scholarly journals Reduction of gravity effect on the results of low-frequency accelerometer calibration

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 365
Author(s):  
G. P. Ripper ◽  
C. D. Ferreira ◽  
R. S. Dias ◽  
G. B. Micheli
Keyword(s):  
Approximation Method ◽  
Low Frequency ◽  
Systematic Errors ◽  
Experimental Results ◽  
Vibration Exciter ◽  
Air Bearing ◽  
Gravity Effect ◽  
Calibration System ◽  
Low Frequencies ◽  
Bearing Vibration

This paper describes a study on the possible sources of systematic errors during the calibration of accelerometers at low-frequencies. This study was carried out on a primary calibration system that uses an air-bearing vibration exciter APS Dynamics 129 and applying the sine-approximation method. Tests performed and actions taken to reduce the effect on experimental results are presented.

scholarly journals Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction

2020 ◽  
Vol 10 (24) ◽  
pp. 8902
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Experimental Results ◽  
Multimedia Content ◽  
The Novel ◽  
Element Analysis ◽  
Low Frequencies ◽  
Acoustic Performance ◽  
Technological Developments ◽  
New Type

In the era of multimedia devices, smartphones have become the primary device for consuming multimedia content. As technological developments have facilitated a more immersive multimedia experience, enlarged displays and the use of several sensors have limited the allowable size of microspeakers. Although sound plays an important role when consuming multimedia content, the limited space for microspeakers in modern devices leads to poor acoustic performance, especially at low frequencies. To address this issue, this paper proposes a novel microspeaker structure that enhances the low-frequency sound pressure level (SPL), while also featuring reduced exterior dimensions. The structure was designed and analyzed using 3D finite element analysis. Through coupling analysis, the simulation results were verified on the basis of the experimental results. The novel microspeaker has one outer magnet surrounding the entire coil, unlike in prototype microspeakers, which have two outer magnets. The gap between the top plates and coil is reduced, and a new type of coil is introduced for the purpose of increasing electromagnetic force. The samples were manufactured, and their SPLs were tested in an anechoic chamber. The experimental results prove that the proposed microspeaker offers an improved SPL at low frequencies compared with prototype microspeakers.

scholarly journals The effect of the ionosphere on ultra-low-frequency radio-interferometric observations

2018 ◽  
Vol 615 ◽  
pp. A179 ◽  
Author(s):  
F. de Gasperin ◽  
M. Mevius ◽  
D. A. Rafferty ◽  
H. T. Intema ◽  
R. A. Fallows
Keyword(s):  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Systematic Errors ◽  
Electron Content ◽  
Satellite Measurements ◽  
Third Order ◽  
Low Frequencies ◽  
Total Electron ◽  
Main Driver ◽  
Systematic Effects

Context. The ionosphere is the main driver of a series of systematic effects that limit our ability to explore the low-frequency (<1 GHz) sky with radio interferometers. Its effects become increasingly important towards lower frequencies and are particularly hard to calibrate in the low signal-to-noise ratio (S/N) regime in which low-frequency telescopes operate. Aims. In this paper we characterise and quantify the effect of ionospheric-induced systematic errors on astronomical interferometric radio observations at ultra-low frequencies (<100 MHz). We also provide guidelines for observations and data reduction at these frequencies with the LOw Frequency ARray (LOFAR) and future instruments such as the Square Kilometre Array (SKA). Methods. We derive the expected systematic error induced by the ionosphere. We compare our predictions with data from the Low Band Antenna (LBA) system of LOFAR. Results. We show that we can isolate the ionospheric effect in LOFAR LBA data and that our results are compatible with satellite measurements, providing an independent way to measure the ionospheric total electron content (TEC). We show how the ionosphere also corrupts the correlated amplitudes through scintillations. We report values of the ionospheric structure function in line with the literature. Conclusions. The systematic errors on the phases of LOFAR LBA data can be accurately modelled as a sum of four effects (clock, ionosphere first, second, and third order). This greatly reduces the number of required calibration parameters, and therefore enables new efficient calibration strategies.

scholarly journals SYNTHESIS OF THE LOW-FREQUENCY VIBRATION EXCITER

2021 ◽  
Vol 3 ◽  
pp. 66-71
Author(s):  
Dmitry Fedorov ◽  
Andrey Khitrov ◽  
Evgeny Veselkov ◽  
Yuliya Domracheva ◽  
Oksana Kozyreva
Keyword(s):  
Control System ◽  
Low Frequency ◽  
Magnetic Suspension ◽  
National Standard ◽  
Vibration Exciter ◽  
Magnetic Conductor ◽  
Low Frequencies ◽  
Modern Equipment ◽  
Mobile Part ◽  
Low Frequency Vibration

The article is devoted to synthesis of the low-frequency vibration exciter for checking of sensors of acceleration. In many areas of the modern equipment sensors of acceleration working in very low range of frequencies are widely used. For checking and graduation of such sensors the vibration exciter capable to provide rectilinear horizontal harmonic oscillations of the calibrated accelerometer in so low range of frequencies are required. Low frequencies of fluctuations cause the necessity of creation of big amplitudes of movements for ensuring the acceptable values of amplitudes of accelerations. The low-frequency electrodynamic vibration exciter with a magnetic suspension of mobile part which is a component of the National Standard of the vibration movement of the Russian Federation is so far created. However, development of the modern equipment demands expansion of frequency ranges to the area of ultralow frequencies. One of requirements shown to the vibration exciter working in the ultralow range of frequencies is increase in amplitude of horizontal movements of a mobile part as with small amplitudes the speed and acceleration of the harmonious law of the movements proportional according to the frequency of fluctuations and a square of this frequency, will have small amplitude values. One of problems of realization of a control system of the electric drive of the vibration exciter consists in that a mobile part possesses indifferent position of balance. The centre of fluctuations of a mobile part is not defined and can be in any point on magnetic conductor length. That fluctuations had the steady centre in an average point of a magnetic conductor without use of a mechanical spring, the drive is supplied with an additional control system of fluctuations, or a so-called electromagnetic spring.

scholarly journals Development of a tri-axial primary vibration calibration system

ACTA IMEKO ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 33 ◽  
Author(s):  
Zhihua Liu ◽  
Chenguang Cai ◽  
Ming Yang ◽  
Mei Yu
Keyword(s):  
Sampling Method ◽  
Cross Coupling ◽  
Measuring System ◽  
Vibration Exciter ◽  
Air Bearing ◽  
Calibration System ◽  
Band Pass ◽  
The Cross ◽  
Set Up ◽  
Relationship Of

A tri-axial primary vibration calibration system has been set up at National Institute of Metrology for simultaneous calibration of motion transducers. The system is driven by three electrodynamics exciters that are mounted along the three orthogonal axes. The cross-coupling unit based on air bearing is developed for force transferring and motion guiding. Spatial orbit vibration is composited from sine vibration components of the three orthogonal axes. Relationship of shapes and orientations of spatial orbits and amplitudes and phases of sine vibration components is discussed. Multi-exciter vibration control for both cross-coupling compensation and amplitudes and phases control of sine vibration components is investigated. The tri-axial measuring system can simultaneously measure the three orthogonal vibration quantities based on the band-pass sampling method. The experiments show that a variety of spatial orbits can be generated by efficiently reducing the cross-coupling of the tri-axial vibration exciter and the magnitude and the phase shift of sensitivities of a tri-axis accelerometer can be determined.

scholarly journals A low-acceleration measurement using anti-vibration table with low-frequency resonance

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 369
Author(s):  
T. Shimoda ◽  
W. Kokuyama ◽  
H. Nozato
Keyword(s):  
Vibration Isolation ◽  
Low Frequency ◽  
Ground Vibration ◽  
Vibration Exciter ◽  
Calibration System ◽  
Acceleration Measurement ◽  
Isolation System ◽  
Vibration Isolation System ◽  
Infrastructure Monitoring ◽  
Vibration Transmissibility

This manuscript describes how NMIJ isolates interferometer optics from the ground vibration for low-acceleration measurement by installing an anti-vibration table. Such a vibration isolation system is designed for an accelerometer calibration system to reduce vibration noise from the microtremor or from reaction of the vibration exciter. Mitigating the vibration of optics enables evaluation of accelerometers at small amplitudes, which is required in aerospace or infrastructure monitoring applications. In this manuscript, vibration transmissibility of the anti-vibration table is measured using a triaxial seismometer, and its benefit in the calibration system is discussed.

Gravity Effect on the Formation of Periodic Precipitation Patterns

2000 ◽  
Vol 65 (9) ◽  
pp. 1438-1442 ◽  
Author(s):  
Vladislav Holba ◽  
Frederik Fusek
Keyword(s):  
Gravitational Field ◽  
Spatial Arrangement ◽  
Experimental Results ◽  
Single Sample ◽  
Gravity Effect ◽  
Periodic Precipitation ◽  
Precipitation Patterns ◽  
Liesegang Bands

The effect of gravity on the formation of Liesegang patterns of Ag2Cr2O7in gelatin and that of PbI2in agar was investigated. Spatial arrangement of Liesegang bands was measured in the parallel and antiparallel orientation to the gravitational field in a single sample with all other parameters kept fixed. The experimental results are discussed in terms of the prenucleation theory of periodic precipitation.

scholarly journals A Multi-Mode Broadband Vibration Energy Harvester Composed of Symmetrically Distributed U-Shaped Cantilever Beams

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 203
Author(s):  
Xiaohua Huang ◽  
Cheng Zhang ◽  
Keren Dai
Keyword(s):  
Energy Harvester ◽  
Low Frequency ◽  
Experimental Results ◽  
Vibration Energy ◽  
Cantilever Beams ◽  
Resonant Frequencies ◽  
Promising Alternative ◽  
Piezoelectric Energy ◽  
Straight Beam ◽  
Resonance Frequencies

Using the piezoelectric effect to harvest energy from surrounding vibrations is a promising alternative solution for powering small electronic devices such as wireless sensors and portable devices. A conventional piezoelectric energy harvester (PEH) can only efficiently collect energy within a small range around the resonance frequency. To realize broadband vibration energy harvesting, the idea of multiple-degrees-of-freedom (DOF) PEH to realize multiple resonant frequencies within a certain range has been recently proposed and some preliminary research has validated its feasibility. Therefore, this paper proposed a multi-DOF wideband PEH based on the frequency interval shortening mechanism to realize five resonance frequencies close enough to each other. The PEH consists of five tip masses, two U-shaped cantilever beams and a straight beam, and tuning of the resonance frequencies is realized by specific parameter design. The electrical characteristics of the PEH are analyzed by simulation and experiment, validating that the PEH can effectively expand the operating bandwidth and collect vibration energy in the low frequency. Experimental results show that the PEH has five low-frequency resonant frequencies, which are 13, 15, 18, 21 and 24 Hz; under the action of 0.5 g acceleration, the maximum output power is 52.2, 49.4, 61.3, 39.2 and 32.1 μW, respectively. In view of the difference between the simulation and the experimental results, this paper conducted an error analysis and revealed that the material parameters and parasitic capacitance are important factors that affect the simulation results. Based on the analysis, the simulation is improved for better agreement with experiments.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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