Fundamental Oscillation Research Articles

An Integrated Test-Based Nonlinear Aeroelastic Analysis Method to Freeplay-Induced Limit-Cycle Oscillations

The nonlinear limit-cycle oscillations induced by aileron rotational freeplay are investigated by numerical simulation and flutter wind tunnel tests. An integrated nonlinear aeroelastic analysis method and procedure based on the nonlinear system identification technology is proposed. Based on the characteristics of the structure, a low-speed nonlinear flutter wing-aileron model that considers both the linear flutter test and the nonlinear limit-cycle oscillation test with aileron rotational freeplay is designed. The wind tunnel tests are conducted with the model, and the stable limit-cycle oscillation is observed by accelerometers under the linear flutter boundary with a 0° angle of attack. Higher-order harmonic vibration is also observed with a low proportion compared to the fundamental oscillation, and the limit-cycle oscillation grows gradually with the increase of airspeed until flutter occurs. The comparison of numerical and experimental investigation shows high consistency.

A hybrid two-dimensional orthogonal wavelet multiresolution and proper orthogonal decomposition technique for the analysis of turbulent wake flow

A hybrid two-dimensional orthogonal wavelet multiresolution and proper orthogonal decomposition technique is developed to analyze the wake flow behind a semi cylinder. The two-dimensional orthogonal wavelet analysis is first applied to decompose the measured velocity fields into four wavelet components based on their spatial scales. Then the extracted multi-scale structures are further investigated based on proper orthogonal decomposition. The modal energy distributions of multi-scale flow structures suggest that the dominance of first two POD modes is reduced and the relative energy becomes more distributed as the flow structure changes from large-scale to small-scale. The first two POD modes of intermediate-scale structure also appear in a mode pair and they are related to secondary resonance accompanied with large-scale flow oscillation. The POD mode 3 of intermediate-scale structure suggest the existence of symmetric vortex shedding pattern. The first two POD modes of small-scale structure also display a symmetrically distributed vortex pair and the distance between adjacent vortices is about half of the case of mode 3 of intermediate-scale structure. The PSD distributions of POD modes of multi-scale structures suggest that the bandwidth of PSD becomes less concentrated as the flow structure varies from large-scale to small-scale. Distinctive flow patterns associated with first and second order harmonics of fundamental flow oscillation can be successfully extracted from the dominating POD modes of intermediate-scale and small-scale structures. The proposed hybrid technique provides a tool for relate the most energetic flow events over a period of time with multi-scale structures cascaded in the turbulence flow.

Tidal Wave Breaking in the Eccentric Lead-in to Mass Transfer and Common Envelope Phases

The evolution of many close binary and multiple star systems is defined by phases of mass exchange and interaction. As these systems evolve into contact, tidal dissipation is not always sufficient to bring them into circular, synchronous orbits. In these cases, encounters of increasing strength occur while the orbit remains eccentric. This paper focuses on the outcomes of close tidal passages in eccentric orbits. Close eccentric passages excite dynamical oscillations about the stars’ equilibrium configurations. These tidal oscillations arise from the transfer of orbital energy into oscillation mode energy. When these oscillations reach sufficient amplitude, they break near the stellar surface. The surface wave-breaking layer forms a shock-heated atmosphere that surrounds the object. The continuing oscillations in the star’s interior launch shocks that dissipate into the atmosphere, damping the tidal oscillations. We show that the rapid, nonlinear dissipation associated with the wave breaking of fundamental oscillation modes therefore comes with coupled mass loss to the wave-breaking atmosphere. The mass ratio is an important characteristic that defines the relative importance of mass loss and energy dissipation and therefore determines the fate of systems evolving under the influence of nonlinear dissipation. The outcome can be rapid tidal circularization (q ≪ 1) or runaway mass exchange (q ≫ 1).

A 0.47-THz Ring Scalable Coupled Oscillator–Radiator Array With Miniature Patch Antennas

This article integrates several techniques for large-scale, high power-efficiency, and area-efficiency terahertz (THz) radiators. First, we present a systematic design method to synthesize a high output power harmonic oscillator at a high fundamental to maximum oscillation frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\mathrm {osc}}/f_{\mathrm {max}})$ </tex-math></inline-formula> ratio by making a quantitative tradeoff between fundamental oscillation and harmonic output power. Then, a ring scalable coupled oscillator array topology is proposed for a flexible and compact layout. Patch antennas are preferred for large-scale radiator arrays, but the size is much larger than the commonly used slot antenna. Therefore, a miniature on-chip patch antenna is proposed for front-side radiation, whose compact size also helps make the design scalable in 2-D. A quartz superstrate is superimposed on the chip to improve the radiation efficiency. A 16-element ring-coupled oscillator–radiator array is designed and fabricated in a 0.8-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> total area using a 65-nm CMOS process to verify the design methods. Maximum radiated power of −2.8 dBm is measured at 472 GHz. This design achieves an area efficiency of 0.66 mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the highest among THz radiator arrays using on-chip patch antennas. It is even higher than most radiator arrays using slot antennas. This design also achieves the state-of-the-art dc-to-THz efficiency and frequency tuning range of 0.12% and 4.2%, respectively. The chip can be easily configured to feed a low-cost Teflon lens. A maximum effective isotropic radiated power (EIRP) of ~30 dBm is measured with a 12-mm diameter lens. The measured directivity is 33.7 dBi. At 472 GHz, the measured phase noise is −71.3 dBc/Hz at the 1-MHz offset.

Pasta properties of the neutron star within effective relativistic mean-field model

We study the properties of pasta structures and their influence on the neutron star observables employing the effective relativistic mean-field (E-RMF) model. The compressible liquid drop model is used to incorporate the finite size effects, considering the possibility of nonspherical structures in the inner crust. The unified equation of states are constructed for several E-RMF parameters to study various properties such as pasta mass and thickness in the neutron star's crust. The majority of the pasta properties are sensitive to the symmetry energy in the subsaturation density region. Using the results from Monte Carlo simulations, we estimate the shear modulus of the crust in the context of quasiperiodic oscillations from soft gamma-ray repeaters and calculate the frequency of fundamental torsional oscillation mode in the inner crust. Global properties of the neutron star such as mass-radius profile, the moment of inertia, crustal mass, crustal thickness, and fractional crustal moment of inertia are worked out. The results are consistent with various observational and theoretical constraints.

Improved Bounds on Ultralight Scalar Dark Matter in the Radio-Frequency Range.

We present a search for fundamental constant oscillations in the range 20kHz-100MHz that may arise within models for ultralight dark matter (UDM). Using two independent optical-spectroscopy apparatuses, we achieve up to ×1000 greater sensitivity in the search relative to previous work [D. Antypas et al., Phys. Rev. Lett. 123, 141102 (2019).PRLTAO0031-900710.1103/PhysRevLett.123.141102]. We report no observation of UDM and thus constrain respective couplings to electrons and photons within the investigated UDM particle mass range 8×10^{-11}-4×10^{-7} eV. The constraints significantly exceed previously set bounds from atomic spectroscopy and, as we show, may surpass in future experiments those provided by equivalence-principle (EP) experiments in a specific case regarding the combination of UDM couplings probed by the EP experiments.

Design and Analysis of 55–63-GHz Fundamental Quad-Core VCO With NMOS-Only Stacked Oscillator in 28-nm CMOS

This article presents a 55–63-GHz fundamental multicore voltage-controlled oscillator (VCO) in a 28-nm bulk CMOS process. The single-core VCO utilizes stacking and magnetic coupling of two NMOS-based resonators, which increases the tank energy for phase noise reduction while maintaining low voltage swings for reliability. In the multi-core configuration, the oscillators are coupled in a way that also simplifies LO distribution toward the transmitter and receiver. The potential parasitic modes that occur both in single-core and multi-core configurations are suppressed by design. The implicit common-mode (CM) impedance control is utilized to reduce phase noise without any large extra tail inductor as used in a conventional complementary oscillator. The distributed nature of energy restoring elements in the proposed stacked oscillator also offers robust parasitic mode suppression compared to alternative implementation based on a conventional complementary oscillator. The working range of the prototype is between 55 and 63 GHz corresponding to a tuning range of 13.4% with power consumption varying from 15.3 to 12 mW across the tuning range. The prototype achieves the best phase noise of −95 and −121.7 dBc/Hz at 1- and 10-MHz offsets from the carrier at 55GHz. The corresponding peak figure of merits (FOMs) achieved are 178 and 185 dBc/Hz at 1- and 10-MHz offsets from the carrier.

Self‐starting generation of tri‐band frequencies using a dual‐parallel Mach–Zehnder modulator‐based optoelectronic oscillator

A scheme for multi-band frequency generation is proposed and experimentally demonstrated using a dual-parallel Mach–Zehnder modulator (DPMZM)-based optoelectronic oscillator (OEO). The principle of this generator is theoretically described in detail. It is found that multiple frequencies with a small power variation can be produced by setting the three working points and the modulation depth of the DPMZM. In the proving experiment, an 8-GHz fundamental oscillation with a side mode suppression ratio of 44 dB is generated. The phase noise is measured to be −96.8 dBc/Hz @ 10 KHz offset with a 100-m and 1-Km optical fibre used in the two oscillation loops. When the oscillating signal is applied to drive the two sub-modulators in the DPMZM, doubled and tripled frequencies are produced at the same time, and the phase noises of the two frequencies are also measured to be −90.2 dBc/Hz and −85.9 dBc/Hz @10 KHz, respectively.

A definition of the asymptotic phase for quantum nonlinear oscillators from the Koopman operator viewpoint.

We propose a definition of the asymptotic phase for quantum nonlinear oscillators from the viewpoint of the Koopman operator theory. The asymptotic phase is a fundamental quantity for the analysis of classical limit-cycle oscillators, but it has not been defined explicitly for quantum nonlinear oscillators. In this study, we define the asymptotic phase for quantum oscillatory systems by using the eigenoperator of the backward Liouville operator associated with the fundamental oscillation frequency. By using the quantum van der Pol oscillator with a Kerr effect as an example, we illustrate that the proposed asymptotic phase appropriately yields isochronous phase values in both semiclassical and strong quantum regimes.

A fully integrated 2TX–4RX 60-GHz FMCW radar transceiver for short-range applications

ABSTRACT A fully integrated 2-transmitter–4-receiver (2TX–4RX) multiple-input multiple-output (MIMO) radar front-end in the 57–64-GHz band for short-range applications is presented in this paper. The proposed architecture with 8 elements within a one-dimensional virtual array enables theoretical angular resolution down to . The TX chains operate in time-division multiplexing (TDM) mode, and each delivers 12 dBm of saturated output power with output-referred 1-dB compression point (OP1dB) larger than 5 dBm over 7-GHz bandwidth. The millimeter-wave (mm-wave) part of the RX chains has a noise figure lower than 13 dB, and a conversion gain of 17 dB in the 60-GHz unlicensed band. The receiver chain shows a maximum conversion gain of 77 dB, while achieving an input-referred 1-dB compression point (IP1dB) greater than – 12.5 dBm, including baseband circuitry. The programmable baseband processing chain with 60-dB gain allows beat frequency selection in the frequency range from 100 kHz up to 1.3 MHz. Linear chirps are synthesized using a fractional-N phase-locked loop (PLL) with a fundamental voltage-controlled oscillator (VCO). The integrated system includes a programmable multiplying delay-locked loop (MDLL) which scales-up external high purity 40-MHz frequency reference to a referent 240-MHz clock used in the frequency-modulated continuous-wave (FMCW) synthesizer. The front-end is implemented in a 130-nm SiGe:C BiCMOS process. The chip occupies an area of 12 mm2 including pads and consumes 930 mW, combined from 1.2-V and 3.3-V supplies.

Efficient 6.5 dBm 55 GHz CMOS VCO with simultaneous phase noise and tuning range optimization

Abstract This paper presents the design and characterization of an efficient high-output-power 55 GHz fundamental oscillator. The performance parameters of the oscillator are analysed as a function of the contributors of the tank capacitance, and the design choices in the varactor for phase noise and for tuning range are exemplified. The circuit was implemented in 22 nm FD-SOI CMOS technology and occupies 0.046 mm2 area including the matching network. On-wafer measurement results have demonstrated 6.5 dBm peak output power, 22% peak DC-to-RF efficiency and −98.3 dBc/Hz phase noise at 1 MHz offset frequency, while the core draws 8.3 mW power. To the best knowledge of the authors, the efficiency is the best, while the output power is the second best among CMOS oscillators in the same frequency range, and the phase noise is the best result for V-band fundamental CMOS oscillators reported to date.

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Transverse kink oscillations of inhomogeneous prominence threads: Numerical analysis and Hα forward modelling

Context. Prominence threads are very long and thin flux tubes that are partially filled with cold plasma. Observations have shown that transverse oscillations are frequent in these solar structures. The observations are usually interpreted as the fundamental kink mode, while the detection of the first harmonic remains elusive. Aims. The properties of oscillations in threads are greatly affected by the density distribution along the flux tube. Here, we aim to study how the density inhomogeneities in the longitudinal and radial directions modify the periods and damping times of kink oscillations and how this effect would be reflected in the observations. Methods. We solved the ideal magnetohydrodynamics equations using two different methods: (a) performing 3D numerical simulations and (b) solving a 2D generalised eigenvalue problem. We studied the dependence of the periods, damping times, and amplitudes of transverse kink oscillations on the ratio between the densities at the centre and at the ends of the tube, and also on the average density. We applied forward modelling to our 3D simulations to compute synthetic Hα profiles. Results. We confirm that the ratio of the period of the fundamental oscillation mode to the period of the first harmonic increases as the ratio of the central density to the footpoint density is increased, or as the averaged density of the tube is decreased. We find that the damping times due to resonant absorption decrease as the central-to-footpoint density ratio increases. Contrary to the case of longitudinally homogeneous tubes, we find that the damping-time-to-period ratio also increases as the density ratio is increased or the average density is reduced. We present snapshots and time-distance diagrams of the emission in the Hα line. Conclusions. The results presented here have implications for the field of prominence seismology. While the Hα emission can be used to detect the fundamental mode, the first harmonic is barely detectable in Hα. This may explain the lack of detections of the first harmonic. A combination of different spectral lines is required to obtain information about the period ratio and to use it to infer physical properties of the threads.

Gravitational radiation back-reaction from f-modes on neutron stars

ABSTRACT The problem of the gravitational radiation damping of neutron star fundamental (f) mode oscillations has received considerable attention. Many studies have looked at the stability of such oscillations in rapidly rotating stars, calculating the growth or decay rate of the mode amplitude. In this paper, we look at the relatively neglected problem of the radiation reaction on the spin of the star. We specialize greatly to the so-called Kelvin modes: the modes of oscillation of (initially) non-rotating incompressible stars. We find the unexpected result that the excitation of a mode of angular momentum δJ on an initially non-rotating star ends up radiating an angular momentum 2δJ to infinity, leaving the star itself with a bulk angular momentum of −δJ. This result is interesting in itself, and also will have implications for the angular momentum budgets of spinning down neutron stars, should such modes be excited.

Radial Oscillations of Quark Stars Admixed with Dark Matter

We investigated compact stars consisting of cold quark matter and fermionic dark matter treated as two admixed fluids. We computed the stellar structures and fundamental radial oscillation frequencies of different masses of the dark fermion in the cases of weak and strong self-interacting dark matter. We found that the fundamental frequency can be dramatically modified and, in some cases, stable dark strange planets and dark strangelets with very low masses and radii can be formed.

Universal relation for supernova gravitational waves

Using the numerical simulation data for two-dimensional core-collapse supernova, we examine the protoneutron star (PNS) asteroseismology with the relativistic Cowling approximation. As shown in the previous study, e.g., [H. Sotani and T. Takiwaki, Mon. Not. R. Astron. Soc. 498, 3503 (2020).], the gravitational wave signals appearing in the numerical simulation can be well identified with the gravity (fundamental) oscillation in the early (later) phase before (after) the avoided crossing between the gravity and fundamental oscillations. On the other hand, the time evolution of supernova gravitational waves strongly depends on the PNS models, such as the progenitor mass and the equation of state for dense matter. Nevertheless, we find that the fundamental and gravity mode frequencies according to the gravitational wave signals appearing in the numerical simulations can be expressed as a function of the protoneutron star average density independently of the PNS models. Using the average density, we derive the empirical formula for supernova gravitational wave frequency. In addition, we confirm that the dependence of the PNS surface density on the PNS average density is almost independent of the PNS models, and we also discuss how the different treatment of the nonuniform matter in the equation of state affects the observables.

Stellar structure and stability of charged interacting quark stars and their scaling behavior

We explore the stellar structure and radial stability of charged quark stars composed of interacting quark matter (IQM) in three classes of commonly used charge models. We adopt a general parametrization of IQM equation of state that includes the corrections from perturbative QCD, color superconductivity, and the strange quark mass into one parameter $\lambda$, or one dimensionless parameter $\bar{\lambda}=\lambda^2/(4B_{\rm eff})$ after being rescaled with the effective bag constant $B_{\rm eff}$. We find that increasing charge tends to increase the mass and radius profiles, and enlarges the separation size in mass between the maximum mass point and the point where zero eigenfrequencies $\omega^2_0=0$ of the fundamental radial oscillation mode occur. The sign of the separation in central density depends on the charge model; this separation also has a dependence on $\lambda$ such that increasing $\lambda$ (which can occur for either large color superconductivity or small strange quark mass) tends to decrease this separation size for the first and third classes of charge models monotonically. Moreover, for the second and third classes of charge models, we manage to numerically and analytically identify a new kind of stellar structure with a zero central pressure but a finite radius and mass. All the calculations and analysis are performed in a general dimensionless rescaling approach so that the results are independent of explicit values of dimensional parameters.

Identifying a Fundamental Climatic Oscillation Using Wavelet Analysis of the Combined Data of Ground and Satellite Observations

Identifying a Fundamental Climatic Oscillation Using Wavelet Analysis of the Combined Data of Ground and Satellite Observations

Fundamental and higher-order excited modes of radial oscillation of neutron stars for various types of cold nucleonic and hyperonic matter

This research paper complements our earlier qualitative study of the effect of viscosity and thermal conductivity on the radial oscillation and relaxation of non-rotating neutron stars. The fundamental and first two lowest-frequency excited modes of radial oscillation have been computed in the high nuclear density regime for a set of seven realistic equations of state (EoS) as functions of central energy density. Various types of zero-temperature EoS of cold nucleonic and hybrid nucleon–hyperon–quark matter models are used in the inner core to determine the internal structure in and around the hydrostatic equilibrium states and investigate the influence of each EoS on the dynamical behavior of non-rotating neutron stars. We confirm the principal results of earlier, related studies that suggest an underlying correlation between the frequency spectrum of the fundamental oscillation mode and the variation of the adiabatic index over the high nuclear-density regime. We provide valuable information to impose further constraints on the plausible set of realistic EoS models, in addition to the practical applications for the rapidly evolving field of asteroseismology of compact objects.

Polarization-dependent YVO4 crystal Raman laser operation with 816 and 890 cm−1 shifts

Polarization-dependent YVO4 crystal Raman laser operations for both X(ZZ)X and X(YY)X Raman configurations were demonstrated. An optical anisotropy Nd:YAP crystal was used as the laser crystal for polarized fundamental laser oscillation. Both first Stokes waves at 1184 nm and 1194 nm converted from 1080 nm were realized based on 816 cm−1 shift in X(YY)X Raman configuration and 890 cm−1 shift in X(ZZ)X Raman configuration, respectively. The maximum average output power of 1.18 W and the conversion efficiency of 16.3% for main output spectrum of 1183.7 nm and average output power of 1.09 W and the conversion efficiency of 15.1% for single output spectrum of 1194.4 nm were achieved with both Raman configurations, respectively. The results show that make full use of the polarization characteristics of YVO4 crystal and its different Raman shifts, the polarized laser output with different Stokes wavelengths could be realized.