scholarly journals Time Domain Performance Evaluation of UWB Antennas

2020 ◽  
Author(s):  
Gopikrishna Madanan ◽  
Deepti Das Krishna
Keyword(s):  
Transfer Function ◽  
Impulse Response ◽  
Time Domain ◽  
Performance Comparison ◽  
Radiation Patterns ◽  
Impulse Responses ◽  
Linear Time Invariant ◽  
Uwb Antennas ◽  
Time Domains ◽  
The Time Domain

The performance of printed wideband antennas has to be optimized both in frequency and time domains, to qualify for UWB applications. This is especially true in multi-resonant antenna topologies where the excitation of different modes can change phase centers and radiation patterns with frequency. The study presented in this chapter intends to demonstrate the simulation and experimental design for the time domain characterization of UWB antennas. Modeling the antenna as a linear time-invariant system with transfer function and impulse response, distortion caused to a nanosecond pulse is analyzed. Two planar monopole antenna designs are considered for the comparative study: the SQMA and RMA. SQMA is a traditional CPW-fed monopole design with ground modifications for ultra wide-bandwidth. RMA is a rectangular CPW-fed monopole with an impedance transformer arrangement at the antenna feed. RMA maintains constant impedance over the entire UWB and contributes towards maintaining uniformity in the radiation patterns over the entire frequency band by its design. Transfer function measurements are performed for both the azimuthal and elevation planes and the impulse responses are deduced by performing IFFT. Parameters such as FWHM and ringing are computed from the impulse response for the performance comparison. To evaluate the influence of the antenna geometry on a transmitted/received pulse, the impulse responses are convoluted with a standard UWB pulse. The time-domain distortion for the designs is then compared by computing the Fidelity parameter.

scholarly journals Analytical approximations for heat release rate laws in the time- and frequency-domains

2020 ◽  
Vol 12 ◽  
pp. 175682772093049
Author(s):  
Sreenath M Gopinathan ◽  
Alessandra Bigongiari ◽  
Maria Heckl
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Impulse Response ◽  
Release Rate ◽  
Time Domain ◽  
Time Lag ◽  
Coupling Coefficients ◽  
Describing Function ◽  
Flame Describing Function ◽  
The Time Domain

This paper focusses on the relationship between the heat release rate and the acoustic field, which is a crucial element in modelling thermoacoustic instabilities. The aim of the paper is twofold. The first aim is to develop a transformation tool, which makes it easy to switch between the time-domain representation (typically a heat release law involving time-lags) and the frequency-domain representation (typically a flame transfer function) of this relationship. Both representations are characterised by the same set of parameters n1, n2, …, nk. Their number is quite small, and they have a clear physical meaning: they are time-lag dependent coupling coefficients. They are closely linked to the impulse response of the flame in the linear regime in that they are proportional to the discretised (with respect to time) impulse response. In the nonlinear regime, the parameters n1, n2, …, nk become amplitude-dependent. Their interpretation as time-lag dependent coupling coefficients prevails; however, the link with the impulse response is lost. Nonlinear flames are commonly described in the frequency-domain by an amplitude-dependent flame transfer function, the so-called flame describing function. The time-domain equivalent of the flame describing function is sometimes mistaken for a ‘nonlinear impulse response’, but this is not correct. The second aim of this paper is to highlight this misconception and to provide the correct interpretation of the time-domain equivalent of the flame describing function.

scholarly journals Research on improving measurement accuracy of acoustic transfer function of underwater vehicle

2021 ◽  
Vol 336 ◽  
pp. 01006
Author(s):  
Jiangqiao Li ◽  
Li Jiang ◽  
Fujian Yu ◽  
Ye Zhang ◽  
Kun Gao
Keyword(s):  
Transfer Function ◽  
Impulse Response ◽  
Time Domain ◽  
Transfer Functions ◽  
Least Squares Method ◽  
Signal To Noise Ratio ◽  
Random Noise ◽  
Phase Compensation ◽  
Acoustic Transfer Function ◽  
The Time Domain

To address the problem that acoustic transfer functions with underwater platforms cannot be measured accurately, this paper presents a method based on phase compensation to improve the accuracy of acoustic transfer function measurements on underwater platforms. The time-domain impulse response signals with multiple cycles are first collected and intercepted, and then their phase differences are estimated using the least-squares method, and phase compensation is used to align the phases of all the signals, and then the impulse response signals are weighted and averaged over all the impulse response signals to cancel out the random noise. The water pool test proves that this method reduces the measurement random noise while obtaining a high-fidelity time domain transfer function, which effectively improves the signal-to-noise ratio of the measurement. The method adopts only one measurement signal, and without changing the measurement system, the random noise is cancelled out by the in-phase superposition of the multi-cycle impulse response signals to avoid the nonlinear distortion of the measurement results.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

scholarly journals Design of Two Novel Dual Band-Notched UWB Antennas

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Bing Li ◽  
Jing-song Hong
Keyword(s):  
Time Domain ◽  
Simple Structure ◽  
The Other ◽  
Ultra Wideband ◽  
Dual Band ◽  
Uwb Antennas ◽  
Monopole Antennas ◽  
Printed Monopole ◽  
The Difference ◽  
The Time Domain

Two novel dual band-notched ultra-wideband (UWB) printed monopole antennas with simple structure and small size are presented. The size of both antennas is25×25×0.8 mm3. The bandwidth of one of the proposed antenna can be from 2.7 GHz to 36.8 GHz, except the bandwidth of 3.2–3.9 GHz for WiMAX applications and 5.14–5.94 GHz for WLAN applications. The bandwidth of the other is ranging for 2.7 to 41.1 GHz, except the bandwidth of 3.2–3.9 GHz for WiMAX applications and 4.8–5.9 GHz for WLAN applications. Bandwidths of the antennas are about 512% and 455% wider than those of conventional band-notched UWB antennas, respectively. In addition, the time-domain characteristics of the two antennas are investigated to show the difference between both antennas.

Reversible Audio Data Hiding in Spectral and Time Domains

2013 ◽  
pp. 19-41 ◽  
Author(s):  
Akira Nishimura
Keyword(s):  
Data Hiding ◽  
Time Domain ◽  
Reversible Data Hiding ◽  
Linear Prediction ◽  
Data Consistency ◽  
Time Domains ◽  
Audio Data ◽  
Hidden Data ◽  
The Time Domain ◽  
Location Map

Reversible data hiding is a technique whereby hidden data are embedded in host data in such a way that the host data consistency is perfectly preserved and the host data are restored when extracting the hidden data. This chapter introduces basic algorithms for reversible data hiding, histogram shifting, histogram expansion, and compression. This chapter also proposes and evaluates two reversible data hiding methods, i.e., hiding data in the frequency-domain using integer Discrete Cosine Transform (DCT) and modified DCT and hiding in the time domain using linear prediction and error expansion. As no location map is required to prevent amplitude overflow, the proposed method in the time domain achieves a storage capacity of nearly 1 bit per sample of payload data. The proposed methods are evaluated by the payload amount, objective quality degradation of stego signal, and payload concealment.

Performance comparison based on single-pixel imaging methods in the time domain

Laser Physics ◽  
2019 ◽  
Vol 30 (1) ◽  
pp. 015202
Author(s):  
Rui Xiong ◽  
Leihong Zhang ◽  
Zilan Pan ◽  
Dawei Zhang ◽  
Zhaorui Wang ◽  
...  
Keyword(s):  
Time Domain ◽  
Performance Comparison ◽  
Imaging Methods ◽  
The Time Domain ◽  
Single Pixel
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