Tissaphern Mirfakhrai

• Engineer at Eaton

Rotary motors of conventional design can be rather complex and are therefore difficult to miniaturize; previous carbon nanotube artificial muscles provide contraction and bending, but not rotation. We show that an electrolyte-filled twist-spun carbon nanotube yarn, much thinner than a human hair, functions as a torsional artificial muscle in a simp...

Supercapacitors operating in aqueous solutions are low cost energy storage devices with high cycling stability and fast charging and discharging capabilities, but have suffered from low energy densities. Here, we grow Ni(OH)2 nanoplates and RuO2 nanoparticles on high quality graphene sheets to maximize the specific capacitances of these materials....

Yarns spun by twisting multiwalled carbon nanotubes (MWNTs) have been reported. Here, we report the application of these yarns as mechanical force sensors. When electrochemically charged, the yarns can respond to a change in the applied tension by generating a change in the cell current (up to about 1.2 nA/MPa per centimeter length of the yarn) or...

Polypyrrole actuators offer high stresses, moderate strains, low voltage operation and biocompatibility. These materials also act as force and displacement sensors. In this paper the properties of polypyrrole sensors are investigated, enabling the first quantitative demonstration of the link between actuation and sensing, and suggesting a new mecha...

Electrochemically driven actuation of polypyrrole in aqueous sodium hexafluorophosphate (NaPF6) solution has been shown to produce repeated large strains (>6%) at low voltages and with high conductivity, making it one of the most promising electroactive conducting polymers. Little is known about the voltage dependent stiffness of this version of th...

In this paper we first use ab initio simulations to study the strains induced by charging an armchair (5,5) carbon nanotube (CNT) segment. The observed behavior is far from a monotonic expansion that one might have expected from a classical point of view. Subsequently a new method is proposed to predict the nonelectrostatic part of the electromecha...

Conducting polymers have been shown to work as force sensors in an electrolyte by generating a voltage or current when the force applied to them is changed. One possible sensing mechanism is the change in the polymer capacitance as a result of an induced tension. This change in capacitance can be related to perturbation of Donnan equilibrium potent...

Metallosalphen complexes with peripheral glucose and galactose substituents were synthesized and characterized. Their self-assembled supramolecular structures were then studied with transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that all of the complexes displayed aggregati...

The effect of cycling on charge-storage, actuation and sensing behavior of a polypyrrole is studied, having its application for an electroactive catheter in mind. It is shown that the electrochemical capacitance of a polypyrrole film decreases by about 15 % over the course of 100 cycles, while the per cycle rate of this decrease drops by 75 % betwe...

Twist-spun yarns made of carbon nanotubes have been shown to work as electrochemical actuators and force sensors. Deep understanding of yarn electrochemical behavior has so far not been possible, in part because of complicated yarn geometry. The electrochemical response of these yarns at different bias potentials was studied using Electrochemical I...

Carbon nanotubes have attracted extensive attention in the past few years because of their appealing mechanical and electronic properties. Yarns made through spinning multiwall carbon nanotubes (MWNTs) have been reported. Here we study the application of these yarns as electrochemical actuators, and as force sensors. MWNT yarns are mechanically str...

Conducting polymer actuators are of interest in applications where low voltage and high work density are beneficial. These actuators are not particularly fast however, with time constants normally being greater than 1 second. Strain in these actuators is proportional to charge, with the rate of charging being found to limit the speed of actuation....

The mechanical actuation of a (5, 5) single-walled carbon nanotube as a result of added charge is simulated using first-principles calculations. It is observed that while both positive and negative charging tend to expand the nanotube in the axial direction for most levels of charge, radial actuation is less even and symmetric with respect to charg...

Carbon nanotubes (CNTs) have attracted extensive attention in the past few years because of their appealing mechanical and electronic properties. Yarns made through spinning multi-walled carbon nanotubes (MWNTs) have been reported. Here we report the application of these yarns as electrochemical actuators, force sensors and microwires. When extra c...

The various types of natural muscle are incredible material systems that enable the production of large deformations by repetitive molecular motions. Polymer artificial muscle technologies are being developed that produce similar strains and higher stresses using electrostatic forces, electrostriction, ion insertion, and molecular conformational ch...

Twist-spun carbon nanotube yarns actuate when extra charge is added to the yarn. This charge can be stored in a doublelayer capacitor formed when the yarn is submersed in an electrolyte. The dependence of the actuation stress and strain on the stored charge must be studied if double layer charging models are to be fully verified over large potentia...

We report on actuation in high tensile strength yarns of twist-spun multi-wall carbon nanotubes. Actuation in response to voltage ramps and potentiostatic pulses is studied to quantify the dependence of the actuation strain on the applied voltage. Strains of up to 0.5% are obtained in response to applied potentials of 2.5 V. The dependence of strai...

Using the notation of the wave variables, this paper introduces an autoregressive predictor, which forecasts the future values of the delay based on its previous values. Using this new knowledge, the teleoperation control system can be tuned to achieve a better and more practical performance. The validity of this modeling is first verified by actua...

Based on the notion of wave variables, and the idea of wave-integral transmission, a new method is suggested to match the system parameters with changes in the delay. An autoregressive model is used as a predictor to forecast the future values of the delay. The predictions are used with a look-up table to tune the gain with which the wave integrals...

Based on the notion of wave variables and the idea of wave-integral transmission, a new method is suggested to match the system parameters with changes in the delay. An autoregressive model is used as a predictor to forecast the future values of the delay. The predictions are used with a lookup table to tune the gain with which the wave integrals a...

The stochastic nature of the communication delay in teleoperation systems makes it hard to predict the behavior of such systems. Although achieving a general-purpose model for the Internet is not easy, if possible at all, stochastic models for specific cases enable us design predictors, which can help in stabilizing the teleoperation systems. In th...

Thesis (M.A. Sc.)--Simon Fraser University, 2002. Includes bibliographical references.