Hongli Ji

Semi-active Vibration Control of a Composite Beam using an Adaptive SSDV Approach

In this paper, an improved semi-active control method is proposed and applied to the vibration control of a composite beam. This method is an improved version of the previously developed SSDV (synchronized switch damping on voltage) approach. In SSDV, a voltage source is connected to the shunting branch, in series with the inductor, which can magnify the inverted voltage and hence improve the control performance. Optimization of the voltage source is an important issue in all SSDV techniques. In the proposed approach, called adaptive SSDV, the voltage coefficient that controls the damping effectiveness is adjusted adaptively. An improved switching algorithm, which prevents the switch from over-frequently switching on-and-off and accordingly improves the control performance, is also proposed. Compared with previous SSDV techniques, this adaptive SSDV is the most stable, is independent of the excitation level, and is more flexible because the voltage coefficient is adjusted adaptively to achieve optimal control performances. The adaptive SSDV has been applied to the vibration control of a composite beam and its control results were compared with those of previously developed SSDV techniques. The effectiveness of the new switching algorithm was also verified by comparing it with the conventional switch. An experimental setup of a semi-active control system for the cantilever composite beam was established, and control experiments were carried out using different SSDV methods.

Semi-active Vibration Control of a Composite Beam by Adaptive Synchronized Switching on Voltage Sources Based on LMS Algorithm

In this article, an adaptive semi-active SSDV (Synchronized Switch Damping on Voltage) method based on the LMS algorithm is proposed and applied to the vibration control of a composite beam. In the SSDV method, the value of voltage source in the switching circuit is critical to its control performance. In the adaptive approach proposed in this study, the voltage source is adjusted adaptively using the LMS algorithm. Two cases of the adjustment are considered. In the first case, as an improvement to the enhanced SSDV, the voltage coefficient is adjusted by the LMS algorithm. In the second case, as an improvement to the classical SSDV, the voltage value is adjusted directly. The new adaptive approach is compared with the derivative-based adaptive SSDV proposed in the former study in the control of the first mode of a composite beam. The control results show that adaptive adjustment of voltage value and adaptive adjustment of voltage coefficient are equally effective in the vibration control of the composite beam and that LMS-based approach is slightly better than the derivative-based approach.

Enhanced synchronized switch harvesting: a new energy harvesting scheme for efficient energy extraction

This paper presents a new technique for optimized energy harvesting using piezoelectric microgenerators called enhanced synchronized switch harvesting (ESSH). This technique is based on the concept of synchronized switch harvesting (SSH), a nonlinear technique developed for energy harvesting from structural vibration. Compared with the standard technique of energy harvesting, the new technique dramatically increases the harvested power by almost 300% at resonance frequencies in the same vibration conditions, and also ensures an optimal harvested power whatever the load connected to the microgenerator. Furthermore, the new technique (ESSH) in this paper can be truly self-powered; a self-powered circuit which implements the technique is proposed. In addition, the overall power dissipation for the control circuitry is relatively constant (only about 121 µW), which is more attractive especially at high excitation. Because the new technique (ESSH) in this paper can be truly self-powered, no external power supply is needed, making the system suitable for more application fields, especially in remote operation.

Multi-modal vibration control using a synchronized switch based on a displacement switching threshold

A new semi-active method for multi-mode vibration control using the nonlinear synchronized switch damping (SSD) approach based on a displacement switching threshold is proposed in this paper. Several extensions of the SSD approach, including SSDI (SSD on inductance), SSDV (SSD on a voltage source), enhanced SSDV, and adaptive SSDV, have been developed to improve the control of the single-mode vibration, but the weakness of the SSD approach for multi-modal vibration control has not been solved. In all these extensions of the SSD approach, the switch is controlled by the same algorithm, that is, it reverses the voltage of the piezoelectric element at all extrema of displacement. This switching algorithm is effective in single-mode control, but it leads to over-frequent switching in multi-mode control. In the method proposed in this study, an improved switching algorithm based on a displacement threshold, which prevents the switch in the shunt circuit from over-frequent on-and-off actions and accordingly increases the converted energy to improve the control performance, is proposed. The switching algorithm is applied to an SSDI system and used in the vibration damping of a beam with two excited modes. Compared to the classical SSDI approach, the control performance of the first mode is improved from 3.7 to 18.2 dB, but that of the second mode is slightly worse, having changed from 3.46 to 2.6.

Two-Step Sintering of the Pure K0.5Na0.5NbO3 Lead-Free Piezoceramics and Its Piezoelectric Properties

The two-step sintering method was successfully applied to fabricate the lead-free alkaline niobate (K0.5Na0.5NbO3) piezoelectric ceramics, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to characterize the samples. The properties of density, piezoelectric and ferroelectric were also investigated. Under the optimal sintering process, the specimens with the relative density 95.2%, which exhibit good electrical properties (d 33 = 121pC/N, k p = 35.2%, Q m = 5, ϵ r = 815). These results show that K0.5Na0.5NbO3 ceramic is a promising lead-free piezoelectric material for the ultrasonic delay-line applications, broadband transducers and sensors. The easy-controlling sintering process can be used in the other piezoelectric ceramics system.

Novel Approach of Self-Sensing Actuation for Active Vibration Control

In a self-sensing actuator, the same piezoelectric element functions as both a sensor and an actuator. Due to their advantages of reducing the number of needed piezoelectric elements and true collocation of sensors and actuators, self-sensing actuators have attracted the attention of many researchers and many studies have been reported. Since the actuator signal and the sensor signal are mixed together in a self-sensing actuator, usually a bridge circuit is used to separate the two signals. It has been found that the two signals cannot be separate ideally, because the bridge is difficult to balance and the actuator signal is much larger than the sensor signal. In this study, the influence of the local strain on the output signal of a piezoelectric sensor is investigated numerically and experimentally. In order to delete the influence of local strain on performance of the self-sensing actuator, a new method using neural network is proposed to identify the strain of global vibration. The identified signal is used as feedback signal for an adaptive control system and the effectiveness in suppressing the beam vibration is verified in the experiment.

Improved piezoelectric properties of poly(vinylidene fluoride) nanocomposites containing multi-walled carbon nanotubes

We improved the piezoelectric properties of poly(vinylidene fluoride) (PVDF) by employing multi-walled carbon nanotubes (MWCNTs) as nanofillers. The MWCNT/PVDF nanocomposite was prepared by the solution casting method with MWCNT content ranging from 0.0 to 0.3?wt%. To induce the piezoelectric ?-phase crystal structure, the nanocomposite films were drawn to 400%?500% elongation and polarized with a step-wise poling method. To evaluate the piezoelectric properties, the output voltages of the nanocomposite films were measured through extensive experimental vibration tests. The experimental results show that the nanocomposite film with 0.05?wt% MWCNT loading possesses the highest output voltage, around two times higher than that of pure PVDF film, as compared to the other loadings. The main reason for this phenomenon is that more ?-crystalline phase can be formed at this MWCNT loading, as confirmed by x-ray diffraction and Fourier transform infrared spectroscopy spectral analysis and polarized optical microscopy observations.

Energy harvesting and vibration control using piezoelectric elements and a nonlinear approach

The piezoelectric materials, as the most widely used functional materials in smart structures, have many outstanding advantages for sensors and actuators, especially in vibration control and energy harvesting, because of their excellent mechanical-electrical coupling characteristics and frequency response characteristics. Semi-active vibration control based on state switching and pulse switching, have been receiving much attention over the past decade because of several advantages. The technique is based on a nonlinear processing of the voltage delivered by the piezoelectric elements. This process increases the amount of electrically converted energy during a mechanical loading cycle of the piezoelectric element. A new approach for energy harvesting from mechanical vibrations is also derived from the nonlinear approach based on Synchronized Switch Damping. The present research activities of vibration control and energy harvesting using piezoelectric elements and a nonlinear approach are introduced.

The influence of switching phase and frequency of voltage on the vibration damping effect in a piezoelectric actuator

In a structural system with piezoelectric actuators, a damping effect can be achieved by properly switching the voltage on the actuators. Switched voltage methods based on piezoelectric actuators, including active bang–bang control and semi-active synchronized switch damping methods, have become an important category of vibration damping approach. Since the switching phase and switching frequency are critical factors to damping performance, their influence on converted energy in a piezoelectric actuator is investigated under the condition that the switched voltage is constant. The converted energy with randomly switched voltage is also investigated theoretically and numerically. Finally an example of beam vibration with synchronized switch damping on inductor (SSDI) control and synchronized switch damping on voltage source (SSDV) control is used to illustrate how the switching frequency can affect the control performance of different modes in a multiple-degree-of-freedom system.

Ferroelectric and Piezoelectric Properties of Pb(Ni1/3Nb2/3)0.5(Ti0.7Zr0.3)0.5O3 Ceramics Fabricated by Tape-Casting Process

Pb(Ni1/3Nb2/3)0.5(Ti0.7Zr0.3)0.5O3 (PNN-PZT) ceramic powders were pre-calcined by solid-state reaction method. PNN-PZT piezoelectric ceramics were fabricated by tape-casting process. The effects of sintering temperature on physical and electrical properties of the PNN-PZT ceramics were studied. The results show that the ceramics sintered at 1225°C have the best overall properties, d33 = 780 pC/N, ϵ r = 6.18 × 103, kp = 0.6, tan δ = 0.017, Pr = 26.36 μC/cm2. Compared to the ceramics with the same composition prepared by the traditional process, the properties of the ceramics prepared by tape-casting process have been improved greatly.