Frequency response

About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.

On the design and implementation of FIR and IIR digital filters with variable frequency characteristics

Abstract: This paper studies the design and implementation of finite-impulse response (FIR) and infinite-impulse response (IIR) variable digital filters (VDFs), whose frequency characteristics can be controlled continuously by some control or tuning parameters. A least squares (LS) approach is proposed for the design of FIR VDFs by expressing the impulse response of the filter as a linear combination of basis functions. It is shown that the optimal LS solution can be obtained by solving a system of linear equations. By choosing the basis functions as piecewise polynomials, VDFs with larger tuning range than that of ordinary polynomial based approach results. The proposed VDF can be efficiently implemented using the familiar Farrow structure. Making use of the FIR VDF so obtained, an Eigensystem Realization Algorithm (ERA)-based model reduction technique is proposed to approximate the FIR VDF by a stable IIR VDF with lower system order. The advantages of the model reduction approach are: 1) it is computational simple which only requires the computation of the singular value decomposition of a Hankel matrix; 2) the IIR VDF obtained is guaranteed to be stable; and 3) the frequency response such as the phase response of the FIR prototype is well preserved. Apart from the above advantages, the proposed IIR VDF does not suffer from undesirable transient response during parameter tuning found in other approaches based on direct tuning of filter parameters. For frequency selective VDFs, about 40% of the multiplications can be saved using the IIR VDFs. The implementation of the proposed FIR VDF using sum-of-powers-of-two (SOPOT) coefficient and the multiplier block (MB) technique are also studied. Results show that about two-third of the additions in implementing the multiplication of the SOPOT coefficients can be saved using the multiplier block, which leads to significant savings in hardware complexity.

Analysis of fibre transfer function and determination of receiver frequency response for dispersion supported transmission

Abstract: It is shown that a frequency modulated optical transmitter at 1.5 µm in conjunction with a standard singlemode fibre can have highpass transfer characteristics. Equalising this frequency response, the characteristics of the receiver lowpass filter can be determined that are required for the method of dispersion supported transmission.

Frequency response of power systems with variable speed wind turbines

Abstract: Summary form only given. As wind penetration levels on power systems increase worldwide and synchronous generation is displaced, the dynamic characteristics of these systems, and hence the protocols for how they are operated, are changing. One issue, of particular concern, is the resulting reduction in system inertia since modern variable speed wind turbines do not inherently contribute to the inertial response of the system. Such devices can, however, be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation. Unlike conventional machines, however, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators. As a result, it is likely that uncertainty will exist over the inertial response capability of the system at high wind penetration levels. In this paper, the frequency response capability is assessed on a test system and the effectiveness of wind turbines' contribution to system inertial response is evaluated in the context of future system requirements.

A normal mode theory for the Rayleigh wave amplifier

Abstract: A Rayleigh acoustic wave traveling on the surface of a semi-infinite piezoelectric medium may be amplified by interaction with drifting carriers in an adjacent semiconductor. The gain and frequency response of this interaction is determined here by using a normal mode expansion of the Rayleigh wave piezoelectric fields. The configuration which uses a thin semiconductor film supported by a semi-infinite dielectric and separated from the piezoelectric by a small air gap is described in detail and the results are expressed in a form that clearly shows the effect of piezoelectric, air gap, and semiconductor parameters. Comparisons with experimental data for the lithium niobate-silicon film configuration show that acoustic gains on the order of 100 dB/cm can be obtained in the frequency range above 0.1 GHz.

Frequency Modeling of Open-Channel Flow

Abstract: A good model is necessary to design automatic controllers for water distribution in an open-channel system. The frequency response of a canal governed by the Saint-Venant equations can be easily obtained in the uniform case. However, in realistic situations, open-channel systems are usually far from the uniform regime. This paper provides a new computational method to obtain a frequency domain model of the Saint-Venant equations linearized around any stationary regime (including backwater curves). The method computes the frequency response of the Saint-Venant transfer matrix, which can be used to design controllers with classical automatic control techniques. The precision and numerical efficiency of the proposed method compare favorably with classical numerical schemes (e.g., Runge–Kutta). The model is compared in nonuniform situations to the one given by a finite difference scheme applied to Saint-Venant equations (Preissmann scheme), first in the frequency domain, then in the time domain. The proposed ...