NEW METHOD FOR ESTIMATION OF MULTI-HARMONIC POWER SIGNAL PARAMETERS

A systematic analytical procedure for simultaneous estimation of the fundamental frequency, the amplitudes and phases of harmonic waves was proposed in this paper. In order to reduce complexity in the calculation of unknown parameters, a completely new reduced analytical expression is derived, which enabled fast and precise estimation with a small numerical error. Individual sinusoidal components stand out from the input complex-harmonic signal with the filter with a finite-impulse response (FIR) comb filters. The algorithm that is proposed in the operation is based on the application of partial derivate of the processed and filtered input signal, after which it is performed weighted estimation procedure to better estimate the values size of the fundamental frequency, amplitude and the multi-sinusoid signal phase. The proposed algorithm can be used in the signal reconstruction and estimation procedures, spectral processing, in procedures for the identification of the system that is observed, as well as other important signal processing areas. Through the simulation check, the effectiveness of the proposed algorithm was assessed, which confirmed its high performance.

Comb filters for the removal of transcranial current stimulation artifacts from single channel EEG recordings

The combination of transcranial alternating current stimulation (tACS) and electroencephalogram (EEG) for mobile and home-based interventions offers the potential for control and adaptation of stimulation parameters. Yet, during stimulation, the EEG is heavily affected by stimulation artifacts. Spatial filters are often unsuited because too few channels are recorded and hardware capabilities are limited. Due to their speed and as they can be used for single channels, we explore the performance of single-channel weighted comb filters on artifact removal. At any given time point t, the recording r(t) is a superposition of a neurophysiological signal n(t), the stimulation artifact a(t) and noise e(t). Now, we can estimate the artifact a(t) based on the recording from an earlier (or later) time-point shifted by the artifacts period. A weighted estimate based on multiple time points has the potential to improve the signal recovery. Therefore, we explored several approaches and evaluated their performance on simulated and real data. The comb kernel filters were implemented in Matlab (https://github.com/agricolab/ARtACS) and Python (https://github.com/agricolab/pyARtACS), and the code is open access under an X11-license. We found that independent of the weighting function, all comb filters exhibit similarity in their suppression of the DC component, the artifacts frequency, and its harmonics. Yet, different weighting functions exhibit different pass-band performance, evident as ringing and amplification, and their induction of time-domain echoes. Interestingly, we note that a causal uniform filter is comparable to more complex approaches, while offering the option for real-time filtering. Comb filters are able to remove tACS artifacts even if only a single channel is available. As comb filters require no assumptions about the shape of the artifact, they might also be useful for filtering of non-sinusoidal, e.g. pulsed or saw-tooth, transcranial current stimulation.

Investigation of a selectable multi-passband microwave photonic filter based on cascaded optical comb filters

A multi-passband microwave photonic filter (MPF) with selectable passband frequency, spanning 0–20 GHz frequency range, is proposed, and experimentally demonstrated, in which passband frequency can be flexibly selected within a maximum passband number to four. The scheme is based on the generation of tunable optical comb lines using a broadband optical source sliced by cascaded optical comb filters, achieved by connecting an in-line birefringence fiber filter and a reconfigurable Lyot filter in series, such that various filter tap spacing and spectral combinations are obtained for the configuration of the MPF. The proposed MPF can operate with four different passband states, namely, single-, dual-, triple-, and quadruple-passband, only by adjusting polarization states of the cascaded optical comb filters. All these passbands are with a 3-dB bandwidth varying from 200 to 460 MHz and more than 20-dB sidelobe suppression.

Reducing the High-Frequency Noise Power in the Automatic Control System Signal by Using Comb Filters

The article addresses the matter of reducing the power of high-frequency noise in the control signal produced by industrial automatic systems through the use of algorithms implementing the properties of comb filters in microprocessor controllers. The specific features relating to the frequency responses of open- and closed-loop automatic control systems of industrial facilities are analyzed - both taken alone and in combination with the characteristics of comb filters. The frequency properties of three filter groups that are conventionally used in continuous automatic control systems are compared with three groups of comb filters that implement similar functions. As applied to control tasks, such filters include real differentiating sections or first-order high-pass filters, first-order lag sections or low-pass filters, and proportional sections. The ratios between the parameters of continuous filters and comb filters at which their frequency properties coincide in the operating frequency band are determined. These ratios known, it becomes possible to synthesize the controllers of systems using the existing techniques. It is shown that the amplitude-frequency responses of comb filters have dips in the high-frequency band, due to which the high frequency noise power is finally decreased by up to 30%. The advantage of comb filters in control systems lies in simplicity of implementing them in digital form in a microprocessor controller. The application of comb filters in automatic control systems makes it possible to cut undesirable harmonic noise of large amplitude in the control signal.