Tech Briefs

Multiaxis, Lightweight, Computer-Controlled Exercise System

This system offers unprecedented versatility for physical conditioning and evaluation The multipurpose, multiaxial, isokinetic dynamometer (MMID) is a computer-controlled system of exercise machinery that can serve as a means for quantitatively assessing a subject’s muscle coordination, range of motion, strength, and overall physical condition with respect to a wide variety of forces, motions, and exercise regimens. The MMID is easily reconfigurable and compactly stowable and, in comparison with prior computer-controlled exercise systems, it weighs less, costs less, and offers more capabilities.

Posted in: Briefs, Bio-Medical, Medical

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White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra.Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent of frequency. White-light WGM resonators have potential as superior alternatives to (1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-opticalmodulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

Posted in: Briefs, Physical Sciences

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Simplified Optics and Controls for Laser Communications

NASA’s Jet Propulsion Laboratory, Pasadena, California A document discusses an architecture of a spaceborne laser communication system that provides for a simplified control subsystem that stabilizes the line of sight in a desired direction. Heretofore, a typical design for a spaceborne laser communication system has called for a high-bandwidth control loop, a steering mirror and associated optics, and a fast steering mirror actuator to stabilize the line of sight in the presence of vibrations. In the present architecture, the need for this fast steering-mirror subsystem is eliminated by mounting the laser-communication optics on a disturbance-free platform (DFP) that suppresses coupling of vibrations to the optics by ≥60 dB. Taking advantage of microgravitation, in the DFP, the optical assembly is free-flying relative to the rest of the spacecraft, and a low-spring-constant pointing control subsystem exerts small forces to regulate the position and orientation of the optics via voice coils. All steering is effected via the DFP, which can be controlled in all six degrees of freedom relative to the spacecraft. A second control loop, closed around a position sensor and the spacecraft attitude-control system, moves the spacecraft as needed to prevent mechanical contact with the optical assembly.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Architecture, Lasers, Optics, Telecommunications, Vibration

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Coherent Detection of High-Rate Optical PPM Signals

Quantum-limited performance is achievable. NASA’s Jet Propulsion Laboratory, Pasadena, California A method of coherent detection of high-rate pulse-position modulation (PPM) on a received laser beam has been conceived as a means of reducing the deleterious effects of noise and atmospheric turbulence in free-space optical communication using focal-plane detector array technologies. In comparison with a receiver based on direct detection of the intensity modulation of a PPM signal, a receiver based on the present method of coherent detection performs well at much higher background levels.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Mathematical analysis, Lasers, Performance tests, Turbulence

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White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra. NASA’s Jet Propulsion Laboratory, Pasadena, California Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent of frequency. White-light WGM resonators have potential as superior alternatives to (1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-optical modulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Lasers, Optics, Spectroscopy

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MEMS to Replace Quartz Oscillators as Frequency Sources

A new encapsulation and packaging technology for MEMS resonators provides a clean, stable environment for reference oscillators. Research on microelectromechanical system (MEMS) resonators dates back to the mid-1960s, but MEMS timing references are only now being introduced commercially. In this time, two fundamental technical challenges have been overcome: finding a stable and predictable material from which to build the resonators, and developing a sufficiently clean hermetic packaging system.

Posted in: Briefs, Electronics & Computers

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“Virtual Feel” Capaciflectors

Increases in capacitance with deviations from desired central positions would be exploited. The term “virtual feel” denotes a type of capaciflector (an advanced capacitive proximity sensor) and a methodology for designing and using a sensor of this type to guide a robot in manipulating a tool (e.g., a wrench socket) into alignment with a mating fastener (e.g., a bolt head) or other electrically conductive object. Unlike robotic vision, capacitive proximity sensing does not require a clear line of sight to the mating fastener. On the contrary, capacitive proximity sensing affords the greatest position-measuring sensitivity in the situation in which it is most needed — when the tool is so close to the fastener as to prevent viewing.

Posted in: Briefs, Electronics & Computers

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