Fabrication and experimental characterization of d31 telescopic piezoelectric actuators

A popular and useful piezoelectric actuator is the stack. Unfortunately with this type of actuation architecture the long lengths normally required to obtain necessary displacements can pose packaging and buckling problems. To overcome these limitations, a new architecture for piezoelectric actuators has been developed called telescopic. The basic design consists of concentric shells interconnected by end-caps which alternate in placement between the two axial ends of the shells. This leads to a linear displacement amplification at the cost of force; yet the force remains at the same magnitude as a stack and significantly higher than bender type architectures. This paper describes the fabrication and experimental characterization of three different telescopic prototypes. The actuator prototypes discussed in this paper mark a definitive step forward in fabrication techniques for complex piezoceramic structures. Materials Systems, Inc. has adapted injection molding for the fabrication of net shape piezoceramic actuators. Injection molding provides several advantages over conventional fabrication techniques, including: high production rate, uniform part dimensions, uniform piezoelectric properties, and reduced fabrication and assembly costs. Acrylate polymerization, developed at the University of Michigan, is similar to gelcasting, but uses a nonaqueous slurry which facilitates the production of large, tall, complex components such as the telescopic actuator, and is ideal for the rapid manufacture of unique or small batch structures. To demonstrate these fabrication processes a five tube telescopic actuator was injection molded along with a very tall three tube actuator that was cast using the acrylate polymerization method. As a benchmark, a third actuator was built from off-the-shelf tubes that were joined with aluminum end-caps. Each prototype's free deflection behavior was experimentally characterized and the results of the testing are presented within this paper.     

Suspension polymerization casting of lead zirconate titanate,Part II: acrylate system

Suspension polymerization casting of lead zirconate titanate (PZT) filled acrylate-based system was investigated using 51 vol% suspension of PZT in an ethoxyethoxy ethyl acrylate-based system. The polymerization process was characterized with chemorheology and differential scanning calorimetry. PZT powder accelerates the process, decreasing the activation energy for polymerization from 132 ± 6 kJ/mol to 98 ± 20 kJ/mol. The influence of monomer ratio, initiator amount, catalyst, and solvent are presented.     

DEPP functionally graded piezoceramics via micro-fabrication by co-extrusion

This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime.     

Anticipatory and fantastic role enactment in preschool triads.

Examined the relationship between 4 types of role enactment (domestic, occupational, fantastic, and peripheral) and object ideation, social organization (solitary vs interactive behavior), and metacommunication. Each of 12 same-age, same-sex triads of 3?- and 5-yr-old children (6 boy triads and 6 girl triads) was observed during 2 30-min sessions, one in which objects with highly specific functions (e.g., trucks and dolls) were available and one in which objects with relatively ambiguous functions (e.g., pipecleaners and cardboard cylinders) were present. Because there was no fantasy role enactment in girls, only data for the boys were used to examine the relationships of primary interest. Results indicate that object ideation was less frequent, and interactive behavior and metacommunication more frequent, during role enactment than during domestic or occupational role enactment. Findings indicate that Ss rehearsed certain social and cognitive skills to varying degrees when they enacted different types of roles. Antecedents of different types of role enactment were also identified. Older boys enacted fantasy and occupational roles more frequently, and peripheral and domestic roles less frequently, than younger boys. Domestic and occupational role enactment was more frequent, and fantastic role enactment less frequent, in the presence of high-specificity toys than in the presence of low-specificity toys. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis and thiol–ene photopolymerization of (meth)allyl‐terminated polysulfides

Thiol‐terminated polysulfides (PS) are cured by mixing with an oxidant, resulting in limited shelf‐ and/or pot‐life, depending on whether formulated as a one‐ or two‐component system. Mixtures of thiol‐ and alkene‐terminated polysulfides offer the potential for an on‐demand curing process through thiol–ene photopolymerization. Thiol end groups of commercial polysulfides, PS‐1 (1000 g/mol) and PS‐2 (3000 g/mol), were converted to alkene by reaction with (meth)allyl bromide. Photopolymerizations were performed by irradiating films of equimolar thiol:ene mixtures at 320–500 nm (30 mW/cm²) in the presence of 5 wt % 2,2‐dimethoxy‐2‐phenyl‐acetophenone (DMPA). Reaction kinetics were measured using real‐time FTIR by monitoring absorbances at 3075 cm^?1 (alkene) or 2550 cm^?1 (thiol). In the absence of any reactive diluent, mixtures of thiol and alkene polysulfides failed to gel notwithstanding high reaction conversion (>90%). Partial or total replacement of the thiol polysulfide component with pentaerythritol tetrakis(3‐mercaptopropionate) (PETMP) yielded solid elastomeric films and ultimate reaction conversions of 80–96% after 5 min irradiation. Crosshatch adhesion measured on glass, aluminum, and steel was very poor (0B) for (meth)allyl PS‐1/PETMP and poor (2B) for (meth)allyl PS‐2/PETMP without adhesion promoters. (3‐Mercaptopropyl)trimethoxysilane (1 wt %) significantly improved adhesion of (meth)allyl PS‐2/PETMP on all substrates (4B) but yielded no improvement for (meth)allyl‐terminated PS‐1/PETMP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45523.     

Visual discrimination and reversal learning in rough-necked monitor lizards (Varanus rudicollis).

Reptile learning has been studied with a variety of methods and has included numerous species. However, research on learning in lizards has generally focused on spatial memory and has been studied in only a few species. This study explored visual discrimination in two rough-necked monitors (Varanus rudicollis). Subjects were trained to discriminate between black and white stimuli. Both subjects learned an initial discrimination task as well as two reversals, with the second reversal requiring fewer sessions than the first. This reduction in trials required for reversal acquisition provides evidence for behavioral flexibility in the monitor lizard genus. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Deflection performance of a bi-directional distributed polymericpiezoelectric micromotor

Distributed piezoelectric micromotor architectures have great potential because they combine the advantages of piezoelectric micromotors with the advantages of distributed architectures. However, to use a distributed architecture paradigm for piezoelectric micromotors, a basic motor building block is needed. To meet this need a piezoelectric micromotor building block, called a C-block, was developed. These C-blocks can be combined together in a variety of distributed architectures to expand their capabilities. This paper introduces a basic polymeric piezoelectric C-block micromotor design and a serial C-block micromotor architecture that demonstrates increased deflection capabilities. For both micromotor designs, simple manufacturing steps are described and analytical deflection models are presented. These micromotors were experimentally tested with prototypes ranging in size from a few millimeters to a few centimeters in scale. Results for an individual C-block micromotor and a serial C-block micromotor are presented. These results demonstrate the accuracy of the models and the feasibility of designing and fabricating polymeric piezoelectric micromotor architectures     

Recurve piezoelectric-strain-amplifying actuator architecture

Various external and internal leverage devices have been developed to amplify strain; however, these devices are commonly inefficient due to transmission losses and can be difficult to pack into constrained application volumes. A Recurve actuator architecture has been designed which amplifies direct material strains and allows for construction of highly compact, high-energy-density actuator arrays. The Recurve architecture enables arrays that can be tailored to produce specific force and displacement output and can be configured in a variety of ways to make efficient use of available design space. This paper describes a Recurve actuator architecture and presents a quasi-static model relating voltage, force, and deflection along with experimental results for fundamental Recurve actuator elements     

Design and static modeling of a semiconductor polymericpiezoelectric microactuator

The design of a semicircular polymeric piezoelectric actuator is presented, the models for its deflection and force are derived, and the results of the experiments used to verify the models are reported. The design is a polymeric piezoelectric bimorph formed in a semicircular shape instead of the standard straight cantilever beam bimorph design. The deflection model is adopted from the straight cantilever beam model and relates the free deflection as a function of the applied voltage field. The force model is developed using Castigliano's second theorem. Two experiments were conducted to verify the model: force-voltage and force-deflection. The models show that a bimorph formed in a semicircular shape produces significantly more force than a straight cantilever beam bimorph of the same length without a significant sacrifice in deflection     

Suspension polymerization casting of lead zirconate titanate, part I: Acrylamide hydrogel system

Suspension polymerization casting of lead zirconate titanate (PZT) filled acrylamide systems was studied. A high solid loading (51 vol%) PZT slurry with low viscosity (about 280 mPa·s at shear rate 10 s^–1) was obtained by optimizing the dispersant amount. The polymerization process for the monomer solution and PZT slurry were characterized with the help of the storage modulus measurement. For the monomer solution, the overall activation energy of gelation was calculated as 60–76 kJ/mol, while for the PZT slurry, this energy increased to 91 ± 9 kJ/mol. The drying, burnout and sintering processes were also addressed.