Modulated Broadband Research Articles

Deep learning approach to generate propeller cavitation noise

In underwater acoustic simulators, propeller cavitation noise has traditionally been modeled as a modulated broadband signal. This study aims to enhance the realism of these simulators by employing deep learning to generate propeller cavitation noise. The training data were collected from the modeled propeller under various pressure conditions in the Samsung Cavitation Tunnel. We have utilized a variant of Generative Adversarial Networks (GANs), wherein both the generator and discriminator are designed with a recursive structure. To assess the advantages of our data-based approach, we analyze the characteristics of the signals generated and compare them with the real signals or the modeled signal based on physics. The results demonstrate the effectiveness of our proposed model in generating realistic propeller cavitation signals. [Work supported by the Korea Research Institute for Defense Technology Planning and Advancement (20-106-B00-003).]

Aerodynamic noise separation of helicopter main and tail rotors using a cascade filter with Vold-Kalman filter and cyclic Wiener filter

The noise issue has become an important factor limiting the massive application of helicopters as the requirements for helicopter reliability and comfort continue to increase. As the primary noise source of helicopters, the main and tail rotor aerodynamic noise should be separated for individual noise reduction investigations. According to the frequency domain characteristics, the rotor aerodynamic noise can be divided into tonal noise and broadband noise. A cascade filtering method with Vold-Kalman filter and cyclic Wiener filter is proposed in this paper to separate the tonal and modulated broadband noise of the main and tail rotors, respectively. The classical method only considers the periodic characteristics of the main and tail rotor aerodynamic noise for harmonic separation. The broadband noise is not considered within the separation of interest due to its randomness, which leads to the inaccuracy of the conventional method for the aerodynamic noise separation of the main and tail rotors. The broadband noise exhibits a second-order cyclostationarity due to the periodic modulation of the rotational motion of the rotor. According to its cyclostationarity, while considering the periodicity of tonal noise for harmonic separation, the proposed cascade filtering method also performs the separation of broadband noise. More precise separations of the main and tail rotor can be obtained by this method. The efficacy of the proposed cascade filtering method is demonstrated in both the simulation and wind tunnel noise measurement.

The Calculation Method of PV Direct Current Energy Based on Modulated Broadband Mode Decomposition and Compound Simpson Integral Algorithm

The application of photovoltaic power is becoming more and more extensive presently, when the existing time-frequency analysis methods are used to analyze photovoltaic mutation signals such as transient rise and transient fall, the cornered signal will produce Gibbs phenomenon and leads to errors. Thus, the Broadband Mode Decomposition (BMD) method is proposed. The main idea of BMD is to search in the associated dictionary that contains the wideband and narrowband signals. However, the BMD algorithm may treat the wideband signal as several narrowband components, when applied to a wideband signal interfered by strong noise, because the relative bandwidth is not sufficiently small. Therefore, a modulated broadband modal decomposition (MBMD) based on the modulation differential operator is proposed. By multiplying a high-frequency single-frequency signal, the relative bandwidth of the effective wideband signal is much smaller than 1, and the wideband signal is processed as an approximate wideband signal. Meanwhile, because the errors of the traditional dot product sum algorithm in DC energy measurement cannot be positive and negative offset, while the compound Simpson integral algorithm has small error and high calculation accuracy. Therefore, a photovoltaic DC power calculation method based on the MBMD and compound Simpson integration is proposed.

Effect of sinusoidally amplitude modulated broadband noise stimuli on stream segregation in individuals with sensorineural hearing loss

Background and Aim: Auditory stream segre­gation is a phenomenon that splits sounds into different streams. The temporal cues that contri­bute for stream segregation have been previ­ously studied in normal hearing people. In peo­ple with sensorineural hearing loss (SNHL), the cues for temporal envelope coding is not usually affected, while the temporal fine structure cues are affected. These two temporal cues depend on the amplitude modulation frequency. The present study aimed to evaluate the effect of sin­usoidal amplitude modulated (SAM) broadband noises on stream segregation in individuals with SNHL. Methods: Thirty normal hearing subjects and 30 subjects with mild to moderate bilateral SNHL participated in the study. Two experi­ments were performed; in the first experiment, the AB sequence of broadband SAM stimuli was presented, while in the second experiment, only B sequence was presented. A low (16 Hz) and a high (256 kHz) standard modulation fre­quency were used in these experiments. The subjects were asked to find the irregularities in the rhythmic sequence. Results: Both the study groups could identify the irregularities similarly in both the experi­ments. The minimum cumulative delay was sli­ghtly higher in the SNHL group. Conclusion: It is suggested that the temporal cues provided by the broadband SAM noises for low and high standard modulation frequencies were not used for stream segregation by either normal hearing subjects or those with SNHL. Keywords: Stream segregation; sinusoidal amplitude modulation; sensorineural hearing loss

Tunable broadband all-silicon terahertz absorber based on a simple metamaterial structure.

We propose and demonstrate a modulatable all-silicon terahertz absorber based on a cylindrical metamaterial structure. Broadband absorption is obtained from 0.86 to 2.00 THz, with an average absorbance of 94%, indicating a wide absorption bandwidth of 1.14 THz. The maximum absorption, around 1.24 THz, is up to 98%. We employ simulation results to investigate the physical properties of the absorption, and we attribute the broadband absorption to a combination of electric dipole and magnetic dipole modes. Furthermore, the tunable response of the all-silicon terahertz absorber under the optical pump beam, with different fluences, is studied using a hierarchical model for simulating the carrier density of the gradient distribution. Moreover, different polarizations and oblique incidences of terahertz waves are used to verify the polarization and angle-of-incidence insensitivity of the device. The absorber provides a simple method to design a modulated broadband terahertz absorber, and the design scheme is scalable to develop various tunable broadband absorbers at other frequencies. This work holds great potential in modulator applications, imaging devices, and energy conversion.

Разрешающая способность и радиоизображения стационарных объектов в наземных MIMO-радиокамерах

The study analysed possible resolution of two ground-based MIMO microwave camera designs by means of two-dimensional spatial cross-sections of a generalized ambiguity function. We used stepped-frequency modulated broadband signals as time-orthogonal probing signals for the microwave camera transmitters. We employed a mathematical simulation of the space-time signal processing system pertaining to MIMO microwave camera receivers to illustrate 2D and 3D microwave imaging of stationary extended multipoint objects situated at various altitudes above the earth surface.

Wing mechanics, vibrational and acoustic communication in a new bush-cricket species of the genus Copiphora (Orthoptera: Tettigoniidae) from Colombia

Male bush-crickets produce acoustic signals by wing stridulation to call females. Several species also alternate vibratory signals with acoustic calls for intraspecific communication, a way to reduce risk of detection by eavesdropping predators. Both modes of communication have been documented mostly in neotropical species, for example in the genus Copiphora. In this article, we studied vibratory and acoustic signals and the biophysics of wing resonance in Copiphora vigorosa, a new species from the rainforest of Colombia. Different from other Copiphora species in which the acoustic signals have been properly documented as pure tones, C. vigorosa males produce a complex modulated broadband call peaking at ca. 30kHz. Since males of this species do rarely sing, we also report that substratum vibrations have been adopted in this species as a persistent communication channel. Wing resonances and substratum vibrations were measured using a μ-scanning Laser Doppler Vibrometry. We found that the stridulatory areas of both wings exhibit a relatively broad-frequency response and the combined vibration outputs fits with the calling song spectrum breadth. The broadband calling song spectrum results from several wing resonances activated simultaneously during stridulation. Under laboratory conditions the calling song duty cycle is very low and males spend more time tremulating than singing.

Broadband cascaded four-wave mixing in As2S3 chalcogenide waveguide with optical feedback and Mach–Zehnder interferometer

A scheme to enhance the efficiency and number of the cascaded four-wave mixing (FWM) products in [Formula: see text] chalcogenide planar waveguide is proposed and investigated numerically. Through introducing the optical feedback cavity and Mach–Zehnder interferometer, the modulated broadband cascaded FWM products can be obtained based on the high nonlinear [Formula: see text] chalcogenide planar waveguide. The numerical results show that the bandwidth of the modulated cascaded FWM is increased and the number of cascaded FWM products is improved compared with the single pass way of generating cascaded FWM products. Moreover, the feedback ratio plays an important role in the modulated cascaded FWM. This research can find important potential applications in nonlinear optics and integrated optics.

Optomechanical Shutter Modulated Broad-Band Cavity–Enhanced Absorption Spectroscopy of Molecular Transients of Astrophysical Interest

We describe a sensitive spectroscopic instrument capable of measuring broad-band absorption spectra through supersonically expanding planar plasma pulses. The instrument utilizes incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) and incorporates an optomechanical shutter to modulate light from a continuous incoherent light source, enabling measurements of durations as low as ∼400 μs. The plasma expansion is used to mimic conditions in translucent interstellar clouds. The new setup is particularly applicable to test proposed carriers of the diffuse interstellar bands, as it permits swift measurements over a broad spectral range with a resolution comparable to astronomical observations. The sensitivity is estimated to be better than 10 ppm/pass, measured with an effective exposure time of only 1 s.

Design and analysis of a dynamic spectral encoding code-division multiple-access communication system

An optical dynamic spectral encoding code division multiple access (CDMA) communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code, named functional code, is also proposed based on a shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for a sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The system is modeled and analyzed taking into account the multiple access interference, phase-induced intensity noise (PIIN), and thermal noise. The performance of this system is shown to be better compared with a fast frequency hopping (FFH) system and a spectral amplitude coding (SAC) system that uses either a Hadamard code, a modified quadratic congruence (MQC) code, or a modified frequency hopping (MFH) code.

Design and analysis of synchronous dynamic frequency hopping code division multiple access communication system

An optical dynamic frequency hopping code division multiple access communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code, named functional code, is also proposed based of shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The system is modeled and analyzed taking into account the multiple access interference, phase induced intensity noise, and thermal noise. The performance of this system is shown to be better compared with a fast frequency hopping system and a spectral amplitude coding system that uses either a Hadamard code, a modified quadratic congruence code (MQC), or a modified frequency hopping code (MFH).

Fast frequency modulation optical code division multiple access communication system

An optical fast frequency modulation code division multiple access communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code named functional code is also proposed based on a shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The performance of this system is shown to be better compared with a fast frequency hopping and a spectral amplitude coding systems.

Broadband beamforming for joint interference cancellation and turbo equalization

This paper considers the turbo equalization of trellis-coded modulated (TCM) broadband wireless signals that are affected by both intersymbol interference (ISI) due to multipath propagation and cochannel interference (CCI) due to the presence of adjacent users. Long channel dispersion causing both impediments to be severe makes the direct application of trellis-based turbo equalizers impossible, particularly for high-order signal modulations. For this reason, we present two computationally feasible space-time turbo receiver architectures employing linear antenna arrays and broadband beamformers. The first receiver uses a beamformer for joint rejection of interfering signals and shortening of the channel corresponding to the desired signal so that a scalar trellis-based turbo equalizer can be applied to its output. At each beamformer branch, the composite effect of the CCI and the white channel noise is viewed as colored noise. Because trellis search algorithms are limited to cases where the observation noise is white, this imposes quadratic noise whitening constraints on the beamformer design that is solved by a Lagrangian relaxation approach. The second receiver architecture removes the dependence on trellis search techniques for equalization by implementing the turbo equalizer directly with a soft-information-aided broadband beamformer at its front end and a soft-input soft-output (SISO) decoder at its back end. We outline the design considerations associated with each receiver and present bit error rate (BER) simulations for the turbo equalization of 8-phase-shift keying (PSK) TCM signals.

Detection of Nitrogen Dioxide by Cavity Attenuated Phase Shift Spectroscopy

We present initial results obtained from an optical absorption sensor for the monitoring of ambient atmospheric nitrogen dioxide concentrations (0-200 ppb). This sensor utilizes cavity attenuated phase shift spectroscopy, a technology related to cavity ringdown spectroscopy. A modulated broadband incoherent light source (a 430-nm LED) is coupled to an optically resonant cavity formed by two high-reflectivity mirrors. The presence of NO(2) in the cell causes a phase shift in the signal received by a photodetector that is proportional to the NO(2) concentration. The sensor, which employed a 0.5-m cell, was shown to have a sensitivity of 0.3 ppb in the photon (shot) noise limit. Improvements in the optical coupling of the LED to the resonant cavity would allow the sensor to reach this limit with integration times of 10 s or less (corresponding to a noise equivalent absorption coefficient of <1 x 10(-8) cm(-1) Hz(-1/2)). Over a 2-day-long period of ambient atmospheric monitoring, a comparison of the sensor with an extremely accurate and precise tunable diode laser-based absorption spectrometer showed that the CAPS-based instrument was able to reliably and quantitatively measure both large and small fluctuations in the ambient nitrogen dioxide concentration.

Brazilian Portuguese speech material and its application in occupational audiology.

Brazilian Portuguese speech test material consisting of nine monosyllabic 25-word lists was developed and digitally recorded on one channel of a compact disk with a speech-weighted modulated broadband noise on the other channel. Speech recognition functions in quiet and in noise, with word and phoneme scores, were obtained, and normative speech recognition data were standardized by determination of the psychometric function in 21 normally-hearing volunteers in quiet, and in 30 normally-hearing subjects in noise. The homogeneity of the nine lists was investigated in phoneme recognition data with 30 normally-hearing subjects. Speech recognition functions in quiet and in noise, with word and phoneme scores, were obtained in 65 noise-exposed workers. These results were very close to normative data, when tested in quiet, but significantly worse when tested in noise. It is concluded that the speech test material can be useful for estimating the communication performance of noise-exposed workers.

Modeling sensorineural hearing loss. II. Application to measures of temporal resolution

Thresholds of hearing‐impaired listeners in temporal‐masking tasks were modeled by the performance of normal listeners with a noise‐simulated hearing loss. This model predicts thresholds for such tasks by assuming the presence of two maskers; a spectrally shaped continuous masker used to simulate the hearing loss and the masker used in the temporal‐masking task. The combined effect of the two maskers was predicted using a masking‐additivity rule similar to that of Lutfi [J. Acoust. Soc. Am. 72, 262–267 (1983)]. Masked detection thresholds from impaired listeners and normal listeners with simulated hearing loss were examined for various temporal‐masking paradigms. Data from the literature were examined for each of the following: (1) detection thresholds in continuous and modulated broadband noise; (2) growth of forward masking with masker level; and (3) decay of forward masking following masker offset. The masking‐additivity approach predicted well the temporally masked detection thresholds for noise‐masked normal listeners with simulated hearing loss, but underestimated the masked thresholds of the hearing impaired by as much as 15 dB. [Work supported by NINCDS.]

Fluctuation strength and temporal masking patterns of amplitude-modulated broadband noise.

Fluctuation strength of sinusoidally amplitude modulated broadband noise was measured by a magnitude-estimation procedure. Fluctuation strength shows, as a function of modulation frequency, a bandpass characteristic with a maximum around 4 Hz. With increasing modulation depth and sound pressure level, fluctuation strength increases. For the same stimulus parameters as used in the experiments on fluctuation strength, temporal masking of amplitude modulated broadband noise was determined. The level difference delta L between the maximum and the minimum of the resulting temporal masking patterns shows a low-pass characteristic as a function of modulation frequency and increases with increasing modulation depth and sound pressure level. A model of fluctuation strength F based on the depth delta L of the temporal masking pattern and the modulation frequency fmod in relation to 4 Hz is proposed as follows: F approximately delta L/((fmod/4 Hz)+(4 Hz/fmod)). The model accounts for the dependence of fluctuation strength on some essential stimulus parameters. The usefulness of temporal masking patterns as an intermediate value for the description of hearing sensations is confirmed.

Effects of hearing loss on the detection of amplitude modulated noise

Hearing loss is known to influence auditory temporal processing; there is a decrease in the time constant of temporal integration for tone bursts however, the same hearing loss increases the time constant for gap detection and forward masking. The detection of amplitude modulated signals, another aspect of temporal processing, was studied in three monaural chinchillas using conditioned avoidance procedures. Pre‐exposure pure tone thresholds were measured from 0.25 to 16 kHz and modulation thresholds (0.002 to 4.096 kHz) were obtained using sinusoidally amplitude modulated broad band noise having an SPL of 53 dB. Chinchillas were initially exposed for 7 days to an octave band of noise centered at 8 kHz. The animals developed a high frequency loss of 50–70 dB and the amplitude modulation function showed a decline in sensitivity. Then the noise exposure band was widened over the next 3 weeks. The hearing loss progressively increased toward the low frequencies; however, the amplitude modulation function remained constant until the lowest frequencies of the audiogram were shifted, then AM function was greatly reduced. The results will be discussed in terms of the influence of the sensation level of the AM noise stimulus. [Work supported by NIH, NIOSH.]