Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft polymer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufacturing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators. 

Shape memory alloys (SMAs) have been widely used to fabricate soft actuators by embedding SMA wires into various soft matrices manufactured by conventional moulding methods or novel three-dimensional (3D) printing techniques. However, soft matrices of SMA based actuators are typically fabricated from only one or two different materials. Here, we exploit the great manufacturing flexibility of multimaterial 3D printing to fabricate various bending, twisting and extensional actuators by precisely controlling the spatial arrangements of different printing materials with different stiffnesses. In order to achieve a broad range of deformations, ten different printing materials were characterized and used in the actuators design. In addition, we developed a finite element model to simulate complex deformations of the printed actuators and facilitate the design process. The model incorporates a user defined material subroutine that describes the nonlinear temperature dependant behavior of SMAs. The results show the efficiency and flexibility of multimaterial 3D printing in tailoring the deformed shape of the SMA based soft actuators, which cannot be accomplished using conventional manufacturing methods such as moulding.

This work reports the bias and pressure sensitivity of AlGaN/GaN High Electron Mobility Transistors (HEMTs) sensing elements strategically placed on a pressure sensitive diaphragm clamped at its edges. The sensitivity was over 150 times greater in the weak inversion regime than in the strong inversion regime of the HEMT, leading to a drain current change of >38% when a pressure of 50 bar was applied. The sensitivity of the HEMT to pressure followed an exponential dependence from atmospheric pressure up to 80 bar, behaviour explained by the response of the density of a two-dimensional electron gas to pressure induced changes in the HEMT threshold voltage in the weak inversion regime. Finally, it was found that the sensitivity of the HEMT was maximum when it was situated in the middle of the diaphragm, whereas a device mounted over the clamping point showed less than 0.02% change in drain current when pressure change of 50 bar was applied.

This study reports on the poling and characteristics of a melt-spun piezoelectric bicomponent fiber with poly(vinylidene fluoride) (PVDF) as its sheath component and a conductive composite with carbon black (CB) and high density polyethylene (HDPE) as its core component. The influence of poling conditions on the piezoelectric properties of the fibers has been investigated. The poling parameters temperature, time and poling voltage have been varied and the piezoelectric effect of both contact- and corona-poled yarns have been evaluated. The results show that a high piezoelectric effect is achieved when the poling voltage is high as possible and the poling temperature is between 60° C and 120 °C. It was also shown that permanent polarization is achieved in a time as short as 2 s in corona-poled fibers. A yarn exposed to a sinusoidal axial tension of 0.07% strain (the corresponding force amplitude was 0.05 N) shows an intrinsic voltage output of 4 V. The mean power from a 25 mm length of yarn is estimated to be 15 nW. To demonstrate the fibers sensor properties, they are woven into a textile fabric from which a force sensor is manufactured and used to detect the heartbeat of a human.

A novel X-ray detector diode, optimized for angular independent (isotropic) dose response, is presented. The diode is designed as a silicon cube with p-n junctions on all six sides, which creates a device that is close to being symmetrical in 3D. The cube edge is 300 μm or 410 μm. Its manufacturing process is based on micromachining, featuring deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrates, doping of vertical walls from gas phase dopants and re-fill of etched trenches with polysilicon. The variation in detector response to 6 MV X-rays, in a ±30° beam angle range, was at best ±0.5% for a cubic diode compared to ±3.3% for conventional diodes, which indicates improvement by a factor 7.