Wideband excitation signal with finite prominent harmonic components is desirable for fast bioimpedance spectroscopy (BIS) measurements. This work introduces a simple method to synthesize and realize a type of periodical stair-step multifrequency synchronized (MFS) signal. The Fourier series analysis shows that the p-order MFS signal f(p, t) has constant 81.06% energy distributed equally on its p 2nth primary harmonics. The synthesis principle is described firstly and then two examples of the 4-order and 5-order MFS signals, f(4, t) and f(5, t), are synthesized. The method to implement the MFS waveform based on a field-programmable gate array (FPGA) and a digital to analog converter (DAC) is also presented. Both the number and the frequencies of the expected primary harmonics can be adjusted as needed. An impedance measurement experiment on a RC three-element equivalent model is performed, and results show acceptable precision, which validates the feasibility of the MFS excitation.
In this paper, the possibility of applying non-obstructive particle damping (NOPD) into the vibration attenuation for heavy-duty machine tool was analyzed and the experimental study on the characteristics of damping vibration attenuation was then carried out. First, the finite-element model for heavy planer type milling machine was built and then the stress state excited by the cutting force in the presence of the holes for filling particles located in the stand column was calculated. Secondly, based on the experiment, the acceleration time-domain waveform and the frequency response function (FRF) between NOPD application and the traditional solid cast-iron column of the planer type milling machine were obtained. Finally it is indicated that NOPD can effectively reduce the amplitude of vibration of heave-duty machine tool and has a good damping effect. Meanwhile, it has some additional effects, such as cost reduction, energy conservation and emission reduction.
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