Frequency response

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

Dynamic visualization of subangstrom high-frequency surface vibrations

Abstract: An optical scanning interferometer for accurate imaging of high-frequency surface vibrations is described. Vertical-displacement (out-of-plane) resolution of the interferometer is ∼0.003 A, while lateral resolution is diffraction limited, typically ∼0.5 μm. The high-frequency response is limited by the detector to ∼6 GHz. Both the magnitude and phase are recorded at each point of the scan, so that an accurate measurement of the instantaneous surface shape is obtained. Furthermore, the phase information allows one to make a slow-motion movie of the vibrating surface. Data are presented for three examples in the frequency range 4 MHz–2 GHz.

Oscillating Superleak Second Sound Transducers

Abstract: The construction and performance of mechanical transducers suitable for generating and detecting second sound in pure 4He, and also in dilute 3He–4He mixtures at millidegree temperatures, are described. It is shown that when the normal fluid density is small, the behavior of the transducers can be explained by a simple acoustical model which enables their sensitivity, frequency response, and reflection coefficient to be calculated in terms of easily measured parameters.

Fundamental bounds on the operation of Fano nonlinear isolators

Abstract: Nonlinear isolators have attracted significant attention for their ability to break reciprocity and provide isolation without the need of an external bias. A popular approach for the design of such devices is based on Fano resonators, which, due to their sharp frequency response, can lead to very large isolation for moderate input intensities. Here, we show that, independent of their specific implementation, these devices are subject to fundamental bounds on the transmission coefficient in the forward direction versus their quality factor, input power, and nonreciprocal intensity range. Our analysis quantifies a general tradeoff between forward transmission and these metrics, stemming directly from time-reversal symmetry, and that unitary transmission is only possible for vanishing nonreciprocity. Our results also shed light on the operation of resonant nonlinear isolators, reveal their fundamental limitations, and provide indications on how it is possible to design nonlinear isolators with optimal performance.

Pattern Synthesis of Narrowband Conformal Arrays Using Iterative Second-Order Cone Programming

Abstract: A new design method is proposed for the power or shaped beam pattern synthesis problem of narrowband conformal arrays, where only the magnitude response is specified. The proposed method iteratively linearizes the non-convex power pattern function to obtain a convex subproblem in the design variables, which can be solved optimally using second-order cone programming (SOCP). In addition, a wide variety of magnitude constraints such as non-convex lower bound magnitude constraints can be incorporated. An efficient technique for determining a reasonably good initial guess to the problem is also proposed to further improve the reliability of the method. Computer simulations show that the initial guesses so obtained converge to satisfactory solutions while satisfying various prescribed magnitude constraints. Design results show that the performance of the proposed method is comparable to the optimal solution previously obtained for uniform linear arrays with isotropic elements. Moreover, we show by means of examples that the proposed method is also applicable to general non-convex power pattern synthesis problems involving arbitrary array geometries, arbitrary polarization characteristics and mutual coupling effect.