Yoseph Bar-Cohen | Jet Propulsion Laboratory, California Institute of Technology (original) (raw)

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Papers by Yoseph Bar-Cohen

Proceedings of SPIE, Apr 19, 2013

Proceedings of SPIE, Aug 5, 2003

In-situ sampling and analysis are important capabilities to allow meeting the major objectives of... more In-situ sampling and analysis are important capabilities to allow meeting the major objectives of future NASA's planetary exploration missions. The development of an ultrasonic device that can serve as a probe, sampler and sensors platform for in-situ analysis is currently underway at JPL. The device is based on the novel Ultrasonic/Sonic Driller/Corer (USDC) technology, which was co-developed by the Non-Destructive Evaluation and Advanced Actuator laboratory (NDEAA, ), JPL, and Cybersonics. This sampling technology requires low axial force, thereby overcoming one of the major limitations of planetary sampling in low gravity using conventional drills. This device allows the design of an effective tool that is compact, low mass and uses low power. To assure effective use of power for drilling/coring rocks in-situ probing is needed to allow selecting rocks with the highest probability of containing information (biological markers, water, etc.). While the major function of the USDC is sampling, drilling and coring, it also has great potential to serve as a probing device. The USDC imparts elastic waves into the sampled medium offering a sounding method for geophysical analysis similar to the techniques used by the oil industry. Also, the characteristic of the piezoelectric actuator, which drives the USDC, is affected by the medium to which it is coupled. Using a variety of device configurations, a series of experiments were conducted to measure the elastic wave velocity, scattering, impedance and the shift in resonance frequency. Various rocks are being tested to determine their characteristics. Preliminary results are encouraging. Currently, investigation is conducted to find methods of minimizing the effect of surface roughness, geometry and sample dimensions on the data.

Proceedings of SPIE, Jul 27, 2004

Electroactive polymers (EAP) are attractive actuation materials because of their large deformatio... more Electroactive polymers (EAP) are attractive actuation materials because of their large deformation, flexibility, and low density. The large deformation, especially in the bending mode, poses a challenge to the material and actuator characterization due to the geometric nonlinearity that is developed during the characterization. A CCD camera system was constructed to record the curved shapes of bending during the activation of EAP films and image-processing software was developed to digitize the bending curve s. A computer program was written to solve the inverse problem of cantilever EAP beams with a tip position limiter. Using the program and acquired curve images with and without a tip position limiter as well as the corresponding tip force, the performance of the beam under different applied voltages and tip force loads was determined. The experimental setup and the principles of the computer program are described and discussed in this paper.

Planetary protection of returned Mars samples to Earth in a future NASA mission is a critical par... more Planetary protection of returned Mars samples to Earth in a future NASA mission is a critical part of preventing uncontrolled biological materials being released from the samples. The planetary protection process requires addressing the potential risks and would involve “breaking the chain of contact (BTC)”, where any returned material reaching Earth for further analysis would have to be sealed inside a container with extremely high confidence. The sterilization process would require destroying any potential biological materials that may contaminate the external surface of the container. A novel process for containing the returning samples has been conceived and is in development at JPL. The process consists of using induction heated brazing to synchronously sterilize, separate, seam and seal the container.

Proceedings of SPIE, Mar 25, 2010

Proceedings of SPIE, Mar 24, 2011

SPIE eBooks, Mar 16, 2010

Implementing EAP materials as actuators requires the availability of a properties database and sc... more Implementing EAP materials as actuators requires the availability of a properties database and scaling laws to allow the actuator or transducer designer to determine their response at the operational conditions. A metric for the comparison of these materials' properties with other electroactive materials and devices is needed to support users in the implementation of these materials as actuators of choice. In selecting characterization techniques it is instructive to look at the various classes of electroactive Polymers and the source of their strain-field response. Generally, two main classes can be identified [Chapter 1 and Topic 3]: (1) Electronic EAP materials -€” These are mostly materials that are dry and are driven by the electric field or Coulomb forces. This category includes piezoelectrics, and electrostrictive and ferroelectric materials. Generally these materials are polarizable with the strain being coupled to the electric displacement. The strain of electrostrictive and ferroelectric materials is proportional to the square of the polarization or electric displacement. In piezoelectric materials the strain couples linearly to the applied field or electric displacement. Charge transfer in these materials is in general electronic and at dc fields they behave as insulators. These properties have been studied for over a century in single crystals and for over three decades in polymers. (2) Ionic EAP materials -€” These materials contain electrolytes and they involve transport of ions/ˆ•molecules in response to an external electric field. Examples of such materials include conductive polymers, IPMCs, and ionic gels. The field controlled migration or diffusion of the various ions∕molecules results in an internal stress distribution. These internal stress distributions can induce a wide variety of strains, from volume expansion or contraction, to bending. In some conductive polymers the materials exhibit both ionic and electronic conductivities. These materials are relatively new as actuator materials and have received much less attention in the literature than the piezoelectric and electrostrictive materials. At present, due to a wide variety of possible materials and conducting species, no generally accepted phenomenological model exists and much effort is underway to determine the commonalities of the various materials systems. A clearer understanding of the characterization techniques would help immensely in determining underlying theories and scaling laws for these actuator materials.

Proceedings of SPIE, Apr 19, 2013

Proceedings of SPIE, Aug 5, 2003

In-situ sampling and analysis are important capabilities to allow meeting the major objectives of... more In-situ sampling and analysis are important capabilities to allow meeting the major objectives of future NASA's planetary exploration missions. The development of an ultrasonic device that can serve as a probe, sampler and sensors platform for in-situ analysis is currently underway at JPL. The device is based on the novel Ultrasonic/Sonic Driller/Corer (USDC) technology, which was co-developed by the Non-Destructive Evaluation and Advanced Actuator laboratory (NDEAA, ), JPL, and Cybersonics. This sampling technology requires low axial force, thereby overcoming one of the major limitations of planetary sampling in low gravity using conventional drills. This device allows the design of an effective tool that is compact, low mass and uses low power. To assure effective use of power for drilling/coring rocks in-situ probing is needed to allow selecting rocks with the highest probability of containing information (biological markers, water, etc.). While the major function of the USDC is sampling, drilling and coring, it also has great potential to serve as a probing device. The USDC imparts elastic waves into the sampled medium offering a sounding method for geophysical analysis similar to the techniques used by the oil industry. Also, the characteristic of the piezoelectric actuator, which drives the USDC, is affected by the medium to which it is coupled. Using a variety of device configurations, a series of experiments were conducted to measure the elastic wave velocity, scattering, impedance and the shift in resonance frequency. Various rocks are being tested to determine their characteristics. Preliminary results are encouraging. Currently, investigation is conducted to find methods of minimizing the effect of surface roughness, geometry and sample dimensions on the data.

Proceedings of SPIE, Jul 27, 2004

Electroactive polymers (EAP) are attractive actuation materials because of their large deformatio... more Electroactive polymers (EAP) are attractive actuation materials because of their large deformation, flexibility, and low density. The large deformation, especially in the bending mode, poses a challenge to the material and actuator characterization due to the geometric nonlinearity that is developed during the characterization. A CCD camera system was constructed to record the curved shapes of bending during the activation of EAP films and image-processing software was developed to digitize the bending curve s. A computer program was written to solve the inverse problem of cantilever EAP beams with a tip position limiter. Using the program and acquired curve images with and without a tip position limiter as well as the corresponding tip force, the performance of the beam under different applied voltages and tip force loads was determined. The experimental setup and the principles of the computer program are described and discussed in this paper.

Planetary protection of returned Mars samples to Earth in a future NASA mission is a critical par... more Planetary protection of returned Mars samples to Earth in a future NASA mission is a critical part of preventing uncontrolled biological materials being released from the samples. The planetary protection process requires addressing the potential risks and would involve “breaking the chain of contact (BTC)”, where any returned material reaching Earth for further analysis would have to be sealed inside a container with extremely high confidence. The sterilization process would require destroying any potential biological materials that may contaminate the external surface of the container. A novel process for containing the returning samples has been conceived and is in development at JPL. The process consists of using induction heated brazing to synchronously sterilize, separate, seam and seal the container.

Proceedings of SPIE, Mar 25, 2010

Proceedings of SPIE, Mar 24, 2011

SPIE eBooks, Mar 16, 2010

Implementing EAP materials as actuators requires the availability of a properties database and sc... more Implementing EAP materials as actuators requires the availability of a properties database and scaling laws to allow the actuator or transducer designer to determine their response at the operational conditions. A metric for the comparison of these materials' properties with other electroactive materials and devices is needed to support users in the implementation of these materials as actuators of choice. In selecting characterization techniques it is instructive to look at the various classes of electroactive Polymers and the source of their strain-field response. Generally, two main classes can be identified [Chapter 1 and Topic 3]: (1) Electronic EAP materials -€” These are mostly materials that are dry and are driven by the electric field or Coulomb forces. This category includes piezoelectrics, and electrostrictive and ferroelectric materials. Generally these materials are polarizable with the strain being coupled to the electric displacement. The strain of electrostrictive and ferroelectric materials is proportional to the square of the polarization or electric displacement. In piezoelectric materials the strain couples linearly to the applied field or electric displacement. Charge transfer in these materials is in general electronic and at dc fields they behave as insulators. These properties have been studied for over a century in single crystals and for over three decades in polymers. (2) Ionic EAP materials -€” These materials contain electrolytes and they involve transport of ions/ˆ•molecules in response to an external electric field. Examples of such materials include conductive polymers, IPMCs, and ionic gels. The field controlled migration or diffusion of the various ions∕molecules results in an internal stress distribution. These internal stress distributions can induce a wide variety of strains, from volume expansion or contraction, to bending. In some conductive polymers the materials exhibit both ionic and electronic conductivities. These materials are relatively new as actuator materials and have received much less attention in the literature than the piezoelectric and electrostrictive materials. At present, due to a wide variety of possible materials and conducting species, no generally accepted phenomenological model exists and much effort is underway to determine the commonalities of the various materials systems. A clearer understanding of the characterization techniques would help immensely in determining underlying theories and scaling laws for these actuator materials.