Haptic devices allow touch-based information transfer between humans and intelligent systems, enabling communication in a salient but private manner that frees other sensory channels. For such devices to become ubiquitous, their physical and computational aspects must be intuitive and unobtrusive. The amount of information that can be transmitted through touch is limited in large part by the location, distribution, and sensitivity of human mechanoreceptors. Not surprisingly, many haptic devices are designed to be held or worn at the highly sensitive fingertips, yet stimulation using a device attached to the fingertips precludes natural use of the hands. Thus, we explore the design of a wide array of haptic feedback mechanisms, ranging from devices that can be actively touched by the fingertips to multi-modal haptic actuation mounted on the arm. We demonstrate how these devices are effective in virtual reality, human-machine communication, and human-human communication.

Inflatable soft robots powered by dielectric elastomer actuators show promise for extra-terrestrial applications. These must be stowed in a deflated configuration for launch, necessitating a method for inflation. Traditional methods, such as stored compressed gas, introduce unwanted mass, volume, and rigidity. Gas Forming Reactions offer an alternative mechanism. Isolating citric acid in a silicone membrane creates a soft balloon which can be safely placed inside a soft structure and surrounded by bicarbonate. By adding an electrical connection inside and a soft electrode to the exterior we can electronically rupture the balloon to release the acid and trigger inflation.

Biomimetics Laboratory, Auckland Bioengineering Institute, University of Auckland, New Zealand Soft compassion sensors provide a sense of touch for robots which plays a crucial role in safe interaction between robots and their environment. Here we report on Carbon black/dimethylsiloxane (PDMS) composite at the top of an interdigitated electrode (IDE) patterned on a printed circuit board (PCB). The sensor's response only depends on the change in relative permittivity of the composite. Any deformation causes a decrease in permittivity due to a change in the filler's network shape. The sensor shows an excellent sensitivity of 7.1%N-1, which is 35 times more than a composite made with insulating particles (BaTiO3). Our sensor combines high sensitivity with a simple fabrication, thus making it ideal for manipulating fragile objects.

To swim well a fish points towards the oncoming flow. This action, termed rheotaxis is partially enabled by the flow-sensitive neuromasts on the skin of the fish. To mimic this we have fitted an elasto-tensegrity, fish-like robot, Robowahoo, with piezoresistive electroactive polymer sensors, and placed it in a flow-controlled water-flume tank. Signals were recorded as the head was slowly turned in yaw, demonstrating the real-time measurement of head alignment to flow. Such cyber-rheotaxis sensors can be directly linked to tail actuators in closed-loop control, thus bringing us closer to the goal of accurate and efficient robotic fish-like swimming.

We present a compact, prehensile and soft gripper capable of varying its stiffness on demand, allowing not only grasping but also manipulation of objects. The gripper consists of fluidic chambers within a silicone structure and two electrostatic clutches bonded to opposite external surfaces. Actuation is achieved by pressurizing the chambers using an integrated electrohydrodynamic ‘ion-drag’ pump while simultaneously blocking one of the clutches, causing the structure to bend around and grasp an object. Once the object is grasped, the second clutch is blocked, significantly increasing the bending stiffness of the structure and allowing the object to be manipulated.

Hydraulically amplified self-healing electrostatic (HASEL) actuators offer mechanical performance suitable for soft robotics and wearable devices. Strain decrease associated with sustained DC voltage application (DCV), however, remains a challenge. Here we discuss the role of charge retention (CR) in the actuation behavior of linearly contracting Peano HASELs under different voltage conditions and material compositions. We then discuss techniques for measuring dielectric absorption of different material combinations used to fabricate HASELs and discuss their relationship to CR. Selection of material combinations significantly impacts CR and is crucial to consider for HASELs and other devices driven by electrostatic forces.

Polyvinyl chloride (PVC) gels have been shown to exhibit mechanoelectrical transduction under varying mechanical inputs. These inexpensive gels can easily be fabricated into planar sections with differing amounts of plasticizer. The plasticizer content within the gel samples can be tuned for optimal mechanoelectrical transduction under expected force inputs. More plasticizer content results in more sensitive gels with lower mechanoelectrical saturation levels, less plasticizer is more ideal for higher expected force inputs. Higher plasticizer content has shown these gels to be very sensitive, providing mechanoelectrical transduction under sub-gram force compressive inputs. By using segmented electrodes these gels can sense both location and magnitude of incoming forces in planar and quasiplanar applications. Different orientations of electrodes are investigated for varying purposes. A square planar sensor with a 3x3 grid of square electrodes is investigated and resolution of this planar sensor is tested with varying force magnitudes and locations. Raw mechanoelectrical responses are shown and a simple application is displayed with some integrated electronics for data acquisition and processing. Some limited work in quasiplanar orientations is also investigated on curved and angled surfaces. This work also provides some insight to the mechanics of mechanoelectrical transduction within PVC gels. The mechanoelectrical transduction has been found to be a surface property, however this study examines the area of contribution to the overall mechanoelectrical transduction. Further experimentation aims to broaden the applications of these sensors.

Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.

Soft ionic actuators that perform fast and large response at low voltages are desirable for soft robotics. However, current actuators have poor performances due to unproper electrode materials. Here, we develop molybdenum disulfide/graphene (MoS2-rGO) nanocomposite with high capacitance from MoS2 and good conductivity from graphene. Therefore, the corresponding ionic actuators multiply performances by over 6.5 times at 0.5 V and 1 Hz, hence can be used to activate soft robotic fingers working on the delicate surfaces of smartphones. These actuation enhancement and soft finger demonstration clearly suggest the high quality of MoS2-rGO nanocomposite and strengthen potentials of ionic actuators in soft robotics.

The characteristics of ionic polymer metal composite (IPMC) based capacitors depends on the pH of the working solution. However, their basic mechanism is not well studied. Therefore, this study investigates the IPMC based capacitor with Platinum electrodes in various pH solutions. Cyclic voltammetry (CV), alternating-current (AC) impedance, and capacitance measurements were then performed to investigate the effects of the pH on the electrochemical properties of the IPMC capacitors. The results are helpful for the use and control of IPMC based capacitors. Although IPMCs are widely studied for their electromechanical or electrochemical properties, most studies have been performed at the ambient conditions. The electrochemical performance of IPMC at higher temperatures is still far from understood. In this study, the effect of temperature on electrochemical behavior of IPMCs is examined. The electrochemical study was conducted in different pH solutions at temperatures ranging from 25 °C to 80°C. The current flow across the IPMC electrode increases with increasing temperature up to 60°C during the charging and discharging cycles.

The soft electroactive polymer material, ionic polymer-metal composites (IPMCs), has been shown to exhibit a unique two-way transduction ability – allowing for both sensing and actuation capabilities. As an artificial mechanotransductor, there are several advantageous properties of IPMCs over existing sensing measurement technology which, along with its ability to be used in aqueous environments, can be used for various underwater sensing applications. Prior, an in-depth analysis of the dominant behaviors of IPMC transduction has been disseminated into an all-encompassing model that accounts for the many complex characteristics that entail IPMC physics. The framework this model was built under depicts the finite-strain deformation of a hyperelastic material, while also considering the details of the polymer’s porous network, and the electrode deforming with the polymer material’s skeleton. The model was developed within the finite element software, COMSOL Multiphysics 5.6, where the derived nondimensional formulations for IPMC actuator and sensor physics were inputted using an equation-based modeling approach. Within the model, open-circuit (O-C) voltage sensor readings are obtained by reading the potential difference between the upper contact floating potential, and the lower contact set to ground. In this study, the sensing aspects of the model previously developed have been further expanded to include Fluid-Structure Interaction (FSI) physics, supplanting the prescribed displacement within the model with conditions similar to an in-lab test chamber. The model has hence been able to provide a comparable O-C voltage response between the model and in-lab conditions via a recirculating swim tunnel. The research proposed herein establishes a basis for expanding IPMC modeling to include FSI and further characterization of the IPMC transduction phenomena.

The soft and compliant nature of ionic polymer-metal composite (IPMC) sensors has recently been investigated for various applications in soft robotic and mechatronic devices. Recent results of physics-based chemoelectromechanical modeling suggest that IPMC asymmetric surface roughening may enhance the sensitivity under compression. This paper presents initial experimental results on IPMC compression sensors fabricated with varying degrees of asymmetric surface roughness. The roughness is created through a simple mechanical sanding process on the base polymer material, referred to as "polymer abrading technique'", followed by traditional electroless plating to create electrodes. Sample sensors are characterized by measuring the voltage response under different compressive loads. The results show consistently increased sensor sensitivity of the asymmetrically roughened IPMCs versus a control sample. Sensitivity increases non-monotonically with rougher electrode surfaces, where maximum sensitivity of about 0.0433 mV/kPa is achieved with sensor electrodes with 53-74~micrometer abrasions. More variability is also observed through augmented electrode roughness, suggesting greater flexibility for IPMC sensor design. These results align with predictions from the existing physics-based chemoelectromechanical model.

The development of novel functional dielectric materials can open the doors to major technological innovations with societal impact. Stretchable capacitors transduce electrical into mechanical energy or vice-versa. Over the last 20 years, they have received significant interest from academia and industry. However, this technology still needs both improved dielectrics as well as conductive elastomers to achieve the desired low driving voltage and to realize devices with attractively high sensitivity. The currently most explored dielectric elastomers are polydimethylsiloxanes (PDMS). However, because of their low dielectric permittivity of only 3, the devices made of them require high voltages for operation. We synthesized polar polysiloxanes with different types and contents of polar groups, investigated their thermal and dielectric properties, and selected the most suitable groups to achieve the highest dielectric permittivity, yet sufficiently low glass transition temperature (Tg) to afford an excellent elastomer at room temperature after cross-linking. This research guided us to several promising polar polysiloxane elastomers modified with nitrile and nitroaniline groups, for which the properties were optimized. We reproducibly achieved dielectric elastomers with a dielectric permittivity of about 18. Some respond to a voltage as low as 200 V, while some give very large actuation and have a breakdown field reaching 100 V μm^-1. By carefully selecting suitable synthetic chemistry, we could also achieve self-healable high permittivity elastomers. The materials can be processed into thin films by melt pressing. Stack actuators can be easily manufactured manually and give 5.4% actuation at an electric field as low as 3.2 V μm^-1. Furthermore, the actuators can self-repair after a breakdown and be recycled after complete failure. A graphene nanoplatelets (GNPs) composite in PDMS as a conductive electrode was developed via in-situ polymerization. The synthesis and the processing by screen-printing were conducted solvent-free, making this composite the greenest electrode for this technology. This presentation gives an overview of recent research on improved materials for dielectric elastomer transducers (DETs) conducted at Empa. We are confident that our materials will impact fields including actuators, sensors, energy harvesting, artificial muscles, and soft robotics.