Bryan P. Ruddy

Design and optimization strategies for muscle-like direct-drive linear permanent-magnet motors

We report a new approach to the design of direct-drive linear permanent-magnet motors for use in general-purpose robotic actuation, with particular attention to applications in bird-scale flapping-wing robots. We show a simple, quantitative analytical modeling framework for this class of actuators, and demonstrate inherent scaling properties that allow the production of motors with force densities and efficiencies comparable to those of biological muscles. We illustrate the effectiveness of our model with finite-element analysis and a comparison with commercially available motors, and discuss future plans for experimental validation. We show how this model leads to a set of practical design specifications for muscle-like motors, and examine the resulting trade-off between thermal management and motor fabrication complexity.

Cortical recording with polypyrrole microwire electrodes

The ability to record from the same neuron for extended periods of time is essential to understanding how the brain reorganizes during learning. Conventional chronic recording microelectrodes are made from metal or silicon. However, the large stiffness mismatch between the electrodes and brain tissue causes shear-induced inflammation, limiting long-term recording stability. The flexibility of polypyrrole microwire has the potential to improve the chronic recording stability by minimizing the stiffness mismatch. In this paper, we report the implantation of a conducting polymer microwire electrode in a rodent brain, and the successful recording of cortical activity using such an electrode.

Conducting Polymer-Based Multifunctional Materials

Conducting polymers are employable as low-voltage actuators, sensors, energy storage and delivery components, structural elements, computational circuitry, memory, and electronic components, making them a versatile choice for creating integrated, multifunctional materials and devices. Here we show one such conducting polymer-based, multifunctional system, derived from the versatility of the conducting polymer polypyrrole. Three functions of polypyrrole (actuation, length sensation, and energy storage) have been individually evaluated and cooperatively combined in the synthesis of a multifunctional, polymeric system that actuates, senses strain deformation, and stores energy. The system operates whereby the strain of a polypyrrole actuator is measured by a polypyrrole length sensor, whilst being powered by an array of polypyrrole supercapacitors. Independently, polypyrrole actuators were evaluated at 250 discrete frequencies ranging from 0.01 to 10 Hz using fixed, ±1 V sinusoidal excitation. Polypyrrole length sensors were evaluated using a thin-film dynamic mechanical analyzer for the same range of frequencies with a 2% sinusoidal input strain. Polypyrrole supercapacitors were evaluated using cyclic voltammetry (−1.0 V to +1.0 V; 12.5 to 100 mV/sec) and galvanostatic charge-discharge cycling (0.5 to 2 mA/mg). As an actuator, polypyrrole samples showed measureable actuation strain between 0.001% and 1.6% for the frequency range tested, with amplitude versus frequency decay behavior similar to a first-order low-pass filter. As a length sensor, polypyrrole samples showed linearelastic behavior up to 3% strain and gauge factors near 4. As a symmetric supercapacitor, polypyrrole had capacitance values higher than 20 kF/kg, energy densities near 20 kJ/kg, and power densities near 2 kW/kg. The evaluation of each component, independently, justified creating a cooperative system composed of these three components operating simultaneously. Polypyrrole supercapacitors provided ample power to excite polypyrrole actuators. Polypyrrole length sensors attached in series to polypyrrole actuators were capable of measuring strain from coupled polypyrrole actuators. Performance metrics and future possibilities regarding conducting polymer-based multifunctional materials are discussed.Copyright