Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Utilizing nonlinear phenomena to locate grazing in the constrained motion of a cantilever beam

Abstract: Grazing behavior in soft impact dynamics of a harmonically based excited flexible cantilever beam is investigated. Numerical and experimental methods are employed to study the dynamic behavior of macro- and micro-scale cantilever beam–impactor systems. For off-resonance excitation at two and a half times the fundamental frequency, the response of the oscillating cantilever experiences period doubling as the separation distance or clearance between the beam axis and the contact surface is decreased. The nonlinear phenomenon is studied by using phase portraits, Poincare sections, and spectral analysis. Motivated by atomic force microscopy, this general dynamic behavior is studied as a means to locating the separation distance corresponding to grazing where the contact force is minimized.

A new tissue harmonic imaging scheme with better fundamental frequency cancellation and higher signal-to-noise ratio

Abstract: Tissue Harmonic Imaging (THI) is a new ultrasound imaging technique, which uses the harmonic components generated by nonlinear acoustic propagation through human tissues to form an image. Several factors affect THI image quality. First, strong suppression of the fundamental signals is necessary to allow the full dynamic range of the harmonic signals to be seen. This will allow the full benefits of harmonic imaging to be seen. Second, since the harmonic components are much weaker (15-20 dB lower) than the fundamental, they must be enhanced as much as possible relative to noise. This will allow the maximum possible image penetration. This paper will compare the phase inversion technique with another data acquisition and processing scheme from the literature in terms of suppression of fundamental frequencies, and signal-to-noise ratio (SNR) improvement. The comparison will be both theoretical, using a very simple model, and experimental, using data acquired in vitro. The phase inversion technique appears to be a better choice to realize THI in an ultrasound imaging system. This technique gives better cancellation of the fundamental frequencies while simultaneously improving SNR.

A 12-36GHz PHEMT MMIC balanced frequency tripler

Abstract: A novel configuration of balanced frequency InGaAs pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuit (MMIC) tripler is proposed. A resonant LC filter is used to eliminate the fundamental frequency and a phase delay line is employed to suppress the second harmonic. The separation of the independent phase shifters makes the tripler more compact and flexible. The conversion loss of the tripler operating from 12 to 36GHz is less than 9.4dB at 9-dBm input power. As compared to the third-harmonic frequency, the fundamental frequency is suppressed more than 21.4dB while for the second harmonic is more than 22.3dB at 36GHz

LED Dimming Techniques Using Spread Spectrum Modulation

Abstract: Circuits and methods of LED dimming are disclosed. Frequency modulation using controlled modulation depth generates deterministic sidebands of both the fundamental frequency and its harmonics. Various filters including low-pass, band-pass, high-pass and combinations of those are used to selectively filter the deterministic frequency components generated by the frequency modulation to achieve LED dimming.

Three phase AC-DC load and harmonic flows

Abstract: The validity of assuming that the fundamental frequency load flow conditions of an AC-DC conversion plant are unaffected by the presence of harmonics is questioned, and an algorithm is derived which is capable of determining the true load flow conditions in the presence of harmonics. The algorithm is unique in its three phase approach to the problem, which is essential if normally unfiltered uncharacteristic harmonics are to be represented. Results of a realistic and relevant test system are used to demonstrate the interaction which exists between the fundamental and harmonic frequencies in the power converter. >