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| Plastic Muscles are a developing technology and the many uses for these devices are still being explored. Thus far, several potential application areas for Plastic Muscle transducers have emerged. Due to their unique capabilities, the opportunities for devices based on ionomer transducers are limited only by imagination. Discover Technologies is constantly seeking new concepts and partners with which to pursue them. If you have an idea for our Plastic Muscle technology, please do not hesitate to contact us. Wall Shear Stress Sensors Discover Technologies is currently developing wall shear stress sensors based on ionomer transducers under contract from the Office of Naval Research. Friction shear stress accounts for most of the drag force on a waterborne vessel, or any high-speed vehicle for that matter. Furthermore, turbulent flow leads to broadband fluctuations in this stress. These fluctuations can have very small time scales and occur over very small spatial dimensions. An understanding of this shear stress and its spatial and temporal distribution is critical for the development of next generation high speed surface and submerged vessels. Additionally, this understanding will lead to fundamental improvements in our comprehension of the physics of fluid / wall interactions and very high Reynolds number turbulent flow. Discover Technologies has fabricated and tested prototype wall shear stress sensors in collaboration with Dr. Pavlos Vlachos in the Mechanical Engineering Department at Virginia Tech. These prototypes were characterized using a custom oscillating plate apparatus designed to generate a Stokes layer. Based on the Stokes layer assumption, the sensors were characterized over a range of shear stress of +/- 3 Pa and a range of frequency of 30 to 130 Hz. Over this range, the sensors exhibited a signal to noise ratio of 60 dB and a mean absolute error of 4.92%, with respect to the full scale range. Discover Technologies and Virginia Tech are currently developing improved sensors and sensor characterization protocols based on this initial success. |
| A prototype wall shear stress sensor. |
| Signal output of a prototype wall shear stress sensor on an oscillating plate at 78 Hz. The shear stress determined analytically using the Stokes layer assumption is shown for reference. |
| Discover Technologies' wall shear sensors will facilitate new flow control strategies for advanced water and aircraft. Prototype sensor arrays have already been demonstrated that could be used to locate lines of separation on these vehicles. These wall shear sensors and sensor arrays will offer many advantages over other currently available techniques, including:
This last point is of critical importance. Many technologies for measuring wall shear stress are actually directly measuring fluid velocity or heat transfer. Because Discover Technologies' sensors perform a direct measurement of wall shear stress, they are capable of operating without a priori knowledge of the flow characteristics. They will also be capable of evaluating the effectiveness of novel friction reducing treatments currently under development. Electroactive Polymer Pumps One potential application for Discover Technologies' ionomer actuators is in small pumps. These pumps could be used for drug delivery, microfluidic devices, active flow control, and a multitude of consumer applications. The most likely configuration for a pump based on ionomer actuators would be a dual diaphragm device. The advantages that an ionomeric pump could offer would be low voltage (battery) operation, extremely low noise signature, high system efficiency, and highly accurate control of flow rate. Discover Technologies has performed initial studies to evaluate the feasibility of a pump operated by ionomer actuators. Thus far a complete prototype has not been tested, but the concept has been demonstrated using a single diaphragm. |
| Concept of a small, double diaphragm pump operated by Plastic Muscle actuators. |
| A prototype diaphragm actuator and evaluation fixture used to test the concept of an EAP pump. The diameter of the actuator is 1 inch. |
| Adaptive Membrane Optics Another technology that can benefit from the unique properties of Plastic Muscle actuators is optical membranes. Due to their low modulus, the mechanical impedance of these actuators is well-matched to common optical membrane materials. Also, a single Plastic Muscle actuator is capable of generating displacements that range from microns to centimeters. For this reason, these materials can be used for static shape correction and jitter suppression. These actuators could also be used to correct for optical aberrations due to atmospheric interference. Membrane optics could also benefit from the scalability of Plastic Muscle transducers. Although these devices are currently manufactured on the centimeter scale, there is no fundamental limitation preventing the eventual realization of meter scale devices. Additionally, Plastic Muscle actuators can be patterned to provide multiple individual domains on an optical membrane that can be individually addressed. Finally, Plastic Muscle transducers can act as both the sensing and actuating elements in an optical system. Signals measured by one set of transducers can be used to provide a control signal for another set. Alternatively, the individual regions of a patterned device could be switched from actuation to sensing depending on the requirements of the situation. Polymer Microphones Another possible application for Plastic Muscle polymer transducers is acoustics. Due to their sensitivity to vibration, Plastic Muscle transducers could be used as polymer microphones. As with the wall shear sensors, it may be possible to create novel arrays of microphones, thus allowing for the development of a sensing skin to be used to map pressure fluctuations over the surface of an object. These microphones could also potentially be made in very small sizes and because of their remarkable sensitivity may be useful as bone conduction pickups. The development of successful microphones based on Plastic Muscle sensors could lead to advances in electronic eavesdropping, hydrophones, weather measurement instruments, and sonar. The advantages for Plastic Muscle transducers in these applications would be their small size, light weight, high sensitivity, and simple design. |
| A prototype microphone utilizing a diaphragm ionomeric sensor as the active element. |
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