FFT Magnitude Research Articles

Separability Measure Supervised Network for Radar Target Recognition

In the radar automatic target recognition (RATR) field, radar high-resolution range profiles (HRRPs) have garnered significant attention. While traditional methods focus on extracting features having physical explanations, including power spectra, FFT magnitudes, etc, the effectiveness of these features relies heavily on personal experience and skills. In contrast, deep learning networks have shown strong competence in extracting discriminative features of HRRPs. However, the deep learning networks’ feature extraction procedure is solely based on the targets’ label information, which has almost no correlation with the feature separability. As a result, this approach can lead to poor convergence and limited recognition performance. To address this issue, we propose a Separability Measure Supervised Network (SMSN), which integrates a separability measure based on the rate-distortion function into the loss function to direct the training of the network. Comparative experiments on the airplane electromagnetic simulation HRRP dataset demonstrate that SMSN achieves higher recognition accuracy compared to the backbone networks, with significantly improved feature separability.

RETROSPECTIVE COMPUTER-ASSISTED IMAGE ANALYSIS OF DOPPLER ECHOCARDIOGRAPHY IN PULMONARY HYPERTENSION PATIENTS

Pulmonary hypertension (PH) is diagnosed invasively by right heart catheterization (RHC), which determines patient’s mean and systolic pulmonary artery pressure (mPAP, sPAP) and pulmonary vascular resistance (PVR). This study sought to identify non-invasive echocardiography parameters useful for screening PH. Patients ([Formula: see text]; 19 normotensive; 17 pre-capillary PH; 48 post-capillary PH) who had undergone transthoracic Doppler echocardiography and RHC within 60 days of each other were identified. Tricuspid regurgitant (TR) jet velocities, velocity spectral densities, average flow rates, and Fourier transforms (FFT) of velocity waveforms were calculated via an in-house MATLAB code. Correlations were found between the FFT magnitude at 0 Hz and sPAP and mPAP for normotensive patients; between the MATLAB-calculated TR jet and sPAP and PVR for all PH patients; and between the sum of FFT magnitudes [Formula: see text][Formula: see text]Hz and mPAP, sPAP, and PVR for post-capillary PH patients. Statistical difference was found between the FFT magnitudes at 2 Hz of pre- and post-capillary PH patients ([Formula: see text]). These results suggest non-invasive parameters with clinical utility for estimating RHC measurements and discriminating between PH types, offering a path forward for less invasive and more accessible PH screening protocol.

Characterization of cavitating flow regimes in an internal sharp-edged orifice by means of Proper Orthogonal Decomposition

Cavitating flow regimes of water at ambient temperature inside a sharp-edged orifice have been characterized by means of a snapshot POD combined with high-speed visualizations. The density related gray level of each experimental image was processed at each pixel point. An estimation of the energy contribution in image reconstruction of each POD eigenvalue was made. Coherent flow structures related to the most significant eigenfaces were detected. Finally an FFT analysis of the temporal eigenfunctions led to the identification of the main modal dynamic properties.It was found that the flow structure of the first POD mode was defined by a single symmetric cavity. This cavity is related to the extension of the cavitating cloud. Conversely polarities and asymmetries in flow structures of higher modes reveal the establishment of advecting vortices and swirling motions. The frequency analysis of the first four POD modes has been used for the characterization of the different cavitation regimes. As the cavitation number decreases, the jet cavitation is characterized by a rapid increase of the frequencies of modes 3 and 4, up to 1000 Hz. Instead, developed cavitation and supercavitation are characterized by a growth in frequency of the second mode up to 300 Hz, as well as they exhibit the highest FFT magnitudes of the first mode.

Quality Analysis of Transformer Oil in Hermitically Sealed Tank using Ultrasonic Lamb Wave Sensor

In this work we propose a simple method for quality analysis of transformer oil in hermitically sealed aluminium tank using ultrasonic lamb wave sensor. Lamb waves generated using acrylic wedge coupled with ultrasonic transducer attached to the tank get reflected from the top edge of tank and are received at ultrasonic transducer. Lamb wave is attenuated with respect to the mechanical properties of the liquid inside the tank. Using Fast Fourier Transform analysis the magnitude of received A0 mode signal is obtained. Acoustic impedance of the liquid inside the tank is determined using the reflection coefficient calculated from FFT magnitude of A0 mode signal.Average acoustic impedance measured experimentally for one year used oil is 4.0021 MRayls and new oil is 2.882 MRayls. Experimental results are compared with the acoustic impedance calculated with density and viscosity determined using other methods and results are in good agreement. The experiment is repeated for 10 times and found consistent result with a standard deviation of 0.056 for one year used oil and 0.112 for new oil. This technique can be developed as new and efficient method to monitor the quality of transformer oil in hermitically sealed tanks in remote locations.

Audio Watermarking Based on Fibonacci Numbers

This paper presents a novel high-capacity audio watermarking system to embed data and extract them in a bit-exact manner by changing some of the magnitudes of the FFT spectrum. The key idea is to divide the FFT spectrum into short frames and change the magnitude of the selected FFT samples using Fibonacci numbers. Taking advantage of Fibonacci numbers, it is possible to change the frequency samples adaptively. In fact, the suggested technique guarantees and proves, mathematically, that the maximum change is less than 61% of the related FFT sample and the average error for each sample is 25%. Using the closest Fibonacci number to FFT magnitudes results in a robust and transparent technique. On top of very remarkable capacity, transparency and robustness, this scheme provides two parameters which facilitate the regulation of these properties. The experimental results show that the method has a high capacity (700 bps to 3 kbps), without significant perceptual distortion (ODG is about 1) and provides robustness against common audio signal processing such as echo, added noise, filtering, and MPEG compression (MP3). In addition to the experimental results, the fidelity of suggested system is proved mathematically.

A Real-Time DSP-Based System for Voice Activity Detection: Design and Implement

Most of the noise in speech communication lines can be considered as Gaussian white noise. Voice activity detection (VAD) in noisy environment is an important process in many speech signal processing algorithms. Unlike the other VAD algorithms, this paper proposes a simple and novel VAD algorithm based on the probability distribution function (PDF) of FFT magnitudes of both clean speech and Gaussian white noise. When the signal-to-noise ratio (SNR) is high enough, the method using Gamma distribution to detect the speech performs well, while the method using Rayleigh distribution under lower SNR can be complementary. In addition, the threshold to determine which method to use is presented based on the tests under different SNR. Simulation results show that the proposed algorithm is efficient. Both the hardware and software of a low cost system for VAD are introduced, with the proposed algorithm achieved in a digital signal processor (DSP). Each detection takes on less than 100 ms, which can be used for real-time processing.

On chirp stimuli and neural synchrony in the suprathreshold auditory brainstem response

The chirp-evoked ABR has been regarded as a more synchronous response than the click-evoked ABR, referring to the belief that the chirp stimulates lower-, mid-, and higher-frequency regions of the cochlea simultaneously. In this study a variety of tools were used to analyze the synchronicity of ABRs evoked by chirp- and click-stimuli at 40 dB HL in 32 normal hearing subjects aged 18 to 55 years (mean=24.8 years, SD=7.1 years). Compared to the click-evoked ABRs, the chirp-evoked ABRs showed larger wave V amplitudes, but an absence of earlier waves in the grand averages, larger wave V latency variance, smaller FFT magnitudes at the higher component frequencies, and larger phase variance at the higher component frequencies. These results strongly suggest that the chirp-evoked ABRs exhibited less synchrony than the click-evoked ABRs in this study. It is proposed that the temporal compensation offered by chirp stimuli is sufficient to increase neural recruitment (as measured by wave V amplitude), but that destructive phase interactions still exist along the cochlea partition, particularly in the low frequency portions of the cochlea where more latency jitter is expected. The clinical implications of these findings are discussed.