Presence Of Frequency Modulation Research Articles

Mechanical squeezing beyond resolved sideband and weak-coupling limits with frequency modulation

It is usually difficult to generate mechanical squeezing in standard optomechanical systems when the decay rate of the cavity or the effective coupling strength of the system is too large. Here we investigate the mechanical squeezing beyond resolved sideband and weak-coupling limits in a standard optomechanical system by using frequency modulation acting on both the cavity field and the mechanical oscillator. It is shown that in the presence of frequency modulation, the beyond 3 dB strong mechanical squeezing can be achieved better than the standard optomechanical system without frequency modulation. Furthermore, the proposed scheme is feasible even in the unstable region of the standard optomechanical system, and a detailed numerical analysis is carried out from the physical essence to illuminate the reason for achieving better mechanical squeezing with frequency modulation. The scheme may open promising perspectives for studying the quantum effect in strong coupling regions without the limitations of system stability and the resolved sideband regime.

An Algorithm for Measurement of the Pitch Frequency of Speech Signals Based on Complementary Ensemble Decomposition Into Empirical Modes

The problem of increasing the precision with which the pitch frequency of speech signals is measured is considered. Existing algorithms for determining this frequency are presented and a new algorithm based on complementary ensemble empirical mode decomposition is developed. The results of the investigations confirm the robustness of the algorithm in the presence of frequency modulation of the pitch of speech signals.

Dynamic regime of coherent population trapping and optimization of frequency modulation parameters in atomic clocks

We theoretically investigate the dynamic regime of coherent population trapping (CPT) in the presence of frequency modulation (FM). We have formulated the criteria for quasi-stationary (adiabatic) and dynamic (non-adiabatic) responses of atomic system driven by this FM. Using the density matrix formalism for Λ system, the error signal is exactly calculated and optimized. It is shown that the optimal FM parameters correspond to the dynamic regime of atomic-field interaction, which significantly differs from conventional description of CPT resonances in the frame of quasi-stationary approach (under small modulation frequency). Obtained theoretical results are in good qualitative agreement with different experiments. Also we have found CPT-analogue of Pound-Driver-Hall regime of frequency stabilization.

Switching atomic fountain clock microwave interrogation signal and high-resolution phase measurements

This paper focuses on the development of tools aiming to solve several problems related to the microwave interrogation signal in atomic fountains. We first consider the problem related to cycle synchronous phase transients caused by the sequential operation of the atomic fountain. To search for such systematic phase variations deeply buried in the microwave synthesizer phase noise, we have developed a novel triggered-phase transient analyzer capable of processing the microwave signal to extract the phase in a synchronous manner even in the presence of frequency modulation. With this device we check in vivo the LNE-SYRTE fountain's interrogation signals with a resolution approaching 1 microradian. In addition, using this device, we investigate an innovative approach to solve a second problem, namely, the shift caused by microwave leakage in the fountain. Our approach consists of switching off the fountain microwave interrogation signal when atoms are outside the microwave cavity. To do that, we have developed a switch that is almost free of phase transients and is thus able to eliminate the frequency shift caused by microwave leakage without inducing significant phase transients on the interrogation signal.

Analysis of whistles produced by the Tucuxi Dolphin Sotalia fluviatilis from Sepetiba Bay, Brazil.

From July 2001 to June 2002, we recorded a total of 2 h 55 min of Tucuxi Dolphin Sotalia fluviatilis vocalizations from Sepetiba Bay, Brazil (22 degrees 35'S-44 degrees 03'W). A total of 3350 whistles were analyzed quantitative and qualitatively and were divided into 124 types, by visual inspection of sonograms. The following parameters were measured: Initial Frequency, Final Frequency, Minimum Frequency, Maximum Frequency, Duration, Number of Inflections, Frequency at the Inflection Points, Frequency at 1/2, 1/4, and 3/4 of whistle duration, Presence of Frequency Modulation and Harmonics. Ascending type whistles (N = 2719) were most common, representing 82% of the total. Dolphin behavior and average group size observed during recording influenced the whistle's quantitative and qualitative parameters. The results demonstrate the great diversity of whistles emitted and indicate a functional role of these vocalizations during the observed behaviors.

Multiple Parameters in the Territorial coo of the Collared Dove: Interactions and Meaning

The perch-coo of the collared dove (Streptopelia decaocto) is used as a territorial signal. We investigated the perception of acoustic variation in the coos by testing the responsiveness to playback in the field. Earlier experiments showed that both temporal and spectral features played an important role in eliciting a behavioural response. In the present study, we used playback experiments to examine whether the impact of temporal features interacts with the impact of spectral features. We show that the increased response level elicited by the presence of frequency modulations is independent of the positioning of frequency modulations within a coo. We conclude that the individual parameters contribute relatively independently of each other to the response. Furthermore, we discuss the functional interpretation of the behavioural response to temporal and spectral features. The nature of inter- and intra-specific variation, and the impact on playback responses may suggest that particular parameters contribute primarily to one function, whereas other features contribute primarily to another. Nevertheless, functions, such as species recognition and quality assessment, may depend on multiple parameters, and there is no evidence for different functions to be separated in specialized processing centres. The concepts of species recognition and quality assessment have to be regarded as labels attached to a particular part of the range of the behavioural response.

Solution of Bloch equations involving amplitude and frequency modulations

The undamped Bloch equations are shown to have a more general analytic solution which includes the famous self-induced-transparency solution of McCall and Hahn, and the nonadiabatic excitation solution of Allen and Eberly as special cases. A generalized area characteristic for a laser pulse of modulated amplitude and frequency of the forms of hyperbolic secant and tangent is given. It resolves the difficulty of the previous area concept in the presence of frequency modulation. The solution provides an exact analytic result for the amplitude- and frequency-modulated pulse of any area.

Sunspot index infers a small relict magnetic field in the Sun's core

Cowling1 long ago suggested the presence of a relict field in the Sun's core and argued that the bulk electrical conductivity was sufficient (provided that the field was dipolar) to prevent decay over the lifetime of the Solar System. Evidence for such a field is obtained by inference from the asymmetry in time of the solar sunspot number taken over many cycles2. As the Sun's dipole field reverses polarity approximately every 11 yr, if a core field of odd multipolarity (presumably dipolar) is present and in reasonable alignment with the oscillating dipole of the convective zone, it follows that in successive 11-yr periods, the two fields will tend first to be additive and then subtractive3,4. Because the net dipole field is the ‘seed’ field from which the much larger toroidal field arises5, the latter will vary in magnitude in alternating half cycles and correspondingly mediate the level of sunspot activity. Whether a fossil or relict field is present can be explored either by a search for the presence of a 22-yr line quintet in the Fourier spectrum of the sunspot index2, or alternatively the time sequence itself can be processed so as directly to bring out evidence for an offset. The latter involves a ‘demodulation’ of the sunspot sequence to emphasize the basic 22-yr Hale cycle. The latter is discussed here, but as the two are interrelated, the former is reviewed briefly first to provide the basis for the subsequent least squares (LS) analysis of the demodulated signal. As the solar cycle is unstable to drifts in frequency, the presence of frequency modulation can lead to a spurious relict field signal. A short summary of limits on frequency modulation (FM) contamination of the sunspot index spectrum is also given.

A Simple Crystal Discriminator for FM Oscillator Stabilization

A crystal discriminator employing only one quartz crystal and very simple in adjustment is described in detail. The stability of center frequency determination in the presence of frequency modulation and variation of component values is calculated in terms of the circuit parameters, and is shown to be adequate for the requirements of broadcast transmitters. Experimental measurements confirm the results of the theoretical analysis. The discriminator was designed for use in a television aural transmitter, and a brief description is given of the complete FM exciter unit.