Low-pass Lter Research Articles

Performance Comparison of QPSK Based Single and Double Stage Digital Interpolators

In this paper, the performance of single stage and double stage digital interpolators has been compared and has been showed that by using multi stage interpolation system the reliability of any communication system increases drastically. Digital signal interpolation systems can be implemented in a variety of ways. The basic interpolator for up-sampling can be a combination of an expander unit with an interpolation low-pass lter in cascade. Complicated implementations can be done by connecting multiple expander and low-pass lter pairs in cascade. This paper presents the e cient implementation of digital interpolation systems for up-sampling of single stage and double stage digital interpolators by using quadrature phase shift keying technique. Comparison is done in terms of spectrum of generated signal, envelope power, modulated signal trajectory, input and output constellation and noise performance.

Assessment of Delamination Fracture Load of Stringer Stiffened Composite Panel

Conclusions The concept and design freedom introduced by adopting spatial Ž lters to second-orderpartial differential equationsystems have been successfully veriŽ ed by an one-dimensional clamped-free shaft-based rotational acceleration rate sensor. It was shown that spatial Ž lters can introduce a no-phase delay low-pass Ž lter by offering a weighting function with the prechosen surface electrode, and the introduction of this odd function brings a differentiation to the transfer function. The method of imaging was introduced to extend the spatial Ž lter application area from a Ž nite structure to an inŽ nite domain, that is, spatial Ž lters can now be placed near or even at the boundaries.BeneŽ ts associatedwith adoptingspatial Ž lters to point sensors successfully demonstrate theoretically as well as experimentally the advantagesof the newly developed rotational acceleration rate sensor. In summary, expanding the bandwidth of rotational accelerationrate sensors by using newly developed Ž nite domain spatial Ž lters has been successfully veriŽ ed both theoretically and experimentally.

Experimental Robustness Study of Positive Position Feedback Control for Active Vibration Suppression

Abstract : POSITIVE position feedback (PPF) control was introduced by Goh and Caughey in 1985 to control vibrations of large exible space structures. A PPF controller has several distinguished advantagesas compared to then widely used velocity feedbackcontrol laws. It is insensitive to spillover, where contributions from unmodeled modes affect the control of the modes of interest. As a second-order low-pass lter, a PPF controller rolls off quickly at high frequencies and is well suited to controlling the lower modes of a structure with well separated modes. Because of these advantages, PPF controller along with smart materials, in particular PZT (lead zirconatetitanate) type of piezoelectricmaterial, has been applied to many exible systems to achieve active damping. The design of a PPF controller requires the natural frequency of a structure. In practice, the structuralnatural frequencymay not be known exactlyor itmay varywith time.When the frequencyused in thePPF controller is different from that of the structure, the performance of the PPF control will adversely affected. Despite that PPF control is widely researched in literature, robustness study of PPF control when natural frequency is inexactly known is not reported. This motivates the authors to conduct experimental study of robustness of PPF control in active vibration suppression of a smart exible structure.