Fundamental Oscillation Frequency Research Articles

Frequency-tunable all-optical clock division using semiconductor laser subjected to external optical injection

All-optical time division was obtained in the frequency range from 9.0GHz to 19.8GHz. Nonlinear dynamics of a Fabry-Perot laser diode subjected to external optical injection is applied for all-optical clock division. The research results indicate that semiconductor laser subjected to external light injection performs period-one oscillation. We obtain the clock division of the signal pulses when the second harmonic frequency of the period-one oscillation approaches the repetition rate of the signal pulse, and the second harmonic and the fundamental frequency of the period-one oscillation were locked by the signal pulses simultaneously. Numerical simulation was performed on the all-optical time division with signal pulse injection using the rate equation of the semiconductor laser. The simulation result is in good agreement with the experiment. Phase noise level of the divided clock is observed to be smaller than -90 dBc/Hz over a frequency detuning range of 1.5GHz by changing the repetition rate of signal pulses under the fixed wavelength detuning value and input signal pulse power.

Chelomei's problem of the stabilization of a statically unstable rod by means of a vibration

Chelomei's problem of the stabilization of an elastic, statically unstable rod by means of a vibration is considered. Formulae for the upper and lower critical frequencies for the stabilization of the rod are obtained and analysed. It is shown that, unlike the high-frequency stabilization of an inverted pendulum with a vibrating suspension point, a rod is stabilized by frequencies of a periodic force of the order of the fundamental frequency of the transverse oscillations of the uncompressed rod lying in a certain range.

Ka Band Phase Locked Loop Oscillator Dielectric Resonator Oscillator for Satellite EHF Band Receiver

This paper describes the design and fabrication of a Ka Band PLL DRO having a fundamental oscillation frequency of 19.250 GHz, used as local oscillator in the low-noise block of a down converter (LNB) for an EHF band receiver. Apposite circuital models have been created to describe the behaviour of the dielectric resonator and of the active component used in the oscillator core. The DRO characterization and measurements have shown very good agreement with simulation results. A good phase noise performance is obtained by using a very highQdielectric resonator.

Optoelectronic oscillator employing reciprocating optical modulator for millimetre-wave generation

An optoelectronic oscillator that employs a reciprocating optical modulator is demonstrated. By giving positive optoelectronic feedback to the modulator, the reciprocating modulation in the modulator effectively multiplies the fundamental oscillation frequency by several times. A 52.8 GHz millimetre-wave signal is generated by self-oscillation.

Coherent terahertz-wave generation from semiconductors and its applications in biological sciences

Coherent terahertz waves are generated by exciting phonon-polariton mode in GaP crystal. We have developed high power, wide frequency tunable terahertz generators and spectrometers, and revealed molecular resonance spectra of biomolecules, such as saccharides, DNA- or RNA-related molecules, amino acids and liquid crystals. It is demonstrated that THz spectral imaging has a possibility to distinguish the cancerous region from the normal tissue. TUNNETT diode, of which fundamental oscillation frequency exceeds 700 GHz, can be utilized for sub-terahertz imaging system for medical and other applications.

Collective Excitations in Electron-Hole Bilayers

We report a combined analytic and molecular dynamics analysis of the collective mode spectrum of a bipolar (electron-hole) bilayer in the strong coupling classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles. In the in-phase spectra we identify longitudinal and transverse acoustic modes wholly maintained by correlations. Strong nonlinear generation of higher harmonics of the fundamental dipole oscillation frequency and the transfer of harmonics between different modes is observed.

Sustainment and Controlment of Noise-Induced Circadian Oscillations in Neurospora: Noise and External Signal Effects

The effect of light noise on a Neurospora circadian clock system in the steady states is investigated. It is found that the circadian oscillations could be induced by light noise, leading to various resonance phenomena including internal signal stochastic resonance (ISSR) and ISSR without tuning in the system. The strength of ISSR could be significantly reinforced with the decrease of the distance of the control parameter to the Hopf bifurcation point of the system. The fundamental frequency of noise-induced circadian oscillations almost does not change with the increment of light noise intensity, which implies that the Neurospora system could sustain intrinsic circadian rhythms. In addition, the ISSR and ISSR without tuning could be both amplified, suppressed or destroyed by tuning the frequency or amplitude of external signal.

Theoretical Analysis of Novel Multi-Order <emphasis emphasistype="italic">LC</emphasis> Oscillators

A conventional differential pair LC oscillator is capable of generating only a single fundamental oscillation frequency. This brief presents the theoretical study of a novel oscillator that incorporates higher order LC filters to produce multiple oscillation frequencies that may be several octaves apart. These multiple oscillation frequencies are obtained from a single oscillator, thereby reducing the area of the circuit when being used for multistandard wireless applications. Moreover, a multi-order oscillator does not suffer from large parasitic capacitances from switches, which is a common drawback in switched-inductor tuned oscillators. A detailed analysis is carried out, and useful design insights are provided

Harmonic QPOs and Thick Accretion Disk Oscillations in the BL Lacertae Object AO 0235+164

Periodic outbursts are observed in many active galactic nuclei (AGNs) and are usually explained with a supermassive black hole binary (SMBHB) scenario. However, multiple periods are observed in some AGNs and cannot be explained in this way. Here we analyze the periodicity of the radio light curves of AO 0235+164 at multiple frequencies and report the discovery of six quasi-periodic oscillations (QPOs) in the integer frequency ratio 1 : 2 : 3 : 4 : 5 : 6, of which the second, with period P2 = 5.46 ± 0.47 yr, is the strongest. We fit the radio light curves and show that the initial phases of the six QPOs have differences of 0 or π relative to each other. We suggest a harmonic relationship among the QPOs. The centroid frequency, relative strength, harmonic relationship, and relative initial phases of the QPOs are independent of radio frequency. The harmonic QPOs are likely due to quasi-periodic injection of plasma from an oscillating accretion disk into the jet. We estimate a supermassive black hole mass of MBH (4.72 ± 2.04) × 108 M☉ and an accretion rate 0.007. With knowledge of the accretion disk, this implies that the inner region of the AO 0235+164 accretion disk is a radiatively inefficient accretion flow. The oscillatory accretion is due to p-mode oscillations of the thick disk, probably excited by a SMBHB. Theoretical predictions for the fundamental oscillation frequency and the harmonics show good consistency with the observations. Harmonic QPOs would disappear if the thick disk became geometrically thin as the result of an increase in accretion rate. We discuss the observations of AO 0235+164 in the context of the SMBHB-thick disk oscillation scenario.

Detection of terahertz radiation in gated two-dimensional structures governed by dc current

We present theoretical and experimental studies of the direct current effect on the detection of subterahertz and terahertz radiation in gated two-dimensional structures. We developed a theory of the current-driven detection both for resonant case, when the fundamental frequency of plasma oscillation is large compared to inverse scattering time, ${\ensuremath{\omega}}_{0}\ensuremath{\tau}⪢1$, and for the nonresonant case, ${\ensuremath{\omega}}_{0}\ensuremath{\tau}⪡1$, when the plasma oscillations are damped. We predict that, in the nonresonant case, even a very small dc current would increase the detection amplitude up to two orders of magnitude. Physically, this increase is related to an abrupt transition from the linear to saturation region near the knee of the current-voltage characteristic. When the current increases up to the saturation value, the electron concentration near the drain becomes very low and can be strongly affected by a small external field. As a consequence, the two-dimensional channel becomes extremely sensitive to external perturbations. In the resonant case, the detection amplitude has maxima when the radiation frequency is equal to fundamental plasma frequency and its harmonics. We predict that the effective linewidths of the respective resonances would decrease with the increasing current. Physically, this happens because dc current shifts the system towards the plasma wave instability. At some critical current value, the width corresponding to the fundamental frequency would turn to zero, indicating the onset of plasma waves generation. Our experimental measurements performed on $\mathrm{GaAs}$ HEMT confirm the theoretical predictions.

Realization of a Second Harmonic Antenna for Rural Communications

In this research, an active antenna operated at the second harmonic frequency is investigated, and is implemented using microstrip antenna material. The antenna consists of a FET oscillator which plays as a fundamental frequency oscillator and a frequency multiplier, and a patch antenna resonated at the second harmonic frequency as the radiator. A maximum second-harmonic output power can be extracted when the load impedance of the oscillator is optimized both at the fundamental and at the second harmonic frequencies. A rectangular patch antenna is used to radiate the second harmonic output power from the oscillator. The patch impedance is matched resistively at the second harmonic frequency. The patch antenna is fabricated using Diclad 522 microstrip substrates (relative permitivity er = 2.5) with a dielectric thickness of 1.57 mm. A GaAs FET AT- 8250 transistor is used as an oscillator and a frequency multiplier and acts as the active component. Fundamental frequency is designed at 2,4 GHz band, so that the second harmonic frequency operates at 4,8 GHz band. The frequency is chosen to facilitate and to extend the needs of communications in rural areas using the unlicensed Industrial Scientific, and Medical (ISM) band. Operating the communication infrastructures intended for the use at 2.4 GHz band at its second harmonic frequency, is intended to alleviate interference levels at 2.4 GHz.

Microwave Chaotic Colpitts Oscillator: Design, Implementation and Applications

In this paper, the mathematic model of Colpitts oscillator is illustrated and the expressions for the main circuit parameters are derived, with which chaotic oscillation can be established. Experimental researches were conducted on the implementations of chaotic Colpitts oscillator using two types of broadband bipolar junction transistors (BJTs), namely BFG520XR and BFG425W with corresponding threshold frequency of 9 GHz and 25 GHz. Experimental results indicate that, chaotic oscillation can be obtained in a wide frequency regime in microwave band. When using BFG425W in the Colpitts circuit, the highest fundamental frequency of the chaotic oscillation can be about 1.6 GHz, and the harmonics observed with Agilent PSA/ESA Spectrum Analyzer are noticeable as far as 12 GHz, which is the highest one reported so far. Several typical applications using such chaotic oscillators are also presented at the end of this paper.

Angle-resolved de Haas–van Alphen study ofSrRuO3

The results of angle-resolved de Haas--van Alphen oscillations in $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ single crystals are reported. At least six fundamental frequencies of oscillation are detected between 100 and 11 000 T. The effective mass of the charge carriers is measured for each orbit and ranges from 4.1 to $6.9\phantom{\rule{0.3em}{0ex}}{m}_{e}$. The mean free path length of the charge carriers is between 640 and 5500 \AA{} or roughly 100--1000 times the unit cell dimensions. The measured frequencies are compared to the Fermi surface calculated by Santi and Jarlborg.

On the role of the additive and converted noise in the generation of phase noise in nonlinear oscillators

In a conventional approach, the oscillator phase noise due to noise sources near carrier is defined as additive phase noise by assuming that the oscillator operates in a near linear fashion. Nevertheless, fundamentally, an oscillator circuit is inherently nonlinear. In this paper, we show that the phase noise generated by noise sources around the fundamental frequency of oscillation is due to two simultaneous and correlated phenomena of the same order of magnitude: additive phase noise and converted phase noise due to conversion from one sideband to another. An analytical calculation applied to a simple purely theoretical circuit allows evaluation of the respective influence of the two above-mentioned phenomena. Numerical simulations performed on a realistic transistor oscillator circuit then confirms the importance of the conversion phenomenon already shown by the analytical evaluation. The converted noise results to be of the order of 6 dB higher than the additive noise. The term of additive phase noise must be intended to characterize the phase noise generated in linear components located out of the nonlinear oscillation loop and, for example, in buffer amplifiers following the oscillator itself.

An Oscillator in a Central Symmetric Field and Oscillator Frequency Quantization

The states of a harmonic oscillator in a central symmetric electric field are calculated, and fundamental oscillator frequency quantization is established.

Effect of Artificially Lengthened Vocal Tract on Vocal Fold Oscillation's Fundamental Frequency

Summary The fundamental frequency of vocal fold oscillation (F 0) is controlled by laryngeal mechanics and aerodynamic properties. F 0 change per unit change of transglottal pressure (dF/dP) using a shutter valve has been studied and found to have nonlinear, V-shaped relationship with F 0. On the other hand, the vocal tract is also known to affect vocal fold oscillation. This study examined the effect of artificially lengthened vocal tract length on dF/dP. dF/dP was measured in six men using two mouthpieces of different lengths. Results: The dF/dP graph for the longer vocal tract was shifted leftward relative to the shorter one. Conclusion: Using the one-mass model, the nadir of the “V” on the dF/dP graph was strongly influenced by the resonance around the first formant frequency. However, a more precise model is needed to account for the effects of viscosity and turbulence.

On the relation between the frequency of oscillation of a virtual cathode and injected current in one-dimensional grounded drift space

The relationship between the injected current density j0 and the dominant fundamental oscillation frequency f of a virtual cathode in a one-dimensional grounded infinite planar drift space of length L is determined numerically. If the electrons, each of mass me and charge e, are injected with velocity v0, it is found that for |j0|≫mev03/18π|e|L2, f∼|j0| which is in contrast to the relation f∼|j0| reported by earlier workers.

Higher harmonics imaging in tapping-mode atomic-force microscopy

In tapping-mode atomic-force microscopy usually amplitude and phase of the cantilever motion are acquired. These signals are related to the fundamental oscillation frequency neglecting information at higher frequencies. However, the nonlinear contact between tip and sample induces higher frequency vibrations that are harmonics of the fundamental. In order to recover the available information the full tip motion has to be analyzed. The higher harmonics can be employed for image formation. A setup that consists of two independently operated lock-in amplifiers is used to detect higher harmonics in the dynamic atomic-force microscopy signal. Higher harmonic imaging proves to be useful to monitor the imaging conditions in tapping mode and can be applied for nanoscale imaging with a material contrast.

Effects of ELF and static magnetic fields on calcium oscillations in islets of Langerhans

Several experimental studies have produced contradictory results on the effects of extremely low frequency (ELF) magnetic fields on cellular processes involving calcium ions. Furthermore, the few positive results have not been independently replicated. In most of these studies, isolated cells were used. Our study used mouse islets of Langerhans, in which very regular oscillations of calcium concentration can be observed at length. These oscillations are sustained by processes that imply energetic and inter-intracellular communication. Various magnetic fields were applied, either sinusoidal at different frequencies (50 Hz or multiples of the natural oscillation frequency) at 0.1 or 1 mT or static at 1 mT. Islets were also exposed to “cyclotron resonance” conditions. There was neither alteration of the fundamental oscillation frequency nor the degree of organisation under all exposure conditions. Using this sensitive model, we could not show new evidence of alterations of calcium processes under exposure to various magnetic fields.

Narrow band noise in the SDW state of (TMTSF) 2PF 6

Narrow band noise has been studied in the SDW phase of (TMTSF) 2PF 6 in a magnetic field. Strong and weak periodic peaks are clearly observed. The spectrum largely changes with increasing current and depends on applied magnetic field. The fundamental frequency of the current oscillations comes from a sliding motion of the SDW condensate. The strong periodic peaks appear at the harmonic frequencies of this fundamental and move to lower frequency at large currents. This is interpreted in terms of the coexistence with the CDW collective excitation.