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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3

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NASA NTRS1975

The Stanford-Ames portable echocardioscope - A case study in technology transfer

The paper describes a lightweight portable battery-powered echocardioscope fabricated largely from readily available components. The transducer contains a piezoelectric crystal which acts as both an ultrasound pulse emitter and echo receiver, and the oscilloscope is of modular construction. The oscilloscope display can be produced in any of three different modes: A-mode, B-mode, and M-mode (time-motion) by sweeping the intensified points of light of the B-mode display vertically along the oscilloscope face. The resulting display can be photographed in a time exposure, thus providing a hardcopy record for the patient's chart or physician's records. The device is clinically validated on both normal subjects and patients by experienced echocardiographers.

Schmidt, G.↗

NASA NTRS1978

A technique for measuring in situ size distribution of aerosols

A multistage cascade impactor instrument employing piezoelectric crystals for real-time aerosol size distribution measurements is described in this paper. The instrument measures the aerosol mass concentration as a function of particle size in 10 size intervals ranging from 0.05 micrometers to 25 micrometers in diameter. The particles are then analyzed for elemental composition and morphology by means of scanning electron microscopy (SEM). Examples of particle size distributions in rocket motor exhaust plumes measured with the instrument are presented together with the elemental composition and morphology obtained by SEM.

Woods, D. C.↗

NASA NTRS1980

An ultrasonic plethysmograph for space flight applications

The development of an ultrasonic plethysmograph based on the transit time measurement principle is reported, which meets the space-imposed requirements for evaluating cardiovascular deconditioning. It consists of a pulse generator, pulse receiver amplifier, voltage comparator, synchronous pulse generator, elapsed time counter, and transmit and receive piezoelectric crystals resonant at 2 MHz and of 3 mm diameter. The transit time for an ultrasonic pulse to propagate across a limb cross section is computed in a digital fashion using a 32 MHz clock, and resolution is 0.049 mm with the range being approximately 200 mm. Experimental results regarding dynamic system response were found comparable in both accuracy and sensitivity to those of a Whitney strain gage using a 50 torr venous occlusion.

Bhagat, P. K.↗

NASA NTRS1984

Portable Fatigue-Testing Machine

Portable machine constructed for fatigue testing of structural materials or machinery parts subjected to fatigue loads. Piezoelectric crystal stack adds oscillatory force to constant force. Machine tests wider variety of objects than with usual rotating-beam fatigue tests.

Lewis, J.↗

NASA NTRS1984

Ultrasonic transducer with Gaussian radial pressure distribution

An ultrasonic transducer that produces an output that is a symmetrical function comprises a piezoelectric crystal with several concentric ring electrodes on one side of the crystal. A resistor network applies different amplitudes of an ac source to each of the several electrodes. A plot of the different amplitudes from the outermost electrode to the innermost electrode is the first half of a Gaussian function. Consequently, the output of the crystal from the side opposite the electrodes has a Gaussian profile.

Claus, R. O.↗

NASA NTRS1983

Ultrasonic transducer with a two-dimensional Gaussian field profile

A transducer is described which generates a two-dimensional Gaussian field by controlling both the position of multiple circular electrodes and the voltage applied to each electrode. The transducer is constructed by depositing concentric rings electrodes onto one flat surface of a circular piezoelectric crystal disk and attaching the rings to an impedance matching network which acts as a voltage divider. Geometrical inter-ring separations and electrical inter-ring impedances are designed to minimize the error between the generated acoustic field, modeled as a piecewise linear function, and the desired Gaussian distribution. Total mean squared error between the averaged far-field data and a Gaussian shape is less than two percent.

Claus, R. O.↗

NASA NTRS1985

Superconducting electromagnetic actuators for astronomical Fabry-Perot interferometers

Two types of superconducting electromagnetic actuators linear and angular - for precise control of Fabry-Perot spectrometer etalons at liquid helium temperature were manufactured and tested successfully. The linear displacement unit (45 Newtons/Amp) has maximum travel of + or - 44 microns with off-axis deviation of less than 1.5 arcseconds for 15 microns path. The angular unit has maximum tilt of + or - 8 arcminutes and can maintain parallelism of two etalons to better than 0.3 arcsecond of angle by compensating the differential contraction upon cooling and off-axis deviation of the linear displacement unit. These actuators are proving especially useful in low temperature infrared instrumentation where other choices, such as piezoelectric crystals, fail and where essentially zero power dissipation permits low infrared backgrounds to be maintained along with long cryogenic lifetimes.

Nishimura, T.↗

NASA NTRS1984

Far-field brainstem responses evoked by vestibular and auditory stimuli exhibit increases in interpeak latency as brain temperature is decreased

The effect of decreasing of brain temperature on the brainstem auditory evoked response (BAER) in rats was investigated. Voltage pulses, applied to a piezoelectric crystal attached to the skull, were used to evoke stimuli in the auditory system by means of bone-conducted vibrations. The responses were recorded at 37 C and 34 C brain temperatures. The peaks of the BAER recorded at 34 C were delayed in comparison with the peaks from the 37 C wave, and the later peaks were more delayed than the earlier peaks. These results indicate that an increase in the interpeak latency occurs as the brain temperature is decreased. Preliminary experiments, in which responses to brief angular acceleration were used to measure the brainstem vestibular evoked response (BVER), have also indicated increases in the interpeak latency in response to the lowering of brain temperature.

Hoffman, L. F.↗

NASA NTRS1986

Broadband Ultrasonic Transducers

New geometry spreads out resonance region of piezoelectric crystal. In new transducer, crystal surfaces made nonparallel. One surface planar; other, concave. Geometry designed to produce nearly uniform response over a predetermined band of frequencies and to attenuate strongly frequencies outside band. Greater bandwidth improves accuracy of sonar and ultrasonic imaging equipment.

Heyser, R. C.↗

NASA NTRS1986

Variable Synthetic Capacitance

Feedback amplifier circuit synthesizes electronically variable capacitance. Variable Synthetic Capacitor is amplifier circuit with follower/feedback configuration. Effective input capacitance depends on input set current. If synthetic capacitor is connected across resonant element of oscillator, oscillator frequency controlled via input set current. Circuit especially suitable for fine frequency adjustments of piezoelectric-crystal or inductor/capacitor resonant oscillators.

Kleinberg, L. L.↗

NASA NTRS1984

Advanced turboprop vibratory characteristics

The assembly of SR5 advanced turboprop blades to develop a structural dynamic data base for swept props is reported. Steady state blade deformation under centrifugal loading and vibratory characteristics of the rotor assembly were measured. Vibration was induced through a system of piezoelectric crystals attached to the blades. Data reduction procedures are used to provide deformation, mode shape, and frequencies of the assembly at predetermined speeds.

Srinivasan, A. V.↗

NASA NTRS1986

An experimental investigation of the structural dynamics of a torsionally soft rotor in vacuum

An extensive data base of structural dynamic characteristics has been generated from an experimental program conducted on a torsionally soft two-bladed model helicopter rotor system. Measurements of vibratory strains for five modes of vibration were made at twenty-one locations on the two blades at speeds varying from 0 to 1000 RPM and for several combinations of precone, droop and flexure stiffness. Tests were conducted in vacuum under carefully controlled conditions using a unique excitation device with a system of piezoelectric crystals bonded to the blade surface near the root. Frequencies, strain mode shapes and dampings are extracted from the time histories and can be used to validate structural dynamics codes. The dynamics of the system are such that there is a clear tendency for the first torsion and second flap modes to couple within the speed range considered. Strain mode shapes vary significantly with speed and configuration. This feature is important in the calcualtion of aeroelastic instabilities. The tension axis tests confirmed that the modulus-weighted centroid for the nonhomogeneous airfoil is slightly off the mass centroid and validated previous static tests done to determine location of the tension axis.

Srinivasan, A. V.↗

NASA NTRS1987

Determining structural performance

An overview is given of the methods and concepts developed to enhance and predict structural dynamic characteristics of advanced aeropropulsion systems. Aeroelasticity, Vibration Control, Dynamic Systems, and Computational Structural Methods are four disciplines that make up the research program at NASA/Lewis Research Center. The Aeroelasticity program develops analytical and experimental methods to minimize flutter and forced vibration of aerospace propulsion systems. Both frequency domain and time domain methods have been developed for applications on the turbofan, turbopump, and advanced turboprop. To improve life and performance, the Vibration Control program conceives, analyzes, develops, and demonstrates new methods to control vibrations in aerospace systems. Active and passive vibration control is accomplished with electromagnetic dampers, magnetic bearings, and piezoelectric crystals to control rotor vibrations. The Dynamic Systems program analyzes and verifies the dynamics of interacting systems, as well as develops concepts and methods for high-temperature dynamic seals. The Computational Structural Methods program uses computer science to improve solutions of structural problems.

Ernst, Michael A.↗

NASA NTRS1988

Development and applications of optical interferometric micrometrology in the angstrom and subangstrom range

The recent development of the scanning electron tunneling microscope and the atomic force microscope requires absolute standards for measurements in the angstrom and subangstrom range. Optical interferometry with lasers and multiple mode laser resonances can provide absolute measurements as the laser wavelengths are very accurately known. A key feature of such measurements is the use of piezoelectric crystals as translators of the highest accuracy for very small disturbances. However, the dimensional changes of these crystals resulting from electrical potential changes depend on many variables, among them the method of mounting, so that accurate calibrations are necessary. Starting from advances in optical metrology made by physicists trying to find gravity waves, advances which led to measurements down to 10 to the -5 A, the author designed and built a much simpler system for the angstrom range. The major limiting factors were mechanical vibrations, air currents, thermal changes and laser instabilities.

Lauer, James L.↗

NASA NTRS1990

A 200 MHz surface acoustic wave mass microbalance

The principle of operation of the surface acoustic wave (SAW) piezoelectric crystals used as microgravimetric sensors in mass microbalances is discussed. Special attention is given to a SAW 200-MHz crystal developed for measuring molecular deposition on spacecrafts, whose operating frequency does not depend on the thickness of the crystal. The frequency stability of the 200 MHz SAW device is better than 5 x 10 exp -9, which corresponds to a lower limit-of-detection of 3 x 10 exp -12 g for a signal-to-noise ratio of 3. A block diagram of the 200 MHz SAW mass microbalance and a schematic diagram of SAW resonator are presented together with performance data of this device.

Bowers, William D.↗

NASA NTRS1990

Determining structural performance

An overview of the methods and concepts developed to enhance and predict structural dynamic characteristics of advanced aeropropulsion systems is presented. Aeroelasticity, vibration control, dynamic systems, and computational structural methods are four disciplines that make up the structural dynamic effort at LeRC. The aeroelasticity program develops analytical and experimental methods for minimizing flutter and forced vibration of aerospace propulsion systems. Both frequency domain and time domain methods were developed for applications on the turbofan, turbopump, and advanced turboprop. In order to improve life and performance, the vibration control program conceives, analyzes, develops, and demonstrates new methods for controlling vibrations in aerospace systems. Active and passive vibration control is accomplished with electromagnetic dampers, magnetic bearings, and piezoelectric crystals to control rotor vibrations. The dynamic systems program analyzes and verifies the dynamics of interacting systems, as well as develops concepts and methods for high-temperature dynamic seals. Work in this field involves the analysis and parametric identification of large, nonlinear, damped, stochastic systems. The computational structural methods program exploits modern computer science as an aid to the solutions of structural problems.

Ernst, Michael A.↗

NASA NTRS1991

Small Business Innovations (Mass Microbalance)

Femtometrics of Costa Mesa, CA, developed the Model 200-1 SAW Mass Microbalance under a NASA Small Business Innovation Research (SBIR) contract with Langley Research Center. The product is described as "the next generation of aerosol mass microbalance technology," because a new type of sensor, the Surface Acoustic Wave (SAW) piezoelectric crystal, offers mass resolution two orders of magnitude greater than the Quartz Crystal Microbalance cascade impactor (QCM) (used at Langley since 1979 for collection and measurement of aerosol particles in the upper atmosphere). The Model 200-1 SAW Mass Microbalance, which provides a 400-fold increase in mass sensitivity per unit area over the QCM, can be used for real-time particle monitoring in clean rooms, measuring chemical vapors in very low concentrations, measuring target chemicals in the stratosphere and in industry as a toxic vapor monitor.

Source record↗

NASA NTRS2004

Recent Developments in NASA Piezocomposite Actuator Technology

In this paper, we present an overview of recent progress in the development of the NASA Macro-Fiber Composite (MFC) piezocomposite actuator device. This will include a brief history of the development of the MFC, a description of the standard manufacturing process used to fabricate MFC actuators, and a summary of ongoing MFC electromechanical characterization testing. In addition, we describe the development of a prototype single-crystal piezoelectric MFC device, and compare its performance with MFC actuator specimens utilizing conventional piezoceramic materials.

Wilkie, William K.↗