As our population ages, and trends in obesity continue to grow, joint degenerative diseases like osteoarthritis (OA) are
becoming increasingly prevalent. With no cure currently in sight, the only effective treatments for OA are orthopaedic
surgery and prolonged rehabilitation, neither of which is guaranteed to succeed.
Gait retraining has tremendous potential to alter the contact forces in the joints due to walking, reducing the risk of one
developing hip and knee OA. Dielectric Elastomer Actuators (DEAs) are being explored as a potential way of applying
intuitive haptic feedback to alter a patient’s walking gait. The main challenge with the use of DEAs in this application is
producing large enough forces and strains to induce sensation when coupled to a patient’s skin.
A novel controller has been proposed to solve this issue. The controller uses simultaneous capacitive self-sensing and
actuation which will optimally apply a haptic sensation to the patient’s skin independent of variability in DEAs and
Dielectric elastomer generators (DEG) are suited for harvesting energy from low frequency and high strain natural
sources including wind, wave and human movement. The stack configuration, for instance, in which a number of layers
of DE membrane are placed one atop the other, offers a robust, compact and solid-state way for arranging the DE
material for energy harvesting during heel strike. But the end conditions at top and bottom of a stack can substantially
limit its ability to strain. Using an analytical model for compression of the stack, we have calculated thickness changes in
capacitive membranes along the stack for several cylindrical shapes. DE generators that are short and fat will have
approximately parabolic profiles with continuous reduction in layer thickness towards the middle. This will result in
higher electrical fields at the middle with greater susceptibility to breakdown. For long, thin DEG stacks, the outward
bulging will be confined to zones at the two ends with a more uniform cylindrical profile in between. The placing of
inexpensive compliant end-caps between the DEG and a rigid structure will promote more homogeneous deformation
across the active layers so that the efficacy of these layers for energy harvesting will improve.
Many devices and processes produce low grade waste heat. Some of these include combustion engines, electrical
circuits, biological processes and industrial processes. To harvest this heat energy thermoelectric devices, using the
Seebeck effect, are commonly used. However, these devices have limitations in efficiency, and usable voltage. This
paper investigates the viability of a Stirling engine coupled to an artificial muscle energy harvester to efficiently convert
heat energy into electrical energy. The results present the testing of the prototype generator which produced 200 μW
when operating at 75°C. Pathways for improved performance are discussed which include optimising the electronic
control of the artificial muscle, adjusting the mechanical properties of the artificial muscle to work optimally with the
remainder of the system, good sealing, and tuning the resonance of the displacer to minimise the power required to drive
Dielectric elastomer Generator(s) (DEG) are highly suited to harvesting from environmental sources because they are
light weight, low cost, and can be coupled directly to rectilinear motions and harvest energy efficiently over a wide
frequency range. Because of these benefits, simple and low cost generators could be enabled using DEG.
Electrical energy is produced on relaxation of a stretched, charged DEG: like-charges are compressed together and
opposite-charges are pushed apart, resulting in an increased voltage. The manner in which the DEG charge state is
controlled greatly influences the amount of energy that is produced. For instance, the highest energy density ever
demonstrated for DEG is 550 mJ/g, whereas the theoretical energy density of DEG has been reported as high as 1700
mJ/g if driven close to their failure limits.
The discrepancy between realised and theoretical energy production highlights that large performance gains can be
achieved through smarter charge control that drives the generator close to its failure limits. To do so safely, we need to
be able to monitor the real-time electromechanical state of the DEG. This paper discusses the potential of self-sensing
for providing feedback on the generator’s electromechanical state. Then we discuss our capacitive self-sensing method
which we have demonstrated to track the displacement of a Danfoss Polypower generator as it was cyclically stretched
and harvested energy.
Dielectric elastomer generators (DEG) provide an opportunity to harvest energy from low frequency and aperiodic sources. Because DEG are soft, deformable, high energy density generators, they can be coupled to complex structures such as the human body to harvest excess mechanical energy. However, DEG are typically constrained by a rigid frame and manufactured in a simple planar structure. This planar arrangement is unlikely to be optimal for harvesting from compliant and/or complex structures. In this paper we present a soft generator which is fabricated into a 3 Dimensional geometry. This capability will enable the 3-dimensional structure of a dielectric elastomer to be customised to the energy source, allowing efficient and/or non-invasive coupling. This paper demonstrates our first 3 dimensional generator which includes a diaphragm with a soft elastomer frame. When the generator was connected to a self-priming circuit and cyclically inflated, energy was accumulated in the system, demonstrated by an increased voltage. Our 3D generator promises a bright future for dielectric elastomers that will be customised for integration with complex and soft structures. In addition to customisable geometries, the 3D printing process may lend itself to fabricating large arrays of small generator units and for fabricating truly soft generators with excellent impedance matching to biological tissue. Thus comfortable, wearable energy harvesters are one step closer to reality.
Dielectric elastomer generators (DEG) are variable capacitor power generators that are a highly promising technology
for harvesting energy from environmental sources because they have the ability to work over a wide frequency range
without sacrificing their high energy density or efficiency. DEG can also take on a wide range of configurations, so they
are customizable to the energy source.
A typical generation cycle requires electrical charge to be supplied and removed from the DEG at appropriate times as it
is mechanically deformed. The manner in which the DEG charge state is controlled greatly influences energy
production. The recently developed self-priming circuit can provide this functionality without any active electronics, but
it is not configurable to match the generator and its energy source. In this paper a highly configurable self-priming
circuit is introduced and an analysis of the self-priming DEG cycle is performed to obtain design rules to optimize the
rate at which it can boost its operating voltage. In a case study we compare the performance of an initial prototype selfpriming
circuit with one that has been intentionally optimized. The optimized generator voltage climbed from 30 V up
to 1500 V in 27 cycles, whereas the same generator required 37 cycles when the suboptimal self-priming circuit was
Unlike electromagnetic actuators, Dielectric Elastomer Actuators (DEAs) can exert a static holding force without
consuming a significant amount of power. This is because DEAs are electrostatic actuators where the electric charges
exert a Maxwell stress. A charged DEA stores its electrical energy as potential energy, in a similar way to a capacitor. To
remove or reduce the Maxwell stress, the stored charge with its associated electrical energy must be removed. Current
DEA driver electronics simply dispose of this stored electrical energy. If this energy can be recovered, the efficiency of
DEAs would improve greatly. We present a simple and efficient way of re-using this stored energy by directly
transferring the energy stored in one DEA to another. An energy transfer efficiency of approximately 85% has been
The Biomimetics Laboratory has developed a soft artificial muscle motor based on Dielectric Elastomers. The motor,
'Flexidrive', is light-weight and has low system complexity. It works by gripping and turning a shaft with a soft gear,
like we would with our fingers.
The motor's performance depends on many factors, such as actuation waveform, electrode patterning, geometries and
contact tribology between the shaft and gear. We have developed a finite element model (FEM) of the motor as a study
and design tool. Contact interaction was integrated with previous material and electromechanical coupling models in
ABAQUS. The model was experimentally validated through a shape and blocked force analysis.
The global demand for renewable energy is growing, and ocean waves and wind are renewable energy
sources that can provide large amounts of power. A class of variable capacitor power generators called
Dielectric Elastomer Generators (DEG), show considerable promise for harvesting this energy because they
can be directly coupled to large broadband motions without gearing while maintaining a high energy density,
have few moving parts, and are highly flexible.
At the system level DEG cannot currently realize their full potential for flexibility, simplicity and low mass
because they require rigid and bulky external circuitry. This is because a typical generation cycle requires
high voltage charge to be supplied or drained from the DEG as it is mechanically deformed.
Recently we presented the double Integrated Self-Priming Circuit (ISPC) generator that minimized external
circuitry. This was done by using the inherent capacitance of DEG to store excess energy. The DEG were
electrically configured to form a pair of charge pumps. When the DEG were cyclically deformed, the charge
pumps produced energy and converted it to a higher charge form. In this paper we present the single ISPC
generator that contains just one charge pump. The ability of the new generator to increase its voltage through
the accumulation of generated energy did not compare favourably with that of the double ISPC generator.
However the single ISPC generator can operate in a wider range of operating conditions and the mass of its
external circuitry is 50% that of the double ISPC generator.
We use our thumbs and forefingers to rotate an object such as a control knob on a stereo system by
moving our finger relative to our thumb. Motion is imparted without sliding and in a precise manner. In
this paper we demonstrate how an artificial muscle membrane can be used to mimic this action. This is
achieved by embedding a soft gear within the membrane. Deformation of the membrane results in
deformation of the polymer gear and this can be used for motor actuation by rotating the shaft.
The soft motors were fabricated from 3M VHB4905 membranes 0.5mm thick that were pre-stretched
equibiaxially to a final thickness of 31 μm. Each membrane had polymer acrylic soft gears inserted at
the center. Sectors of each membrane (60° sector) were painted on both sides with conducting carbon
grease leaving gaps between adjoining sectors to avoid arcing between them. Each sector was
electrically connected to a power supply electrode on the rigid acrylic frame via narrow avenues of
carbon-grease. The motors were supported in rigid acrylic frames aligned concentrically. A flexible
shaft was inserted through both gears. Membranes were charged using a step wave PWM voltage
signal delivered using a Biomimetics Lab EAP Control unit. Both membrane viscoelasticity and the
resisting torque on the shaft influence motor speed by changing the effective circumference of the
This new soft motor opens the door to artificial muscle machines molded as a single part.
Life shows us that the distribution of intelligence throughout flexible muscular networks is a highly successful solution
to a wide range of challenges, for example: human hearts, octopi, or even starfish. Recreating this success in engineered
systems requires soft actuator technologies with embedded sensing and intelligence. Dielectric Elastomer Actuator(s)
(DEA) are promising due to their large stresses and strains, as well as quiet flexible multimodal operation. Recently
dielectric elastomer devices were presented with built in sensor, driver, and logic capability enabled by a new concept
called the Dielectric Elastomer Switch(es) (DES). DES use electrode piezoresistivity to control the charge on DEA and
enable the distribution of intelligence throughout a DEA device.
In this paper we advance the capabilities of DES further to form volatile memory elements. A set reset flip-flop with
inverted reset line was developed based on DES and DEA. With a 3200V supply the flip-flop behaved appropriately and
demonstrated the creation of dielectric elastomer memory capable of changing state in response to 1 second long set and
reset pulses. This memory opens up applications such as oscillator, de-bounce, timing, and sequential logic circuits; all of
which could be distributed throughout biomimetic actuator arrays.
Future work will include miniaturisation to improve response speed, implementation into more complex circuits, and
investigation of longer lasting and more sensitive switching materials.
Dielectric Elastomer Generator(s) (DEG) have many unique properties that give them advantages over
conventional electromagnetic generators. These include the ability to effectively generate power from slow and
irregular motions, low cost, relatively large energy density, and a soft and flexible nature. For DEG to generate
usable electrical energy circuits for charging (or priming) the stretched DEG and regulating the generated
energy when relaxed are required. Most prior art has focused on the priming challenge, and there is currently
very little work into developing circuits that address design issues for extracting the electrical energy and
converting it into a usable form such as low DC voltages (~10 V) for small batteries or AC mains voltage (~100
This paper provides a brief introduction to the problems of regulating the energy generated by DEG. A buck
converter and a charge pump are common DC-DC step-down circuits and are used as case studies to explore the
design issues inherent in converting the high voltage energy into a form suitable for charging a battery. Buck
converters are efficient and reliable but also heavy and bulky, making them suitable for large scale power
generation. The smaller and simpler charge pump, though a less effective energy harvester, is better for small
and discrete power generation. Future development in miniature DE fabrication is expected to reduce the high
operational voltages, simplifying the design of these circuits.
We are developing a hybrid Dielectric Elastomer Generator (DEG)-Microbial Fuel Cell (MFC) energy harvester . The
system is for EcoBot, an Autonomous Robot (AR) that currently uses its MFCs to extract electrical energy from
biomass, in the form of flies. MFCs, though reliable are slow to store charge. Thus, EcoBot operations are
characterized by active periods followed by dormant periods when energy stores recover. Providing an alternate
energy harvester such as a DEG, driven by wind or water, could therefore increase active time and also provide high
voltage energy for direct use by on-board systems employing dielectric elastomer actuators (DEAs).
Energy can be harvested from a DEG when work is done on its elastomer membrane.. However, the DEG requires an
initial charge and additional charge to compensate for losses due to leakage. The starting charge can be supplied by
the EcoBot MFC capacitor.
We have developed a self-primer circuit that uses some of the harvested charge to prime the membrane at each cycle.
The low voltage MFC initial priming charge was boosted using a voltage converter that was then electrically
disconnected. The DEG membrane was cyclically stretched producing charge that replenished leakage losses and
energy that could potentially be stored. A further study demonstrated that the DEG with self-primer circuit can boost
voltage from very low values without the need for a voltage converter, thus reducing circuit complexity and improving
Dielectric Elastomer Generator(s) (DEG), are essentially variable capacitor power generators formed by hyper-elastic
dielectric materials sandwiched between flexible electrodes.
Electrical energy can be produced from a stretched, charged DEG by relaxing the mechanical deformation whilst
maintaining the amount of charge on its electrodes. This increases the distance between opposite charges and packs likecharges
more densely, increasing the amount of electrical energy. DEG show promise for harvesting energy from
environmental sources such as wind and ocean waves. DEG can undergo large inhomogeneous deformations and
electric fields during operation, meaning it can be difficult to experimentally determine optimal designs. Also, the circuit
that is used for harnessing DEG energy influences the DEG output by controlling the amount of charge on the DEG.
In this paper an integrated DEG model was developed where an ABAQUS finite element model is used to model the
DEG and data from this model is input to a system level LT-Spice circuit simulation. As a case-study, the model was
used as a design tool for analysing a diaphragm DEG connected to a self-priming circuit. That is, a circuit capable of
overcoming electrical losses by using some of the DEG energy to boost the charge in the system. Our ABAQUS model
was experimentally validated to predict the varying capacitance of a diaphragm DEG deformed inhomogeneously to
within 6% error.
Dielectric Elastomer (DE) transducers are essentially compliant capacitors fabricated from highly flexible materials that
can be used as sensors, actuators and generators. The energy density of DE is proportional to their dielectric constant
(ε<sub>r</sub>), therefore an understanding of the dielectric constant and how it can be influenced by the stretch state of the material is required to predict or optimize DE device behavior. DE often operate in a stretched state. Wissler and Mazza, Kofod
et al., and Choi et al. all measured an ε<sub>r</sub> of approximately 4.7 for virgin VHB, but their results for prestretched DE
showed that the dielectric constant decayed to varying degrees. Ma and Cross measured a dielectric constant of 6 for the
same material with no mention of prestretch. In an attempt to resolve this discrepancy, ε<sub>r</sub> measurements were
performed on parallel plate capacitors consisting of virgin and stretched VHB4905 tape electroded with either gold
sputtered coatings or Nyogel 756G carbon grease. For an unstretched VHB tape, an ε<sub>r</sub> of 4.5 was measured with both
electrode types, but the measured ε<sub>r</sub> of equibiaxially stretched carbon specimens was lower by between 10 to 15%. The
dielectric constant of VHB under high fields was assessed using blocked force measurements from a dielectric elastomer
actuator. Dielectric constants ranging from 4.6-6 for stretched VHB were calculated using the blocked force tests.
Figure of merits for DE generators and actuators that incorporate their nonlinear behavior were used to assess the
sensitivity of these systems to the dielectric constant.
We describe a low profile and lightweight membrane rotary motor based on the dielectric elastomer actuator (DEA). In
this motor phased actuation of electroded sectors of the motor membrane imparts orbital motion to a central gear that
meshes with the rotor.
Two motors were fabricated: a three phase and four phase with three electroded sectors (120°/sector) and four sectors
(90°/sector) respectively. Square segments of 3M VHB4905 tape were stretched equibiaxially to 16 times their original
area and each was attached to a rigid circular frame. Electroded sectors were actuated with square wave voltages up to
2.5kV. Torque/power characteristics were measured. Contactless orbiter displacements, measured with the rotor
removed, were compared with simulation data calculated using a finite element model.
A measured specific power of approximately 8mW/g (based on the DEA membrane weight), on one motor compares
well with another motor technology. When the mass of the frame was included a peak specific power of 0.022mW/g was
calculated. We expect that motor performance can be substantially improved by using a multilayer DEA configuration,
enabling the delivery of direct drive high torques at low speeds for a range of applications.
The motor is inherently scalable, flexible, flat, silent in operation, amenable to deposition-based manufacturing
approaches, and uses relatively inexpensive materials.
Our work focuses on a contractile dielectric elastomer actuator (DEA) based on the McKibben pneumatic muscle
concept. A coupled-field ABAQUS (Hibbit, Karlsson & Sorensen, Inc., USA) FEA model has been developed where
the constraints of the orthotropic fibre weave and end caps of this actuator design are included. The implementation of
the Maxwell pressure model that couples electrical inputs to mechanical loads using the ABAQUS user subroutine
DLOAD is the focus of this paper. Our model was used to perform a study of actuator design parameters including the
fibre weave angle, dielectric thickness, and the DEA's length. At a fibre angle of 45° relative to the longitudinal axis, no
axial deformation was predicted by our model. A weave angle above this resulted in an axial expansion during
actuation, whereas axial compression occurred if the fibre angle was less than 45°. For instance, at a fibre angle of 30°
with respect to the longitudinal axis, this model predicted a compressive axial strain of 4.5% before mechanical failure
for an actuator with an outer radius of 2mm, wall thickness of 0.5mm, and length of 20mm.