Frequency Response Profiles Research Articles

Filtering Eye-Tracking Data From an EyeLink 1000: Comparing Heuristic, Savitzky-Golay, IIR and FIR Digital Filters.

In a prior report (Raju et al., 2023) we concluded that, if the goal was to preserve events such as saccades, microsaccades, and smooth pursuit in eye-tracking recordings, data with sine wave frequencies less than 75 Hz were the signal and data above 75 Hz were noise. Here, we compare five filters in their ability to preserve signal and remove noise. We compared the proprietary STD and EXTRA heuristic filters provided by our EyeLink 1000 (SR-Research, Ottawa, Canada), a Savitzky- Golay (SG) filter, an infinite impulse response (IIR) filter (low-pass Butterworth), and a finite impulse filter (FIR). For each of the non-heuristic filters, we systematically searched for optimal parameters. Both the IIR and the FIR filters were zero-phase filters. All filters were evaluated on 216 fixation segments (256 samples), from nine subjects. Mean frequency response profiles and amplitude spectra for all five filters are provided. Also, we examined the effect of our filters on a noisy recording. Our FIR filter had the sharpest roll-off of any filter. Therefore, it maintained the signal and removed noise more effectively than any other filter. On this basis, we recommend the use of our FIR filter. We also report on the effect of these filters on temporal autocorrelation.

HAPSEA: Hydraulically Amplified Soft Electromagnetic Actuator for Haptics

Novel actuators that can provide squeeze, vibration, and localized forces while remaining soft and comfortable are essential for next-generation augmented reality applications. Despite this need, there are currently few soft actuator topologies that can provide high forces and high bandwidths at low voltages and temperatures. In this work, we present a new type of soft electromagnetic actuator architecture for haptics. These low-cost, easy-to-manufacture, and conformal actuators are composed of a coil, magnet, thin-film material, and water. Adding a thin ferromagnetic sheet further enables the creation of a latching actuator variant, which can improve force output while reducing power consumption. Each actuator combines low voltage (up to 2 V), high-bandwidth electromagnetics with hydraulics to amplify force output. In addition to force amplification, the hydraulics provide cooling and thermal mass, which enable the actuator to be used safely in wearables for longer durations. In this work, we characterize the output forces, frequency response, efficiency, and thermal profiles of the prototype actuators. Results from tabletop experiments show that with hydraulic amplification, a nonlatching actuator is able to exert 1.3 N of force at 4 A, and a latching actuator is able to exert up to 5.2 N when preloaded with 3.7 N of compression. Furthermore, the prototype actuator has a bandwidth of 30 Hz when operating in air. After 120 s of continuous operation (1.3 W) in ambient air (26 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C), the maximum actuator temperature reaches 36 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, making it safe for haptic applications. Using these designs, we develop a prototype wearable wristband device that can render body-grounded squeeze and vibration. By expanding on the operating principles described in this work, novel augmented reality applications can potentially become possible.

D-Band MUTC Photodiodes With Flat Frequency Response

Novel back-illuminated modified uni-traveling- carrier photodiodes (MUTC-PDs) are reported to demonstrate wide bandwidth and high output power performance at D-band (110–170 GHz) regime. A comprehensive design model is employed to predict and tune the frequency response by incorporating coplanar waveguides (CPWs) with different inductive peaking effects. As a demonstration, 4.5-μm-diameter photodiodes with two types of CPWs are fabricated to exhibit different frequency response profiles. Both PDs exhibit a 3-dB bandwidth over 150 GHz and the measured frequency responses are in excellent agreement with simulations. Thanks to the proper design of the CPW electrodes, the two PDs exhibit an output power roll-off of only 4.3 dB and 4.8 dB from dc to 170 GHz, respectively, and high saturation performance is maintained over the broadband frequency range of 130–170 GHz.

Three‐dimensional spatially resolved phase graph framework

An open-source spatially resolved phase graph framework is proposed for simulating arbitrary pulse sequences in the presence of piece-wise constant gradients with arbitrary orientations in three dimensions. It generalizes the extended phase graph algorithm for analysis of nonperiodic sequences while preserving its efficiency, and is able to estimate the signal modulation in the 3D spatial domain. The framework extends the recursive magnetization-evolution algorithm to account for anisotropic diffusion and exploits a novel 3D k-space grid-merging method to balance the computational effort and memory requirements against acceptable simulation errors. A new postsimulation module is proposed to track and visualize the signal evolution both in the k-space and in the image domain, which can be used for simulating image artifacts or finding frequency-response profiles. To illustrate the developed technique, three examples are presented: (1) fast off-resonance calculation for dictionary building in MR fingerprinting, (2) validation of a steady-state sequence with quasi-isotropic diffusion weighting, and (3) investigation of the magnetization evolution in PRESS-based spectroscopic imaging. The grid-merging algorithm of the proposed framework demonstrates high calculation efficiency exemplified by frequency-response simulation of pseudo steady-state or diffusion-weighted steady-state sequences. It further helps to visualize the signal evolution in PRESS-based sequences. The proposed simulation framework has been validated based on several different example applications for analyzing signal evolution in the frequency and spatial domain.

Reducing bias in dual flip angle T1 -mapping in human brain at 7T.

To address the systematic bias in whole-brain dual flip angle (DFA) T1 -mapping at 7T by optimizing the flip angle pair and carefully selecting radiofrequency (RF) pulse shape and duration. Spoiled gradient echoes can be used to estimate whole-brain maps of T1 . This can be accomplished by using only two acquisitions with different flip angles, that is, a DFA-based approach. Although DFA-based T1 -mapping is seemingly straightforward to implement, it is sensitive to bias caused by incomplete spoiling and incidental magnetization transfer effects. Further bias is introduced by the increased B0 and inhomogeneities at 7T. Experiments were performed to determine the optimal flip angle pair and appropriate RF pulse shape and duration. Obtained T1 estimates were validated using inversion recovery prepared echo planar imaging and compared to literature values. A multi-echo readout was used to increase signal-to-noise ratio, enabling quantification of and susceptibility, χ. Incomplete spoiling was observed above a local flip angle of approximately 20°. An asymmetric gauss-filtered sinc pulse with a constant duration of 700 μs showed a sufficiently flat frequency response profile to avoid incomplete excitation in areas with high B0 offsets. A pulse duration of 700 μs minimized effects from incidental magnetization transfer. When performing DFA-based T1 -mapping one should (a) limit the higher flip angle to avoid incomplete spoiling, (b) use a RF pulse shape insensitive to B0 inhomogeneities and (c) apply a constant RF pulse duration, balanced to minimize incidental magnetization transfer.

A broadband electret-based vibrational energy harvester using soft magneto-sensitive elastomer with asymmetrical frequency response profile

This letter reports a broadband electret-based vibrational energy harvester (eVEH) targeting at applications in low frequency (4–10 Hz) and low excitation (0.1–0.2 g) scenarios. A soft magneto-sensitive elastomer (SMSE) cantilever with low resonance and strong softening nonlinear behaviour is utilized as the broadband oscillator. A spring suspended end-stopper attached to the electret converts low frequency excitation of the SMSE cantilever to high frequency vibrations of the eVEH for efficiency enhancement. An asymmetrical frequency response profile for the SMSE cantilever is intentionally designed to preserve its softening behaviour for broadband performance when the end-stopper is engaged. A proof-of-concept prototype is fabricated and the experiment shows that within a working frequency range of 4.0–8.2 Hz, the eVEH can harvest the average power output of 40.23 μW under a base excitation of 0.2 g.

Amplifier Design for Specified Frequency Response Profiles Using Nullors–Hearing Aids, a Case Study

Applications of nullors and fixator-norator pairs (FNP) for designing amplifiers with certain frequency profiles are discussed. The paper is focused on the design of front-end or stand-alone analog amplifiers that are used in hearing aids. For a given hearing profile (audiogram), a circuit called an audiogram generator circuit (AGC) is initially constructed to produce a frequency response similar to that of an actual audiogram. The hearing aid amplifier is then designed next. As demonstrated, the amplifier is constructed by a combination of an FNP with an AGC. This causes the frequency response of the amplifier to be the inverse of that of the AGC. Hence, the voice received is amplified in such a manner that the patient hears and comprehends a flat and uniform voice for the entire dynamic range. In the second part of this paper, a more advanced design procedure is discussed. The amplifier so designed is capable of producing a specified (non-flat) final hearing profile. Finally, an alternative methodology using feedback theory is discussed in the Appendix. It is shown that with proper buffering this design can also produce a flat hearing profile, as well.

The neural response properties and cortical organization of a rapidly adapting muscle sensory group response that overlaps with the frequencies that elicit the kinesthetic illusion.

Kinesthesia is the sense of limb movement. It is fundamental to efficient motor control, yet its neurophysiological components remain poorly understood. The contributions of primary muscle spindles and cutaneous afferents to the kinesthetic sense have been well studied; however, potential contributions from muscle sensory group responses that are different than the muscle spindles have not been ruled out. Electrophysiological recordings in peripheral nerves and brains of male Sprague Dawley rats with a degloved forelimb preparation provide evidence of a rapidly adapting muscle sensory group response that overlaps with vibratory inputs known to generate illusionary perceptions of limb movement in humans (kinesthetic illusion). This group was characteristically distinct from type Ia muscle spindle fibers, the receptor historically attributed to limb movement sensation, suggesting that type Ia muscle spindle fibers may not be the sole carrier of kinesthetic information. The sensory-neural structure of muscles is complex and there are a number of possible sources for this response group; with Golgi tendon organs being the most likely candidate. The rapidly adapting muscle sensory group response projected to proprioceptive brain regions, the rodent homolog of cortical area 3a and the second somatosensory area (S2), with similar adaption and frequency response profiles between the brain and peripheral nerves. Their representational organization was muscle-specific (myocentric) and magnified for proximal and multi-articulate limb joints. Projection to proprioceptive brain areas, myocentric representational magnification of muscles prone to movement error, overlap with illusionary vibrational input, and resonant frequencies of volitional motor unit contraction suggest that this group response may be involved with limb movement processing.

A profile of auditory-responsive neurons in the larval zebrafish brain.

Many features of auditory processing are conserved among vertebrates, but the degree to which these pathways are established at early stages is not well explored. In this study, we have observed single cell activity throughout the brains of larval zebrafish with the goal of identifying the cellular responses, brain regions, and brain-wide pathways through which these larvae perceive and process auditory stimuli. Using GCaMP and selective plane illumination microscopy, we find strong responses to auditory tones ranging from 100 Hz to 400 Hz. We also identify different categories of auditory neuron with distinct frequency response profiles. Auditory responses occur in the medial octavolateral nucleus, the torus semicircularis, the medial hindbrain, and the thalamus, and the flow of information among these regions resembles the pathways described in adult fish and mammals. The details of these patterns, however, indicate that auditory processing is still rudimentary in larvae. The range of frequencies detected is small, and while different neurons have distinct response profiles, most are sensitive to multiple frequencies, and distinct categories show substantial overlap in their responses. Likewise, while there are signs of nascent spatial representations of frequency in the larval brain, this only faintly resembles the clear tonotopy seen in adult fish and mammals. Overall, our results show that many fundamental properties of the auditory system are established early in development, and suggest that zebrafish will provide a good model in which to study the development and refinement of these pathways.

Magnetic Tuning of Nonlinear MEMS Electromagnetic Vibration Energy Harvester

Ambient mechanical vibrations are an untapped yet attractive energy source for powering wireless sensor nodes in the upcoming Internet-of-Things. Here we demonstrate the magnetically induced frequency tuning effect in a MEMS electromagnetic vibrational energy harvester. Spiral-shaped springs and double-layer copper micro-coils are fabricated on silicon substrate using MEMS fabrication processes. Numerical simulations and finite-element analysis exhibit substantial transformation in the potential energy and stiffness profiles due to controlled changes in the magnetic repulsion force between the transducing and tuning magnets, which effectively modifies the frequency response profile. Specifically, by increasing the repulsive interaction between the transducing and tuning magnets, both the linear and nonlinear frequency response profiles can be shifted toward higher frequencies. This experimentally validated magnetic tuning mechanism can potentially be implemented in MEMS vibrational energy harvesters with other transduction mechanisms and in other micro-mechanical oscillators for broader frequency response tunability.

Indoor Nearby Channel Condition Estimation System

The proposed channel estimation system is based on the collaboration with nearby users channel estimation information. Channel status condition is inaccurate while the estimating pilot sequence applied is undersized to avoid overloading the system throughput and bandwidth efficiency. In this study, we have tried to ascertain the indoor channel varying conditions by way of nearby users’ channel estimated statistics. The distance of the surrounding nearby users has very high correlation to the channel frequency response profile. We have examined the channel profile performance under the proposed nearby channel condition estimations in both line-of-sight (LOS) and non-line-of sight (NLOS) indoor environments statuses.

Investigation of Silicon Nitride as an Excellent Membrane Material for MEMS Ultrasonic Transducers

Silicon micromachining techniques developed over the last few decades’ aid in precise control over nanometer scale structures. Using these techniques to fabricate transducer elements with small electrode spacing efficient and broadband ultrasonic air transducers can be made. In this paper frequency response profile of a circular capacitive micromachined ultrasonic transducer (CMUT) element with silicon nitride as the membrane material is analytically modelled and compared with FEM simulation results. It is observed that the resonance frequency is highly dependent on the membrane material and structural properties. Silicon nitride serves as an excellent material for generation and detection of ultrasonic waves in air. The results are compared with published experimental values and appreciable agreement is obtained.

Spatio-temporal frequency response analysis of forced slip velocity effect on solute concentration oscillations in a reverse osmosis membrane channel

A spatio-temporal frequency response analysis is developed based on the multi-dimensional Fourier transform, which decomposes spatio-temporal input and output signals into travelling waves of different spatial wavenumbers and temporal frequencies. A spatio-temporal pulse test is also developed to allow for simultaneous input of multiple wavenumber–frequency combinations. This analysis is applied to a membrane channel, where the input is an effective streamwise fluid velocity at the wall that varies along the membrane length and in time. The combined effect of the temporal frequencies and spatial wavenumbers of the slip velocity on the resulting solute concentration oscillations, which have the potential for reducing the susceptibility of the membrane to fouling, is analysed at Reynolds numbers of 280 and 560, and Schmidt numbers of 600 and 1200. Frequencies up to 800Hz and wavenumbers up to 500m−1 are studied. It is found that for each wavenumber there is a corresponding temporal frequency that results in a maximum amplitude ratio. Developing a spatio-temporal frequency response profile for such a system helps the design of control input profiles that decrease fouling in membrane systems.

Towards an understanding of the roles of visual areas MT and MST in computing speed.

Towards an understanding of the roles of visual areas MT and MST in computing speed.

Spectral receptive field properties of visually active neurons in the caudate nucleus

Recent studies stress the importance of the caudate nucleus in visual information processing. Although the processing of moving visual signals depends upon the capability of a system to integrate spatial and temporal information, no study has investigated the spectral receptive field organization of the caudate nucleus neurons yet. Therefore, we tested caudate neurons of the feline brain by extracellular single-cell recording applying drifting sinewave gratings of various spatial and temporal frequencies, and reconstructed their spectral receptive fields by plotting their responsiveness as a function of different combinations of spatial and temporal frequencies. The majority of the caudate cells (74%) exhibited peak tuning, which means that their spatio-temporal frequency response profile had a characteristic region of increased activity with a single maximum in the spatio-temporal frequency domain. In one-quarter of the recorded caudate neurons ridge tuning was found, where the region of increased activity, forming an elongated ridge of maximal sensitivity parallel or angled to the spatial or the temporal frequency axis, indicating temporal (16%), spatial (5%) or speed (5%) tuning, respectively. The velocity preference of the ridge tuned caudate nucleus neurons is significantly lower than that of the peak tuned neurons. The peak tuned neuron could encode high velocities, while the ridge tuned neurons were responsible for the detection of moderate and lower velocities. Based upon our results, we suggest that the wide variety of spatio-temporal frequency response profiles might represent different functional neuronal groups within the caudate nucleus that subserve different behaviors to meet various environmental requirements.

The printed circuit board Rogowski coils for plasma current measurements on the J-TEXT tokamak

Compared with the conventional Rogowski coils made by winding wire loops, a printed circuit board (PCB) based on Rogowski coils has some favourable advantages for current measurements, such as large effective area, good linearity, high frequency response, precise geometry and thin profile. This type of Rogowski coil has been widely applied in electrical systems as the current sensor. Nevertheless, the PCB Rogowski coils are introduced for the first time to measure the plasma current on the Joint Texas Experimental Tokamak (J-TEXT). The measurements have shown that this novel PCB Rogowski coil works perfectly and is very suitable for studies of disruption, equilibrium reconstruction, etc.

Temporal Limitations in Object Processing Across the Human Ventral Visual Pathway

Behavioral studies have shown that object recognition becomes severely impaired at fast presentation rates, indicating a limitation in temporal processing capacity. Here, we studied whether this behavioral limit in object recognition reflects limitations in the temporal processing capacity of early visual areas tuned to basic features or high-level areas tuned to complex objects. We used functional MRI (fMRI) to measure the temporal processing capacity of multiple areas along the ventral visual pathway progressing from the primary visual cortex (V1) to high-level object-selective regions, specifically the fusiform face area (FFA) and parahippocampal place area (PPA). Subjects viewed successive images of faces or houses at presentation rates varying from 2.3 to 37.5 items/s while performing an object discrimination task. Measures of the temporal frequency response profile of each visual area revealed a systematic decline in peak tuning across the visual hierarchy. Areas V1-V3 showed peak activity at rapid presentation rates of 18-25 items/s, area V4v peaked at intermediate rates (9 items/s), and the FFA and PPA peaked at the slowest temporal rates (4-5 items/s). Our results reveal a progressive loss in the temporal processing capacity of the human visual system as information is transferred from early visual areas to higher areas. These data suggest that temporal limitations in object recognition likely result from the limited processing capacity of high-level object-selective areas rather than that of earlier stages of visual processing.

Spectral receptive field properties of neurons in the feline superior colliculus

The spatio-temporal frequency response profiles of 73 neurons located in the superficial, retino-recipient layers of the feline superior colliculus (SC) were investigated. The majority of the SC cells responded optimally to very low spatial frequencies with a mean of 0.1 cycles/degree (c/deg). The spatial resolution was also low with a mean of 0.31 c/deg. The spatial frequency tuning functions were either low-pass or band-pass with a mean spatial frequency bandwidth of 1.84 octaves. The cells responded optimally to a range of temporal frequencies between 0.74 cycles/s (c/s) and 26.41 c/s with a mean of 6.84 c/s. The majority (68%) of the SC cells showed band-pass temporal frequency tuning with a mean temporal frequency bandwidth of 2.4 octaves, while smaller proportions of the SC units displayed high-pass (19%), low-pass (8%) or broad-band (5%) temporal tuning. Most of the SC units exhibited simple spectral tuning with a single maximum in the spatio-temporal frequency domain, while some neurons were tuned for spatial or temporal frequencies or speed tuned. Further, we found cells excited by gratings moving at high temporal and low spatial frequencies and cells whose activity was suppressed by high velocity movement. The spatio-temporal filter properties of the SC neurons show close similarities to those of their retinal Y and W inputs as well as those of their inputs from the cortical visual motion detector areas, suggesting their common role in motion analysis and related behavioral actions.

Study of the Enhancement of Dipolar Resonant Excitation by Linear Ion Trap Simulations

Resolution improvements in dipolar resonant excitation have been examined in a round-rod quadrupolar collision cell for values of the Mathieu characteristic exponent beta equal to n/p, where n and m are small integers (prime beta values) versus other beta values where n and p are not small (ordinary beta values). The trajectories of ions moving in the time-varying electric fields of a quadrupole with and without buffer-gas molecules were calculated to determine the relationship of prime and ordinary beta values to frequency resolution for resonant ion excitation and ejection. For prime beta values, the ion trajectory in the hyperbolic quadrupole field will be exactly periodic with a period of at most 4 pi p/Omega, where Omega is the angular frequency of the main drive radio-frequency (RF) potential. Ion trajectory simulations with prime beta versus ordinary beta values show that the motion of ions with prime beta values have simpler trajectories of shorter periods. Frequency response profiles (FRPs) for round-rod quadrupoles at zero pressure show that dipolar resonant excitations with prime beta values exhibit significantly narrower bandwidths than those with ordinary beta values. Simulations show that at 0.05 to 0.8 mTorr of nitrogen, it is possible to reduce the FRP bandwidth by 20% (measured at 50% depth).

The effects of damping on the amplitude and frequency response of a freely vibrating cylinder in cross-flow

We have studied the effects of controlled damping on the amplitude and frequency response profiles of an elastically mounted cylinder in cross-flow. The dimensionless damping parameter, b^*=2b/ρLDU, which is closely related to the traditional “mass-damping” parameter, m^*ζ, was varied over a wide range of values through the use of a variable magnetic eddy current damping system. For low damping and sufficiently high Reynolds number we observe the previously described large-amplitude, three-branch (initial, upper, lower) response profile, and for high damping or low Reynolds number we observe the small-amplitude, two-branch (initial and lower) response profile. However we find that, because of the influence of Reynolds number, the traditional labels of “high mass-damping” and “low mass-damping” are incomplete with regard to predicting a large or small-amplitude response profile. In our experiments, as damping is systematically increased, we observe a transition between these two profiles characterized by a gradual “erosion” and eventual disappearance of the large-amplitude section (upper branch) and the scaling down of the lower branch region. We find that jumps from the upper to the initial branch originate on the 2S/2P boundary in the Williamson–Roshko plane. Another new finding is a hysteresis between the lower branch and the desynchronized region, which only appears at low Reynolds numbers. We also explore changes in the frequency response profile, which are connected with the changes in the amplitude profile, for our upper branch cases. We observe that analogous to the three amplitude branches, there are three distinct branches for the frequency response.