Electroactive actuators
The invention relates to actuators based on electroactive polymeric materials for use in pumping fluids or in other applications where a contractile actuation is required, in particular, although not necessarily exclusively, for use in vascular pulsation devices such as a variable aortic tension device. Embodiments disclosed include an actuator comprising: an inner tubular structure; an outer tubular structure surrounding the inner tubular structure and comprising a plurality of layers of a dielectric elastomeric material and a tubular elastic support structure, the elastic support structure configured to maintain a pre-stress in the layers of the dielectric elastomeric material, wherein the outer tubular structure is configured to contract in a radial direction around the inner tubular structure upon application of an actuation voltage signal across the dielectric elastomeric material layers.
1. An actuator comprising:
an inner tubular structure; and
an outer tubular structure surrounding the inner tubular structure;
wherein:
the outer tubular structure comprises a plurality of layers of a dielectric elastomeric material;
the outer tubular structure comprises a tubular elastic support structure;
the tubular elastic support structure is configured to maintain a pre-stress in the plurality of layers of the dielectric elastomeric material;
the outer tubular structure is configured to contract in a radial direction around the inner tubular structure upon application of an actuation voltage signal across the dielectric elastomeric material layers; and
the tubular elastic support structure comprises an auxetic structure configured such that a ratio between expansion in the circumferential direction and contraction in the axial direction of the tubular elastic support structure when unconstrained is zero or negative.
2. The actuator of claim 1 wherein the inner tubular structure is a braided tubular structure.
3. An implantable device comprising the actuator according to claim 1 and an electronic controller configured to apply the actuation voltage signal to the plurality of layers of the dielectric elastomeric material.