Wave Chirp Research Articles

SAW chirp Fourier transform for MB-OFDM UWB receiver

In the conventional multiband orthogonal frequency division multiplexing ultra wideband (MB-OFDM UWB) receiver, the fast Fourier transform (FFT) algorithm is realized by the expensive and power-consuming digital signal processor (DSP) chips. In this article, the lower power, lower cost, and lower complexity real-time analog surface acoustic wave (SAW) chirp Fourier transform devices were used to replace the DSP part. A MB-OFDM UWB receiver based on the M-C-M SAW chirp Fourier transform was presented, and the step of signal transformation from input signals was also depicted. The simulation results show that the proposed receiver provides similar bit error performance compared to the fully digital receiver when used in the channel environments proposed by the IEEE 802.15SG3a.

On the profile of pulses generated by fiber lasers:the highly-chirped positive dispersion regime (similariton)

I model the nonlinear fiber laser using an expanded Ginzburg-Landau equation (GLE) which includes the self-steepening (SS) and intrapulse Raman scattering (IRS) effects. I show that above a minimum value of the Raman effect, it is possible to find two chirped solitary pulses for the laser system. The smaller chirped solitary wave corresponds to the dispersion-managed (DM) regime whereas the larger chirped solitary wave corresponds to the so-called similariton regime.

In situ monitoring of solid fat content by means of pulsed nuclear magnetic resonance spectrometry and ultrasonics

AbstractAn ultrasonic technique was developed to study the crystallization process of edible fats on‐line. A chirp wave was used instead of the conventional pulser signal, thus achieving a higher signal‐to‐noise ratio. This enabled measurements to be made in concentrated systems [≈20% solid fat content (SFC)] through a 8.11‐cm thick sample without significant signal loss. Fat samples were crystallized at 20, 25, and 30°C at a constant agitation rate of 400 rpm for 90 min. The crystallization process was followed by ultrasonic spectroscopy and a low‐resolution pulsed nuclear magnetic resonance spectrometer. Specific relationships were found between ultrasonic parameters [integrated response, time of flight (TF), and full width half maximum] and SFC. TF, which is an indirect measurement of the ultrasonic velocity (v), was highly correlated to SFC (r2>0.9) in a linear fashion (v=2.601 SFC+1433.0).

Correlator bank detection of gravitational wave chirps—False-alarm probability, template density, and thresholds: Behind and beyond the minimal-match issue

The general problem of computing the false-alarm probability vs the detection-threshold relationship for a bank of correlators is addressed, in the context of maximum-likelihood detection of gravitational waves in additive stationary Gaussian noise. Specific reference is made to chirps from coalescing binary systems. Accurate (lower-bound) approximants for the cumulative distribution of the whole-bank supremum are deduced from a class of Bonferroni-type inequalities. The asymptotic properties of the cumulative distribution are obtained, in the limit where the number of correlators goes to infinity. The validity of numerical simulations made on small-size banks is extended to banks of any size, via a Gaussian-correlation inequality. The result is used to readdress the problem of relating the template density to the fraction of potentially observable sources which could be dismissed as an effect of template space discreteness.

How many templates for GW chirp detection? The minimal-match issue revisited

Refined estimates for the template density (or minimal match) yielding the best trade-off between a detector's performance (in terms of false dismissals) and computational burden are obtained in the context of the maximum likelihood of detection of gravitational wave chirps from coalescing binaries with unknown parameters, using a recently derived accurate representation of the no-signal cumulative distribution of the detection statistic.

Present status of large-scale cryogenic gravitational wave telescope

The large-scale cryogenic gravitational wave telescope (LCGT) is the future project of the Japanese gravitational wave group. Two sets of 3 km arm length laser interferometric gravitational wave detectors will be built in a tunnel of Kamioka mine in Japan. LCGT will detect chirp waves from binary neutron star coalescence at 240 Mpc away with a S/N of 10. The expected number of detectable events in a year is two or three. To achieve the required sensitivity, several advanced techniques will be employed such as a low-frequency vibration-isolation system, a suspension point interferometer, cryogenic mirrors, a resonant side band extraction method, a high-power laser system and so on. We hope that the beginning of the project will be in 2005 and the observations will start in 2009.

Radar investigations of breaking water waves at low grazing angles with simultaneous high‐speed optical imagery

This paper describes the results of radar scattering experiments carried out at the wavetank facility at the University of Maryland, College Park. Spilling and plunging breakers with a water wavelength of approximately 80 cm were generated through dispersive focusing of a chirped wave packet, and were then imaged with a high‐speed camera in conjunction with a laser sheet. Simultaneously, the radar backscatter generated by the breakers when viewed with an “up‐wave” look direction was measured by an ultrawideband, dual‐polarized, X‐band radar with a range resolution of approximately 4 cm. The nominal grazing angle of the radar was 12°. In addition to providing both quantitative profiles of the evolving water surface and the corresponding ultrahigh resolution radar backscatter, this experimental setup also included a moving instrument carriage that allowed the sensors to follow the breakers throughout their entire evolution. Numerical scattering simulations that use the measured surface profiles as inputs were also conducted in order to further dissect the scattering mechanism. An analysis of the results shows that for the spilling breaker, over 90% of the horizontally (HH) polarized radar backscatter is generated during the initial stage of breaking by the small bulge near the wave crest. For vertical (VV) polarization, the crest bulge produces about 60% of the total backscattered energy. For both polarizations, the Doppler velocity associated with this energy is very close to that of the phase speed of the dominant wave in the water wave packet. For VV, the remainder of the backscattered energy is generated by the turbulent, postbreaking surface, and in fact a close correlation is observed between increases in the VV backscatter amplitude and the shedding of vortex ripples after the wave breaks. For the plunging breaker, the initial feature on the crest (an overturning jet) generates a lower percentage of the total backscattered energy. For the spilling breaker, agreement between the experimental and numerical results is good, particularly in the Doppler domain. The simulations also indicate uncertainty in the polarization ratio measurements that is related to multipath scattering. To the extent that they can be applied to the open ocean, these results can serve as a guide for the development of future breaker models.

Gravitational wave chirp search: no-signal cumulative distribution of the maximum likelihood detection statistic

The cumulative distribution of the supremum of a set (bank) of correlators is investigated in the context of maximum likelihood detection of gravitational wave chirps from coalescing binaries with unknown parameters. Accurate (lower-bound) approximants are introduced based on a suitable generalization of previous results by Mohanty. Asymptotic properties (in the limit where the number of correlators goes to infinity) are highlighted. The validity of numerical simulations made on small-size banks is extended to banks of any size, via a Gaussian correlation inequality.

Broadband Transducer for Diagnostics Using a Plano-Concave Ultrasonic Transducer Driven by Chirp Wave

In order to obtain tomographic images with high resolution by ultrasonic diagnostic equipment, a broadband transducer that enables one to widely change the center frequency and bandwidth of the radiation ultrasonic pulse using only a probe is investigated in this study. As it is generally difficult to widely change the frequency and bandwidth, we examined the possibility of using a plano-concave ultrasonic transducer and the chirp wave as its excitation pulse. As a result, it was clarified that the center frequency and bandwidth could be controlled freely over a wide frequency range in comparison with the conventional method by using the plano-concave transducer and the chirp wave modulated by amplitude.

Optimum placement of post-1PN gravitational wave chirp templates made simple at any match level via Tanaka-Tagoshi coordinates

A simple recipe is given for constructing a maximally sparse regular lattice of spin-free post-1PN gravitational wave chirp templates under a given minimal-match constraint, using Tanaka-Tagoshi coordinates. Cardinal interpolation among the resulting maximally sparse templates is discussed.

First observations of the water masers with the Urumqi 25m radio telescope

A new radio spectral receiving system has been installed on the 25 m radio telescope of the Urumqi Astronomical Observatory. The back end is a surface acoustic wave chirp transform spectrometer (SAW CZT), used for the first time in radio astronomy. The calibration of the line observations has carefully been investigated for the new-type spectrometer. In order to test the feasibility of the prototype spectrometer, we observed water maser emission from a number of known Galactic sources. We describe the observed spectra of W49N, W3(OH), 2248 + 600 and 1909 + 090. We found that W49N spectrum showed high-velocity features ranging from −330 to 146 km s−1. In comparison with the spectra observed by Medicina, the feature at the LSR velocity −52 km s−1 in the W3(OH) presented the rapid variation in flux density.

More on the Tanaka-Tagoshi parametrization of post-1PN spin-free gravitational wave chirps: Equispaced and cardinal interpolated lattices

The conclusions reached in our recent paper [R.P. Croce, Th. Demma, V. Pierro, and I.M. Pinto, Phys. Rev. D 64, 042005 (2001)] are shown to be valid also if the full 2.5PN expansion of the chirp phase is used.

Tanaka-Tagoshi parametrization of post-first-post-Newtonian spin-free gravitational wave chirps: Equispaced and cardinal interpolated lattices for first generation interferometric antennas

The spin-free binary-inspiral parameter-space introduced by Tanaka and Tagoshi to construct a uniformly spaced lattice of post-first-post Newtonian (PN) templates is shown to work for all first generation interferometric gravitational wave antennas. This allows us to extend the minimum-redundant cardinal interpolation techniques of the correlator bank developed by the authors to the highest available order PN templates. The total number of templates to be computed for a minimal match $\ensuremath{\Gamma}=0.97$ is reduced by a factor 4, as in the 1PN case.

Radar backscatter from mechanically generated transient breaking waves. I. Angle of incidence dependence and high resolution surface morphology

This paper describes the results of an experimental investigation of the microwave backscatter from several laboratory generated transient breaking waves. The breaking waves were generated mechanically in a 35 m/spl times/0.7 m/spl times/1.14 m deep wave tank, utilizing chirped wave packets spanning the frequency range 0.8-2.0 Hz. Backscatter measurements, were taken by a X/K-band (10.525 GHz, 24.125 GHz) continuous wave Doppler radar at 30/spl deg/, 45/spl deg/, and 60/spl deg/ angles of incidence, and at azimuth angles of 0/spl deg/ and 180/spl deg/ relative to the direction of wave propagation. Surface profiles were measured with a high-speed video camera and laser sheet technique. Specular facets were detected by imaging the surface from the perspective of the radar. The maximum radar backscatter occurred in the upwave direction prior to wave breaking, was nearly polarization independent and corresponded to the detection of specular facets on the steepened wave face. This peak radar backscatter was predicted through a finite conductivity corrected physical optics technique over the measured surface wave profiles. Post break backscatter was predicted using a roughness corrected physical optics technique and the small perturbation method, which was found to predict the returns for vertical polarization, but to under predict the horizontal returns.

Radar backscatter from mechanically generated transient breaking waves. II. Azimuthal and grazing angle dependence

For Pt. I see ibid. vol. 26, pp. 181-200 (2001). This paper describes the results of experimental investigations into the microwave backscatter from mechanically generated transient breaking waves. The investigations were carried out in a 110 m/spl times/7.6 m/spl times/4 m deep model basin, utilizing chirped wave packets spanning 0.75-1.75 Hz. Backscatter measurements were taken by a K-band continuous wave radar (24.125 GHz) at 40/spl deg/ angle of incidence, and at azimuth angles of 0/spl deg/, 45/spl deg/, 90/spl deg/, 135/spl deg/ and 180/spl deg/ relative to the direction of wave propagation. Grazing measurements were conducted using an X-band (10.525 GHz) FMCW radar at 85/spl deg/ angle of incidence, and azimuth angles of 0/spl deg/ and 180/spl deg/. Results show that the maximum radar backscatter was obtained in the upwave direction prior to wave breaking and was caused by the specular or near specular presentation of the wave to the radar. After breaking, the backscatter transitioned from a specular or near-specular dominated scattering, primarily seen in the upwave direction, to a small scale roughness dominated scattering, observed at all azimuths. Physical optics solutions were found to correctly predict the backscatter for the specular or near-specular dominated scattering and the small perturbation method was found to accurately model the VV polarization post-break radar backscatter.

Ultrashort pulse reflectometry for electron density profile measurements on SSPX

A broadband ultrashort pulse reflectometry (USPR) diagnostic has been developed for measuring electron density profiles of the sustained spheromak physics experiment (SSPX) device. In USPR, an extremely short pulse or chirped wave form is propagated which contains a broad range of frequency components spanning the desired plasma density profile (or a significant fraction thereof). Upon reflection, each frequency component in the incident waveform reflects from a different spatial location (density layer) in the plasma, thus spreading out the reflected wave packet in time. By simultaneously collecting double-pass time delay data at many distinct frequencies, the time delay data may then be inverted to generate plasma density profiles using a single source and a single set of measurements. On SSPX, wideband mixers are utilized to up- and downconvert 6–18 GHz chirp signals to millimeter-wave frequencies (33–158 GHz) to form a 48 channel O-mode reflectometer system. In this article we describe details of the new USPR system installed on the SSPX device and provide preliminary time-of-flight results.

Nearly minimum redundant correlator interpolation formula for gravitational wave chirp detection

An absolute lower bound on the number of templates needed to keep the fitting factor above a prescribed minimal value $\ensuremath{\Gamma}$ in correlator-bank detection of (Newtonian) gravitational wave chirps from unknown inspiraling compact binary stars is derived, resorting to the theory of quasi-band-limited functions in the ${L}^{\ensuremath{\infty}}$ norm. An explicit nearly minimum redundant cardinal-interpolation formula for the (reduced, noncoherent) correlator is introduced. Its computational burden and statistical properties are compared to those of the plain lattice of (reduced, noncoherent) correlators, for the same $\ensuremath{\Gamma}.$ An extension to post-Newtonian models is outlined.

Gravitational wave chirp search: Economization of post-Newtonian matched filter bank via cardinal interpolation

The final inspiral phase in the evolution of a compact binary consisting of black holes and/or neutron stars is among the most probable events that a network of ground-based interferometric gravitational wave detectors is likely to observe. Gravitational radiation emitted during this phase will have to be dug out of noise by matched-filtering (correlating) the detector output with a bank of several ${10}^{5}$ templates, making the computational resources required quite demanding, though not formidable. We propose an interpolation method for evaluating the correlation between template waveforms and the detector output, and show that the method is effective in substantially reducing the number of templates required. Indeed, the number of templates needed could be a factor of $\ensuremath{\sim}4$ smaller than required by the usual approach, when the minimal overlap between the template bank and an arbitrary signal (the so-called minimal match) is $0.97.$ The method is amenable to easy implementation, and the various detector projects might benefit by adopting it to reduce the computational costs of inspiraling neutron star and black hole binary searches.

SAW device implementation of a weighted stepped chirp code signal for direct sequence spread spectrum communications systems

This paper introduces a new weighted stepped chirp code signal for direct sequence spread spectrum (DS/SS) communications systems. This code signal uses the truncated cosine series functions as the chip functions, and it is the result of discretizing a continuous wave (CW) chirp that results in enhanced performance versus a pseudonoise (PN) code and equivalent performance and easier implementation than a CW chirp. This code signal will be shown to have improved compression ratio (CR) and peak sidelobe level (PSL) versus a PN code with identical code length and chip length. It also will be shown to have a similar CR and PSL compared to a CW chirp with identical pulse length and frequency deviation. The code signal is implemented on surface acoustic wave (SAW) devices that will be used as the code generator at the transmitter and the correlator at the receiver. The design considerations for the SAW device implementation of the code signal are discussed, including the effects of intersymbol interference. Experimental data is presented and compared to the predicted results for 8 different SAW devices examining the effects of code length (9 or 13 chips), weighting (uniform, cosine-squared, and Hamming), and sampling on the performance of the code signal.

Double-hump solitary waves in quadratically nonlinear media with loss and gain

We report the existence of a family of bright chirped localized waves in quadratic media with loss and gain. It is shown that the fundamental field component of the symbiotic solitary wave may exhibit a double-hump shape. The conditions of the solitary wave's existence are identified. Numerical experiments disclose different scenarios of instability as well as domains of rather robust behavior of these objects upon propagation.