Complex Frequency Modulation Research Articles

Specific Emitter Identification Based on Synchrosqueezing Transform for Civil Radar

Time-frequency (TF) signal features are widely used in specific emitter identification (SEI) which commonly arises in many applications, especially for radar signals. Due to data scale and algorithm complexity, it is difficult to obtain an informative representation for SEI with existing TF features. In this paper, a feature extraction method is proposed based on synchrosqueezing transform (SST). The SST feature has an equivalent dimension to Fourier transform, and retains the most relevant information of the signal, leading to on average approximately 20 percent improvement in SEI for complex frequency modulation signals compared with existing handcrafted features. Numerous results demonstrate that the synchrosqueezing TF feature can offer a better recognition accuracy, especially for the signals with intricate time-varying information. Moreover, a linear relevance propagation algorithm is employed to attest to the SST feature importance from the perspective of deep learning.

Complex frequency modulation detection and discrimination at low and high frequencies

Whether frequency modulation (FM) is represented by place (tonotopic) or temporal (phase-locking) information in the peripheral system may depend on the carrier frequency (fc) and the modulation rate (fm), with only fcs below 4 kHz and fms below 10 Hz thought to involve temporal coding. This study tested the role of temporal coding in harmonic complexes by measuring FM detection and discrimination for two F0s (200 Hz and 1400 Hz), modulated at slow (1 Hz) and fast (20 Hz) rates, for tones with lower (2-5) or upper (6-9) harmonics embedded in threshold equalizing noise. Pure-tone FM detection was measured for fcs between 200 and 12000 Hz at the same fms. In detection tasks, participants selected which of two intervals contained FM. In discrimination tasks, participants selected which of three FM complex tones was incoherently modulated. Preliminary results suggest better FM detection for slow than fast rates, even when all tones are above 4 kHz. However, this effect was stronger at lower frequencies, where phase-locking cues may be viable. Most participants were only able to discriminate inharmonicity for slow fms in conditions with components below 8000 Hz. [Work supped by NIH grant R01DC005216 and an Eva O. Miller Fellowship.]

Single-stage high-power-factor electronic ballast with complex frequency modulation for HID lamps

A single-stage, complex frequency-modulated (CFM), high-frequency-driven electronic ballast for high-intensity-discharging (HID) lamps is proposed. The presented ballast combines a power-factor-correction (PFC) converter with a half-bridge series-resonant parallel-loaded inverter as well as a CFM controller. The switching frequency of the integrated inverter is non-periodically modulated by the CFM signal that integrates DC-bus voltage ripples with an additional high-frequency sine-wave signal. Compared with constant-frequency and frequency-modulated (FM) control, the presented ballast offers a widely continuous power spectrum of lamp current with decreased amplitude in order to effectively expand the lamp power as well as reducing sideband frequencies and allowing for a much lower energy level of the eigen frequency that supplies the lamp. Because of its CFM operation, no acoustic resonance occurs; additionally, the obtained results include a 13 dBm reduction of power spectrum at the centre switching frequency compared with FM control, and a 22 dBm reduction compared with constant-frequency control. The ballast offers high power factor (0.99), high efficiency (90%), cost-effectiveness and a simple, easy-to-implement controller. A prototype ballast utilising the CFM control method with 110 V utility-line input voltage has been built, and experimental results were carried out on three different brands of 70 W metal-halide-type HID lamps

Spreading of Thermonuclear Flames on the Neutron Star in SAX J1808.4-3658: An Observational Tool

We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX 51808.4-3658. We present evidence of a complex frequency modulation of oscillations during burst rise, and correlations among the time evolution of the oscillation frequency, amplitude, and the inferred burning region area. We discuss these findings in the context of a model, based on thermonuclear flame spreading on the neutron star surface, that can qualitatively explain these features. From our model, we infer that for the 2002 Oct. 15 thermonuclear burst, the ignition likely occurred in the mid-latitudes, the burning region took approx. 0.2 s to nearly encircle the equatorial region of the neutron star, and after that the lower amplitude oscillation originated from the remaining asymmetry of the burning front in the same hemisphere where the burst ignited. We emphasize that studies of the evolution of burst oscillation properties during burst rise can provide a powerful tool to understand thermonuclear flame spreading on neutron star surfaces under extreme physical conditions.

Optical generation of linearly chirped microwave pulses using fiber Bragg gratings

We demonstrate a new method to generate broad spectrum chirped microwave pulses using an electrooptical system. Two fiber Bragg gratings and a mode-locked fiber laser were used to generate pulses with a linear frequency chirp. The bandwidth of the microwave pulses can be significantly broader than the bandwidth that can be obtained using electronic systems. The parameters of the chirp can be easily controlled by adjusting the parameters of the optical system. The same method can be used to generate microwave pulses with a complex frequency modulation.

New Microhylid Frog (Plethodontohyla) with a Supraocular Crest from Madagascar

We describe a new microhylid frog from the rain forests of central eastern Madagascar. Plethodontohyla coronata reaches 21–23 mm snout–vent length and is similar to Plethodontohyla serratopalpebrosa by having a supraocular crest of three dermal spines. It differs by having a smaller body size, shorter hind limbs, relative finger and toe length, and smaller relative tympanum size. Its first toe is very short, reminiscent of the state in miniaturized species of Stumpffia, but the presence of vomerine and maxillary teeth clearly confirm the assignation of P. coronata to Plethodontohyla. The advertisement call of this fossorial frog is a series of notes with complex frequency modulation.

Brewster-plate spoiler: a novel method for reducing the amplitude of interference fringes that limit tunable-laser absorption sensitivities

A simple method is described for substantially reducing the amplitude of interference fringes that limit the sensitivities of tunable-laser high-resolution absorption spectrometers. A lead-salt diode laser operating in the 7-micron region is used with a single Brewster-plate spoiler to reduce the fringe amplitude by a factor of 30 and also to allow the detection of absorptances 0.001 percent in a single laser scan without subtraction techniques, without complex frequency modulation, and without distortion of the molecular line-shape signals. Application to multipass-cell spectrometers is described.