Piezoelectric actuators can offer high resolution of displacement and this makes them suitable for precise driving tasks. However, most piezoelectric actuators are made of piezoceramics which have a major drawback related to their natural hysteresis nonlinearity. To compensate the hysteresis nonlinearity of piezoelectric actuators, many hysteresis models have been proposed such as the Preisach model, the classical Prandtl-Ishlinskii model, and so on. This paper provides a new approach to model the asymmetric hysteresis nonlinearity of piezoelectric actuators. Unlike the classical Prandtl-Ishlinskii model, the proposed model is based on a combination of two asymmetric operators which can independently simulate the ascending branch and descending branch of hysteresis. Moreover, the proposed model can be calculated using the recursive least-squares method and this makes the model easy and convenient to be calculated. The validity of the proposed model is demonstrated by comparing its simulation results with experimental measurements. The results show that the proposed model is capable of modeling asymmetric hysteresis of piezoelectric actuators with very high accuracy.

This paper investigates and compares the efficiencies of four different interfaces for vibrationbased energy harvesting systems. Among those four circuits, two circuits adopt the synchronous switching technique, in which the circuit is switched synchronously with the vibration. In this study, a simple source-less trigger circuit used to control the synchronized switch is proposed and two interface circuits of energy harvesting systems are designed based on the trigger circuit. To validate the effectiveness of the proposed circuits, an experimental system was established and the power harvested by those circuits from a vibration beam was measured. Experimental results show that the two new circuits can increase the harvested power by factors 2.6 and 7, respectively, without consuming extra power in the circuits.

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A broad beamwidth stacked patch antenna with wide circularly polarised (CP) bandwidth is presented. The proposed antenna consists of a stacked structure with a rectangular shell under its ground structure to obtain CP characteristics and wide beamwidth. The radiation quality is excellent over the entire upper hemisphere. The 3 dB beamwidth of the proposed antenna on 2.4 GHz is larger than 140°. Moreover, the CP bandwidth, determined from the 3 dB axial ratio, is found to be about 240 MHz. CP bandwidth of 10.2% and the impedance bandwidth of 52.8% centred on 2.4 GHz are obtained. The proposed antenna is a good candidate for wide angle scanning phased arrays.Introduction: Microstrip patch antennas (MPAs) are widely used in current and future mobile communication systems which require small, low-profile and low-cost antennas. Moreover, with the development of communication and radar systems, wide beamwidth antennas have absorbed in burgeoning concern. To increase the 3 dB beamwidth of the MPA, many effective techniques have been employed. According to [1][2][3][4], many theoretical studies of the finite ground-plane effects on microstrip antenna radiation characteristics have been conducted. These studies have illustrated that the structure and dimensions of the antenna's ground plane can control the radiation patterns of the microstrip antenna.A circularly polarised (CP) microstrip antenna mounted on a threedimensional square structure is introduced in [5]. The antenna consists of a three-layer ground structure that makes the 3 dB beamwidth of CP radiation larger than 110°. In [6], it is illustrated that a curved grounding structure can increase both the impedance bandwidth and the beamwidth of the patch antenna. In [7], a corner-truncated squarepatch CP antenna mounted on a pyramidal ground plane and partially enclosed by a flat conducting wall is introduced. To make a wide beamwidth CP antenna lightweight and of low profile, the work presented in [8] uses a folded conducting wall to reduce the height of the CP antenna to about 0.04λ and meanwhile provides a 3 dB CP radiation beamwidth of about 106°. However, the inherent narrow bandwidth of the microstrip antennas is one of their major drawbacks. The CP bandwidth of the antenna presented in [5] is about 1.5% referenced to the centre frequency at 2323 MHz. Moreover, the impedance bandwidth and 3 dB axial ratio (AR) bandwidth of the antennas proposed in [7,8] are only about 2 and 5%. In the practical design of CP antennas, however, techniques for achieving wideband polarisation characteristics, as well as wideband impedance characteristics, are of great importance. A microstrip-monopole antenna is proposed in [9], where the beamwidth and bandwidth are obtained by loading four cylinders which are perpendicular to the radiating patch. Reference [10] illustrates a broadband dual CP patch antenna with wide beamwidth, which is excited by four crossslots via a microstrip line. The 10 dB impedance bandwidth is 24% and the 3 dB AR bandwidth is 16%. On the other hand, stack...

Irregular networks based on the condensation reaction of hydroxyl‐terminated poly(dimethylsiloxane) with cross‐linkers were investigated. The networks have excellent damping properties in a wide temperature range utilizing the viscoelastic relaxation of the irregular network with dangling chains. NMR Cross‐link Density Spectroscopy was used to explore the weight fraction of pendant chains and elastic chains in the elastomer. The transverse relaxation time for the elastomer was studied to explore the influence of pendant chains. The effects of the structure of cross‐linkers and the molecular weight of precursors were studied in detail. Elastomers cross‐linked by tetra‐functional cross‐linker (TEOS) have higher damping properties than the elastomers cross‐linked by tri‐functional cross‐linkers (MTMS and OTMS). A damping elastomer based on irregular networks with effective damping (tanδ > 0.3) temperature range of more than 250°C (from lower than −60°C to 190°C) was prepared. POLYM. ENG. SCI., 56:97–102, 2016. © 2015 Society of Plastics Engineers

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In this study, the authors present a geometrically symmetrical fractal structure called circular fractal structure. The iterative process of the geometric construction is illustrated and the dimension of the proposed circular fractal structure is 1.5729 based on the similarity dimension. Then, a polarisation insensitive multiband perfect metamaterial absorber (MMA) is proposed based on the circular fractal structure. The proposed MMA has three near‐perfect absorption bands for both transverse electric (TE) and transverse magnetic (TM) polarisations based on the theory of the fractal geometry. The current distribution on the top and bottom surfaces of the MMA are presented to preferably understand the physical mechanism behind the multiband absorption. The simulated results match the experimental results well. For both TE and TM polarisations, the three absorption frequencies are f1 = 2.29 GHz, f2 = 4.28 GHz, and f3 = 11.71 GHz, with the absorptivity of 98.7, 99.4, and 99.5%. Both experimental and simulated results indicate that the proposed circular fractal MMA is a promising candidate for absorbing elements in scientific and military applications.

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