Complex Transfer Function Research Articles

Instant Volume Visualization using Maximum Intensity Difference Accumulation

AbstractIt has long been recognized that transfer function setup for Direct Volume Rendering (DVR) is crucial to its usability. However, the task of finding an appropriate transfer function is complex and time‐consuming even for experts. Thus, in many practical applications simpler techniques which do not rely on complex transfer functions are employed. One common example is Maximum Intensity Projection (MIP) which depicts the maximum value along each viewing ray. In this paper, we introduce Maximum Intensity Difference Accumulation (MIDA), a new approach which combines the advantages of DVR and MIP. Like MIP, MIDA exploits common data characteristics and hence does not require complex transfer functions to generate good visualization results. It does, however, feature occlusion and shape cues similar to DVR. Furthermore, we show that MIDA – in addition to being a useful technique in its own right – can be used to smoothly transition between DVR and MIP in an intuitive manner. MIDA can be easily implemented using volume raycasting and achieves real‐time performance on current graphics hardware.

The complex controller for three-phase induction motor direct torque control

This paper proposes a design and tuning method for a complex gain controller, based on the three-phase induction motor mathematical model complex transfer function to be used in the direct torque control at low speed which is a problem so far. The design and tuning of the complex gain is done by using the closed loop system frequency-response function. Experimental results are presented to validate the controller and operation at low speed is also explored.

Low-Voltage Log-Domain Complex Filters

Two systematic methods for designing low-voltage log-domain complex filters are introduced in this paper. The first one is based on the transposition of the signal flow graph representation of the linear-domain complex leapfrog prototype filter to the corresponding one in the log-domain. The last one is based on the transposition of the wave equivalents of the elements of the complex passive prototype filter to the corresponding log-domain complex equivalents. Both transpositions are performed by employing an appropriate set of complementary operators that facilitates the derivation of low-voltage log-domain filter configurations. Two design examples are given, where a 12th-order log-domain complex transfer function is realized in order to fulfill the Bluetooth specifications. The derived log-domain filter structures operate at a single 1.2-V-power supply-voltage, and their behavior was evaluated through simulation results. In addition, a comparison concerning important quality factors of both of the proposed structures is performed, and the obtained results are further discussed.

Experimental determination of coupledmicroring filter parameters via pole-zero extraction

A method for directly extracting the coupling coefficients, the resonant frequency detunings and the loss of an N(th)-order serially-coupled microring resonator filter from the measured power spectral responses is presented. The device parameters are obtained from the through-port complex transfer function, which is constructed from the experimentally extracted poles and zeros of the filter. We applied the method to determine the parameters of a symmetric microring doublet fabricated in the Silicon-on- Insulator material platform. Simulated spectral responses using the extracted parameters showed good agreement with the measured data. The extracted parameters along with the poles and zeros of the device provide important information about the fabrication process and can be used to guide the post-fabrication trimming of high-order microring filters.

Compact 10 GHz loopback arrayed-waveguide grating for high-fidelity optical arbitrary waveform generation

We demonstrate a high-performance optical arbitrary waveform shaper based on a single 10 GHz arrayed-waveguide grating with 64 loopback waveguides and integrated amplitude and phase modulators on each waveguide. The design is compact and self-aligning and allows for bidirectional operation. The device's complex transfer function is manipulated and measured over the full 640 GHz passband. To demonstrate optical arbitrary waveform shaping, high-fidelity 15-line shaped waveforms are measured with cross-correlation frequency-resolved optical gating.

Indoor Power-Line Communications Channel Characterization up to 100 MHz—Part II: Time-Frequency Analysis

Estimations of coherence bandwidth and time-delay parameters from wideband channel sounding measurements made in the 30 kHz-100 MHz band in several indoor environments are described in and taken back in this paper. Powerline communications (PLC) modems rather see a channel which starts almost from 2 MHz . A comparison between coherence bandwidth and time-delay parameters estimated in both frequency bands 30 kHz-100 MHz and 2 MHz-100 MHz is elaborated in this paper. Results are intended for applications in high-capacity indoor power-line networks. The investigation is aimed to show that the PLC channel studies in a band starting from a frequency lower than 2 MHz distorts the real values that an implementer should take, as the PLC modem see only the frequencies from 2 MHz. The coherence bandwidth and the time delay parameters are estimated from measurements of the complex transfer functions of the PLC channels. For the 30 kHz-100 MHz frequency band, the 90 th percentile of the estimated coherence bandwidth at 0.9 correlation level stay above 65.5 kHz and below 691.5 kHz. It was observed to have a minimum value of 32.5 kHz. The maximum excess delay spread results show that 80% of the channels exhibit values between 0.6 s and 6.45 s. And a mean rms delay spread of 0.413 s is obtained. The passage to the 2 MHz-100 MHz frequency band induced an increase of the coherence bandwidth, whose min value is brought back to 43.5 kHz, and an important reduction of the time delay parameters: The min, max, mean, and standard deviation values of the maximum excess delay are almost divided by 2. For the twice frequency bands, this paper studies, also, the variability of the coherence bandwidth and time-delay spread parameters with the channel class , and thus with the location of the receiver with respect to the transmitter, and finally relates the rms delay spread to the coherence bandwidth.

Indoor Power-Line Communications Channel Characterization Up to 100 MHz—Part I: One-Parameter Deterministic Model

Advanced communication technologies have allowed the power-line-communication (PLC) channel to be a transmission medium that enables the transfer of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents a deterministic model describing the magnitude and phase of complex transfer functions of power-line networks using only one parameter. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath characteristic of PLC channels is introduced. A statistical-based channel magnitude generator is built, and a group delay-based phase model is suggested.

Rapid updating of optical arbitrary waveforms via time-domain multiplexing

We demonstrate high-fidelity optical arbitrary waveform generation with 5 GHz waveform switching via time-domain multiplexing. Compact, integrated waveform shapers based on silica arrayed-waveguide grating pairs with 10 GHz channel spacing are used to shape (line-by-line) two different waveforms from the output of a 10-mode x 10 GHz optical frequency comb generator. Characterization of the time multiplexer's complex transfer function (amplitude and phase) by frequency-resolved optical gating permits compensation of its impact on the switched waveforms and matching of the measured and target waveforms to better than G'=5%.

HRTF modeling in due consideration variable torso reflections

Head related transfer functions (HRTFs) describe the physical path from an acoustical source to the ears. It can be gained within the relation of two measurements. The first will give the reference sound pressure in the virtual middle of the head the second has to be done in both ears. In literature exhaustive investigations concerning the idealized location of the second position can be found. Beyond that measurements with various artificial heads and human-beings considering various source directions (azimuth and elevation) with different angular resolutions have been undertaken. The obtained HRTFs exhibit, with subject to the examined source position, frequency dependent magnitude and phase. These complex transfer functions are caused by various reflections, diffractions, pressure superelevation, and shadowing, respectively. Reflections are caused form pinna, head and torso, too. Heretofore during determination of the transfer functions the influence of various head-torso arrangements have not be considered. Within this paper the differences which will be caused due to different head-torso angles will be highlighted. Beyond that a numerical model based on interpolation using spherical harmonics will be presented. By the aid of that model the integration within an existing binaural resynthesis model can be realized and perceptual differences within a dynamic system can be investigated.

Co-FXLMS 알고리듬을 이용한 능동소음제어 성능의 향상

The active control technique mostly uses the least-mean-square(LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time, particularly when the Filtered-X LMS(FXLMS) algorithm is applied to an active noise control(ANC) system. However, FXLMS algorithm has the demerit that stability of the control is decreased when the step size become larger but the convergence speed is faster because the step size of FXLMS algorithm is fixed. As a result, the system has higher probability which the divergence occurs. Thus the Co-FXLMS algorithm was developed to solve this problem. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Co-FXLMS algorithm is presented in comparison with the FXLMS algorithm. Simulation and experimental results show that active noise control using Co-FXLMS is effective in reducing the noise in duct system.

Modeling of Three-Phase Dynamic Systems Using Complex Transfer Functions and Transfer Matrices

A compilation of methods for modeling and analysis of three-phase dynamic systems-such as AC machines, resistance-inductance-capacitance components, and power electronic converters including their control algorithms-using complex transfer functions and transfer matrices is presented. Restrictions of the two modeling methods and relations between them are given. Various frequency-domain results, including closed-loop stability theory, are presented. The theory is illustrated by several examples showing areas of application.

Sea Ice and Current Response to the Wind: A Vector Regressional Analysis Approach

The authors describe a two-dimensional (vector) regressional model for examining the anisotropic response of ice drift and ocean current velocity (“drift velocity”) to surface wind forcing. Illustration of the method is limited to sea ice response. The principal mathematical and physical properties of the model are outlined, together with estimates of the “response matrices” and the corresponding “response ellipses” (drift velocity response to a unity wind velocity forcing). For each direction, φ, of the wind vector the method describes a corresponding “wind factor” α(φ) (relative drift speed) and “turning angle” θ(φ) (the angle between the drift velocity and wind vector). The major ellipse axis corresponds to the direction of the “effective wind” (φ = φmax) and the minor axis to the direction of the “noneffective” wind. The eigenvectors of the response matrix define wind directions that are the same as the wind-induced drift velocity directions. Depending on the water depth and offshore distance, six analytical cases are possible, ranging from rectilinear response ellipses near the coast to purely circular response ellipses in the open ocean. The model is used to examine ice drift along the western shelf of Sakhalin Island (Sea of Okhotsk). Responses derived from the vector regression (four parameter) method are less constrained and therefore more representative of wind-induced surface motions than those derived using the traditional complex transfer function (two parameter) approach.

A system model for assessing scalar dissipation measurement accuracy in turbulent flows

A system model is developed to investigate independent and coupled effects of resolution, noise and data processing algorithms on the accuracy of the scalar gradient and dissipation measurements in turbulent flows. Finite resolution effects are simulated by spectral filtering, noise is modelled as an additive source in the model spectrum and differencing stencils are analysed as digital filters. In the current study, the effective resolution is proposed to be a proper criterion for quantifying the resolution requirement for scalar gradient and dissipation measurement. Both effective resolution and noise-induced apparent dissipation are mainly determined by the system transfer function. The finite resolution results, based upon a model scalar energy spectrum, are shown to agree with non-reacting experimental data. The coupled resolution-noise results show three regions in the mean scalar dissipation rate measurement: noise-dominated region, noise-resolution correlated region and resolution-dominated region. Different noise levels lead to different resolution error curves for the measured mean scalar dissipation rate. Experimental procedures and guidelines to improve the scalar gradient and dissipation experiments are proposed, based on these model study results. The proposed system approach can also be applied to other derived quantities involving complex transfer functions.

Evaluation of head‐related transfer function on the opposite side to a sound source

A head‐related transfer function (HRTF) is a complex acoustic transfer function because it includes the effect of reflection and refraction due to the head and ears. The HRTFs on the opposite side to a sound source have more complex characteristics and lower power than HRTFs that are on the same side as a sound source. Moreover, many previous studies about monaural sound localization showed that performances of sound localization on the opposite side were not precise. From these results, it can be assumed that the HRTFs on the opposite side are not necessary to use listener’s own. In our experiments, several stimuli that convolved with the HRTFs were presented to evaluate individuality. The left ear HRTF was the subject’s own, and the right ear HRTF was the subject’s own and others. The differences between the subject’s HRTF and others’ HRTFs were evaluated using the spectral distortion score. The sound source azimuths were from 0 to 180 deg at intervals of 30 deg; the front was 0 deg, the left side was 90 deg, and the back was 180 deg. The results shows that the right ear HRTFs between 30 and 150 deg azimuth have low individualities.

An approach for powertrain gear transmission error prediction using the non-linear finite element method

Research has established that gear transmission error (TE) is the predominant source of system excitation and via a complex transfer function produces noise in the powertrain system. Thus, reduction and control of TE will result in improved NVH performance. This paper will introduce an accurate method for estimating TE in powertrain transmission systems through an accurate gear contact analysis. To achieve high geometry accuracy, gear tooth geometry will be mathematically generated by using Python script interfacing with finite element analysis (FEA) software instead of importing from other computer aided design (CAD) packages. Real rolling and sliding contact simulations have been achieved by the latest nonlinear FEA techniques. High-quality meshes for contact surfaces have been obtained by advanced surface-based tie constraint techniques. An effective way to reduce TE is through gear microgeometry modification, i.e. crowning, tip relief, and lead correction. Gear micro-geometry modification will be mathematically achieved through Python script interfaced with finite element models.

Force constant calibration corrections for silicon position detectors in the near-infrared

The accurate calibration of the force constant of the probe in atomic force microscopy and optical tweezers applications is extremely important for force spectroscopy. The commonly used silicon detectors exhibit a complex transfer function for wavelengths >850 nm, which limits the detection bandwidth leading to serious errors in the force constant determination. We show that this low-pass effect can be compensated for using the frequency response of the detector. This is applicable for calibrations in both atomic force microscopy and optical tweezers. For optical tweezers an additional correction method is discussed based on fitting an expression in which the low-pass characteristics are already accounted for.

On the balance between delay, bandwidth and signal distortion in slow light systems based on stimulated Brillouin scattering in optical fibers

We describe systematic measurements of the gain and delay spectra in a slow light system based on stimulated Brillouin scattering in optical fibers. The measurements yield the system complex transfer function with which delays and signal distortion can be calculated for any input signal. The theoretical predictions are confirmed experimentally for single pulses as well as 50 Mb/s data streams in a system which employs pump modulation to modify the gain and delay spectra of the SBS process.

Prediction of variation in MIMO channel capacity for the populated indoor environment using a Radar cross-section-based pedestrian model

Multipath propagation is a fundamental requirement for the operation of multiple-input multiple-output (MIMO) wireless systems. However, at ultrahigh frequency (UHF) and above, pedestrian movement may significantly affect the multipath propagation conditions in indoor environments. For the first time, a systematic analysis of the effect of pedestrian movement on channel capacity for an otherwise line-of-sight MIMO link in a single room is presented. A novel channel model for the populated indoor environment is also introduced, based on geometrical optics and a detailed radar cross-section representation of the human body. The new model generates a temporal profile for the complex transfer function of each antenna combination in the MIMO system in the presence of specified pedestrian movement. Channel capacity values derived from this data are important in terms of understanding the limitations and possibilities for MIMO systems. Capacity results are presented for a 42-m/sup 2/ single room environment, using a 2.45-GHz narrowband 8/spl times/8 MIMO array with 0.4/spl lambda/ element spacing. Although the model predicts significant increases in the peak channel capacity due to pedestrian movement, the improvement in mean capacity values was more modest. For the static empty room case, the channel capacity was 10.9 b/s/Hz, while the mean capacity under dynamic conditions was 12.3 b/s/Hz for four pedestrians, each moving at the same speed (0.5 m/s). The results presented suggest that practical MIMO systems must be sufficiently adaptive if they are to benefit from the capacity enhancement caused by pedestrian movement.

Wideband Measurements of Ice Sheet Attenuation and Basal Scattering

We are developing a multifrequency multistatic synthetic aperture radar (SAR) for determining polar ice sheet basal conditions. To obtain data for designing and optimizing radar performance, we performed field measurements with a network-analyzer-based system during the 2003 field season at the North Greenland Ice Core Project camp (75.1 N and 42.3 W). From the measurements, we determine the ice sheet complex transfer function over the frequency range from 110-500 MHz by deconvolving out the system transfer function. Over this frequency range, we observe an increase in total loss of 8/spl plusmn/2.5 dB using a linear regression to the log-scale data. With the ice sheet transfer function and an ice extinction model, we estimate the return loss from the basal surface to be approximately 37 dB. These measurements have broad applicability to interpreting radar-sounding data, which are widely used in glaciological studies of the polar ice sheets. These data have also been used in the link budget for the design considerations of the multifrequency multistatic SAR system.

Approximation of complex IIR bandpass filters without arithmetic symmetry

Complex transfer functions are not restricted to having complex-conjugate symmetry in the frequency-domain, as is the case for real filters. This gives them more flexibility when they are used in communication systems with complex signals, such as intermediate frequency signals of wireless communication systems. This paper describes a set of algorithms and procedures that can be used in solving the approximation problem involved in deriving complex infinite-impulse-response bandpass transfer functions directly, without the requirement of first designing a real-transfer-function prototype filter, which is then frequency translated. Because the requirement for a real prototype filter is eliminated, the filters need not have arithmetic symmetry; this results in superior stopbands with smaller filter orders. The procedures can be used for both continuous and discrete-time filters, can allow for arbitrary stopband specifications, and can be used for either equi-ripple or monotonic passbands.