure except for the actuating moment, and the former is much larger than the latter and is thus preferable for controlling the structural radial vibration. To make full use of this actuating force, the actuator should not be placed at a point of large surface strain as is usual but at one of large radial deformation.

https://iopscience.iop.org/article/10.1088/0964-1726/17/3/035024/pdf

Numerical and experimental investigation of active vibration control in a cylindrical shell partially covered by a laminated PVDF actuator

To enhance the low-frequency vibration isolation performance of the high-static–low-dynamic stiffness (HSLDS) isolator, a novel design of the geometric nonlinear damping (GND) comprising semi-active electromagnetic shunt damping is proposed. The GND is dependent on the vibration displacement and velocity, which can make the HSLDS isolator attain different damping characteristics in different frequency bands. Firstly, the configuration of the HSLDS isolator assembled with GND is presented, and then the restoring force, stiffness, and damping are derived. The dynamics of the mount under both base and force excitations are investigated based on the harmonic balance method, which are then verified by numerical simulations. After that, the effects of GND on the displacement and force transmissibility are studied, and the excellent performance caused by GND is analyzed based on the equivalent viscous damping mechanism. Finally, the comparison between the GND and cubic nonlinear damping is performed. The results demonstrate that the HSLDS isolator assembled with GND can realize the requirements of an isolation system under both base and force excitations of broadband vibration isolation performance and a low resonance peak with the high-frequency attenuation unaffected. Moreover, the GND outperforms the linear damping no matter the base excitation or force excitation is applied. For base excitation, the GND exhibits some desirable properties that the cubic nonlinear damping does not have at high frequencies.

Yahong Zhang

Papers

Analytical study of a quasi-zero stiffness coupling using a torsion magnetic spring with negative stiffness

Negative impedance shunted electromagnetic absorber for broadband absorbing: experimental investigation

Numerical and experimental investigation of active vibration control in a cylindrical shell partially covered by a laminated PVDF actuator

Enhanced isolation performance of a high-static–low-dynamic stiffness isolator with geometric nonlinear damping

Analytical study of the low frequency multi-direction isolator with high-static-low-dynamic stiffness struts and spatial pendulum