Frequency response

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

Secondary resonances of electrically actuated resonant microsensors

Abstract: We investigate the response of a microbeam-based resonant sensor to superharmonic and subharmonic electric actuations using a model that incorporates the nonlinearities associated with moderately large displacements and electric forces. The method of multiple scales is used, in each case, to obtain two first-order nonlinear ordinary-differential equations that describe the modulation of the amplitude and phase of the response and its stability. We present typical frequency–response and force–response curves demonstrating, in both cases, the coexistence of multivalued solutions. The solution corresponding to a superharmonic excitation consists of three branches, which meet at two saddle-node bifurcation points. The solution corresponding to a subharmonic excitation consists of two branches meeting a branch of trivial solutions at two pitchfork bifurcation points. One of these bifurcation points is supercritical and the other is subcritical. The results provide an analytical tool to predict the microsensor response to superharmonic and subharmonic excitations, specifically the locations of sudden jumps and regions of hysteretic behavior, thereby enabling designers to safely use these frequencies as measurement signals. They also allow designers to examine the impact of various design parameters on the device behavior.

Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings.

Abstract: We demonstrate a distributed sensing network with 500 identical ultra-weak fiber Bragg gratings (uwFBGs) in an equal separation of 2m using balanced Michelson interferometer of the phase sensitive optical time domain reflectometry (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3 × 3 coupler demodulation. Lab experiments on detecting sound waves in water tank are carried out. The results show that this system can well demodulate distributed acoustic signal with the pressure detection limit of 0.122Pa and achieve an acoustic phase sensitivity of around −158dB (re rad/μPa) with a relatively flat frequency response between 450Hz to 600Hz.

Traveling-wave photodetector theory

Abstract: Photodetector efficiency decreases as bandwidth increases, Bandwidth-efficiency limitations of traveling-wave photodetectors (TWPDs) are substantially greater than those of lumped-element photodetectors because the velocity-mismatch bandwidth limitation is independent of device length. TWPDs can be long for high efficiency without significantly compromising bandwidth. The TWPD is modeled by a terminated section of transmission line with a position-dependent photocurrent source propagating on it at the optical group velocity. A wave model for the transmission line confirms the accuracy of an equivalent-circuit model for electrical wave propagation. The velocity-mismatch impulse and frequency response are determined by absorption coefficient and wave velocities rather than junction capacitance and load resistance. The velocity-mismatch bandwidth limitations can be written in a simple form which elucidates the factors affecting device response, A discretized periodic TWPD is described by the same equations as the fully distributed version. This more complicated device offers additional degrees of freedom in design and potentially improved performance.

Solution to short-term frequency response of wind farms by using energy storage systems

Abstract: The increasing high penetration of wind power is bringing a serious challenge to the frequency regulation of power system, for wind turbine generators are unable to naturally contribute to system frequency response. To address this problem, this study proposes a control strategy to compensate the lack of short-term frequency response ability of wind farms (WFs) by the energy storage system (ESS). First, the rated power and capacity of the ESS, which is installed at the point of common coupling of the WF to make it have similar short-term frequency response ability to that of synchronous generators, are determined. The theoretical minimum rated power of the ESS should be about 5% rated power of the WF, only if the active power output of the ESS is controlled as its rated power during the whole inertial response process. Then, a fuzzy logic controller is designed for the ESS so that the required rated power of the ESS could reach its theoretical minimum value as closer as possible. Simulation results of a simplified practical power system show that WFs with the proposed strategy could response to the frequency change rapidly and support short-term frequency control effectively under various disturbances.