Frequency response

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

Microwave Microfluidic Sensor Based on a Microstrip Splitter/Combiner Configuration and Split Ring Resonators (SRRs) for Dielectric Characterization of Liquids

Abstract: A microwave microfluidic sensor for dielectric characterization of liquids in real time is presented in this paper. The sensor is implemented in microstrip technology and consists of a symmetric splitter/combiner configuration loaded with a pair of identical split ring resonators (SRRs) and microfluidic channels placed on top of them (gap region). The sensor works in differential mode and sensing is based on frequency splitting. Thus, if the structure is unloaded or if it is symmetrically loaded with regard to the axial plane, only one transmission zero (notch) in the frequency response appears. However, if the axial symmetry is disrupted (e.g., by the presence of different liquids in the channels), two transmission zeros arise, and the difference in magnitude (notch depth) and frequency between such transmission zeros is indicative of the difference in the dielectric properties (complex dielectric constant). A circuit schematic, including transmission line sections to describe the distributed components, lumped elements to account for the SRRs and their coupling to the lines and lumped elements to model the liquid properties, is presented and validated. After proper calibration, the functionality of the proposed sensor is demonstrated by measuring the complex permittivity in solutions of deionized water and ethanol as a function of the ethanol content.

An Assessment of the Impact of Wind Generation on System Frequency Control

Abstract: Rising wind generation penetrations and the distinctive inertial characteristics of associated turbine technology will impact system frequency control. While wind production will displace conventional synchronous plant, empirical study data presented also suggest that the relationship between the total stored turbine kinetic energy and the total system power production for wind is a variable that exhibits significant nonlinearity. Changing trends in system frequency behavior of a power system following the loss of the largest generator are studied in detail here, using simplified frequency control models and extensive simulations of wind penetration scenarios over an extended multiyear timeframe. The system frequency response is characterized by the rate of change of frequency and the frequency nadir. Results show that increasing levels of doubly fed induction generators and high-voltage dc interconnection alter the frequency behavior significantly, and that system operators may have to be proactive in developing solutions to meet these challenges.

Primary Frequency Response From Electric Vehicles in the Great Britain Power System

Abstract: With the increasing use of renewable energy in the Great Britain (GB) power system, the role of electric vehicles (EVs) contributes to primary frequency response was investigated. A tool was developed to estimate the EV charging load based on statistical analysis of EV type, battery capacity, maximum travel range and battery state of charge. A simplified GB power system model was used to investigate the contribution of EVs to primary frequency response. Two control modes were considered: disconnection of charging load (case I) and discharge of stored battery energy (case II). For case II, the characteristic of the EV charger was also considered. A case study shows results for the year 2020. Three EV charging strategies: “dumb” charging, “off-peak” charging, and “smart” charging, were compared. Simulation results show that utilizing EVs to stabilize the grid frequency in the GB system can significantly reduce frequency deviations. However the requirement to schedule frequency response from conventional generators is dynamic throughout the day.

Fractional-Frequency Generators Utilizing Regenerative Modulation

Abstract: By the application of the principle of regeneration to certain modulation systems, a generator of submultiple or other fractional frequency ratio may be obtained. A simple example is obtained by considering a second-order modulator whose output is connected back to a conjugate input by means of a feedback loop including an amplifier and a selective network. If an inputfrequencyfo is applied, it is found that afrequency component f 0 /2 appearing in the feedback path will modulate with the applied frequency to produce sidebands of f 0 /2 and 3f 0 /2. The network and amplifier, being especially efficient for the frequency f 0 /2 and having a gain higher than the modulator loss, will reinforce this component causing it to build up to some steady-state value. Similar processes are possible by which greater submultiple ratios may be obtained. Since the output wave is obtained by a modulation process involving the input wave, it will appear only when an input is applied and then bears a fixed frequency ratio with respect to it. Experiments show that the ability of the generator to produce a fractional frequency is independent of phase shift in the feedback path. Circuits are possible in which the amplitude of the fractional-frequency wave will bear a linear relation to the input wave over a reasonable range and at the same time maintain a constant phase angle between the two waves. Typical circuits are discussed which make use of copper oxide as the modulator elements.

A statistical path loss model for in-home UWB channels

Abstract: This paper describes a simple statistical model for evaluating the path loss in residential environments. It consists of detailed characterization of path loss model parameters of ultra-wideband band (UWB) signals having a nominal center frequency of 5 GHz. The proposed statistical path loss model is for the in-home channel and it is based on over 300,000 frequency response measurements. Probability distributions of the model parameters for different locations are presented. Also, time domain results such as RMS delay spread and percent of captured power are presented.