Low-pass Filter Characteristics Research Articles

Climatic and geologic controls on the piezometry of the Querença-Silves karst aquifer, Algarve (Portugal)

Karst aquifers in semi-arid regions, like Querenca-Silves (Portugal), are particularly vulnerable to climate variability. For the first time in this region, the temporal structure of a groundwater-level time series (1985–2010) was explored using the continuous wavelet transform. The investigation focused on a set of four piezometers, two at each side of the S. Marcos-Quarteira fault, to demonstrate how each of the two sectors of the aquifer respond to climate-induced patterns. Singular spectral analysis applied to an extended set of piezometers enabled identification of several quasi-periodic modes of variability, with periods of 6.5, 4.3, 3.2 and 2.6 years, which can be explained by low-frequency climate patterns. The geologic forcing accounts for ~15 % of the differential variability between the eastern and western sectors of the aquifer. The western sector displays spatially homogenous piezometric variations, large memory effects and low-pass filtering characteristics, which are consistent with relatively large and uniform values of water storage capacity and transmissivity properties. In this sector, the 6.5-year mode of variability accounts for ~70 % of the total variance of the groundwater levels. The eastern sector shows larger spatial and temporal heterogeneity, is more reactive to short-term variations, and is less influenced by the low-frequency components related to climate patterns.

High-bandwidth control of piezoelectric steering mirror for suppression of laser beam jitter

Laser beam steering or pointing, which stabilizes the beam direction, is critical in many areas, such as optical communication systems, astronomy and directed-energy systems etc. However, the disturbances including atmospheric turbulence and mechanical jitter on platform may degrade the pointing accuracy. A proportional-integral (PI) feedback control commonly has been used in the track loop with a fast steering mirror. To compensate dynamic disturbance effectively, the laser beam steering control system must have a larger bandwidth than the disturbance bandwidth. But the control bandwidth is limited by the noise of the sensor, computing latency, and the light energy. So, a simple proportional-integral (PI) feedback controller of a piezoelectric fast steering mirror (PFSM) can only compensate the broadband disturbance of the atmospheric turbulence, but cannot effectively compensate a larger amplitude narrowband jitter because of the low control bandwidth. Moreover, when the control bandwidth is tuned to high, the mechanical resonance of the PFSM can cause the instability of the system. An improved dual two-order filter assisted high-bandwidth control algorithm to improve the pointing accuracy and error attenuation capability is proposed. This method can control a PFSM for suppression of laser beam jitter. The influence of filter parameters on frequency characteristics is analyzed, and then, a practical design method is proposed. The dual two-order filter can combine the characteristics of traditional notch filter and two-order low-pass filter, and can also obtain any desired amplitude in the interesting frequency ragion with little influence on the others. The principle of the proposed filter for suppressing the mechanical resonance of the PFSM and the narrowband disturbance is elaborated. And then, the different dual two-order filters are designed according to the frequency content of the PFSM and the narrowband disturbance. Finally, the proposed dual two-order filter assisted PI control algorithm and classic PI control algorithm are compared with each other. Experimental results show that, in the same conditions, the pointing accuracy of the proposed two-order filter assisted PI control algorithm is nearly 5 times better than that of the classic PI control algorithm, and the error attenuation bandwidth is one time higher. It also indicates that the proposed algorithm does not need an additional sensor; it is simple and effective for the suppression of the mechanical resonance of a PFSM and that of the narrowband disturbance, hence it improves the system error attenuation bandwidth and the beam pointing accuracy.

An Active Filter for Delta-Sigma-Modulated Josephson Waveforms

We present the design and electrical characteristics of an active low-pass filter. It will be used in a reference waveform source based on a programmable Josephson voltage standard with multilevel delta–sigma modulation to generate accurate and spectrally pure arbitrary waveforms. The filter has a fifth-order Butterworth characteristic with high input impedance, low distortion, high stopband attenuation, and stable passband performance, including dc.

Induction frequency affects cortico-striatal synaptic plasticity with implications for frequency filtering

Long-term synaptic depression (LTD) in cortico-striatal circuits is initiated by depolarization of striatal medium spiny neurons through a convergent cortical glutamatergic input. This produces retrograde endocannabinoid signaling to presynaptic cortical terminals and eventually results in long term (>30min) decreases in glutamate release. These same circuits can also undergo short-term depression (STD) through a less well-defined process in which the magnitude of postsynaptic responses returns to baseline levels within 10min. Additionally, the cortico-striatal circuit shows characteristics of a GABAA receptor-dependent low-pass filter, which results in significant attenuation of high frequency cortical inputs. The majority of in vitro studies of LTD have used a 100-Hz induction paradigm and it is unclear whether other frequencies, which may also have physiological relevance, have equivalent ability to induce this form of plasticity. Here we have investigated the effectiveness of a range of induction paradigms in producing LTD in cortico-striatal circuits, and demonstrate that some lower frequency paradigms, with perhaps more physiological relevance, are more effective at inducing LTD. We also show that GABAA receptor-dependent frequency filtering in this circuit is altered following the induction of LTD and STD suggesting an important role for synaptic depression in signal processing in these circuits.

Resonance suppression method based on digital filter for servo system

According to mechanical resonance problem in flight simulation servo system( turntable system),the principles of resonance suppression about traditional notch filter and second-order low-pass filter were analyzed. Afterwards the two-second resonance suppression digital filter was proposed. The two-second digital filter combines the characteristics of traditional notch filter and second-order low-pass filter,and it can suppress the resonance point and the anti-resonance point at the same time. Through theoretical analysis and simulation combination,the principle of the two-second digital filter restraining the resonance point and the anti-resonance point simultaneously was explained. The experiments were also conducted,in which above all filters were joined into the turntable system respectively. Experimental results show that,the proposed filter ensures high tracking precision meanwhile effectively widens the bandwidth of the servo system.

Preliminary Results on the Influence of Engineered Artificial Mucus Layer on Phonation

PURPOSE Previous studies have confirmed the influence of dehydration and an altered mucus (e.g., due to pathologies) on phonation. However, the underlying reasons for these influences are not fully understood. This study was a preliminary inquiry into the influences of mucus architecture and concentration on vocal fold oscillation. METHOD Two excised human larynges were investigated in an in vitro setup. The oscillations of the vocal folds at various airflow volume rates were recorded through the use of high-speed imaging. Engineered mucus containing polymers (interconnected polymers and linear polymers) was applied to the vocal folds. From the high-speed footage, glottal parameters were extracted through the use of objective methods and were compared to a gold standard (physiological saline solution). RESULTS Variations were found for all applications of mucus. Fundamental frequency dropped and the oscillatory behavior (speed quotient [SQ], closing quotient [CQ]) changed for both larynges. The 2 applied mucus architectures displayed different effects on the larynges. The interconnected polymer displayed clear low-pass filter characteristics not found for the linear polymer. Increase of polymer concentration affected parameters to a certain point. CONCLUSION The data confirm results found in previous studies. Furthermore, the different effects-comparing architecture and concentration-suggest that, in the future, synthetic mucus can be designed to improve phonation.

Electrical Measurement of Ink Sedimentation

Characterization of inks, particularly sedimentation in particle inks, is an important challenge in inkjet printing. This paper proposes the approach of ink characterization by electrical measurements. A conductivity cell is used for the application of alternating current. This provides well-defined ink characteristics without changing ink properties. Thus, the method can be used not only in ink formulation but also for on-line monitoring during the printing process.Two different ink compositions are investigated regarding impedance and phase angle. Silver inks, common as the conductive component in printed circuits and barium titanate inks. The latter inks comprise of an insulating (dielectric) material. The method is proved to be applicable here. Both compositions show low-pass filter characteristics. Accordingly, similar analysis methods are used. The low-pass frequency response allows for the implementation of the random walk method to obtain equivalent capacity and resistance.From the measured values, accurate discrimination of the actual solid substance content is possible for both inks.

CRLH 전송선로를 이용한 초광대역 대역통과 필터의 설계 및 구현

A novel design method of ultra wideband based on the composite right-/left handed (CRLH) transmission line is presented in this paper. Defected ground structure and microstrip interdigital coupler are used to implement the CRLH transmission line. The proposed CRLH transmission line in this paper have composite characteristics of low pass filter and high pass filter, also it has good advantages of low insertion loss and ultra wide passband characteristics. The structure with different cell number are studied, and the UWB filter using 3-cell CRLH transmission line is fabricated and measured, which shows a good agreement between simulated and measured results. It has center frequency of 5 GHz, fractional bandwidth of 105 %, and insertion loss of 0.7 dB at center frequency.

Based on the CO<sub>2</sub> Gas Shielded Welding Molten Pool Image Edge Detection Algorithm

This paper use the passive vision system through high-speed camera collects molten pool images; and then according to the frequency domain characteristics of the weld pool image Butterworth low-pass filter; gradient method for image enhancement obtained after pretreatment. Research Roberts, Sobel, Prewitt, Log, Zerocross, and Canny 6 both traditional differential operator edge detection processing results. Through comparison and analysis of choosing threshold for [0.1, 0. Canny operator can get the ideal molten pool edge character, for subsequent welding molten pool defect recognition provides favorable conditions.

Low-frequency dielectric dispersion of brain tissue due to electrically long neurites

The dielectric properties of brain tissue are important for understanding how neural activity is related to local field potentials and electroencephalograms. It is known that the permittivity of brain tissue exhibits strong frequency dependence (dispersion) and that the permittivity is very large in the low-frequency region. However, little is known with regard to the cause of the large permittivity in the low-frequency region. Here, we postulate that the dielectric properties of brain tissue can be partially accounted for by assuming that neurites are of sufficient length to be "electrically long." To test this idea, we consider a model in which a neurite is treated as a long, narrow body, and it is subjected to a stimulus created by electrodes situated in the region external to it. With regard to this electric stimulus, the neurite can be treated as a passive cable. Assuming adequate symmetry so that the tissue packed with multiple cables is equivalent to an isolated system consisting of a single cable and a surrounding extracellular resistive medium, we analytically calculate the extracellular potential of the tissue in response to such an externally created alternating-current electric field using a Green's function that we obtained previously. Our results show that brain tissue modeled by such a cable existing within a purely resistive extracellular medium exhibits a large effective permittivity in the low-frequency region. Moreover, we obtain results suggesting that an extremely large low-frequency permittivity can coexist with weak low-pass filter characteristics in brain tissue.

Analysis & Study of Harmonics’ Impact on Analog Integrator’s Calibration

Having studied harmonic’s impact on electronic integrator’s Calibration. The mathematics model of the integrator and the response of the integrator simulator to volt-second pulse periodic signal have been established through SIMUNLINK in the MATLAB, it theoretically analyzes the low-pass filtering characteristics of ideal integrators and the impact of pulse signal harmonics on approximate integrators. The experiment shows that the bigger the harmonics elements in the volt-second’s pulse signal is, the less accurate its calibration of integrator will be.

Studies on an automobile muffler with the acoustic characteristic of low-pass filter and Helmholtz resonator

Tail pipe is a most common structure in mufflers to silence low frequency noise from an engine for its acoustic performance of low-pass filter. Based on the typical structure, a muffler with an interconnecting hole on the tail pipe was proposed to improve its acoustic performance in the present research. Acoustic performances of the proposed muffler were studied experimentally and theoretically in frequency and time domain. It was found that the interconnecting hole enabled the proposed muffler to have a noise attenuation performance of Helmholtz resonator. So the proposed muffler can attenuate the noise of low frequency and middle frequency at the same time. The frequency equation of this structure was derived using the acoustic-electronic analogy. It is useful for estimating the attenuation performance at the stages of predesign or tuning. The influence of structure parameters of the proposed muffler on its acoustic performance was studied. According to the results, the design guideline of this muffler was concluded in the present research.

Scheduling methods for multi-user optical wireless asymmetrically-clipped OFDM

Diffuse optical wireless (DOW) systems have the advantage that they do not require point-to-point siting so one transmitter can communicate with several receivers. In this paper, we investigate multiple access scheduling methods for downlink orthogonal frequency division multiplexing (OFDM) in diffuse optical wire- less networks. Unlike the radio frequency (RF) channel, the DOW channel has low-pass filter characteristics and so requires different scheduling methods than those developed for the RF channel. Multi-user diversity orthogonal frequency division multiple access (OFDMA) systems nominate a cluster of subcarriers with the largest signal-to-noise-ratio for transmission. However, in a DOW channel, most users would choose the lowest frequency clusters of subcarriers. To remedy this problem, we make two proposals. The first is to use a variable cluster size across the subcarriers; the lower frequency clusters will have fewer subcarriers while the higher frequency clusters will have more subcarriers. This will equalize the capacity of the clusters. The second proposal is to randomize a user's cluster selection from a group of clusters satisfying a minimum threshold. Through simulation it is shown that combining these strategies can increase the throughput while ensuring a fair distribution of the available spectrum.

Control design for human-like reaching movements using redundancy in robot arm-trunk systems

This paper develops a control algorithm to show the human-like reaching movements in humanoid redundant systems involving the trunk. This algorithm neither requires the computation of pseudo-inverse of Jacobian nor does it need the optimization of any artificial performance index. The control law accommodates the time-varying temporal properties of the muscle stiffness and damping as well as low-pass filter characteristics of human muscles. It uses a time-varying damping shaping matrix and a bijective joint muscle mapping function to describe the spatial characteristics of human reaching motion like quasi-straight line trajectory of the end-effector and symmetric bell shaped velocity profile as well as the temporal characteristics like the occurrence of the peak velocity of the trunk motion after the peak velocity of the arm motion. The aspect of self-motion is also analyzed using the null-space motion of the manipulator Jacobian. The effects of the control parameters on the motion pattern are analyzed in detail and some basic guidelines have been provided to select their proper values. Simulation results show the efficacy of the newly developed algorithm in describing humanmotion characteristics.

가속도 측정에 있어 고주파 잡음 제거를 위한 기계적 필터의 재료 특성에 관한 실험적 연구

Accelerometers are widely used to measure the lateral vibrations of pipe-like structures such as a gun tube under impulse loads. Stress waves that precede the lateral vibrations due to the explosion within a gun contribute little to the vibrations, but saturate the accelerometer input. A mechanical filter eliminates this high-frequency stress wave and only transmits the signal corresponding to the lateral vibrations. The mechanical filter consists of a mechanical structure for mounting the accelerometers and a damping material. The low-pass filter characteristics are determined from the equivalent damping and stiffness property of this damping material. In this paper, we tested nine commercially available damping materials for their vibration characteristics by using a test rig. We also observed the change in the vibration characteristics while compressing the material. We designed and manufactured a mechanical filter and verified its filtering performance.

Cellular and Network Contributions to Vestibular Signal Processing: Impact of Ion Conductances, Synaptic Inhibition, and Noise

Head motion-related sensory signals are transformed by second-order vestibular neurons (2°VNs) into appropriate commands for retinal image stabilization during body motion. In frogs, these 2°VNs form two distinct subpopulations that have either tonic or highly phasic intrinsic properties, essentially compatible with low-pass and bandpass filter characteristics, respectively. In the present study, physiological data on cellular properties of 2°VNs of the grass frog (Rana temporaria) have been used to construct conductance-based spiking cellular models that were fine-tuned by fitting to recorded spike-frequency data. The results of this approach suggest that low-threshold, voltage-dependent potassium channels in phasic and spike-dependent potassium channels in tonic 2°VNs are important contributors to the differential, yet complementary response characteristics of the two vestibular subtypes. Extension of the cellular model with conductance-based synapses allowed simulation of afferent excitation and evaluation of the emerging properties of local feedforward inhibitory circuits. This approach revealed the relative contributions of intrinsic and synaptic factors on afferent signal processing in phasic 2°VNs. Additional extension of the single-cell model to a population model allowed testing under more natural conditions including asynchronous afferent labyrinthine input and synaptic noise. This latter approach indicated that the feedforward inhibition from the local inhibitory network acts as a high-pass filter, which reinforces the impact of the intrinsic membrane properties of phasic 2°VNs on peak response amplitude and timing. Thus, the combination of cellular and network properties enables phasic 2°VNs to work as a noise-resistant detector, suitable for central processing of short-duration vestibular signals.

Compact low-pass filters using novel ϕ-shape defected ground structure

A novel ϕ-shape defected ground structure (DGS) is proposed in this article.Low-pass filters are designed using the ϕ-shape DGS with H shape open stubs line. Single, two-cascaded and three-cascaded ϕ-shape DGS low-pass filters are designed, simulated, fabricated, and measured. The resonant characteristic of the two-cascaded ϕ-shape DGS low-pass filter shows its advantages of compact size, high selectivity, low insertion loss, and excellent passband performance. The frequency response of the three-cascaded ϕ-shape DGS low-pass filter presents the advantages of compact size, high selectivity, low insertion loss, better passband performance, and high outband suppression. The measured results show a good agreement with the simulated results. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1456–1459, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25968

Vestibular signal processing by separate sets of neuronal filters

Second-order vestibular neurons (2°VN) are the central element for the transformation of body motion-related sensory signals into extraocular motor commands for retinal image stabilization during locomotion. The wide range of motion dynamics necessitates sensory signal transformation in parallel, frequency-tuned channels. Accordingly, in various vertebrates, 2°VN have been shown to form differently tuned functional subgroups. In frog, these neurons subdivide into two separate populations with distinctly different intrinsic membrane properties, discharge dynamics and synaptic response characteristics. Frog tonic 2°VN exhibit low-pass filter characteristics and membrane properties that cause amplification of synaptic inputs, whereas phasic 2°VN form band-pass filters that allow frequency-dependent shunting of repetitive inputs. The differential, yet complementary membrane properties render tonic 2°VN particularly suitable for synaptic integration and phasic 2°VN for differentiation and event detection. Differential insertion of the two cell types into local circuits reinforces the functional consequences of the intrinsic membrane properties, respectively. As a consequence, the synergy of cellular and network properties creates sets of neuronal elements with particular filter characteristics that form flexible, frequency-tuned components for optimal transformation of all dynamic aspects of body motion-related multisensory signals.

Electronically Tunable Minimum Component Biquadratic Filters for Interface Circuits

In this paper, two new electronically tunable filter configurations are proposed. The proposed filters operate current-mode (CM), voltage-mode (VM), transimpedance-mode (TIM) and transadmittance-mode (TAM). The first configuration realizes second-order VM band-pass and TAM high-pass filter characteristics from the same configuration. The second one realizes second-order TIM band-pass and CM low-pass filter characteristics from the same configuration. They also use minimum number of electronic components (two capacitors and one active component namely; current controlled current difference transconductance amplifier). The workability of the proposed structures has been demonstrated by simulation results.

A Novel Narrow Passband Millimeter Filter Using Suspended Improved Compact Microstrip Resonant Cell

A novel millimeter wave narrowband bandpass filter using improved suspended compact microstrip resonant cell is proposed in this paper. Compared to the traditional high/low step-impedance filter, the improved CMRC structure possesses good lowpass filter characteristics. Besides, it can shorten the circuit size over 50%. And a suspended CMRC has better filter characteristics of low return loss and sharper stopband rejection than a traditional CMRC. Based on the improved suspended CMRC, a novel millimeter wave narrowband BPF operating at center frequency of 40 GHz is designed and tested. The investigation results show that the BPF has low insertion loss below 1 dB in the narrow passband with a bandwidth of 10% and sharp rejection in the stopband.