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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Dog-Bone Horns for Piezoelectric Ultrasonic/Sonic Actuators

A shape reminiscent of a dog bone has been found to be superior to other shapes for mechanical-amplification horns that are components of piezoelectrically driven actuators used in a series of related devices denoted generally as ultrasonic/sonic drill/corers (USDCs). The first of these devices was reported in Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO-20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. The dog-bone shape was conceived especially for use in a more recent device in the series, denoted an ultrasonic/ sonic gopher, that was described in Ultrasonic/Sonic Mechanisms for Drilling and Coring (NPO-30291), NASA Tech Briefs, Vol. 27, No. 9 (September 2003), page 65. The figure shows an example of a dog-bone-shaped horn and other components of an ultrasonic gopher. Prerequisite to a meaningful description of this development is an unavoidably lengthy recapitulation of the principle of operation of a USDC and, more specifically, of the ultrasonic/sonic gopher as described previously in NASA Tech Briefs. The ultrasonic actuator includes a stack of piezoelectric rings, the horn, a metal backing, and a bolt that connects the aforementioned parts and provides compressive pre-strain to the piezoelectric stack to prevent breakage of the rings during extension. The stack of piezoelectric rings is excited at the resonance frequency of the overall ultrasonic actuator. Through mechanical amplification by the horn, the displacement in the ultrasonic vibration reaches tens of microns at the tip of the horn. The horn hammers an object that is denoted the free mass because it is free to move longitudinally over a limited distance between hard stops: The free mass bounces back and forth between the ultrasonic horn and a tool bit (a drill bit or a corer). Because the longitudinal speed of the free mass is smaller than the longitudinal speed of vibration of the tip of the horn, contact between the free mass and the horn tip usually occurs at a phase of the vibration favorable to transfer of momentum from the horn to the free mass. Therefore, the free mass picks up momentum and is accelerated back to the tool bit. Upon impact of the free mass on the tool bit, momentum is transferred to the tool bit. The impacts of the free mass on the tool bit repeat at a sonic frequency that can range from tens of hertz to about 1 kHz. The shock waves caused by the impacts of the free mass propagate to the interface between the tool bit and the medium (typically, rock, ice, or other brittle material) to be drilled or cored. The medium becomes fractured when its ultimate strain is exceeded at the medium/tool-bit interface. This concludes the description of the principle of operation.

Sherrit, Stewart↗
NASA NTRS1971

A comparison of orthogonal transformations for digital speech processing.

Discrete forms of the Fourier, Hadamard, and Karhunen-Loeve transforms are examined for their capacity to reduce the bit rate necessary to transmit speech signals. To rate their effectiveness in accomplishing this goal the quantizing error (or noise) resulting for each transformation method at various bit rates is computed and compared with that for conventional companded PCM processing. Based on this comparison, it is found that Karhunen-Loeve provides a reduction in bit rate of 13.5 kbits/s, Fourier 10 kbits/s, and Hadamard 7.5 kbits/s as compared with the bit rate required for companded PCM. These bit-rate reductions are shown to be somewhat independent of the transmission bit rate.

Campanella, S. J.↗
NASA NTRS1982

Serial data correlator/code translator

A system for analyzing asynchronous signals containing bits of information for ensuring the validity of said signals, by sampling each bit of information a plurality of times, and feeding the sampled pieces of bits of information into a sequence controlled is described. The sequence controller has a plurality of maps or programs through which the sampled pieces of bits are stepped so as to identify the particular bit of information and determine the validity and phase of the bit. The step in which the sequence controller is clocked is controlled by a storage register. A data decoder decodes the information fed out of the storage register and feeds such information to shift registers for storage.

Morgan, L. E.↗
NASA NTRS1984

Comparison of the information content of data from the LANDSAT 4 Thematic Mapper and the multispectral scanner

Evaluation of information contained in data from the visible and near-IR channels of LANDSAT 4 TM and MSS for five agricultural scenes shows that the TM provides a significant advance in information gathering capability as expressed in terms of bits per pixel or bits per unit area. The six reflective channels of the TM acquire 18 bits of information per pixel out of a possible 48 bits, while the four MSS channels acquire 10 bits of information per pixel out of a possible 28 bits. Thus the TM and MSS are equally efficient in gathering information (18/48 to approximately 10/28), contrary to the expected tendency toward lower efficiency as spatial resolution is improved and spectral channels are added to an observing system. The TM thermal IR data appear to be of interest mainly for mapping water bodies, which do not change temperature during the day, for assessing surface moisture, and for monitoring thermal features associated with human activity.

Price, J. C.↗
NASA NTRS1984

Performance Simulation for Unit-memory Convolutional Codes with Byte-oriented Viterbi Decoding Algorithm

A software package developed to simulate the performance of the byte-oriented Viterbi decoding algorithm for unit-memory (UM) codes on both 3-bit and 4-bit quantized AWGN channels is described. The simulation is shown to require negligible memory and less time than that for the RTMBEP algorith, although they both provide similar performance in terms of symbol-error probability. This makes it possible to compute the symbol-error probability of large codes and to determine the signal-to-noise ratio required to achieve a bit error rate (BER) of 0.000001 for corresponding concatenated systems. A (7, 10/48) UM code, 10-bit Reed-Solomon code combination achieves the required BER at 1.08 dB for a 3-bit quantized channel and at 0.91 dB for a 4-bit quantized channel.

Vo, Q. D.↗
NASA NTRS1985

Neighborhood comparison operator

Digital values in a moving window are compared by an operator having nine comparators connected to line buffers for receiving a succession of central pixels together with eight neighborhood pixels. A single bit of program control determines whether the neighborhood pixels are to be compared with the central pixel or a threshold value. The central pixel is always compared with the threshold. The omparator output plus 2 bits indicating odd-even pixel/line information about the central pixel addresses a lookup table to provide 14 bits of information, including 2 bits which control a selector to pass either the central pixel value, the other 12 bits of table information, or the bit-wise logical OR of all nine pixels through circuit that implements a very wide OR gate.

Gennery, D. B.↗
NASA NTRS1986

Method and apparatus for operating on companded PCM voice data

The method and apparatus constructed in accordance with this invention permits a plurality of parties to speak to each other on a conference line with a minimum of interference. The apparatus digitizes audio signals. Each of the parties has an audio transmitter and receiver provided for transmitting and receiving audio signals. The audio signals are converted to a PCM companded eight-bit parallel signal followed by a conversion to a serial signal for transmitting to a remote location and then reconverting each of the companded signals to a first-eight-bit parallel signal. The eight-bit parallel signal is fed to one input of a pre-programmed ROM. This eight-bit signal provides one-half of a sixteen-bit address of a lookup ROM. The other half of the sixteen-bit ROM address is supplied by another suscriber over an identical circuit.

Byrne, F.↗
NASA NTRS1988

Monolithic GaAs digitizer for space-based laser pulse spreading effect

A 6-bit 1-GHz digitizer was designed to analyze the 1-ns pulse spreading effects in a space based altimeter. The digitizer consisted of four 4-bit flash A/D converters and a 6-bit encoder. Also, the converter utilized four 4-bit converters and a 4-to-6 bit encoder to achieve 6 bit resolution at the 1 GHz sample rate. The design was unique because it utilized only the inverters and NOR gates for the converters and encoder, hence it could be fabricated using the existing state-of-the-art GaAs processing techniques. This GHz digitizer has many commercial applications. It could be applicable to: (1) digital microwave transmission system for the telecommunication industries, (2) pulse monitoring in high kinetic chemical reactions, (3) transient signals in the medical field, and (4) microwave signals in astronomy.

Lao, Bennig↗
NASA NTRS1994

Modulation and synchronization technique for MF-TDMA system

This report addresses modulation and synchronization techniques for a multi-frequency time division multiple access (MF-TDMA) system with onboard baseband processing. The types of synchronization techniques analyzed are asynchronous (conventional) TDMA, preambleless asynchronous TDMA, bit synchronous timing with a preamble, and preambleless bit synchronous timing. Among these alternatives, preambleless bit synchronous timing simplifies onboard multicarrier demultiplexer/demodulator designs (about 2:1 reduction in mass and power), requires smaller onboard buffers (10:1 to approximately 3:1 reduction in size), and provides better frame efficiency as well as lower onboard processing delay. Analysis and computer simulation illustrate that this technique can support a bit rate of up to 10 Mbit/s (or higher) with proper selection of design parameters. High bit rate transmission may require Doppler compensation and multiple phase error measurements. The recommended modulation technique for bit synchronous timing is coherent QPSK with differential encoding for the uplink and coherent QPSK for the downlink.

Faris, Faris↗
NASA NTRS1987

Neighborhood comparison operator

Digital values in a moving window are compared by an operator having nine comparators (18) connected to line buffers (16) for receiving a succession of central pixels together with eight neighborhood pixels. A single bit of program control determines whether the neighborhood pixels are to be compared with the central pixel or a threshold value. The central pixel is always compared with the threshold. The comparator output, plus 2 bits indicating odd-even pixel/line information about the central pixel, addresses a lookup table (20) to provide 14 bits of information, including 2 bits which control a selector (22) to pass either the central pixel value, the other 12 bits of table information, or the bit-wise logic OR of all neighboring pixels.

Gennery, Donald B.↗
NASA NTRS1988

Alignment system for encoders

An improved encoder alignment system is disclosed which provides an indication of the extent of misalignment and a measure of the rate at which the misalignment may be changing. The invention is adapted for use with a conventional encoder which provides a digital coarse word having at least significant bit and a digital fine word having a least significant bit and a most significant bit. The invention generates the exclusive or of the least significant bit of the coarse digital signal and the least significant bit of the fine digital signal to provide a first signal. The invention then generates the exclusive or of the first signal and the complement of the most significant bit of the fine digital signal to provide an output signal which represents the misalignment of the encoder.

Villani, Daniel D.↗
NASA NTRS2008

Ultrasonic/Sonic Impacting Penetrators

Ultrasonic/sonic impacting penetrators (USIPs) are recent additions to the series of apparatuses based on ultrasonic/sonic drill corers (USDCs). A USIP enables a rod probe to penetrate packed soil or another substance of similar consistency, without need to apply a large axial force that could result in buckling of the probe or in damage to some buried objects. USIPs were conceived for use in probing and analyzing soil to depths of tens of centimeters in the vicinity of buried barrels containing toxic waste, without causing rupture of the barrels. USIPs could also be used for other purposes, including, for example, searching for pipes, barrels, or other hard objects buried in soil; and detecting land mines. USDCs and other apparatuses based on USDCs have been described in numerous previous NASA Tech Briefs articles. The ones reported previously were designed, variously, for boring into, and/or acquiring samples of, rock or other hard, brittle materials of geological interest. To recapitulate: A USDC can be characterized as a lightweight, low-power, piezoelectrically driven jackhammer in which ultrasonic and sonic vibrations are generated and coupled to a tool bit. As shown in the figure, a basic USDC includes a piezoelectric stack, a backing and a horn connected to the stack, a free mass (free in the sense that it can slide axially a short distance between the horn and the shoulder of tool bit), and a tool bit, i.e., probe for USIP. The piezoelectric stack is driven at the resonance frequency of the stack/horn/backing assembly to create ultrasonic vibrations that are mechanically amplified by the horn. To prevent fracture during operation, the piezoelectric stack is held in compression by a bolt. The bouncing of the free mass between the horn and the tool bit at sonic frequencies generates hammering actions to the bit that are more effective for drilling than is the microhammering action of ultrasonic vibrations in ordinary ultrasonic drills. The hammering actions are so effective that the axial force needed to make the tool bit advance into the material of interest is much smaller than in ordinary twist drilling, ultrasonic drilling, or ordinary steady pushing.

Bao, Xiaoqi↗
NASA NTRS2008

Fault-Tolerant Coding for State Machines

Two reliable fault-tolerant coding schemes have been proposed for state machines that are used in field-programmable gate arrays and application-specific integrated circuits to implement sequential logic functions. The schemes apply to strings of bits in state registers, which are typically implemented in practice as assemblies of flip-flop circuits. If a single-event upset (SEU, a radiation-induced change in the bit in one flip-flop) occurs in a state register, the state machine that contains the register could go into an erroneous state or could hang, by which is meant that the machine could remain in undefined states indefinitely. The proposed fault-tolerant coding schemes are intended to prevent the state machine from going into an erroneous or hang state when an SEU occurs. To ensure reliability of the state machine, the coding scheme for bits in the state register must satisfy the following criteria: 1. All possible states are defined. 2. An SEU brings the state machine to a known state. 3. There is no possibility of a hang state. 4. No false state is entered. 5. An SEU exerts no effect on the state machine. Fault-tolerant coding schemes that have been commonly used include binary encoding and "one-hot" encoding. Binary encoding is the simplest state machine encoding and satisfies criteria 1 through 3 if all possible states are defined. Binary encoding is a binary count of the state machine number in sequence; the table represents an eight-state example. In one-hot encoding, N bits are used to represent N states: All except one of the bits in a string are 0, and the position of the 1 in the string represents the state. With proper circuit design, one-hot encoding can satisfy criteria 1 through 4. Unfortunately, the requirement to use N bits to represent N states makes one-hot coding inefficient.

Naegle, Stephanie Taft↗
NASA NTRS2010

Ultrasonic rotary-hammer drill

A mechanism for drilling or coring by a combination of sonic hammering and rotation. The drill includes a hammering section with a set of preload weights mounted atop a hammering actuator and an axial passage through the hammering section. In addition, a rotary section includes a motor coupled to a drive shaft that traverses the axial passage through the hammering section. A drill bit is coupled to the drive shaft for drilling by a combination of sonic hammering and rotation. The drill bit includes a fluted shaft leading to a distal crown cutter with teeth. The bit penetrates sampled media by repeated hammering action. In addition, the bit is rotated. As it rotates the fluted bit carries powdered cuttings helically upward along the side of the bit to the surface.

Bar-Cohen, Yoseph↗
NASA NTRS2012

Free-Mass and Interface Configurations of Hammering Mechanisms

A series of free-mass designs for the ultrasonic/ sonic driller/corer (USDC) has been developed to maximize the transfer of energy from the piezoelectric transducer through the horn to the bit, as well as to minimize potential jamming. A systematic development was made producing novel designs of free-mass configurations where the impact force is spread across a minimal area maximizing the impact on the bit. The designed free masses were made to operate at high temperatures (500 C) as on Venus, and they can be made to operate at extremely low temperature, too. In normal operation, the free mass bounces between the horn and the bit, impacting both repeatedly. The impact stress profile, maximum stress, contact time duration, and the required yielding stress for the materials of the free mass, bit, and horn are all affected by the contact area. A larger contact area results in lower stress in the contact region, and avoids yielding of the materials. However, before the excitation voltage is applied to the transducer, the horn, free mass, and the bit are pressed together. Larger contact area results in a stronger coupling of the bit to the horn transducer, which greatly changes the vibration characteristics of the transducer, and makes the USDC difficult to start. To obtain optimum performance, a catalog of free-mass designs is required, allowing maximum flexibility during trade-off for these conflicting contact area requirements. For this purpose, seven different designs were conceived: point contacts, circular contacts, point/circular contacts, line contacts, ring contacts, line/ring contacts, and dashed line contacts. Besides point/circular and line/ring contacts, the free mass can be designed as any of the above shapes. Depending on the ratio of the diameter to the height, and the free-mass retention method used (the cup or rod), the free mass can be configured with one or more sliding surfaces on the outside or inside diameter surface or both. Matching horn tips and free mass may also offer some utility in maximizing the stress pulse.

Bao, Xiaoqi↗
NASA NTRS1974

Basic memory module

Construction and electrical characterization of the 4096 x 2-bit Basic Memory Module (BMM) are reported for the Space Ultrareliable Modular Computer (SUMC) program. The module uses four 2K x 1-bit N-channel FET, random access memory chips, called array chips, and two sense amplifier chips, mounted and interconnected on a ceramic substrate. Four 5% tolerance power supplies are required. At the Module, the address, chip select, and array select lines require a 0-8.5 V MOS signal level. The data output, read-strobe, and write-enable lines operate at TTl levels. Although the module is organized as 4096 x 2 bits, it can be used in a 8196 x 1-bit application with appropriate external connections. A 4096 x 1-bit organization can be obtained by depopulating chips.

Tietze, F. C.↗
NASA NTRS1979

Digital data reformatter/deserializer

A method and apparatus is presented for reformatting and de-serializing a serially-received sequence of data words, each consisting of a fixed number of binary data bits. A block of nm bits is serially fed into a shift register or serially-connected group of shift registers. In lieu of the(nm-1)th shifts, the bits are rearranged within the shift register in parallel fashion, according to a prescribed scheme. Shifting then continues, until the first bit of each data word appears in the last bit position in the shift register, at which time that data word is shifted in parallel into an output buffer stage, from which it is outputted in parallel, after a fixed delay.

Engel, A.↗
NASA NTRS1977

Minimax decoding of cyclic block codes

A minimax decoding algorithm utilizing soft bit detection of an (n,k) cyclic block code is described which will permit the correction of up to n-k bit errors interspersed at random locations throughout the block. The decoding solution consists of: (1) identifying the ordered soft bit set and, (2) finding the minimum order solution to the resulting syndrome equations where the nonzero error vector components are constrained to be a subset of the soft bit set. An efficient implementation of the decoding operation is described. In essence, this algorithm focuses the correction capability of the code on those bit positions which have the lowest a posteriori probabilities of correct detection.

Greene, E. P.↗