scholarly journals Μελέτη, ανάλυση και βελτίωση της λειτουργίας αερομεταφερόμενου ραντάρ συνθετικής απεικόνισης (SAR) χαμηλών συχνοτήτων

2002 ◽  
Author(s):  
Αθανάσιος Πότσης
Keyword(s):  
Data Processing ◽  
High Performance ◽  
Dynamic Range ◽  
Low Frequency ◽  
Low Noise ◽  
Electromagnetic Spectrum ◽  
System Operation ◽  
Low Frequencies ◽  
Technological Advances ◽  
Sar Data

Because of its high resolution, frequency scattering properties and indifference to day/night or cloud cover, Synthetic Aperture Radar (SAR) has become into vogue in the last years. The field of SAR remote sensing has changed dramatically with the operational introduction of new high performance signal processing techniques and new operational modes, like the polarimetry in 1980’s and the interferometry in 1990’s. Additionally, technological advances in antenna design, low noise amplifiers, band-pass filters, digital receiver technology and high frequency digital sampling devises, increase the availability and the performance of airborne as well as spaceborne SAR sensors. All these technological advances result to real time SAR system operation and in most of the frequency bands of the electromagnetic spectrum. These advanced hardware components combined with the new radar techniques result to large variety of operational and research applications. In several of the new coming applications there is the need for a SAR system to penetrate vegetation and foliage. As a result of this, a new class of SAR systems, using low frequencies, has emerged. The combination of low frequency with high bandwidth allows a variety of new military as well as civilian applications. In the frame of this thesis, several hardware and software modifications made in the E-SAR P-Band system operated by DLR aiming the improvement of the collected and processed data quality is described. The basic P-Band inherent problems like the low Signal-To-Noise-Ratio (SNR), the presence of Radio Frequency Interferences (RFI) as well as the high dynamic range of the backscattered signal are addressed. A new mode of operation called “Listen Only” (LO) channel mode gave us the unique opportunity to study and analyze the special characteristics of the interfering signals and the nature of the low frequency backscattered signal. Based on this analysis new RFI suppression algorithms have been developed and the system operation parameters have been set to the correct value resulting to high quality collected data. The effect of RFI signals in fully polarimetric SAR data processing and applications are analyzed in detail. One of the principal items of this thesis is the development of a new robust sub-aperture algorithm for improved Motion Compensation (MoCo) in wide azimuth beam SAR data processing. The new algorithm is incorporated to the Extended Chirp Scaling SAR data processing algorithm. The improved MoCo algorithm results to focused images with high SNR, contrast, higher resolution and better geometric correctness. The performance and the correction accuracy of the proposed algorithms are analyzed by using mainly real data collected by the E-SAR system of DLR.

Preamplifier With Ultra Low Frequency Cutoff for Infrasonic Condenser Microphone

2012 ◽  
Author(s):  
Rasmus Trock Kinnerup ◽  
Arnold Knott ◽  
Ole Cornelius Thomsen ◽  
Kresten Marbjerg ◽  
Per Rasmussen
Keyword(s):  
Input Impedance ◽  
Dynamic Range ◽  
Cutoff Frequency ◽  
Low Frequency ◽  
Input Resistance ◽  
Bias Current ◽  
Microphone Signal ◽  
Low Frequencies ◽  
Pass Filter ◽  
Condenser Microphone

Measuring infrasonic sound sets high requirements on the instruments used. Typically the measurement chain consists of a microphone and a preamplifier. As the input resistance of the preamplifier forms a high pass filter with the capacitance of the microphone in the picofarad range, measuring ultra low frequencies becomes a challenge. The electric preamplifier presented in this paper together with a prepolarized condenser microphone form a measurement system. The developed preamplifier connects the microphone signal directly to the input of an operational amplifier with ultra high input impedance. The bias current for the preamplifier further complicates the signal amplification. A configuration of two diode-connected FETs provide the input bias current. The resulting input impedance of nearly 1 TΩ yields a total lower limiting −3 dB cutoff frequency of 8 mHz and a dynamic range of 95 dB. Being able to measure down to ultra low frequencies in the infrasonic frequency range will aid actors in the debate on wind turbine noise. Sonic booms from supersonic flights include frequencies down to 10 mHz and the preamplifier proposed in this paper will aid scientists trying to modify the N-shaped shock wave at high level which prohibits flights in land zones.

Localizing the Source of Type II Emission Around a CME with the Sun Radio Interferometer Space Experiment (SunRISE) and MHD Simulations

2021 ◽  
Author(s):  
Alexander Hegedus ◽  
Ward Manchester ◽  
Justin Kasper ◽  
Joseph Lazio ◽  
Andrew Romero-Wolf
Keyword(s):  
Data Processing ◽  
Low Frequency ◽  
Solar Energetic Particle ◽  
Radio Interferometer ◽  
Valuable Insight ◽  
Type Ii ◽  
Plasma Parameters ◽  
Low Frequencies ◽  
The Earth ◽  
Type Ii Bursts

<p>The Earth’s Ionosphere limits radio measurements on its surface, blocking out any radiation below 10 MHz. Valuable insight into many astrophysical processes could be gained by having a radio interferometer in space to image the low frequency window, which has never been achieved. One application for such a system is observing type II bursts that track solar energetic particle acceleration occurring at Coronal Mass Ejection (CME)-driven shocks. This is one of the primary science targets for SunRISE, a 6 CubeSat interferometer to circle the Earth in a GEO graveyard orbit. SunRISE is a NASA Heliophysics Mission of Opportunity that began Phase B (Formulation) in June 2020, and plans to launch for a 12-month mission in mid-2023. In this work we present an update to the data processing and science analysis pipeline for SunRISE and evaluate its performance in localizing type II bursts around a simulated CME.</p><p>To create realistic virtual type II input data, we employ a 2-temperature MHD simulation of the May 13th 2005 CME event, and superimpose realistic radio emission models on the CME-driven shock front, and propagate the signal through the simulated array. Data cuts based on different plasma parameter thresholds (e.g. de Hoffman-Teller velocity and angle between shock normal and the upstream magnetic field) are tested to get the best match to the true recorded emission.  This model type II emission is then fed to the SunRISE data processing pipeline to ensure that the array can localize the emission. We include realistic thermal noise dominated by the galactic background at these low frequencies, as well as new sources of phase noise from positional uncertainty of each spacecraft. We test simulated trajectories of SunRISE and image what the array recovers, comparing it to the virtual input, finding that SunRISE can resolve the source of type II emission to within its prescribed goal of 1/3 the CME width. This shows that SunRISE will significantly advance the scientific community’s understanding of type II burst generation, and consequently, acceleration of solar energetic particles at CMEs.  This unique combination of SunRISE observations and MHD recreations of space weather events will allow an unprecedented look into the plasma parameters important for these processes. </p>

Influence of Materials on the Performance Limits of Microactuators

2007 ◽  
Vol 1052 ◽  
Author(s):  
Prasanna Srinivasan ◽  
S. Mark Spearing
Keyword(s):  
Thin Films ◽  
Shape Memory ◽  
High Performance ◽  
Low Frequency ◽  
Beam Theory ◽  
Performance Limits ◽  
Low Frequencies ◽  
Thermal Actuators ◽  
Work Volume ◽  
Selection Of

AbstractThe selection of actuators at the micro-scale requires an understanding of the performance limits of different actuation mechanisms governed by the optimal selection of materials. This paper presents the results of analyses for elastic bi-material actuators based on simple beam theory and lumped parameter thermal models. Comparisons are made among commonly employed actuation schemes (electro-thermal, piezoelectric and shape memory) at micro scales and promising candidate materials are identified. Polymeric films on Si subjected to electro-thermal heating are optimal candidates for high displacement, low frequency devices while ferroelectric thin films of Pb-based ceramics on Si/ DLC are optimal for high force, high frequency devices. The ability to achieve ∼10 kHz at scales < 100μm make electro-thermal actuators competitive with piezoelectric actuators considering the low work/volume obtained in piezoelectric actuation (∼ 10−8J.m−3.mV−2). Although shape memory alloy (SMA) actuators such as Ni-Ti on Si deliver larger work (∼ 1 J.m−3K−2) than electro-thermal actuators at relatively low frequencies (∼ 1 kHz), the critical scale associated with the cessation of the shape memory effect forms the bounding limit for the actuator design. The built-in compressive stress levels (∼ 1GPa) in thin films of Si and DLC could be exploited for realizing a high performance actuator by electro-thermal buckling.

scholarly journals Computer simulation of low‐frequency electromagnetic data acquisition

Geophysics ◽  
1983 ◽  
Vol 48 (9) ◽  
pp. 1219-1232 ◽  
Author(s):  
William A. San Filipo ◽  
Gerald W. Hohmann
Keyword(s):  
Computer Simulation ◽  
Data Acquisition ◽  
Dynamic Range ◽  
Low Frequency ◽  
Noise Removal ◽  
Digital Data ◽  
Low Frequencies ◽  
Pass Filter ◽  
Natural Field ◽  
Field Noise

Computer simulation of low‐frequency electromagnetic (EM) digital data acquisition in the presence of natural field noise demonstrates several important limitations and considerations. Without a remote reference noise removal scheme, it is difficult to obtain an adequate ratio of signal to noise below 0.1 Hz for frequency‐domain processing and below 0.3 Hz base frequency for time‐domain processing for a typical source‐receiver configuration. A digital high‐pass filter substantially facilitates rejection of natural field noise above these frequencies; however, at lower frequencies where much longer stacking times are required, it becomes ineffective. Use of a remote reference to subtract natural field noise extends these low‐frequency limits by one decade, but the remote reference technique is limited by the resolution and dynamic range of the instrumentation. Gathering data in short segments so that natural field drift can be offset for each segment allows a higher gain setting to minimize dynamic range problems. The analysis is also applicable to the induced polarization technique in which similar problems arise at low frequencies in the presence of telluric noise.

scholarly journals Digital signal processsing functions for ultra-low frequency calibrations

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 374
Author(s):  
Henrik Ingerslev ◽  
Soren Andresen ◽  
Jacob Holm Winther
Keyword(s):  
Signal Processing ◽  
Low Frequency ◽  
Digital Signal ◽  
Low Noise ◽  
Key Comparison ◽  
Low Frequencies ◽  
Dual Channel ◽  
Ultra Low Noise ◽  
Lower Noise ◽  
Better Than

The demand from industry to produce accurate acceleration measurements down to ever lower frequencies and with ever lower noise is increasing. Different vibration transducers are used today for many different purposes within this area, like detection and warning for earthquakes, detection of nuclear testing, and monitoring of the environment. Accelerometers for such purposes must be calibrated in order to yield trustworthy results and provide traceability to the SI-system accordingly. For these calibrations to be feasible, suitable ultra low-noise accelerometers and/or signal processing functions are needed. <br />Here we present two digital signal processing (DSP) functions designed to measure ultra low-noise acceleration in calibration systems. The DSP functions use dual channel signal analysis on signals from two accelerometers measuring the same stimuli and use the coherence between the two signals to reduce noise. Simulations show that the two DSP functions are estimating calibration signals better than the standard analysis. <br />The results presented here are intended to be used in key comparison studies of accelerometer calibration systems, and may help extend current general low frequency range from e.g. 100 mHz down to ultra-low frequencies of around 10mHz, possibly using somewhat same instrumentation.

Low Frequency Electrochemical Accelerometer with Low Noise Based on MEMS

2012 ◽  
Vol 503 ◽  
pp. 75-80 ◽  
Author(s):  
Wen Tao He ◽  
De Yong Chen ◽  
Guang Bei Li ◽  
Jun Bo Wang
Keyword(s):  
Early Warning ◽  
Dynamic Range ◽  
Low Frequency ◽  
Inertial Mass ◽  
Low Noise ◽  
Fabrication Process ◽  
Frequency Range ◽  
Wide Dynamic Range ◽  
Geological Disaster ◽  
Excellent Property

Petroleum prospecting and early warning of some geological disaster increasingly depend on the accelerometers which can detect vibrate of frequency below 1Hz, but it’s embarrassing that accelerometers based on Si or SiO2 structure make an awful performance in this frequency range. Electrochemical accelerometers were developed in 1990s. With fluidics to be inertial mass, electrochemical accelerometer not only show an excellent property in low frequency, but also has a wide dynamic range. However, traditional fabrication process of electrochemical accelerometer is rather complex and can’t eliminate the noise due to the inconsistency and asymmetry of electrodes. To solve these problems, a scheme based on MEMS is proposed here, including design, fabrication and package. Properties of electrochemical accelerometer (EAM) are tested in two conditions at last.

Low-frequency noise correlations in lateral pnp bipolar transistors

1992 ◽  
Vol 70 (10-11) ◽  
pp. 1112-1117
Author(s):  
A. Nathan ◽  
E. Charbon ◽  
W. Kung ◽  
A. Salim
Keyword(s):  
Integrated Circuit ◽  
Low Frequency ◽  
Intrinsic Noise ◽  
Low Noise ◽  
Bipolar Transistors ◽  
Current Gain ◽  
Low Noise Amplifiers ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies

Measurement results of low-frequency noise behaviour, and in particular, the noise correlations in lateral pnp bipolar transistors are presented for various bias conditions in both forward active and saturation regimes. The correlation in output collector noise is very high with a value close to unity only when the device is in medium injection. At extremely high injection, the degree of coherence degrades, depicting a behaviour similar to the forward current gain of the device. This degradation can be attributed to emitter-crowding effects. The correlation in output noise can be exploited to drastically suppress the intrinsic noise, particularly at low frequencies, making such devices useful for the input stage of amplifiers; the first step towards realisation of ultra low-noise amplifiers in standard integrated circuit technology.

scholarly journals Very low-frequency IEPE accelerometer calibration and application to a wind energy structure

2021 ◽  
Author(s):  
Clemens Jonscher ◽  
Benedikt Hofmeister ◽  
Tanja Grießmann ◽  
Raimund Rolfes
Keyword(s):  
Measurement Data ◽  
Low Frequency ◽  
Calibration Procedure ◽  
Low Noise ◽  
Energy Structure ◽  
Frequency Range ◽  
Low Frequencies ◽  
Iir Filters ◽  
Very Low Frequency ◽  
Ac Response

Abstract. In this work, we present an experimental setup for very low-frequency calibration measurements of low-noise Integrated Electronics Piezo Electric (IEPE) accelerometers and a customised signal conditioner design for using IEPE sensor down to 0.05Hz. AC-response IEPE accelerometer and signal conditioners have amplitude and phase deviations at low frequencies. As the standard calibration procedure in the low-frequency range is technically challenging, IEPE accelerometers with standard signal conditioners are usually used in frequency ranges above 1 Hz. Vibrations on structures with low eigenfrequencies like wind turbines are thus often monitored using DC-coupled micro-electro-mechanical systems (MEMS) capacitive accelerometers. This sensor type suffers from higher noise levels compared to IEPE sensors. To apply IEPE sensors instead of MEMS sensors, in this work the calibration of the entire measurement chain of three different IEPE sensors with the customised signal conditioner is performed with a low-frequency centrifuge. The IEPE sensors are modelled using IIR filters to apply the calibration to time-domain measurement data of a wind turbine support structure. This procedure enables an amplitude and phase-accurate vibration analysis with IEPE sensors in the low-frequency range down to 0.05 Hz.

A More Capable Array Infrastructure

2021 ◽  
Author(s):  
Tim Parker ◽  
Val Hamilton ◽  
Andrew Moores
Keyword(s):  
Dynamic Range ◽  
Low Noise ◽  
Low Frequencies ◽  
Corrosion Resistant ◽  
Dual Sensor ◽  
Local Earthquake ◽  
Array Performance ◽  
New Instruments ◽  
Higher Sensitivity

&lt;p&gt;A more capable infrastructure would enable greater monitoring capabilities. We propose a deeper grouted casing and using borehole best practices to ensure improved coupling and a better environment for reducing site and emplacement noise in both high and low frequencies and specifically the horizontal component recording. Casing emplacements should be a one to two day operation for installation. Stations using the new Trillium T120PH Slim or dual sensor Cascadia Slim in a single cased hole will have wider bandwidth, larger dynamic range, resiliency and low noise recording that would enable new observations along with higher sensitivity for local earthquake recording. Dry cased holes are the standard for long term geophysical observatories and a better investment when all the associated costs of operating observatories are considered. Facilities are both renewing old stations and trying to improve array performance through these new instruments.&amp;#160; This line of Trillium borehole instruments are very robust with low SWaP (Size, Weight and Power), a 300 meter continuous immersion rating and of corrosion resistant construction.&amp;#160; These sensors can be installed in bedding material or with a hole lock and are compatible with the ultimate installation, grouting it in!&lt;/p&gt;

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