Data Transfer for Multiple Sensor Networks

instrumentation
Data Transfer for Multiple Sensor Networks (LEW-TOPS-76)
Performs well over a broad temperature range
Overview
At extreme temperatures, few electronic components are available to support intelligent data transfer over a common, linear combining medium such as wire or the airwaves. NASA Glenn's innovation allows the operating frequency of a sensor instrument to be time variant because the sensor is part of the frequency generator's transfer function. Each instrument associated with a sensor imparts a unique (orthogonal) signature onto the continuous output of that sensor. As a consequence, the outputs of numerous instruments may be simultaneously superimposed upon one another via a linear combining medium and then be separated at a common receiving node in a more temperate location using any number of linear source separation techniques. A listening node, using various techniques, can pick out the signal from a single sender, if it has unique qualities; e.g., a "voice." This technique is analogous to the human brain recognizing and following a single conversation in a party full of people talking and other distracting noises.

The Technology
High-temperature sensors have been used in silicon carbide electronic oscillator circuits. The frequency of the oscillator changes as a function of changes in the sensor's parameters, such as pressure. This change is analogous to changes in the pitch of a person's voice. The output of this oscillator, and many others may be superimposed onto a single medium. This medium may be the power lines supplying current to the sensors, a third wire dedicated to data transmission, the airwaves through radio transmission, or an optical or other medium. However, with nothing to distinguish the identities of each source, this system is useless. Using frequency dividers and linear feedback shift registers, comprised of flip flops and combinatorial logic gates connected to each oscillator, unique bit stream codes may be generated. These unique codes are used to amplitude modulate the output of the sensor (both amplitude shift keying and on-off keying are applicable). By using a dividend of the oscillator frequency to generate the code, a constant a priori number of oscillator cycles will define each bit. At the receiver, a detected frequency will have associated with it a stored code pattern. Thus, a detected frequency will have a unique modulation pattern or "voice," disassociating it from noise and from other transmitting sensors. These codes may be pseudorandom binary sequences (PRBS), ASCII characters, gold codes, etc. The detected code length and frequency are measured, offering intelligent data transfer. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.
Oil Pump NASA Glenn's innovation has great potential for high temperature sensing in jet engines
Benefits
  • High temperature: Allows detection of desired sensor parameters at elevated temperatures
  • Efficient: Uses a gate count orders of magnitude less than if a full processor was embedded
  • Light weight: Allows many sensors to operate on the same wire bus

Applications
  • High temperature sensing in jet engines, missiles, and rockets
  • Deep hole sensing for energy extraction (oil, gas, geothermal)
  • Ground vehicle internal combustion engine sensing
Technology Details

instrumentation
LEW-TOPS-76
LEW-18910-1 LEW-18910-2
Similar Results
Front Image
Tunable Multi-Tone, Multi-Band, High-Frequency Synthesizer
Glenn's revolutionary new multi-tone, high-frequency synthesizer can enable a major upgrade in the design of high data rate, wide-band satellite communications links, in addition to the study of atmospheric effects. Conventional single-frequency beacon transmitters have a major limitation: they must assume that atmospheric attenuation and group delay effects are constant at all frequencies across the band of interest. Glenn's synthesizer overcomes this limitation by enabling measurements to be made at multiple frequencies across the entire multi-GHz wide frequency, providing much more accurate and actionable readings. This novel synthesizer consists of a solid-state frequency comb or harmonic generator that uses step-recovery semiconductor diodes to generate a broad range of evenly spaced harmonic frequencies, which are coherent and tunable over a wide frequency range. These harmonics are then filtered by a tunable bandpass filter and amplified to the necessary power level by a tunable millimeter-wave power amplifier. Next, the amplified signals are transmitted as beacon signals from a satellite to a ground receiving station. By measuring the relative signal strength and phase at ground sites the atmospheric induced effects can be determined, enabling scientists to gather essential climate data on hurricanes and climate change. In addition, the synthesizer can serve as a wideband source in place of a satellite transponder, making it easier to downlink high volumes of collected data to the scientific community. Glenn's synthesizer enables a beacon transmitter that, from the economical CubeSat platform, offers simultaneous, fast, and more accurate wideband transmission from space through the Earth's atmosphere than has ever been possible before.
Ground Station
Signal Combiner for Wideband Communication
Through low-loss signal combination, Glenn is leading the way to optimize radio transmission remotely during self-checking routines. Glenn's signal combiner offers a simple method to minimize signal loss significantly when combining two signals. Using conventional combiners in bit-error-rate testing results in a loss of 3 to 4 dB per band, and with a directional coupler the secondary signal experiences losses of 10 dB or more. Moreover, during signal measurements, the additional components must be placed and later removed to prevent any impact to the measurement, making for a cumbersome process. Glenn's solution is to combine the primary and secondary signals in the frequency domain through the use of a frequency division diplexer/multiplexer in combination with a wideband ADC. The multiplexer selects one or more bands in the frequency domain, and the ADC performs a non-linear conversion to digital domain by folding out-of-band signals in with the primary signal. NASA makes use of subsampling a given band within the ADC bandwidth to fold it into another band of interest, effectively frequency-shifting them to a common frequency bandwidth. Glenn's breakthrough method has two significant advantages over the conventional use of a power combiner or directional coupler in bit-error-rate testing: 1) it combines signal and noise (secondary signal) with very low loss, and 2) it enables the selection of the desired signal-to-noise ratio with no need for the later cumbersome removal of components. This streamlined process allows for invaluable in-situ or installed measurement. Glenn's novel technology has great potential for satellite, telecommunications, and wireless industries, especially with respect to equipment testing, measurement, calibration, and check-out.
Multi-colored Lasers
Optical Tunable-Based Transmitter for Multiple High-Frequency Bands
NASA Glenn's researchers have developed a means of transporting multiple radio frequency carriers through a common optical beam. In contrast to RF infrastructure systems alone, this type of hybrid RF/optical system can provide a very high data-capacity signal communication and significantly reduce power, volume, and complexity. Based on an optical wavelength division multiplexing (WDM) technique, in which optical wavelengths are generated by a tunable diode laser (TDL), the system enables multiple microwave bands to be combined and transmitted all in one unit. The WDM technique uses a different optical wavelength to carry each separate and independent high-frequency microwave band (e.g., L, C, X, Ku, Ka, Q, or higher bands). Since each RF carrier operates at a different optical wavelength, the tunable diode laser can, with the use of an electronic tunable laser controller unit, adjust the spacing wavelength and thereby minimize any crosstalk effect. Glenn's novel design features a tunable laser, configured to generate multiple optical wavelengths, along with an optical transmitter. The optical transmitter modulates each of the optical wavelengths with a corresponding RF band and then encodes each of the modulated optical wavelengths onto a single laser beam. In this way, the system can transmit multiple radio frequency bands using a single laser beam. Glenn's groundbreaking concept can greatly improve the system flexibility and scalability - not to mention the cost of - both ground and space communications.
Satellite Starry Sky
Multimode Directional Coupler
Glenn's researchers originally created the MDC to improve the beacon sources for atmospheric propagation studies. These studies are typically conducted to test atmospheric conditions to determine the signal strength needed for satellite communications. A low-power transmitter (e.g., a beacon source) is attached to the satellite, and transmits a continuous waveform (CW) signal to a receiving station on Earth. However, when a separate frequency is desired, building a new beacon source for the transmitter on the satellite - especially one that will operate at higher frequencies - presents numerous challenges. For one, a single-frequency beacon source requires a temperature-stabilized oscillator for frequency generation separate from that provided by the spacecraft receiver. To solve such problems, Glenn's innovators fabricated the MDC from two sections of waveguide: a primary waveguide for the fundamental frequency (Ku-band), and a secondary waveguide for the harmonics (Ka-band). These sections are joined together so that precision-machined slots in the second waveguide selectively couple the harmonics, for amplification and transmission. The harmonics can then be used as an additional beacon source with very small power losses to the fundamental signal. Once the separation takes place, the second or higher harmonic can be amplified and transmitted to a station on Earth. The efficiency and performance of the MDC can be optimized through appropriate computer modeling software and currently available high-precision fabrication techniques. Without the complexity and expense involved in building separate traveling wave tube amplifiers to generate additional frequencies, Glenn's MDC enables satellites to produce multiple signals that can be received by multiple stations - a significant leap forward in satellite productivity.
Fireman Burning Building
Polymer Electrolyte-Based Ambient Temperature Oxygen Microsensor
Conventional ambient-temperature oxygen sensors are limited in various ways: optically based sensors can be expensive and challenging to manufacture; electrochemical cells with liquid electrolytes can have limited lifetimes and become leak sources; and both types of sensors are difficult to miniaturize. These problems are addressed with Glenn's novel ambient temperature oxygen microsensor, which is based on a Nafiontm polymer electrolyte, microfabricated using thin-film technologies. In the past, one drawback of Nafiontm film has been that it can lose conductivity when the moisture content in the film is too low, potentially affecting sensor operation. Glenn researchers devised a method to use certain salts to hold water molecules in the Nafiontm film structure at room temperature. The presence of these salts provides extra sites in the film to promote proton (H+) mobility, thus improving film conductivity and overall sensor performance, particularly in arid and high-temperature environments. The innovative use of metal/metal oxide as the reference electrode enables miniaturization by eliminating the reference gas and sealing the reference electrode. The combination of interdigitized electrodes with the unique metal/metal oxide reference electrode permits sensor operation in either potentiometric or amperometric mode, as appropriate. In potentiometric mode, which measures voltage differences between working and reference electrodes in different gases, the voltage differences can be monitored with a voltmeter; however, the sensor itself does not need a power source. In room-temperature testing, the sensor achieved repeatable responses to 21 percent oxygen in nitrogen (using nitrogen as a baseline gas), and also detected oxygen from 7 to 21 percent, making Glenn's breakthrough technology usable for personal health monitoring as well as fire detection, fuel-leak detection, and environmental monitoring.
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