Commercial dielectric elastomers and their modification methods are reviewed. A method is proposed to overcome the complex interdependency of their properties allowing quick comparison and selection of suitable materials for soft actuator applications.

This paper presents an inductor-less start-up converter for a sub-100-mV energy harvester based on an Armstrong oscillator topology using a piezoelectric transformer and a normally ON MOSFET. Two models of the converter have been detailed and validated experimentally for the start-up phase and steady-state operation to, respectively, determine the minimum start-up input voltage and the voltage gain. The models have been validated experimentally in a setup associating the converter and a thermoelectric generator. Based on a Rosen-type piezoelectric transformer and off-the-shelf components, the proposed start-up topology begins to oscillate at 15 mV and achieves a 1-V output voltage at only 43 mV. Compared to the literature, the topology needs no inductive component and achieves self-starting operation with a smaller input voltage.

Although heart transplant is the preferred solution for patients suffering from heart failures, cardiac assist devices remain key substitute therapies. Among them, aortic augmentation using dielectric elastomer actuators (DEAs) might be an alternative technological application for the future. The electrically driven actuator does not require bulky pneumatic elements (such as conventional intra‐aortic balloon pumps) and conforms tightly to the aorta thanks to the manufacturing method presented here. In this study, the proposed DEA‐based device replaces a section of the aorta and acts as a counterpulsation device. The feasibility and validation of in vivo implantation of the device into the descending aorta in a porcine model, and the level of support provided to the heart are investigated. Additionally, the influence of the activation profile and delay compared to the start of systole is studied. We demonstrate that an activation of the DEA just before the start of systole (30 ms at 100 bpm) and deactivation just after the start of diastole (0–30 ms) leads to an optimal assistance of the heart with a maximum energy provided by the DEA. The end‐diastolic and left ventricular pressures were lowered by up to 5% and 1%, respectively, compared to baseline. The early diastolic pressure was augmented in average by up to 2%.

Dielectric elastomer actuators (DEAs) can be described as compliant capacitors formed by a dielectric elastomer film sandwiched between two electrodes. An applied voltage results in a compressive Maxwell stress, a thickness reduction and thus an expansion in the other dimensions. In order to favor large uni-axial deformations, it is predicted that DEAs ought to be constrained in the other direction. This can be achieved by reinforcing the DEA with unidirectional fibers. In this paper, the behavior of uni-axial fiber-reinforced DEAs is established and the proposed model innovates by taking into consideration the fiber properties such as their Young’s modulus and dimensions, and is characterized by transversely isotropic models. A novel fabrication process is then presented for reinforced DEAs by using 3D printed fibers with four different materials, namely Nylon, PETG, ABS and PLA, and different coverages of fibers are considered. Fiber reinforcement is shown to increase uni-axial strain up to 75% in the manufactured DEAs when compared to traditional DEAs. This behavior corresponds to the one predicted by the proposed model.

In this paper, we propose an improvement of a dielectric elastomer actuator (DEA) based augmented aorta. The actuator is a multi-layered tubular DEA subject to the internal pressure of the blood. When activated in synchronisation with the heart, the DEA supplies energy and limits the load on the left ventricle. The improvement consists in implementing a constraint on the radial displacement of the actuator. This addition allows to increase the electromechanical stability of the device by avoiding snap-through of the material leading to irreversible breakdown. By increasing the stability of the device, it allows to reach higher activation voltages and thus, a higher energy. In order to help the design of this new actuator, we have developed an analytical model of the inflation of a tubular DEA. In addition to previous works, the new model takes into account the multi-layered structure of the device as well as the constraint on the radial displacement to obtain accurate characteristics of the DEA. After validation with specially design experiments, the modelling is used to study the influence of the radial limitation value on the performances of the DEA.