Design Of Comb Filters Research Articles

The Application of EMD Denoising in Sampled Grating Comb Filter Design

In order to design sampled grating comb filter, the effect of sampled fiber grating’s parameters on reflective spectrum was analyzed. Sampled grating comb filter can be applied in the intensive optical communication system. Sampled grating reflective spectrum was simulated by changing the parameters. Four kinds of sampled grating optical comb filter were designed. In order to optimize the function of sampled grating comb filter, a filtering analysis and denoising method by using EMD were proposed. This method divides intrinsic mode function into two modes by EMD. One of mode was that signal components mode play dominant role, the other mode was that ınoise component mode plays dominant role. The mode of noise component play dominant role was removed. It can denoise reflective spectrum through restructuring signal. The smooth reflective spectrum and delay spectrum can be got after denoising. So that the peak value of sampled grating can be judged accurately.

Design and FPGA implementation of multiplierless comb filter

SummaryThe main objective of this paper is to design and implement minimum multiplier, low latency structures of a comb filter. Multipliers are the most area and power consuming elements; therefore, it is desirable to realize a filter with minimum number of multipliers. In this paper, design of comb filters based on lattice wave digital filters (LWDF) structure is proposed to minimize the number of multipliers. The fundamental processing unit employed in LWDF requires only one multiplier. These lattice wave digital comb filters (LWDCFs) are realized using Richards' and transformed first‐order and second‐order all‐pass sections. The resulting structural realizations of LWDCFs exhibit properties such as low coefficient sensitivity, high dynamic range, high overflow level, and low round‐off noise. Multiplier coefficients of the proposed structures are implemented with canonic signed digit code (CSDC) technique using shift and add operations leading to multiplierless implementation. This contributes in reduction of number of addition levels which reduces the latency of the critical loop. A field programmable gate array (FPGA) platform is used for evaluation and testing of the proposed LWDCFs to acquire advantages of the parallelism, low cost, and low power consumption. The implementation of the proposed LWDCFs is accomplished on Xilinx Spartan‐6 and Virtex‐6 FPGA devices. By means of examples, it is shown that the implementations of the proposed LWDCFs attain high maximum sampling frequency, reduced hardware, and low power dissipation compared with the existing comb filter structures. Copyright © 2017 John Wiley & Sons, Ltd.

Design of variable comb filter using FIR variable fractional delay element

In this paper, a new approach is proposed for the design of infinite-impulse-response (IIR) comb filter. The problem of the comb filter design is transformed into that of fractional delay filter design. Using the proposed method, the multiplier inside the proposed structure can be fixed regardless the value of fundamental frequency of harmonic interferences. This improvement makes the proposed structure be possible for the design of variable cases. To realize variable comb (VC) filter, the variable fractional-delay (VFD) filter is designed in weighted least-squares (WLS) sense first. Then, by embedding the designed VFD filter with a switch, the variable comb filter could be implemented in a proposed structure. Several experimental results and examples are presented to demonstrate the effectiveness of the proposed method.

Analysis of polarization-independent tunable optical comb filter by cascading MZI and phase modulating Sagnac loop

A novel scheme of tunable optical comb filter constructed by cascading a polarization-swapping MZI and a phase modulating Sagnac loop is proposed. The key features of this comb filter design are its polarization-independence and high speed in wavelength tuning. The wavelength tunability can be readily achieved by incorporating an electro-optic phase modulator into the Sagnac loop. In addition, the filter can be made amplitude adjustable as well. The filter will be desirable for multi-wavelength fiber lasers, multi-channel optical signal processing and optical WDM systems.

Multifrequency characterization of viscoelastic polymers and vapor sensing based on SAW oscillators

Simplified relations for the changes in SAW velocity and attenuation due to thin polymer coatings and vapor sorption are presented by making analytic approximations to the complex theoretical model developed earlier by Martin et al. [Anal. Chem. 66 (14) (1994) 2201–2219]. The approximate velocity relation is accurate within 4% for the film thicknesses up to 20% of the acoustic wavelength in the polymer film, and is useful for analyzing the mass loading, swelling and viscoelastic effects in SAW vapor sensors. The approximate attenuation relation is accurate within 20% for very thin films, (less than 2% of the acoustic wavelength in the film). Based on these relations, a new procedure for determination of polymer viscoelastic properties is described that exploits the frequency dependence of the velocity and attenuation perturbations, and employs multifrequency measurement on the same SAW platform. Expressions for individual contributions from the mass loading, film swelling and viscoelastic effects in SAW vapor sensors are derived, and their implications for the sensor design and operation are discussed. Also, a new SAW comb filter design is proposed that offers possibility for multimode SAW oscillator operation over a decade of frequency variation, and illustrates feasibility for experimental realization of wide bandwidth multifrequency SAW platforms.

Inharmonic dispersion tunable comb filter design using modified IIR band pass transfer function

An excitation/filter system of Inharmonic sound synthesis signal is presented with an application to piano, a stiff string instrument. Specific features of the piano string important in wave propagation, dispersion due to stiffness, frequency dependent losses and presence of phantom partials are included in the proposed model. The modified narrow bandpass filter is used as a basic building block in modeling the vibrating structure. The parallel bank of narrow band pass filters is used to model the dispersion. The center frequencies of narrow bandpass filters can be tuned to follow the same relation as the partial frequencies of piano tone. Novel loss filter is designed to implement frequency dependent losses. The resulting model is called as Inharmonic Dispersion Tunable Comb filter.

Perceptually balanced filter response for binaural dichotic presentation to reduce the effect of spectral masking

Earlier investigations show that the scheme of binaural dichotic presentation with spectral splitting of speech signal helps in reducing the effect of spectral masking for persons with moderate bilateral sensorineural hearing impairment. Speech perception improved by employing filters with interband crossover gain adjusted between 4 and 6 dB below the pass band gain. The relationship between scaling factors for a tone presented to the two ears, so that perceived loudness is that of a monaural presentation, is investigated for design of comb filters with improved perceptually balanced response. Results from the listening tests show that, for perceptual balance, the sum of the two scaling factors should be constant, indicating that the magnitude response of the comb filters should be complementary on a linear scale.

Signal representation and estimation of spectral parameters by inharmonic comb filters with application to the piano

A method for signal representation in the frequency domain is described, using a comb filter design with nonequidistant spacing of the filter bands (inharmonic comb filter). This approach offers several advantages when studying the properties of a signal source with inharmonic components. An analytical relation between the partial frequencies, or some hypothesis of this relation, is needed beforehand. An application of the method is presented in which piano tones are visualized in a new way, allowing for an automatic and accurate measurement of fundamental frequency and inharmonicity coefficient. Possible directions for further development and some interesting application areas are discussed.

An active comb filter design for harmonic interference removal

The active comb filter without the use of inductors is very useful for removing harmonic noise such as power line interference in bio‐medical signals. This paper presents an approach for the design of an active comb filter. A table composed of 62 bandpass filters is proposed, which can be used in the design of the presented active comb filter. Simulation results and performance tests are given to demonstrate the feasibility of the presented active comb filter

A comb filter design using fractional-sample delay

In this paper, a new comb filter design method using fractional sample delay is presented. First, the specification of the comb filter design is transformed into that of fractional delay filter design. Then, conventional finite impulse response (FIR) and allpass filter design techniques are directly applied to design fractional delay filter with transformed specification. Next, we develop a constrained fractional delay filter design approach to improve the performance of the direct design method. Finally, several design examples and an experiment of power line interference removal in an electrocardiogram (ECG) signal is demonstrated to illustrate the effectiveness of this new design approach.

A targeting-and-extracting technique to enhance hearing in the presence of competing speech.

A targeting-and-extracting procedure of speech enhancement for hearing aids in the presence of background noise, especially competing speech, is proposed. The procedure is composed of two steps: targeting by a fixed (or deterministic) beamforming array, followed by a post-targeting extracting step. Emphasis is placed on the extracting step, which performs noise cancellation based on the acoustic difference between the desired speech and interfering speech. Either comb filtering or attenuation is applied to the signal in accordance with the current voiced/unvoiced/silence state of the desired signal. The comb filter design is based on the fundamental pitch frequency of the desired speech. Algorithms for deciding the voiced/unvoiced/silence state and determining the fundamental frequency are developed. The performance of the system is evaluated through computer simulation. The simulation results indicate significant noise cancellation and intelligibility improvement.

Studies of design parameters for interferometric methane sensors

Methane detectors based on the absorption of infrared radiation show some promise as the basis of sensitive and accurate industrial instrumentation. Comb filter methods that utilize the vibration-rotation structure of the methane spectrum in an optically efficient manner have recently aroused particular interest in this context. We describe a mathematical model to simulate the behavior of scanning interferometric comb filters in methane detection systems and discuss the use of the model to investigate optimum design parameters for such systems. The behavior of prototype methane detectors based on scanning Fabry-Pérot and Mach-Zehnder interferometers is briefly reported. Possible techniques for obtaining further improvements in the design of comb filters for methane detection are suggested.