Actuators2015, 4(3), 135-155; doi:10.3390/act4030135 - published 26 June 2015 Show/Hide Abstract
Abstract: Previous studies of electrorheological fluids (ERFs) were motivated by brake, clutch, damping, haptic and resistive applications, but never motivated towards developing an ERF based-hydraulic rotary actuator. One design to make such an actuator is to use ERF-based valves. To fully understand the performance of such an actuator, it is imperative to study ERF valves. For this reason, this paper presents a summary of design considerations for creating ERF-based actuators, an ERF-based valve design for an ERF actuator and a new experimental test-bed to obtain viscosity and yield characteristics of the ERF at flow rates as low as 0.049 L/min, an order of magnitude lower than industrial rheometers. The new test-bed successfully measured the dynamic viscosity of the ERF to be at 0.6 Pa-s for low flow rates and 0.2 Pa-s for higher flow rates. The presented valve design can successfully resist 1 MPa of fluid pressure, which is an operation mode higher than any haptic and damping applications in the literature. The experiments also shows that higher flow rates negatively affect the ERF’s yield characteristics for the first time in a situation where the ERF valve completely blocks flow. When the flow rates are increased, the response time to a fully-closed valve increases, the effective yield capability of the ERF decreases and the conductivity of the ERF increases.
Actuators2015, 4(2), 127-134; doi:10.3390/act4020127 - published 29 May 2015 Show/Hide Abstract
Abstract: Mn-doped 0.7BiFeO3-0.3BaTiO3 (BFO-0.3BTO+Mn 1% mol) lead-free piezoelectric ceramic were fabricated by traditional solid state reaction. The phase structure, microstructure, and ferroelectric properties were investigated. Additionally, lead-free 1–3 composites with 60% volume fraction of BFO-BTO+Mn ceramic were fabricated for ultrasonic transducer applications by a conventional dice-and-fill method. The BFO-BTO+Mn 1-3 composite has a higher electromechanical coupling coefficient (kt = 46.4%) and lower acoustic impedance (Za ~ 18 MRayls) compared with that of the ceramic. Based on this, lead-free piezoelectric ceramic composite, single element ultrasonic transducer with a center frequency of 2.54 MHz has been fabricated and characterized. The single element transducer exhibits good performance with a broad bandwidth of 53%. The insertion loss of the transducer was about 33.5 dB.
Actuators2015, 4(2), 114-126; doi:10.3390/act4020114 - published 19 May 2015 Show/Hide Abstract
Abstract: Ionic polymer metal composite (IPMC), of which a low actuating voltage (<5 V), high power efficiency and biocompatibility makes it a proven candidate for low power devices. However, due to its inherent nonlinear behaviour and time-variance, feedback control, as well as reliable sensing means, are required for accurate operations. This paper presents an IPMC actuator implemented with an inductive sensor to enhance the reliability and compactness of the overall device. A practical, low cost and importantly, compact inductive sensor fabricated on a printed circuit board (PCB) is proposed here. Target material selections and coil design considerations are discussed. It is experimentally determined that the inductive sensor has comparable performance to a laser sensor. Based on a proportional-integral-derivative (PID) control results the inductive sensor has demonstrated to be an alternative to a laser sensor allowing devices using IPMC actuators to be compact.
Actuators2015, 4(2), 99-113; doi:10.3390/act4020099 - published 8 May 2015 Show/Hide Abstract
Abstract: B-site substitution in KNN with tantalum results in a higher d33 and dielectric constant. This higher value makes KNNT interesting for lead-free actuator applications. KNNT fibers with diameters of 300 and 500 μm have been extruded and sintered at 1200 °C in a KNNT-enriched atmosphere. Subsequently, the influence of fiber diameter on the microstructure (porosity and grain size) was investigated. The measurements revealed that with decreasing fiber diameter, the porosity increases, whereas the grain size decreases. The influence of these microstructural differences on the piezoelectric properties was evaluated using a novel characterization procedure for single fibers. The larger diameter fibers show an increase in the electromechanical properties measured, i.e., d33, tanδ, Pr, Ec and the free longitudinal fiber displacement, when compared to smaller diameter fibers. The lower alkali losses result in a larger grain size, a higher density during sintering and lead to higher electromechanical properties.
Actuators2015, 4(2), 77-98; doi:10.3390/act4020077 - published 5 May 2015 Show/Hide Abstract
Abstract: The piezoelectric actuator has gained popularity over the last few years. Attention has been directed towards the study of their electromechanical response in active repair and the control of damaged structures. This has been made possible through the development of various numerical and analytical techniques for such studies. The shift of focus towards the piezoelectric based approaches has been due to their advantages, which include strategic cost benefits in maintenance, as well as an increase in the life cycle of the repaired structures. Furthermore, adhesively bonded joints are widely used in the manufacturing and repairing of structures in many industries, especially automotive and aerospace engineering. This is due to the requirement for lightweight materials as well as the potential adhesive used to join materials with different characteristics. The piezoelectric actuator has also shown the capacity in controlling and lowering the shear stress concentration and joint edge peel in adhesively bonded joint systems. The structure’s control of stress and repair can generally be viewed as a reinforcement that influences the structure’s damage tolerance. Therefore, the interest of this review is on the applications of the piezoelectric actuators in both structural damage and the bonded adhesive joint system. The specific goal is to recognize the contemporary scientific challenges, including future opportunities.
Actuators2015, 4(2), 60-76; doi:10.3390/act4020060 - published 21 April 2015 Show/Hide Abstract
Abstract: In this work, we have investigated the design, fabrication and testing of ZnO-on-SOI fourth-order contour mode disk resonators for mass sensing applications. This study aims to unveil the possibility for real-time practical mass sensing applications by using high-Q ZnO-on-SOI contour-mode resonators while taking into account their unique modal characteristics. Through focused ion beam (FIB) direct-write metal deposition techniques, the effects of localized mass loading on the surface of three extensional mode devices have been investigated. Ten microfabricated 40 mm-radius disk resonators, which all have a 20 mm-thick silicon device layer and 1 mm-thick ZnO transducer layer but varied anchor widths and numbers, have exhibited resonant frequencies ranging from 84.9 MHz to 86.7 MHz with Q factors exceeding 6000 (in air) and 10,000 (in vacuum), respectively. It has been found that the added mass at the nodal locations leads to noticeable Q-factor degradation along with lower induced frequency drift, thereby resulting in reduced mass sensitivity. All three measured devices have shown a mass sensitivity of ~1.17 Hz·fg−1 at the maximum displacement points with less than 33.3 ppm of deviation in term of fractional frequency change. This mass sensitivity is significantly higher than 0.334 Hz·fg−1 at the nodal points. Moreover, the limit of detection (LOD) for this resonant mass sensor was determined to be 367 ag and 1290 ag (1 ag = 10−18 g) for loaded mass at the maximum and minimum displacement points, accordingly.