Alberto Mazzoldi

Electromechanical characterisation of dielectric elastomer planar actuators: comparative evaluation of different electrode materials and different counterloads

This work intends to extend the electromechanical characterisation of dielectric elastomer actuators. Planar actuators were realised with a 50m-thick film of an acrylic elastomer coated with compliant electrodes. The isotonic transverse strain, the isometric transverse stress and the driving current, due to a 2 s high voltage impulse, were measured for four electrode materials (thickened electrolyte solution, graphite spray, carbon grease and graphite powder), four transverse prestress values (19.6, 29.4, 39.2 and 49.0 kPa) and different driving voltages (up to the dielectric breakdown voltage). Results showed that the electrode material and prestress strongly influence the electromechanical performances of the devices. Actuators with graphite spray electrodes and transverse prestress of 39.2 kPa exhibited an isotonic transverse strain of 6% at 49 V/m, with a driving current per unit electrode area of 3.5 A/cm 2 , and an isometric transverse stress of 49 kPa at 42 V/m. An electromechanical coupling efficiency of 10% at 21 V/m was calculated for actuators with thickened electrolyte solution electrodes and a transverse prestress of 29.4 kPa. The presented data permits to choose the best electrode material and the best prestress value (among those tested), to obtain the maximum isotonic transverse strain, the maximum isometric transverse stress or the maximum efficiency for different ranges of applied electric field.

Strain-sensing fabrics for wearable kinaesthetic-like systems

In recent years, an innovative technology based on polymeric conductors and semiconductors has undergone rapid growth. These materials offer several advantages with respect to metals and inorganic conductors: lightness, large elasticity and resilience, resistance to corrosion, flexibility, impact strength, etc. These properties are suitable for implementing wearable devices. In particular, a sensitive glove able to detect the position and the motion of fingers and a sensorized leotard have been developed. Here, the characterization of the strain-sensing fabric is presented. In the first section, the polymerization process used to realize the strain sensor is described. Then, the thermal and mechanical transduction properties of the strain sensor are investigated and a geometrical parameter to invariantly codify the sensor response during aging is proposed. Finally, a brief outline of ongoing applications is reported.

Performance and Work Capacity of a Polypyrrole Conducting Polymer Linear Actuator

Abstract This paper reports a performance analysis of a conducting polymer film actuator made of polypyrrole (PPy). Electrochemomechanical characterizations of the active displacement and the developed force of a PPy free-standing film at different loading conditions are performed. Two driving signals are used: the former, a cyclic voltammetry at 1 mV/s between ± 1 V, is used to carry out an accurate on-line analysis of the film displacement; the latter, a current square wave between 0.02 and 0.1 Hz, is helpful for evaluating the effectiveness of the actuator in terms both of actuation strain and of developed force. The experimental results indicate that 1 % displacement, 3 MPa force and working density of 73 kJ/m3 are achievable goals for a conducting polymer linear actuator, which are interesting results if compared with the limiting specifications of skeletal muscle. Additionally, two different approaches to the electrochemomechanical modeling of the conducting polymerfluid electrolyte system are illustrated, together with a discussion about foreseen improvements in the implementation of actuating structures.

Dressware: wearable hardware

Abstract Conventional fabrics coated with a thin conducting polymer layer are described which possess remarkable properties of strain and temperature sensing. Sensing figures of merit are comparable to those of sensitive strain gauge materials and inorganic thermistors. Also, spun conductive polymer fibers show electromechanical actuation. The isometric contractile stress of the actuating fibers is higher than skeletal muscle, between 1 and 15 times. The fabrication of active electronic and electromechanical systems onto substrates which are not only flexible, but ideally conformable to the human body may represent a breakthrough in man–machine interface technology.

Characterization and modelling of a conducting polymer muscle-like linear actuator

The demand for actuators featuring biomimetic properties, such as linearity, high power density and compliance, is growing in microrobotics and bioengineering. In the present paper a novel linear actuator is presented. It exploits the electromechanochemical phenomena of -electron conjugated conducting polymers, occuring when ionic species are exchanged with the surrounding medium, i.e. solid or liquid electrolyte. In our experiments, a polypyrrole film doped with benzensulphonate anions is considered as the conducting polymer and a liquid electrolyte bath as the ionic reservoir. The actuating properties of the material are investigated and quantified in terms of both isotonic displacement and isometric developed force. A lumped parameter, muscle-like model of the system is proposed and verified with respect to the experimental data. The results of the electromechanical characterization and the goodness of fit of the model provide favourable indications for the utilization of the material as an effective muscle-like linear actuator, once the response time is decreased by means of a suitable scaling down of the film thickness.

Actuative properties of polyaniline fibers under electrochemical stimulation

Abstract In the last period, the interest in the development of devices that simulate the properties of the ‘par excellence’ biological actuator, the human muscle, is considerably grown. The recent advances in the field of conducting polymers open new interesting prospects in this direction: by this point of view polyaniline (PANi), since it is easily produced in fiber form, represents an interesting material. In this paper, we illustrate the development of a linear actuator prototype that makes use of PANi fibers. All fabrication steps (fiber extrusion, solid polymer electrolyte preparation, compound realization) and experimental set-up are described. Quantitative measurements of isotonic length changes and isometric stress generation during electrochemical stimulation are performed. An overall assessment of the PANi fibers actuative properties in wet and dry conditions is reported and possible future developments are proposed.

Actuation properties of electrochemically driven polypyrrole free-standing films

In this paper we report about investigations on coupled electrochemomechanical phenomena in polypyrrole (PPy) free-standing films. Quantitative measurements of isotonic length and relaxed elastic modulus changes are performed on PPy samples during cyclic voltammetry and square-wave amperometry. The link between dimensional and mechanical changes in the samples and doping salt exchange kinetics is investigated and a possible interpretation is proposed.

Steerable Microcatheters Actuated by Embedded Conducting Polymer Structures

Steerable microstructures, i.e., catheters, are presented. They exploit the electromechanochemical phenomena of ir-electron conjugated conducting polymers occurring when ionic species are exchanged with the surrounding medium. In this paper we considered polypyrrole as conducting polymer and a fast ionic conductor solid polyelectrolyte as ionic reservoir. Experimental determination of the governing material constants, modelling of conducting polymer/solid polyelectrolyte composite material and finite element computer simulations of the mechanical properties of cylindrical structures provide favourable indication about the feasibility of effective steerable, miniaturised catheters.

Conductive-polymer-based structures for a steerable catheter

Commercial steerable catheters and catheter prototypes actuated by active materials still present limitations in terms of self-sustaining capability and miniaturization. Specifications for the intravascular catheter we are developing are: bending angle up to 20°, bending stiffness of a few N/m, response time of the order of seconds. Simulations with finite element method (FEM) showed these specifications can be satisfied using a polymer with active strain of 1 percent and elastic modulus E=4.5 GPa and a solid polymer electrolyte (SPE) matrix with E=MPa. The actuator is thought to be made of a composite structure which includes polyaniline fibers, a copper wire electrode and SPE matrix. Its measured characteristics are: active strain 0.2%, active stress 2 MPa, fiber elastic modulus 1.5 GPa, SPE elastic modulus 1-2 MPa. The major problem to realize the catheter is the stiffness of SPE, which has to be considerably augmented. Fiber active strain is below the required value, but it can be increased by proper drive. The production of fibers with a diameter of 10 microns will reduce the response time to the required value.

Electroactive fabrics for distributed, conformable and interactive systems

Posture and gesture analysis and body kinematics monitoring is a field of increasing interest in bioengineering and several connected disciplines. We propose wearable systems able to read and record posture and movements of a subject wearing them. We used strain gage sensors, deposited directly onto textile fibers realizing, in contrast with different strategies, truly wearable and unintrusive systems.