Scott T McGovern

Finding NEMO (novel electromaterial muscle oscillator): a polypyrrole powered robotic fish with real-time wireless speed and directional control

This paper presents the development of an autonomously powered and controlled robotic fish that incorporates an active flexural joint tail fin, activated through conducting polymer actuators based on polypyrrole (PPy). The novel electromaterial muscle oscillator (NEMO) tail fin assembly on the fish could be controlled wirelessly in real time by varying the frequency and duty cycle of the voltage signal supplied to the PPy bending-type actuators. Directional control was achieved by altering the duty cycle of the voltage input to the NEMO tail fin, which shifted the axis of oscillation and enabled turning of the robotic fish. At low speeds, the robotic fish had a turning circle as small as 15 cm (or 1.1 body lengths) in radius. The highest speed of the fish robot was estimated to be approximately 33 mm s−1 (or 0.25 body lengths s−1) and was achieved with a flapping frequency of 0.6–0.8 Hz which also corresponded with the most hydrodynamically efficient mode for tail fin operation. This speed is approximately ten times faster than those for any previously reported artificial muscle based device that also offers real-time speed and directional control. This study contributes to previously published studies on bio-inspired functional devices, demonstrating that electroactive polymer actuators can be real alternatives to conventional means of actuation such as electric motors.

A New Image Analysis Based Method for Measuring Electrospun Nanofiber Diameter

In this paper, a new image analysis based method for electrospun nanofiber diameter measurement has been presented. The method was tested by a simulated image with known characteristics and a real web. Mean (M) and standard deviation (STD) of fiber diameter obtained using this method for the simulated image were 15.02 and 4.80 pixels respectively, compared to the true values of 15.35 and 4.47 pixels. For the real web, applying the method resulted in M and STD of 324 and 50.4 nm which are extremely close to the values of 319 and 42 nm obtained using manual method. The results show that this approach is successful in making fast, accurate automated measurements of electrospun fiber diameters.

Visualizing dynamic actuation of ultrathin polypyrrole films

We report on the use of electrochemical atomic force microscopy (EC-AFM) to visualize the dynamic actuation of ultrathin polypyrrole films doped with polystyrene sulfonate. By varying the film thickness over 3 orders of magnitude from the micrometer to the nanometer range and measuring their actuation height displacement as a function of the applied potential and its change in frequency, we are able to differentiate between diffusion and current limiting processes that determine the rate at which charge balancing ions move in and out of the polymer during actuation. In particular, we observe a 100-350% increase in strain and strain rate when the film thickness is reduced below 100 nm and provide unique insight into how the nanoscale architecture of these ultrathin films is correlated to their actuation performance.

Tri-layer conducting polymer actuators with variable dimensions

The ability of conducting polymer actuators to convert electrical energy into mechanical energy is influenced by many factors ranging from the actuators physical dimensions to the chemical structure of the conducting polymer. In order to utilise these actuators to their full potential, it is necessary to explore and quantify the effect of such factors on the overall actuator performance. The aim of this study is to investigate the effect of various geometrical characteristics such as the actuator width and thickness on the performance of tri-layer polypyrrole (PPy) actuators operating in air, as opposed to their predecessors operating in an appropriate electrolyte. For a constant actuator length, the influence of the actuator width is examined for a uniform thickness geometry. Following this study, the influence of a varied thickness geometry is examined for the optimised actuator width. The performance of the actuators is quantified by examination of the force output, tip displacement, efficiency as a function of electrical power and mechanical power, and time constant for each actuator geometry. It was found that a width of 4mm gave the greatest overall performance without curling along the actuator length (which occurred with widths above 4mm). This curling phenomenon increased the rigidity of the actuator, significantly lowering the displacement for low loads. Furthermore, it was discovered that by focussing a higher thickness of PPy material in certain regions of the actuators length, greater performances in various domains could be achieved. The experimental results obtained set the foundation for us to synthesize PPy actuators with an optimised geometry, allowing their performance to reach full potential for many cutting applications.

Measuring Electrospun Nanofibre Diameter: a Novel Approach

A new method based on image analysis for electrospun nanofibre diameter measurement is presented. First, the SEM micrograph of the nanofibre web obtained by electrospinning process is converted to binary image using local thresholding method. In the next step, skeleton and distance transformed image are generated. Then, the intersection points which bring about untrue measurements are identified and removed from the skeleton. Finally, the resulting skeleton and distance transformed image are used to determine fibre diameter. The method is evaluated by a simulated image with known characteristics generated by ?-randomness procedure. The results indicate that this approach is successful in making fast, accurate automated measurements of electrospun fibre diameters.

Modelling and Performance Enhancement of a Linear Actuation Mechanism Using Conducting Polymers

In this paper, we report on our investigation into modelling and performance enhancement of a linear actuation system based on cantilevered-type conducting polymer actuators, which can operate in air and aqueous media. We have employed the model to predict the linear displacement and force output of the actuation system, and to determine the optimum values of the system design parameters. The linear actuation system is a five bar parallel mechanism, articulated with two polymer actuators. Kinematic and force analyses of the mechanism including numerical results are presented, and its payload handling ability was experimentally evaluated. The experimental results prove that it is possible to generate an accurate linear movement and a corresponding rectilinear force from this mechanism. This mechanism can be employed as a motion and force transmission mechanism, which not only has a light weight, but also consumes a small electrical power.

The use of embedded sensors for the monitoring of adhesive joints in marine environments

A copolymer incorporating polyaniline was used as a sensing medium in the construction of a resistance based humidity sensor. Aniline monomer was polymerised in the presence of poly (butyl acrylate / vinyl acetate) and a copolymer containing polyaniline emeraldine salt was obtained. The sensing medium was then developed by redissolving 1-2 w/w% of the resulting polymer residue in dichloromethane to produce a processable polymer blend solution. Some of this polymer residue was also de-doped in a solution of ammonia, and then washed with distilled water until the waste water had a neutral pH. This residue was then redissolved at 1-2 w/w% in dichloromethane to produce a second processable polymer blend this time containing polyaniline emeraldine base. The final sensor design utilised 125μm polyester insulated platinum wire as conducting electrodes that were dip coated in the emeraldine salt copolymer solution and allowed to dry in a desiccator. The sensor was then dip-coated in a protective barrier layer of the emeraldine base copolymer to prevent over-oxidation and/or de-protonation of the emeraldine salt sensing medium under this coating. The sensors had an overall final thickness of less than 150μm and showed high sensitivity to humidity, low resistance, and good reversibility without hysteresis. Sensors were monitored for 2-probe resistance changes when in contact with water. Calibration curves for each sensor were produced to convert the resistance reading to mass uptake of water. Individual sensors were embedded within Aluminium 5083 / Araldite 2015 adhesive joints to monitor mass uptake of water when exposed to marine environments. Correlations between mass uptake of water and joint strength were made. There are various advantages of such a sensor design. Polymer based thin film humidity sensors have the advantage that the high processability of the material allows for simple fabrication of a range of geometries including smaller sensor designs. The ease of processing gives a low cost sensor, whilst the small size and good mechanical properties gives a robust sensor which has the flexibility to be able to be used in applications where dynamic stresses and strains are encountered. Such sensors may find uses in a number of areas including electronic textiles, food/ electronics packaging and corrosion detection.

Highly processable method for the construction of miniature conducting polymer moisture sensors

A polymer blend incorporating polyaniline (PAn) was used as a sensing medium in the construction of a resistance based humidity sensor. Aniline monomer was polymerised to PAn emeraldine salt (ES) in the presence of poly (butyl acrylate-co-vinyl acetate) and the processable blend was developed by redissolving 1-2 w/w% of the resulting sensing polymer residue in dichloromethane (DCM). Some of this residue was washed in ammonia solution to de-dope the PAn to emeraldine base (EB) to act as a protective layer on the surface of the sensing polymer. This residue was then washed with distilled water until a neutral pH was realised with the waste water, dried and redissolved in DCM at 1-2 w/w% to create a processable blend barrier polymer solution. The final sensor design utilised 125μm polyester insulated platinum wire as conducting electrodes that were dip coated in the PAn ES blend solution and dried in a desiccator. A protective coating was then applied by dip coating in the EB blend solution. The sensors had an overall final thickness of less than 200μm and showed high sensitivity to humidity, low resistance, and good reversibility without hysteresis. The EB protective layer was shown to give more stable and predictable responses to the sensors when placed inside curing epoxies. Polymer based thin film humidity sensors have the advantage that the high processability of the material allows for simple fabrication of a range of geometries including smaller sensor designs. Such sensors may find uses in detecting water content in a number of areas including composite materials, electronic textiles, food/electronics packaging and corrosion detection.