Numerical techniques 'fuel' space vehicles
Future spacecraft may use a planet's atmosphere to generate aerodynamic forces that modify the crafts' orbits without using fuel. University of Illinois (Champaign, IL) researchers developed a numerical technique that can optimize the paths of these aero-assisted orbital transfer vehicles. "Today's spacecraft use propellant-powered thrusters to move from one orbit to another," says Bruce Conway, a professor of aeronautical and astronautical engineering. "But each pound of fuel carried aloft means a corresponding reduction in the weight of the mission payload. A next-generation spacecraft may switch orbits at a substantial fuel savings by dipping into the atmosphere, generating aerodynamic lift and drag on airplane-like control surfaces, and then climbing to a new orbit." The concept is similar to aerodynamic braking, a technique that uses a planet's atmosphere to reduce the speed of a space vehicle. Applications in Earth orbit include atmospheric sampling, satellite repair missions, surveillance, and missile interception. E-mail: email@example.com or call: 217-244-1073
More efficient transformers
Thinner laptop computers and flat-screen TVs may be possible with a simple change in the geometry of piezoelectric transformers. "Conventional [rectangular] electromechanical transformers are big, very heavy and produce a great deal of magnetic noise that, without shielding, can wipe floppy disks, tapes, and hard drives," says Kenji Uchino, professor of electrical engineering and member of Penn State's Materials Research Laboratory (University Park, PA). So Uchino and fellow team members developed a circular configuration made with improved materials that can increase the conversion ratio without adding volume or weight. Electromagnetic transformers consist of two coils of wire that convert high voltages to lower ones or lower voltages to higher ones. The size of the step-up or step-down depends on the difference between the number of turns of wire in each coil. Large electromagnetic transformers are very efficient, but miniaturization decreases the efficiency. Using an enhanced piezoelectric material consisting of a lead, zirconium, titanium ceramic doped with manganese and cerium, Uchino; Burhanettin Koc, postdoctoral associate in electrical engineering; and Yongkang Gao, graduate student in materials science and engineering; solved this problem. In the circular wafer, about one-third of the wafer is used for a crescent-shaped input electrode with the remaining two-thirds as output. The disk transformer provides a voltage step up ratio of about 60 rather than the rectangular rate of just over 40 because it uses more than one vibration mode. "Piezoelectric transformers are not only more efficient, smaller and lighter, but they are also much less expensive to manufacture than conventional coil wound transformers," says Uchino. He warns, however, that piezoelectric transformers are not necessarily the answer to all power problems. For one thing, in any transformer, as the voltage is increased, the current decreases, so transformers are only applicable where current is unimportant. E-mail: Uchino at firstname.lastname@example.org or call: (814) 863-8035.
Driving without glare
At the annual meeting of the Materials Research Society in December, Penn State University's Iam-Choon Khoo described an optical limiting film that could be used to protect human eyes and optical sensors from intense light and continuous glare. The liquid crystal-based films could be used on car windshields, communications satellites, sunglasses, or photographic systems. The film consists of a liquid crystal material sandwiched between two sheets of glass. Researchers mixed in a small amount of a dye, methyl red, to enhances the crystal's sensitivity to low levels of light. Because liquid crystals respond to light in a nonlinear way, they can protect against glare and even laser flashes. As the intensity increases, the liquid crystal lets in dramatically less light. "The optical limiting film can reduce light with the intensity of 140 milliwatts to only 5 microwatts," says Khoo. In the past, Khoo used this property to create an optical switch that reacts in a fraction of a nanosecond to damaging laser intensity by shutting out the light. E-mail: email@example.com or call: (814) 863 2299.
Robotic snakes slither across rugged terrain
Robotic dogs. Robotic cats. Now, robotic snakes. Gavin Miller, an animator in Palo Alto, CA, developed a snake whose movements are so lifelike, you might be tempted to run it over with your new sport utility vehicle, if you are that type of individual. Miller created the spinal column with a train of universal joints that provides two degrees of freedom to each segment. Using pairs of servos in opposition in a novel arrangement enables the snake to undulate vertically as well as horizontally. Miller wanted his snake to move in a sidewinding motion as well as the conventional horizontal undulatory progression. To accomplish this, Miller placed a single wheel under the middle of each segment, allowing the snake to move along like a train of inline skates. Steering and speed are controlled using one joystick while a second joystick controls lift and the amount of sidewinding. Miller hopes to sell his idea to toy companies. But NASA hopes to use the robot to explore rough terrain on other planets. Miller's latest creation, S3, debuted as the ring-bearer at his wedding last year. To see the snake slither for yourself, go to www.snakerobots.com. E-mail: DrGavin@aol.com.
Yes Virginia, polymer lasers that emit infrared are possible
Polymer-based solid-state lasers offer a cheap alternative to semiconductor lasers because the organic precursors are low cost and can be processed from solution at low temperature rather than requiring molecular beam epitaxy techniques. Until now, most of the research in this area has focused on visible and ultraviolet light because it was believed that the optical transitions required for the emission of longer wavelengths were not possible with organic polymers. However, in a theoretical study where they modified the chemical groups attached to the polymer trans-polyacetylene, which does not emit light, rather than changing the bonding in the polymer chain, Alok Shukla and Sumit Mazumdar, physicists at the University of Arizona (Tucson, AZ), demonstrated that light can be emitted from small bandgaps. Their work appeared in the November 8, 1999 issue of Physical Review Letters.
Doctors get a clearer image of one's heart
Heart surgery? Or just exercise and a change of diet? A new imaging technology could soon help physicians decide this serious matter in minutes. At Johns Hopkins University (Baltimore, MD), engineers Jerry Prince and Nael Osman developed the HARP MRI or harmonic phase magnetic resonance imaging process. This system gives doctors almost immediate detailed images of the heart so that cardiologists will be able to see the condition of heart muscles while a patient is still inside a magnetic resonance imaging (MRI) scanner. Currently, it is too costly and impractical for physicians to use an MRI scanner to examine the heart during a typical cardiac stress test. And though an MRI, coupled with cutting- edge "tagging" technology, could provide highly detailed heart data, this method is rarely used because the pictures take several hours to process and interpret. To eliminate this delay, Prince and Osman developed HARP, a combination of software and scanner modifications aimed at producing images of heart function within minutes, making an MRI tagging stress test more practical. "I think the HARP concept could revolutionize or dramatically change the way we do cardiac stress testing," says cardiologist Joao Lima, who has used the system. "It allows us to see the degree and extent of the heart problems (quickly). He is working to create three-dimensional views. Fax (410) 516-5251
Sensor helps eye surgeons
Not surprisingly, precision is crucial during eye surgery. A slight miscalculation could result in partial blindness and damage to the retina. But a sensor being developed at the Department of Energy's Pacific Northwest National Laboratory (Richland, WA) could reduce those risks by alerting surgeons to the location of critical retinal tissues. Researchers designed and built a proximity sensor that could be connected to an endoscope, the tool surgeons use when operating on the back of the eye. The sensor calculates distance of the endoscope's needle to the retina and tissue. The proximity sensor also could be applied to other surgery, such as spinal operations that require surgeons to know the location of nerves. The sensor relies on a fiber smaller than a strand of hair to transmit and receive light. The system begins by sending electricity into a laser diode, which connects to a fiber. The diode converts electricity into light, which then bounces back and forth along the fiber's walls until reaching the retina. Here, the retina absorbs about 80 percent of the energy and reflects the remaining 20 percent back to the proximity sensor. An electronic circuit translates the voltage level into distance. If the distance reaches two millimeters or less, the system would trigger an audible alarm to alert the surgeon.
Measuring high-power radio frequency made easy
The National Institute of Standards and Technology, in order to meet the demand for higher power calibrations, developed a new system for measuring up to one kilowatt of radio-frequency power in the range from 2 to 1,000 megahertz. The technique makes use of calibrated low-power sensors called bolometers, and a calibrated chain of up to five 10-dB couplers. The couplers reduce the high-power level to be measured down to the one to 10-milliwatt level of the sensors. A comparison of results from the new system with those of NIST's older low-frequency measurement system shows that there is good agreement in the area of overlapup to 30 megahertz. The new system and a mathematical analysis of its operation and uncertainties is described in Technical Note 1510, Switched-Coupler Measurements for High-Power RF Calibrations. If interested, e-mail firstname.lastname@example.org, or call (303) 497-3237 for paper No. 47-99.