Notch Filters

We develop a canonical, adaptive cascade-structure IIR notch filter to detect and track multiple time-varying frequencies in additive white Gaussian noise. The algorithm uses allpass frequency transformation filters and a truncated gradient. Simulations indicate that our algorithm is computationally simple, converges rapidly, and has good frequency resolution

Background: In monitoring mode only two leads are used so that ECG waveform has large R wave amplitude so lead II is chosen. The monitoring mode bandwidth is 0.5-50 Hz as only rhythmic information is required. The present paper deals with the digital filtering method to reduce noise artifacts in the ECG signal. 4th order Butterworth, Chebyshev 1, Chebyshev 2 and elliptic filters are used to reduce noise interference from ECG signals. Method: ECG signal is taken from physionet database. A ECG signal (without noise) is added with 50 Hz interference, base line wander noise of .15 Hz and high frequency noise of 150 Hz and processed by low pass filter of cutoff frequency of 50 Hz, High pass filter of cutoff frequency of 0.5 Hz and notch filter of 3 dB stop band bandwidth 0.2(49.9–50.1) Hz. The order of filter is taken as 4. In this paper 4th order Butterworth, Chebyshev 1, Chebyshev 2 and elliptic filters are applied on the noisy ECG signal. Simulation results are also shown. Comparison of these filters are done. All the designs are implemented using MATLAB FDA tool.

Harmonics pollution, due to the increasing use of nonlinear loads, such as converters and solid state switching devices, has become a serious problem in power systems. Active power filters have been used effectively to eliminate harmonic components generated by nonlinear loads. Precision of harmonic detection is one of the most important factors of active power filters. This paper describes a harmonic detection method to extract harmonic components in a distorted signal. Experimental results verify its validity.

Keywords: Power Quality, Active Harmonic Filters, Harmonic Detection, Notch filter, Switched-Capacitor Filter.

A compact, circular UWB fractal antenna with triple reconfigurable notch rejection bands is proposed. It rejects the crowded frequency bands WiMAX, WLAN and X band interferences produced in UWB communication systems. The proposed fractal structure consists of a basic circular patch with circular fractal iterations. By employing this new structure of fractals, the overall size of antenna is reduced 53% to 21x25 mm, in comparison with traditional circular monopole antenna. The implemented antenna operates at 3.1-10 GHz. Re-configurability is realized by designing slots and split ring resonators in desired frequencies with the attached PIN diodes. WLAN band rejection was realized by creating a pair of optimized L-shaped slots in the ground plane. By etching a split ring resonator and a U-shaped slot, X and WiMAX bands were also rejected. Furthermore, by attaching diodes to aforementioned slots and designating the diodes on/off, different bands can be included or rejected. In time domain, the antenna properties are evaluated by a figure of merit called fidelity factor. Finally, the antenna properties are measured in anechoic chamber and the results agrees with simulation findings.

Filtering is a common technique to develope a filtered, clean and obvious signal from source in the field of medical signal processing. In the experiment we will use Matlab to build such a Notch Filter for removal of power-line noise without any disturbance of any useful signals.

This paper presents a digital implementation of a new and simple control technique for single-phase Hybrid Active Power Filter (HAPF). The main control consists of an accurate estimation technique used to extract harmonic current generated by nonlinear loads. The estimation of harmonic current is done by using multiple units of an Adaptive Notch Filter (ANF) linked together in parallel structure; each unit is used to estimate a specified harmonic component. The frequency estimation is then carried out based on the output of these units. Therefore, the sum of these harmonic components will be the reference signal for the active power filter to generate the appropriate compensation signal. A laboratory prototype model of the HAPF was developed and its control strategy was implemented digitally in TMS320F2808. The theoretical expectations were verified and demonstrated experimentally.