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Electronic Communications
Published in Dale R. Patrick, Stephen W. Fardo, Electricity and Electronics Fundamentals, 2020
Dale R. Patrick, Stephen W. Fardo
Examine the FM signal of Figure 7-28. Note that the modulating component is low-frequency AF and the carrier is RF. In commercial FM, the modulating component could be an audio signal of 20 Hz to 15 kHz. The carrier would be of some RF value between 88 and 108 MHz. As the modulating component changes from 0° to 90°, it causes an increase in the carrier frequency. The carrier rises above the center frequency during this time. Between 90° and 180° of the audio component, the carrier decreases in frequency. At 180° the carrier re-turns to the center frequency. As the audio signal changes from 180° to 270°, it causes a decrease in the carrier frequency. The carrier drops below the center frequency during this period. Between 270° and 360° the carrier rises again to the center frequency, showing that without modulation applied the carrier rests at the center frequency. With modulation, the carrier will shift above and below the center frequency.
Frequency Weighting and Filters
Published in Eddy B. Brixen, Audio Metering, 2020
In sound technology, ten standard octaves are used, as a rule, as set in the ISO standard (see Chapter 27: Spectrum Analyzer, Preferred Frequencies,Table 27.1). The center frequency is the geometric average of the upper and lower cutoff frequencies: fc=fu×f1 The upper and lower boundaries are determined in the following manner: fu=2×fl;fl=fc2;fu=fc×21/3 octave filter The 1/3 octave filter, like the octave filter, has a constant relative bandwidth. There are also standardized center frequencies for these. The bandwidth is 22%.
Measurement Systems: Calibration and Response
Published in Patrick F. Dunn, Michael P. Davis, Measurement and Data Analysis for Engineering and Science, 2017
Patrick F. Dunn, Michael P. Davis
Systems often are characterized by their bandwidth and center frequency. Bandwidth is the range of frequencies over which the output amplitude of a system remains above 70.7 % of its input amplitude. Over this range, M(ω) ≥ 0.707 or −3 dB. The lower frequency at which M(ω) < 0.707 is called the low cut-off frequency. The higher frequency at which M(ω) > 0.707 is called the high cut-off frequency. The center frequency is the frequency equal to one-half of the sum of the low and high cut-off frequencies. Thus, the bandwidth is the difference between the high and low cut-off frequencies. Sometimes bandwidth is defined as the range of frequencies that contain most of the system’s energy or over which the system’s gain is almost constant. However, the above quantitative definition is preferred and used most frequently.
Displacement transmissibility based system identification for polydimethylsiloxane integrating a combination of mechanical modelling with evolutionary multi-objective optimization
Published in Engineering Optimization, 2020
Arun Kumar Sharma, Rituparna Datta, Shubham Agarwal, Bishakh Bhattacharya
Figure 13 justifies the use of multi-objective optimization for this study by comparing the Q-factor and associated error in the half-power point frequencies concerning the experimental transmissibility curve. The Q-factor is a dimensionless parameter that characterizes system behaviour around a resonant frequency relative to its centre frequency. A high Q-factor value indicates a lower rate of energy loss relative to the stored energy. In the present case, it is difficult for a single objective function to characterize system behaviour in all the controlled regions, and especially to model damping behaviour around the resonant frequency; hence the need for another objective function. Thus, to account for any un-modelled dynamics and to address the challenge of reaching closer to experimental damping, a second objective function of minimizing the peak transmissibility error bounded by the half-power point frequency error has been incorporated into the study. It can be discerned from Figures 13(b–d) that the Zener model is competent to be in the closest horizon of the experimental Q-factor and half-power frequency error, closely pursued by the Kelvin–Voigt model.