The development of thin-film dielectric elastomer strain sensors for the characterization of smooth muscle cell (SMC) contraction is presented here. Smooth muscle disorders are an integral part of diseases such as asthma and emphysema. Analytical tools enabling the characterization of SMC function i.e. contractile force and strain, in a low-cost and highly parallelized manner are necessary for toxicology screening and for the development of new and more effective drugs. The main challenge with the design of such tools is the accurate measurement of the extremely low contractile cell forces expected as a result of SMC monolayer contraction (as low as ~ 100 μN). Our approach utilizes ultrathin (~5 μm) and soft elastomer membranes patterned with elastomer-carbon composite electrodes, onto which the SMCs are cultured. The cell contraction induces an in-plane strain in the elastomer membrane, predicted to be in the order 1 %, which can be measured via the change in the membrane capacitance. The cell force can subsequently be deduced knowing the mechanical properties of the elastomer membrane. We discuss the materials and fabrication methods selected for our system and present preliminary results indicating their biocompatibility. We fabricate functional capacitive senor prototypes with good signal stability over the several hours (~ 0.5% variation). We succeed in measuring in-plane strains of 1 % with our fabricated devices with good repeatability and signal to noise ratio.
We present a theoretical model to optimise the unidirectional motion of a rigid object bonded to a miniaturized dielectric elastomer actuator (DEA), a configuration found for example in AMI’s haptic feedback devices, or in our tuneable RF phase shifter. Recent work has shown that unidirectional motion is maximized when the membrane is both anistropically prestretched and subjected to a dead load in the direction of actuation. However, the use of dead weights for miniaturized devices is clearly highly impractical. Consequently smaller devices use the membrane itself to generate the opposing force. Since the membrane covers the entire frame, one has the same prestretch condition in the active (actuated) and passive zones. Because the passive zone contracts when the active zone expands, it does not provide a constant restoring force, reducing the maximum achievable actuation strain. We have determined the optimal ratio between the size of the electrode (active zone) and the passive zone, as well as the optimal prestretch in both in-plane directions, in order to maximize the absolute displacement of the rigid object placed at the active/passive border. Our model and experiments show that the ideal active ratio is 50%, with a displacement twice smaller than what can be obtained with a dead load. We expand our fabrication process to also show how DEAs can be laser-post-processed to remove carefully chosen regions of the passive elastomer membrane, thereby increasing the actuation strain of the device.
We present the successful operation of the first dielectric elastomer actuator (DEA) driven tunable millimeter-wave
phase shifter. The development of dynamically reconfigurable microwave/millimeter-wave (MW/MMW) antenna
devices is becoming a prime need in the field of telecommunications and sensing. The real time updating of antenna
characteristics such as coverage or operation frequency is particularly desired. However, in many circumstances
currently available technologies suffer from high EM losses, increased complexity and cost. Conversely, reconfigurable
devices based on DEAs offer low complexity, low electromagnetic (EM) losses and analogue operation. Our tunable
phase shifter consists of metallic strips suspended a fixed distance above a coplanar waveguide (CPW) by planar DEAs.
The planar actuators displace the metallic strips (10 mm in length) in-plane by 500 μm, modifying the EM field
distribution, resulting in the desired phase shift. The demanding spacing (50 ±5 μm between CPW and metallic strips)
and parallel alignment criteria required for optimal device operation are successfully met in our device design and
validated using bespoke methods. Our current device, approximately 60 mm x 60 mm in planar dimensions, meets the
displacement requirements and we observe a considerable phase shift (~95° at 25 GHz) closely matching numerical
simulations. Moreover, our device achieves state of the art performance in terms of phase shift per EM loss ~235°/dB
(35 GHz), significantly out performing other phase shifter technologies, such as MMIC phase shifters.
Dielectric Elastomer Actuators (DEAs) are an emerging actuation technology which are inherent lightweight and
compliant in nature, enabling the development of unique and versatile devices, such as the Dielectric Elastomer
Minimum Energy Structure (DEMES). We present the development of a multisegment DEMES actuator for use in a
deployable microsatellite gripper. The satellite, called CleanSpace One, will demonstrate active debris removal (ADR) in
space using a small cost effective system. The inherent flexibility and lightweight nature of the DEMES actuator enables
space efficient storage (e.g. in a rolled configuration) of the gripper prior to deployment. Multisegment DEMES have
multiple open sections and are an effective way of amplifying bending deformation. We present the evolution of our
DEMES actuator design from initial concepts up until the final design, describing briefly the trade-offs associated with
each method. We describe the optimization of our chosen design concept and characterize this design in terms on
bending angle as a function of input voltage and gripping force. Prior to the characterization the actuator was stored and
subsequently deployed from a rolled state, a capability made possible thanks to the fabrication methodology and
materials used. A tip angle change of approximately 60° and a gripping force of 0.8 mN (for small deflections from the
actuator tip) were achieved. The prototype actuators (approximately 10 cm in length) weigh a maximum of 0.65 g and
are robust and mechanically resilient, demonstrating over 80,000 activation cycles.