Lower Corner Frequency Research Articles

Induced seismic activity and source parameter characteristics in the Datong coal mine, China

To clarify the activity patterns and source characteristics of coal mining–induced microseismicity, this study analyzed the spatial distribution characteristics of microseismic events in the Datong coal mining area based on records from the regional digital seismic network. We conducted a detailed characterization of the depth distribution characteristics of microseismic events using the double-difference localization method. Additionally, the source parameters, including corner frequency ( fc), source rupture radius ( r), seismic moment ( M0), source radiated energy ( Es), and stress drop (Δσ), were calculated for 136 mine-induced earthquakes with magnitudes ranging from ML1.3 to ML3.2. The results show that ML ≥ 2.0 mining-induced seismic events occur mainly within numerous microfractures in the Datong mining area. The depth of the seismic sources in the mining area is concentrated at 200∼500 m, with significant north–south differences and a close correlation with the mining depth. The displacement spectra of microseismic sources show agreement with the Brune source model [Formula: see text] attenuation pattern. As M0 gradually increases, r, Δσ, and Es show an increasing trend, while fc gradually decreases, exhibiting characteristics similar to those of tectonic earthquakes. Compared to tectonic earthquakes, coal mining-induced earthquakes have lower corner frequencies and stress drop levels mainly because mining activities alter the originally stable geological structure and stress state, leading to weakened rock strength, decreased elastic modulus, and shallower source depths. These factors contribute to the reduction in corner frequencies. As mining operations continue, microfracturing occurs in the coal and surrounding rock mass, intensifying the dynamic instability of the rock mass that was already under high stress conditions. This situation triggers larger-magnitude, mining-induced seismic events under lower stress conditions.

Baseline Calibration of L-Band Spaceborne Bistatic SAR TwinSAR-L for DEM Generation

The Terrain Wide-swath Interferometric L-band Synthetic Aperture Radar (TwinSAR-L) mission is a spaceborne bistatic synthetic aperture radar (SAR) mission to derive a high-quality global digital elevation model (DEM). The prerequisite of the high-accuracy DEM is knowing the interferometric baseline with high precision. The challenging problem is that the baseline of the bistatic system is highly dynamic due to the fast relative motion between the two satellites. In this paper, a pixel-related baseline model based on the geometrical shift is proposed to accurately reflect the position change of satellites. The baseline error is then calibrated using height gradient information and a small number of point targets with a slight incidence angle difference, eliminating the need for low-frequency corner reflectors and avoiding the difficulty of selecting a calibration site. The proposed method has been successfully exploited during the initial Commissioning Phase of TwinSAR-L, demonstrating its effectiveness in evaluating the precise baseline and supporting the generation of high-precision DEM.

MBE-Grown Hybrid Axial Core–Shell n-i-p GaAsSb Heterojunction Ensemble Nanowire-Based Near-Infrared Photodetectors up to 1.5 μm

In this paper, high-performance self-assisted molecular beam epitaxy (MBE)-grown conventional core–shell (C–S) n-i-p GaAsSb nanowires (NWs) and a novel hybrid axial C–S n-i-p GaAsSb ensemble NW-based near-infrared photodetector (NIRPD) on nonpatterned Si substrate are demonstrated. The conventional room-temperature (RT) C–S n-i-p GaAsSb NW with a high responsivity of 190 A/W and a higher detectivity of 1.1 × 1014 Jones at −1 V bias and wavelength of 1.1 μm is reported by optimizing the intrinsic region thickness and appropriately compensating the intrinsic p-type behavior with n-dopant Te. Furthermore, hybrid axial C–S n-i-p GaAsSb has been band-gap-engineered for wavelength up to 1.5 μm, exhibiting responsivity of 18 A/W and detectivity of 1.1 × 1013 Jones operating at RT. In this hybrid design, we have combined both axial and radial intrinsic (i-) segments of different Sb% compositions to enhance the photoabsorption in the NIR region; hence, the photogenerated current and also the high-band-gap axial i-region help to suppress the trap-assisted tunneling mechanism, which is found to be advantageous over conventional C–S NW architectures. In addition, high rectification ratio from current–voltage (I–V) measurements, suppression of low-frequency noise, lack of 1/f noise, a low corner frequency of ∼2.5 Hz beyond which there is the presence of only frequency-independent white noise from low-frequency noise (LFN) measurements, and bias- and frequency-dependent capacitance–voltage (C–V) measurements suggest the formation of a high-quality C–S junction in the hybrid structure. Thus, our findings reveal that the hybrid axial C–S NW architecture provides the flexibility of three-dimensional (3D) design, which offers an unprecedented prospect for expanding IRPD and other next-generation optoelectronic device applications.

Spectral characteristics of P-and S-wave quarry blasts in Aswan region, South Egypt

The Aswan broadband seismic network, consisting of high-sensitivity sensors with dense stations coverage, provided the opportunity to study and analysed the spectral properties of the quarry blasts in the Aswan region, southern Egypt. We comprehensively analysed 757 digital seismograms from 128 quarry blasts with local magnitude (ML) between 1.7 and 3.1 during time span from 2010 to 2021. A Generalized Inversion Technique (GIT) constrained by a reference site is applied to isolate the attenuation, site responses of the seismic stations, and the source spectra from the observed seismograms by means of iterative least square analysis. The displacement source spectra for P-and S-waves are computed for all quarry blasts based on the theoretical omega-square seismic source model (Brune's model). The spectral analysis demonstrated that both P-and S-waves displacement source spectra of the quarry blasts used in this study have low corner frequency values. The corner frequency of the quarry blasts used in this study ranged from 1.0 to 2.6 Hz and from 1.5 to 4.6 Hz for P-and S-waves, respectively. The P-and S-wave corner frequency ratio (fCP/fCS) is computed for each event. We obtained that the fCP/fCS ratio is less than 1.0 Hz for 106 events (94%) and equal to 1.0 Hz and less than 1.2 Hz for only six selected data events (6%). The analysis indicates that the observed displacement source spectra show discrepancies with the omega-square type spectrum, and they generally have a steep fall off at high frequencies. We also found that the selected quarry blasts have a narrow seismic moment range (from 2.03E+11 to 1.35E+12 Nm), and stress drop values range from 0.001 to 0.023 MPa. The distribution of the used quarry blast stress drop demonstrated a self-similar character.

Emergence of Low-Frequency Aftershocks of the 2019 Ridgecrest Earthquake Sequence

ABSTRACTLow-frequency earthquakes (LFEs) generally have relatively stronger spectral components in the lower frequency range compared with what is expected for regular earthquakes based on their magnitude. LFEs generally occur in volcanic systems or deep (>∼15 km) in plate boundary fault zones; however, LFEs have also been observed in nonvolcanic, upper crustal settings. Because there are few studies that explore the spatiotemporal behaviors of LFEs in the shallow crust, it remains unclear whether the shallow-crustal LFEs reflect local attenuation in their immediate vicinity or differences in their source mechanism. Therefore, it is important to identify shallow-crustal LFEs and to characterize their spatiotemporal activity, which may also improve our understanding of LFEs. In this study, we focus on detecting shallow-crustal LFEs and explore the possible generation mechanisms. We analyze 29,646 aftershocks in the 2019 Ridgecrest, California, earthquake sequence, by measuring the frequency index (FI) to identify candidate low-frequency aftershocks (LFAs), while accounting for the magnitude dependency of the FI. Using small earthquakes (ML 1–3) recorded in the borehole stations to minimize the attenuation effects in near-surface layers, we identify 68 clear LFAs in total. Based on their distribution and comparisons with other seismic parameters measured by Trugman (2020), the LFAs possess distinct features from regular events in the same depths range, including low corner frequencies and low stress drops. Events in the close vicinity of LFAs exhibit lower average FI values than regular aftershocks, particularly if the hypocentral distance between an LFA and its neighbors is less than 1 km. Our results suggest that LFAs are related to local heterogeneity or a highly fractured fault zone correlated with an abundance of cross faults induced by the aftershock sequence at shallow depths. Zones of high pore-fluid pressure in intensely fractured fault zones could cause the bandlimited nature of LFAs and LFEs in general.

Highly Configurable 100 Channel Recording and Stimulating Integrated Circuit for Biomedical Experiments

This paper presents the design results of a 100-channel integrated circuit dedicated to various biomedical experiments requiring both electrical stimulation and recording ability. The main design motivation was to develop an architecture that would comprise not only the recording and stimulation, but would also block allowing to meet different experimental requirements. Therefore, both the controllability and programmability were prime concerns, as well as the main chip parameters uniformity. The recording stage allows one to set their parameters independently from channel to channel, i.e., the frequency bandwidth can be controlled in the (0.3 Hz–1 kHz)–(20 Hz–3 kHz) (slow signal path) or (0.3 Hz–1 kHz)–4.7 kHz (fast signal path) range, while the voltage gain can be set individually either to 43.5 dB or 52 dB. Importantly, thanks to in-pixel circuitry, main system parameters may be controlled individually allowing to mitigate the circuitry components spread, i.e., lower corner frequency can be tuned in the 54 dB range with approximately 5% precision, and the upper corner frequency spread is only 4.2%, while the voltage gain spread is only 0.62%. The current stimulator may also be controlled in the broad range (69 dB) with its current setting precision being no worse than 2.6%. The recording channels’ input-referred noise is equal to 8.5 µVRMS in the 10 Hz–4.7 kHz bandwidth. The single-pixel occupies 0.16 mm2 and consumes 12 µW (recording part) and 22 µW (stimulation blocks).

Study on the source parameters of the micro-earthquakes in Laohutai coal mine based on double difference relocation

Seismicity related to industrial mining activities needs to be understood and quantified in order to ensure safe mining operations. It is of great important to determine if the sources of such events follow the common models and theories, and determine the source rupture property and scale of such events. Moreover, the location of the source is very important to obtain the source parameters. For this purpose, we analyze 103 events recorded in the Laohutai coal mine that are related to fault structure and mining activities to determine their source properties based on relocation. Firstly, the 103 micro-earthquakes were relocated based on double difference algorithm. Then, the source parameters of seismic moment M0, source radius R, corner frequency f0, seismic attenuation Q, energy E, stress drop △σ and apparent stress σa are computed based on relocation, Brune model and grid-search method. The relationship between the other source parameters and seismic moment, the relationship between ML and Mw, and the influence of location on source parameters and magnitude are further analyzed. Finally, the difference of the source parameters between Laohutai coal mine, Qianqiu coal mine and natural earthquakes are analyzed. We find that the source location can be effectively corrected based on double difference algorithm; ω2 model is well suited to estimate source parameters of micro-earthquakes in the Laohutai coal mine. The source spectra show strong directivity effects. Stations in the rupture direction have higher corner frequencies, while stations away from rupture direction have lower corner frequencies. With the increase of M0, the source parameters of R, E and △σ basically show a linear increase, the source parameter f0 basically show a linear decrease and the apparent stress fluctuate up and down around a certain value as a whole. After relocation, the location of the source has a significant effect on the quality attenuation factor Q and has no obvious effect on other source parameters. The influence of relocation on moment magnitude and local magnitude is not obvious. The moment magnitude is linear with the local magnitude. Considering Mw, ML1 can relatively well be used to evaluate the magnitude of the earthquakes in Laohutai coal mine; For the micro-earthquakes with the same magnitude, the values of corner frequency, stress drop, apparent stress and energy in Qianqiu coal mine are greater than those in Laohutai coal mine, the value of source radius in Laohutai coal mine is greater than those in Qianqiu coal mine. For the events with the same magnitude, the corner frequency and the stress drop value of micro-earthquakes are smaller than those of natural earthquake. These indicate that the rupture properties and scales of micro-earthquakes in Laohutai coal mine are different from those of the micro-earthquakes in Qianqiu coal mine and natural earthquakes. The results help us to effectively evaluate the property and magnitude of microseismic source, and better understand causes and consequences of microseismicity in coal mine.

Very-Long-Period (VLP) Seismic Artifacts during the 2018 Caldera Collapse at Kīlauea, Hawai‘i

AbstractThroughout the 2018 eruption of Kīlauea volcano (Hawai‘i), episodic collapses of a portion of the volcano’s summit caldera produced repeated Mw 4.9–5.3 earthquakes. Each of these 62 events was characterized by a very-long-period (VLP) seismic signal (>40 s). Although collapses in the later stage of the eruption produced earthquakes with significant amplitude clipping on near-summit broadband seismometers, the first 12 were accurately recorded. For these initial collapse events, we compare average VLP seismograms at six near-summit locations to synthetic seismograms derived from displacements at collocated Global Positioning System stations. We show that the VLP seismic signal was generated by a radially outward and upward ramp function in displacement. We propose that at local distances the period of the VLP seismic signal is solely dependent on the duration of this ramp function and the instrument transfer function, that is, the seismic VLP is an artifact of the bandlimited instrument response and not representative of real ground motion. The displacement ramp function imposes a sinc-function velocity amplitude spectrum that cannot be fully recovered through standard seismic instrument deconvolution. Any near-summit VLP signals in instrument-response-corrected velocity or displacement seismograms from these collapse events are subject to severe band limitation. Similarly, the seismic amplitude response is not flat through the low-frequency corner, for example, instrument-response-uncorrected seismograms scaled by instrument sensitivity are equally prone to band limitation. This observation is crucial when attempting to clarify the different contributions to the VLP source signature. Not accounting for this effect could lead to misunderstanding of the magmatic processes involved.

A robust, low-cost and well-calibrated infrasound sensor for volcano monitoring

Volcano acoustic signals contain valuable information on shallow magmatic and hydrothermal processes. In some cases, the detection of acoustic waves is the only clear evidence of the occurrence of volcanic explosions. Their study is thus complementary to that of seismic signals. For this reason, acoustic sensors are more and more frequently integrated in volcano monitoring systems as well as in temporary instrumental deployments. We have developed a broadband, robust and low-cost infrasound sensor designed for the detection and analysis of acoustic waves on volcanoes. It is based on a microelectromechanical differential pressure transducer (MEMS). The reference pressure is balanced with the atmospheric pressure through a pneumatic high-pass filter. Its low corner frequency, usually set to 60 mHz, can be adjusted from a few to tens of mHz. Its amplitude range is ±240 Pa and its sensitivity is 20 mV Pa−1, with a noise level <0.05 Pa RMS. The power consumption is 42 mW (3.5 mA with 12 V voltage). A direct output of the MEMS also provides a signal with sensitivity of about 500 μV Pa−1 and range ± 1245 Pa. This sensor is not sensitive to mechanical vibrations. The instrumental response of each infrasound sensor is carefully measured from 1 mHz to >100 Hz using two specially designed calibration systems which deliver sinusoidal pressure variations. The mechanical elements of the sensor are produced by 3D printer and filled with epoxy resin which guarantees high robustness in the aggressive environment of most volcanoes. The sensor dimensions (26x45x80 mm) and weight (100 g) makes it very easy to handle and install.

Spectral ratio analyses of explosion earthquakes at Sakurajima Volcano, Japan

It's quite important to clarify what physical parameters control the magnitude of volcanic explosion to understand magma processes in the conduit. Analyses of explosion earthquakes, which are associated with vulcanian eruptions, enable us to quantitatively evaluate dynamic process of the explosive eruptions. In the present study, we analyze hundreds of explosion earthquakes recorded at Sakurajima volcano, Japan, during 2012–2013. Applying a spectral ratio method that can retrieve the source spectral information without being disturbed by heterogeneous structure to three-component seismograms recorded at three stations operated by Japan Meteorological Agency, we examine scaling relations in explosion earthquakes. To obtain an averaged feature, we group the observed explosion earthquakes into five classes (I, II, III, IV, V) according to their maximum amplitudes and calculate the spectral ratios between the five classes. Because vulcanian eruptions continue to effuse volcanic ash for several to tens of minutes, spectral amplitude ratios are calculated by shifting a time window of 10 s for five successive 10s-long time windows from the onset to coda wave. The results show that the spectral amplitude ratios are characterized by the low and high corner frequencies: about 2 Hz and 3.5 Hz, respectively. With increasing the magnitude of explosion earthquakes, amplitude ratios at low and high frequency ranges, which are 0.5–2 Hz and 3.5–10 Hz, respectively, increase, while the corner frequencies do not significantly change. Since the explosion earthquakes at Sakurajima volcano occur at a same crater without changing the vent radius, the observed spectral amplitude ratio change may be attributed to pressure changes in the conduit. Another finding is that the amplitudes of spectral ratio gradually decrease with lapse time keeping the corner frequencies. Such a lapse time dependence of spectral ratios is completely different from those of tectonic earthquakes in which direct and coda waves show a same spectral amplitude ratio. We infer that the early part of the seismic waves of explosion earthquakes is generated by an initial rapid pressure release in the conduit while coda waves are by successive oscillations of the magma system during continuous ash emission.

Neural sensitivity to dynamic binaural cues: Human electroencephalogram and chinchilla single-unit responses

Animals encounter dynamic binaural timing information in broadband sounds such as speech and background noise due to moving sound sources, self motion, or reverberation. Most physiological studies of interaural time delay (ITD) or interaural correlation (IAC) sensitivity have used static stimuli; neural sensitivity to dynamic ITD and IAC is rarely systematically addressed. We used a system-identification approach using maximum-length sequences (MLS) to characterize neural responses to dynamically changing ITDs and IACs in broadband sounds. Responses were recorded from humans (electroencephalogram; EEG) and from single neurons in terminally anesthetized chinchillas (auditory nerve fibers; ANFs). Chinchilla medial superior olive (MSO) responses were simulated based on binaural coincidence from recorded ANF spike times in response to left- and right-channel input. Estimated ITD and IAC transfer functions were low-pass, with corner frequencies in the range of hundreds of Hz. Human EEG-based transfer functions, likely reflecting cortical responses, were also low-pass, but with much lower corner frequencies in the region of tens of Hz. Human behavioral detection of dynamic IAC extended beyond 100 Hz consistent with the higher brainstem limits. On the other hand, binaural unmasking effects were only evident for low-frequency ITD/IAC dynamics in the masking noise.

Efficient calibration and modelling of charge amplifiers for dynamic measurements

Charge amplifier calibration at low frequencies is a time-consuming service. This paper presents a method to speed up the process by measuring decades of frequencies in a single run. Based on the calibration results gained, a filter design process is introduced that facilitates a multi-rate approach to digital IIR filters in order to circumvent the complications arising from high-pass filtering with low corner frequency at high sampling rates.

Expedited simulation-driven design optimization of UWB antennas by means of response features

In this work, a method for fast design optimization of broadband antennas is considered. The approach is based on a feature-based optimization (FBO) concept where reflection characteristics of the structure at hand are formulated in terms of suitably defined feature points. Redefinition of the design problem allows for reducing the design optimization cost, because the dependence of feature point coordinates on antenna dimensions is less nonlinear than for the original frequency characteristics (here, S-parameters). This results in faster convergence of the optimization algorithm. The cost of the design process is further reduced using variable-fidelity electromagnetic (EM) simulation models. In case of UWB antennas, the feature points are defined, among others, as the levels of the reflection characteristic at its local in-band maxima, as well as location of the frequency point which corresponds to acceptable reflection around the lower corner frequency within the UWB band. Also, the number of characteristic points depends on antenna topology and its dimensions. Performance of FBO-based design optimization is demonstrated using two examples of planar UWB antennas. Moreover, the computational cost of the approach is compared with conventional optimization driven by a pattern search algorithm. Experimental validation of the numerical results is also provided.

2048 Action Potential Recording Channels with 2.4 µVrms Noise and Stimulation Artifact Suppression.

Here, we present 2048 low-noise, low-offset, and low-power action-potential recording channels, integrated in a multi-functional high-density microelectrode array. A resistively loaded open-loop topology has been adapted for the first-stage amplifier to achieve 2.4 µVrms noise levels at low power consumption. Two novel pseudo-resistor structures have been used to realize very low HPF corner frequencies with small variations across all channels. The adjustability of pseudo resistors has been exploited to realize a "soft" reset technique that suppresses stimulation artifacts so that the amplifiers can recover from saturation within 200 µs. The chips were fabricated in a 0.18 µm 6M1P CMOS process, and measurement results are presented to show the performance of the proposed circuit structures and techniques.

Pressure regulation for earth pressure balance control on shield tunneling machine by using adaptive robust control

Most current studies about shield tunneling machine focus on the construction safety and tunnel structure stability during the excavation. Behaviors of the machine itself are also studied, like some tracking control of the machine. Yet, few works concern about the hydraulic components, especially the pressure and flow rate regulation components. This research focuses on pressure control strategies by using proportional pressure relief valve, which is widely applied on typical shield tunneling machines. Modeling of a commercial pressure relief valve is done. The modeling centers on the main valve, because the dynamic performance is determined by the main valve. To validate such modeling, a frequency-experiment result of the pressure relief valve, whose bandwidth is about 3 Hz, is presented as comparison. The modeling and the frequency experimental result show that it is reasonable to regard the pressure relief valve as a second-order system with two low corner frequencies. PID control, dead band compensation control and adaptive robust control (ARC) are proposed and simulation results are presented. For the ARC, implements by using first order approximation and second order approximation are presented. The simulation results show that the second order approximation implement with ARC can track 4 Hz sine signal very well, and the two ARC simulation errors are within 0.2 MPa. Finally, experiment results of dead band compensation control and adaptive robust control are given. The results show that dead band compensation had about 30° phase lag and about 20% off of the amplitude attenuation. ARC is tracking with little phase lag and almost no amplitude attenuation. In this research, ARC has been tested on a pressure relief valve. It is able to improve the valve’s dynamic performances greatly, and it is capable of the pressure control of shield machine excavation.

Constraints on the source parameters of low‐frequency earthquakes on the San Andreas Fault

AbstractLow‐frequency earthquakes (LFEs) are small repeating earthquakes that occur in conjunction with deep slow slip. Like typical earthquakes, LFEs are thought to represent shear slip on crustal faults, but when compared to earthquakes of the same magnitude, LFEs are depleted in high‐frequency content and have lower corner frequencies, implying longer duration. Here we exploit this difference to estimate the duration of LFEs on the deep San Andreas Fault (SAF). We find that the M ~ 1 LFEs have typical durations of ~0.2 s. Using the annual slip rate of the deep SAF and the average number of LFEs per year, we estimate average LFE slip rates of ~0.24 mm/s. When combined with the LFE magnitude, this number implies a stress drop of ~104 Pa, 2 to 3 orders of magnitude lower than ordinary earthquakes, and a rupture velocity of 0.7 km/s, 20% of the shear wave speed. Typical earthquakes are thought to have rupture velocities of ~80–90% of the shear wave speed. Together, the slow rupture velocity, low stress drops, and slow slip velocity explain why LFEs are depleted in high‐frequency content relative to ordinary earthquakes and suggest that LFE sources represent areas capable of relatively higher slip speed in deep fault zones. Additionally, changes in rheology may not be required to explain both LFEs and slow slip; the same process that governs the slip speed during slow earthquakes may also limit the rupture velocity of LFEs.

Highly Matched TO Pseudo-resistors for Multi-channel Neural Signal Recording Applications

Event Abstract Back to Event Highly Matched TΩ Pseudo-resistors for Multi-channel Neural Signal Recording Applications Vijay Viswam1*, Yihui Chen2, Raziyeh Bounik2, Amir Shadmani1, Jelena Dragas2, Jan Müller2 and Andreas Hierlemann2 1 ETH Zürich, Department of Biosystems Science and Engineering, Switzerland 2 ETH Zurich, Department of Biosystems Science and Engineering, Switzerland Motivation To reduce drift and offset of electrodes, neural amplifiers usually employ high pass filters with very low corner frequencies (e.g., fHPF<10Hz). This approach requires huge on-chip resistances (~T½). To keep the silicon area small, "pseudo-resistors" (MOS transistors biased in the weak inversion region) are frequently used [1], but their resistance may considerably vary due to processing and fabrication spread, temperature fluctuations, and even different locations on the same chip may feature different properties. Here, specific new pseudo-resistor structures have been devised to achieve small fHPF variations. Material and Methods The new pseudo-resistors were implemented in a CMOS high-density MEA system incorporating 2048 readout channels [2]. Two different kinds of pseudo-resistor topologies were devised. For the 1st stage, open-loop amplifiers were used, while, for the 2nd stage closed-loop amplifiers were implemented. Aided by the current mirrors and level shifters, the first-order dependence of the overdrive voltages of the transistors inside RPR1 and RPR2 on their threshold voltages was cancelled out. Thus, RPR1 and RPR2 variations were substantially reduced, which lead to small fHPF variations. A wide range of resistances could also be realized by changing the bias currents, which could be digitally tuned with 7-bit current DACs implemented on-chip. Results High pass filter corner frequency (fHPF) of the the neural amplifiers tuned by pseudo-resistors were measured. The uniformity of fHPF showed the inter-channel matching of pseudo resistors across 2048 channels in the high and low frequency range. Conclusions Current-biased pseudo-resistors for neural signal recording applications are introduced in this work. The two new structures enable to realize very large resistances while keeping the silicon area small. Results on the transfer function of the neural amplifiers and the matching of the pseudo-resistors have been shown in this paper. The circuits were fabricated in 180nm 6M1P CMOS technology.

Correcting EM system bandwidth limitations

All EM transmitters, sensors and data acquisition systems have bandwidth limitations. Transmitters have upper bandwidth limitations due to finite slew rate issues, and systems have a lower bandwidth set by the base frequency used. Receivers and data acquisition systems ideally should have a flat bandwidth response that spans the transmitted signal bandwidth. The data acquisition system should sample fast enough to capture the highest frequencies of interest, with anti-alias filters to prevent data contamination from unwanted signals. Sensors however may have physical bandwidth limitations, for example fluxgates and feedback MT sensors may have an upper corner frequency of a few kHz, and ARMIT and feedback MT sensors have lower corner frequencies in the sub 1 Hz range. In many cases, the sensor corner frequency can be mathematically described as a single- or multi-pole response. In this case, it is possible to exactly deconvolve the data to exactly correct for the sensor imperfection. A limitation of this process is that noise as well as signal may be amplified in this correction process. Without correction, data may be incorrectly modelled or interpreted. This paper illustrates the correction of fluxgate (mostly a time delay of hundred or more microseconds), ARMIT 2 (where a significant but exact correction is required), ANT23 feedback and 3D3 dBdt data.

Research of 100 MHz ultra-low-jitter clock generating circuit.

Jitter which quantifies the quality of a clock is an important specification. It is of great significance for an electronic system. To obtain a good signal-to-noise ratio for sampling systems, there must be clocks with low jitter performances. By using the relationship between jitter and phase noise, the 100 MHz clock generating circuit with ultra-low jitter and phase noise characteristics are studied in this paper. Bipolar junction transistor with low noise figure and low corner frequency should be selected. Inductance and capacitance in the feedback circuit are obviously the main contributions to the jitter. Impacts of the loaded quality factor (Q(L)) of the circuit on the jitter are analyzed, and the explicit expression for the jitter based on circuit components is derived as well. The simulation and experiment results are proved to show that the jitter and phase noise characteristics can be improved by increasing Q(L) of the circuit.

Research on Magnetoelectric Seismometer's Low Frequency Extension Technology

Magnetoelectric seismometer has many outstanding features, such as low cost, small size, light weight, high sensitivity, low noise, good high frequency response, and reliable operation, simple set up, so these type of seismometer is widely used in several areas. However, because the structure of magnetoelectric seismometer (inertial mass and elastic support module), there has the material and mechanical structure limitation, so the inherent frequency is around between 5 to 30Hz, hard to be lower, hence, the low frequency characteristic is poor. To extend the seismometer's range of application, post compensation is needed. The researchers from both home and aboard proposed many different method to deal with the low frequency response of this seismometer, such as “inverse filter” method, “Lippmann” method, which uses negative resistance and feedback coil. These methods have got some results separately. In this paper, we will propose a low frequency integral method to extend the seismometer's frequency response. It is accomplished through balanced integration and high precision chips to suppress the circuit drifting and noise interference. The results from vibration table shows, after integration, the seismometer's low frequency corner frequency is extended from 2 Hz to under 0.1 Hz, the sensitivity is enhanced from 200V/m·s-1to 400V/m·s-1.