Engineering topics
Bar-Cohen, Y.
Publications and source records attributed to Bar-Cohen, Y..
Crawlers as Robotic Scanner Platform for Miniature NDT Instruments
The current use of aging aircraft significantly longer than their design life added a great degree of urgency to the ongoing need for low-cost, rapid, simple-to-operate, reliable and efficient NDE methods for detection and characterization of flaws.
Defects Detection and Characterization Using Leaky Lamb Wave (LLW) Dispersion Data
Composite materials are being used at a significant level of usage for flaw critical structures and they are taking a growing percentage of the makeup of aircraft and spacecraft. Composite structues are now reaching service duration, for which the issue of aging is requiring adquate attention.
Smart Sensor System for NDE or Corrosion in Aging Aircraft
The extension of the operation life of military and civilian aircraft rather than replacing them with new ones is increasing the probability of aircraft component failure as a result of aging. Aircraft that already have endured a long srvice life of more than 40 years are now being considered for another 40 years of service.
Noninvasive Medical Diagnostics & Treatment Using Ultrasonics
In parallel to the industrial application of NDE to flaw detection and material property determination, the medical community has succesfully adapted such methods to the noninvasaive diagnostics and treatment of many conditions and disorders of the human body.
Flexible, Low-Mass Robotic Arm Actuated by Electronic Polymers (EAP) and Operated Equivalently to Human Hand
Miniature, lightweight, low-cost actuators that consume low-power can be used to develop unmatched robotic devices to make an impact on many technolgy areas.
Ionic Polymer-Metal Composites (IPMC) as Biomimetric Sensors and Actuators-Artificial Muscles
This paper discusses a number of recent findings in connection with ion-exchange polymer-noble metal composites (IPMC) as biomimetic sensors and actuators.
Low-Mass Muscle Actuators Using Electroactive Polymers (EAP)
NASA is seeking to reduce the mass, size, consumed power, and cost of the instrumentation used in its future missions.
Rotary Ultrasonic Motors Actuated by Traveling Flexural Waves
Efficient miniature actuators that are compact and consume low power are needed to drive telerobotic devices and space mechanisms in future NASA missions. Ultrasonic rotary motors have the potential to meet this NASA need and they are developed as actuators for miniature telerobotic applications.
Ionic Polymer-Metal Composites (IPMCs) as Biomimetic Sensors, Actuators and Artificial Muscles: A Review
This paper presents an introduction to ionic polymer-metal composites and some mathematical modeling pertaining to them. It further discusses a number of recent findings in connection with ion-exchange polymer-metal composites (IPMCS) as biomimetic sensors and actuators. Strips of these composites can undergo large bending and flapping displacement if an electric field is imposed across their thickness. Thus, in this sense they are large motion actuators. Conversely by bending the composite strip, either quasi-statically or dynamically, a voltage is produced across the thickness of the strip. Thus, they are also large motion sensors. The output voltage can be calibrated for a standard size sensor and correlated to the applied loads or stresses. They can be manufactured and cut in any size and shape. In this paper first the sensing capability of these materials is reported. The preliminary results show the existence of a linear relationship between the output voltage and the imposed displacement for almost all cases. Furthermore, the ability of these IPMCs as large motion actuators and robotic manipulators is presented. Several muscle configurations are constructed to demonstrate the capabilities of these IPMC actuators. This paper further identifies key parameters involving the vibrational and resonance characteristics of sensors and actuators made with IPMCS. When the applied signal frequency varies, so does the displacement up to a critical frequency called the resonant frequency where maximum deformation is observed, beyond which the actuator response is diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. Also the load characterizations of the IPMCs were measured and it was shown that these actuators exhibit good force to weight characteristics in the presence of low applied voltages. Finally reported are the cryogenic properties of these muscles for potential utilization in an outer space environment of a few Torrs and temperatures of the order of - 140 degrees Celsius. These muscles are shown to work quite well in such harsh cryogenic environments and thus present a great potential as sensors and actuators that can operate at cryogenic temperatures.
Real-Time Characterization of Materials Degradation Using Leaky Lamb Wave
Leaky Lamb wave (LLW) propagation in composite materials has been studied extensively since it was first observed in 1982. The wave is induced using a pitch-catch arrangement and the plate wave modes are detected by searching minima in the reflected spectra.
Ultrasonic Characterization of Flaws in Composites Using Plate Waves Dispersion Data
Leaky Lamb wave (LLW) propagation in composite materials has been studied extensively since it was first observed in 1982. The wave is induced using a pitch-catch arrangement and the plate wave modes are detected by searching minima in the reflected spectra.
Oblique Insonification Ultrasonic NDE of Composite Materials for Space Applications
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(abstract) Oblique Insonification Ultrasonic NDE of Composite Materials for Space Applications
In recent years, a great deal of research has been exerted to developing NDE methods for the characterization of the material properties of composites as well as other space structural materials. The need for information about such parameters as the elastic properties, density, and thickness are critical to the safe design and operation of such structural materials. Ultrasonics using immersion methods has played an important role in these efforts due to its capability, cost effectiveness, and ease of use. The authors designed a series of ultrasonic oblique insonification experiments in order to develop a practical field applicable NDE method for space structures.
Low Mass Muscle Actuators (LoMMAs) Using Electroactive Polymers
NASA is using actuation devices for many space applications and there is an increasing need to cut their cost as well as reduce their size, mass, and power consumption. Existing transducing actuators, such as piezoceramics, are inducing limited displacement levels. Potentially, electroactive polymers (so called EAP) can be formed as inexpensive, low-mass, low-power, miniature muscle actuators that are superior to the widely used actuators.
Rotary Piezoelectric Motors Actuated by Traveling Waves (abstract)
Piezoelectric rotary motors are being developed as a drive mechanism for miniature spacecraft instruments and subsystems. The technology that has recently emerged in commercial products requires more rigorous analytical tools for effective design. The theoretical predictions and the experimental corraboration showed a remarkable agreement and they will be presented and discussed in this paper.
Electroactive Polymers (EAP) low Mass Muscle Actuators
Actuation devices are used for many space applications with an increasing need to reduce their size, mass, and power consumption as well as cut their cost. Existing transducing actuators, such as piezoceramics, induce limited displacement levels. Potentially, electroactive polymers (EAP) have the potential for low-mass, low-power, inexpensive miniature muscle actuators that are superior to the widely used actuators.
Flexible, Low-mass Robotic Arm Actuatd by Electroactive Polymers (EAP) and Operated Equivalently to Human Hand
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