Limits of sensitivity of inertial seismometers with velocity transducers and electronic amplifiers

1990 ◽  
Vol 80 (6A) ◽  
pp. 1725-1752 ◽  
Author(s):  
Mark A. Riedesel ◽  
John A. Orcutt ◽  
Robert D. Moore
Keyword(s):  
Noise Level ◽  
Low Frequency ◽  
Noise Spectrum ◽  
Displacement Transducer ◽  
Ocean Bottom ◽  
Good Resolution ◽  
Low Frequencies ◽  
Amplifier Noise ◽  
Order Of Magnitude ◽  
Ground Noise

Abstract Portable instruments such as ocean bottom seismographs and the PASSCAL recorders often use rugged, portable geophones. The desire to use such sensors for relatively low-frequency work has raised questions about the limits of their sensitivity. The lower and upper frequency limits of performance of seismic sensors are determined by the sensor's mass, period, and Q, and by the amplifiers used with those sensors. We have tested Mark Products 1 Hz, 2 Hz, and 4.5 Hz velocity transducers against Streckeisen seismometers in order to examine the limits of their performance in measuring ground noise, particularly at low frequencies. Among the velocity transducers, only the 1 Hz Mark Products L-4 sensor provided good resolution of the 6-sec microseism peak. For this sensor, the lower limits of sensitivity was at approximately 0.06 Hz, although this depends on the amplifier used and the noise level at a given site. The amplifiers examined included conventional, low power, and commutating auto-zero operational amplifiers. It was found that the noise levels of the amplifiers intersected the ground noise level at frequencies ranging between 0.06 and 0.2 sec, depending on the amplifier and the exact circuit design. Measurements indicated that by modeling the amplifier noise for a given circuit correctly, the performance of an amplifier can be predicted with a high degree of accuracy, obviating the need for actual circuit construction to determine performance in the field. Given the very steep slope of the ground noise spectrum between 0.05 and 0.1 Hz and the rapid fall off in a seismometer's output below its resonant frequency, it would require a lowering of amplifier noise by more than an order of magnitude to be able to resolve ground noise at frequencies lower than 0.05 Hz using relatively small geophones such as the L-4. To resolve ground noise at lower frequencies, it is necessary to use a seismometer with a displacement transducer to sense the mass position, such as Guralp or Streckeisen sensors.

Characteristics of Low-Frequency Horizontal Noise of Ocean-Bottom Seismic Data

2021 ◽  
Author(s):  
Chao An ◽  
Chen Cai ◽  
Lei Zhou ◽  
Ting Yang
Keyword(s):  
Water Waves ◽  
Noise Source ◽  
Random Noise ◽  
Low Frequency ◽  
Ocean Bottom ◽  
Coherent Noise ◽  
Infragravity Waves ◽  
Low Frequencies ◽  
Bottom Currents ◽  
Ocean Bottom Seismographs

Abstract Horizontal records of ocean-bottom seismographs are usually noisy at low frequencies (< 0.1 Hz). The noise source is believed to be associated with ocean-bottom currents that may tilt the instrument. Currently horizontal records are mainly used to remove the coherent noise in vertical records, and there has been little literature that quantitatively discusses the mechanism and characteristics of low-frequency horizontal noise. In this article, we analyze in situ ocean-bottom measurements by rotating the data horizontally and evaluating the coherency between different channels. Results suggest that the horizontal noise consists of two components, random noise and principle noise whose direction barely changes in time. The amplitude and the direction of the latter are possibly related to the intensity and direction of ocean-bottom currents. Rotating the horizontal records to the direction of the principle noise can largely suppress the principle noise in the orthogonal horizontal channel. In addition, the horizontal noise is incoherent with pressure, indicating that the noise source is not ocean surface water waves (infragravity waves). At some stations in shallow waters (<300 m), horizontal noise around 0.07 Hz is found to be linearly proportional to the temporal derivative of pressure, which is explained by forces of added mass due to infragravity waves.

scholarly journals Effects of impulse noise from small arms on the organ of hearing when anti-noise devices are used

2019 ◽  
pp. 84-89
Author(s):  
C. M. Logatkin ◽  
M. A. Ryzhikov ◽  
M. S. Kuznetsov
Keyword(s):  
External Auditory Canal ◽  
Impulse Noise ◽  
Low Frequency ◽  
Study Groups ◽  
Noise Spectrum ◽  
Maximum Increase ◽  
Low Frequencies ◽  
Small Arms ◽  
Equal Energy ◽  
Hearing Thresholds

Relevance. The basis of modern rationing of noise and assessing its safety is the principle of equal energy: regardless of the source, effects are equal. However, this approach is not valid for impulse noise reaching the external auditory canal through the means of individual hearing protection. This issue needs further research.Intention. To assess effects of impulse noise when anti-noise devices are used on the auditory sensitivity and safety of military personnel.Methods. Effects of impulse noise of equal energy without anti-noise devices and reaching the external auditory canal through the means of protection was carried out in two groups of volunteers aged 18–23 years without contraindications for working under noise conditions. Shooters from the 1st group (12 persons) fired from an AK74M assault rifle (150 shots) in a free acoustic field. Shooters from the 2nd group (13 persons) used 6M2 noise protection headsets when shooting (330 shots).Results and discussion. The equivalent level of impulse noise affecting the hearing organ of the shooters from both study groups amounted to 99.4 dBA. Impulse noise filtering through a 6M2 noise protection headset led to a shift in the noise spectrum to the low-frequency region, therefore the maximum increase in hearing thresholds was noted not at high (as without anti-noise devices), but at low frequencies – 250 and 500 Hz. At the same time, the hearing thresholds restored after shooting without anti-noise devices within a day, and after shooting with noise protection headsets – in two hours.Conclusion. It was established that the impulse noise from small arms of the same equivalent level when reaching the external auditory canal through the anti-noise headphones is less dangerous in terms of hearing restoration than after direct exposure.

scholarly journals Low-frequency wave-energy amplification in graded two-dimensional resonator arrays

2019 ◽  
Vol 377 (2156) ◽  
pp. 20190104 ◽  
Author(s):  
L. G. Bennetts ◽  
M. A. Peter ◽  
R. V. Craster
Keyword(s):  
Numerical Simulations ◽  
Low Frequency ◽  
Square Lattice ◽  
Two Dimensional ◽  
Low Frequencies ◽  
Frequency Wave ◽  
Periodic Arrays ◽  
Order Of Magnitude ◽  
Infinite Array ◽  
Energy Amplification

Energy amplification in square-lattice arrays of C-shaped low-frequency resonators, where the resonator radii are graded with distance, is investigated in the two-dimensional linear acoustics setting for both infinite (in one dimension) and finite arrays. Large amplifications of the incident energy are shown in certain array locations. The phenomenon is analysed using: (i) band diagrams for doubly-periodic arrays; (ii) numerical simulations for infinite and finite arrays; and (iii) eigenvalue analysis of transfer matrices operating over individual columns of the array. It is shown that the locations of the large amplifications are predicted by propagation cut-offs in the modes associated with the transfer-matrix eigenvalues. For the infinite array, the eigenvalues form a countable set, and for the low frequencies considered, only a single propagating mode exists for a given incident wave, which cuts off within the array, leading to predictive capabilities for the amplification location. For the finite array, it is shown that (in addition to a continuous spectrum of modes) multiple discrete propagating modes can be excited, with the grading generating new modes, as well as cutting others off, leading to complicated amplification patterns. The numerical simulations reveal that the largest amplifications are achieved for a single row array, with amplifications an order of magnitude smaller for the corresponding infinite array. This article is part of the theme issue ‘Modelling of dynamic phenomena and localization in structured media (part 1)’.

ANALYSIS OF FLUCTUATIONS IN WIND DEPENDENT SHALLOW WATER AMBIENT NOISE SPECTRUM

2007 ◽  
Vol 07 (03) ◽  
pp. L313-L319 ◽  
Author(s):  
S. RAMJI ◽  
G. LATHA ◽  
S. RAMAKRISHANAN
Keyword(s):  
Shallow Water ◽  
Frequency Band ◽  
Noise Level ◽  
Ambient Noise ◽  
Low Frequency ◽  
Noise Spectrum ◽  
Sea State ◽  
Spectrum Level ◽  
Frequency Bands ◽  
Lower Frequency Band

In this work, the fluctuations in the spectrum level of shallow water ambient noise is analyzed for 3 different sea states. The shallow water ambient noise data were collected of Bay of Bengal using an omni directional hydrophone and a portable data acquisition system.100 sets of data were collected and organized according to the three different sea states using Beaufort scale. Fluctuations in noise spectrum level at different sea states were studied by dividing the spectral bandwidth of 12 kHz into low, mid and high frequency bands. Mean noise spectrum level for each sea state was calculated and the result shows the noise spectrum level increases with the sea state. Further it was found that the noise level was higher in lower frequency band and decreases in the higher frequency band. Also the correlation between the noise level and sea state was higher in the low frequency band and tend to decrease in the mid frequency band and there was no correlation in the higher frequency bands. The higher noise levels were associated with lower frequencies of the bandwidth whereas it is less in higher frequencies. The fluctuations were found to be higher in the lower frequency band than the mid and higher frequency band. In this paper the data collection, data processing and noise spectrum analysis are presented in detail. As the fluctuations in power spectrum level of the ambient noise is one of the primary factor which decides the signal to noise ratio of most of the acoustic instruments, these results seems to be significant.

The Research of Noise Characteristics on Shenzhen Metro Platform

2015 ◽  
Vol 741 ◽  
pp. 426-430
Author(s):  
Jian Hui Tian ◽  
Bing Li ◽  
Lian Jian
Keyword(s):  
Noise Level ◽  
Air Conditioning ◽  
Low Frequency ◽  
Noise Spectrum ◽  
Vibration Measurement ◽  
Frequency Noise ◽  
Fan Noise ◽  
Noise Characteristics ◽  
Analysis System ◽  
System Time

The noise SPL and spectrum characteristics were tested and analyzed for the Shenzhen metro platform when the metro is inbound and outbound by using the noise and vibration measurement and analysis system. Time-domain SPL distribution diagrams shows, causing the largest noise level inside platform is mainly from the station radio, when no station radio, metro wheel-rail noise and air-conditioning fan noise have become a major SPL source in platform. The noise level at the platform is between 73dB-76dB. Frequency domain noise spectrum diagram shows, the noise SPL peak appeared in both low frequency and mid frequency ranges. Low frequency noise peak appears at 125Hz and 250Hz frequency band, mainly from the site of passengers talking and footsteps. Mid frequency noise peak is located in the 500Hz-1000Hz range, mainly from station radio, metro wheel-rail noise and air-conditioning fan and so on. This study provides a reference for noise reduction design of the metro platform.

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.

Methods to isolate retrograde and prograde Rayleigh-wave signals

2019 ◽  
Vol 219 (2) ◽  
pp. 975-994 ◽  
Author(s):  
Gabriel Gribler ◽  
T Dylan Mikesell
Keyword(s):  
Rayleigh Wave ◽  
Time Domain ◽  
Fundamental Mode ◽  
Poisson Ratio ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Low Frequencies ◽  
Retrograde Motion ◽  
Mode Identification ◽  
Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

Optimally Sensitive and Efficient Compact Loudspeakers for Low Audio Frequencies

2007 ◽  
Vol 38 (7) ◽  
pp. 11-17
Author(s):  
Ronald M. Aarts
Keyword(s):  
Optimality Criterion ◽  
Low Frequency ◽  
Audio Signal ◽  
Design Procedure ◽  
Frequency Range ◽  
Force Factor ◽  
Low Frequencies ◽  
Limited Frequency ◽  
The Cost ◽  
Higher Sensitivity

Conventionally, the ultimate goal in loudspeaker design has been to obtain a flat frequency response over a specified frequency range. This can be achieved by carefully selecting the main loudspeaker parameters such as the enclosure volume, the cone diameter, the moving mass and the very crucial “force factor”. For loudspeakers in small cabinets the results of this design procedure appear to be quite inefficient, especially at low frequencies. This paper describes a new solution to this problem. It consists of the combination of a highly non-linear preprocessing of the audio signal and the use of a so called low-force-factor loudspeaker. This combination yields a strongly increased efficiency, at least over a limited frequency range, at the cost of a somewhat altered sound quality. An analytically tractable optimality criterion has been defined and has been verified by the design of an experimental loudspeaker. This has a much higher efficiency and a higher sensitivity than current low-frequency loudspeakers, while its cabinet can be much smaller.

An Analytical Model for the Interaction of Mass Inclusions in Heterogeneous (HG) Blankets

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
A. Wagner ◽  
M. E. Johnson ◽  
K. Idrisi ◽  
D. P. Bartylla
Keyword(s):  
Elastic Layer ◽  
Analytical Approach ◽  
Low Frequency ◽  
Control Device ◽  
Effective Stiffness ◽  
Special Focus ◽  
Dynamic Vibration Absorber ◽  
Low Frequencies ◽  
Dynamic Vibration ◽  
The Masses

The heterogeneous (HG) blanket is a passive treatment used to reduce the low frequency transmission of sound through partitions. HG blankets, glued onto a structure, consist of an elastic medium with embedded mass inhomogeneities that mechanically replicate a mass-spring-damper system to reduce efficient radiating structural modes at low frequencies. The elastic layer typically used has sound absorption properties to create a noise control device with a wide bandwidth of performance. The natural frequency of an embedded dynamic vibration absorber is determined by the mass of the inhomogeneity as well as by its effective stiffness due to the interaction of the mass inclusion with the elastic layer. A novel analytical approach has been developed to describe in detail the interaction of the mass inclusions with the elastic layer and the interaction between the masses by evaluating special elastomechanical concepts. The effective stiffness is predicted by the analytical approach based on the shape of the mass inclusions as well as on the thickness and material properties of the layer. The experimental validation is included and a simplified direct equation to calculate the effective stiffness of a HG blanket is proposed. Furthermore, the stress field inside the elastic material will be evaluated with focus on the stresses at the base to assess the modeling of one or more masses placed on top of the elastic layer as dynamic vibration absorbers. Finally, the interaction between two (or more) masses placed onto the same layer is studied with special focus on the coupling of the masses at low distances between them.

Sign in / Sign up

Export Citation Format

Share Document