Time-domain Impulse Response Research Articles

A Miniature Planar Antenna for Bluetooth and UWB Applications

The paper puts forward a miniature microstrip antenna at the operating frequency of 2.4–2.5 GHz (Bluetooth) and 3.1–10.6 GHz (UWB). The omnidirectional radiation patterns can be obtained at the whole operating frequency band by cutting the ground conductor and adding a branch at the top of the antenna. Simulated results show that the antenna has attractive characteristics such as stable phase center, constant group delay, linear phase and good time-domain impulse response. Both the reflection coefficient and radiation patterns of the antenna are in good agreement with measured results. Experiment also shows that the cross polarization level is very low with flat gain. Consequently, the proposed antenna can well meet the requirements of wireless communication in both the Bluetooth and UWB bands.

Theoretical Analysis of Wireless Passive Impedance-Loaded SAW Sensors

This paper concentrates on the theoretical analysis of wireless passive surface acoustic wave (SAW) impedance-loaded sensors. A general method is proposed for simulating the impedance-loaded SAW sensors. It is based on the combined finite-element method and boundary element method (FEM/BEM). A FEM is used to account for the mass loading effect of electrodes and a Green's function is used to model the piezoelectric substrate. Comparison between the simulations and measurements on SAW devices shows a good agreement. The calculated amplitude variation of the impulse response in time domain shows a resonant characteristic with the change of the loaded impedance. It is found that the return loss reaches the maximum value when the resonant frequency of the loaded circuits matches the center frequency of the short-circuited SAW transponder. This phenomenon is successfully explained by using the proposed model. Some high-performance sensors with greater amplitude modulation and larger sensitive range could be designed using this method.

An Analog Gabor Transform Using Sub-Threshold 180-nm CMOS Devices

The Gabor transform can be used to represent a signal in terms of a set of pseudo basis functions, allowing a signal to be split into parallel paths of a lower bandwidth. An analog Gabor transform using sub-threshold CMOS continuous time filters designed from time domain impulse responses is described. A novel method for designing low power gm-C filters using simple models of identical transconductors is used to specify the transistor sizes. Measured results show that the transform consumes 7 ¿W for an input signal bandwidth of 4 kHz, making it suitable for ultra low power systems.

Broadband Space-Time Measurements in Reverberation Chamber Including Comparison With Real Environment

Spatial variations of the broadband time-domain impulse response in a reverberation chamber are studied experimentally. The goal is to introduce the technique as a means for characterizing reverberation chambers and to demonstrate typical results and the information that can be extracted. Similar measurements are performed in a lab room for comparison. The results provide new insights regarding the signal environment inside a reverberation chamber and how it compares to real-life environments. The minimum number of signal paths in the chamber is calculated based on the spatial and temporal resolutions used in the characterization.

Jitter Analysis of Nonautonomous MOS Current-Mode Logic Circuits

In this paper, we analyze the occurrence of jitter due to random and deterministic disturbances in nonautonomous current-mode logic circuits. First, we present an analytical model that explains the transformation of noise into jitter as a linear time-variant process, with its time-domain impulse response function and a frequency-domain system function. The model is then used to analyze jitter in two different circuits, with different sources of noise. In the first example, we use the model to predict jitter due to device noise in a frequency divider, and identify devices that are the main contributors to the jitter. In the second example, we examine jitter of a buffer with deterministic ground noise. Jitter predictions are compared to the results obtained through exhaustive simulation. According to the comparison, the method predicts jitter with an error of up to 3.4%.

Identification of an unknown dielectric target in a half‐space using the E‐pulse technique

This paper describes an approach to model the impulse response of a dielectric target below a half‐space using a time domain deconvolution technique. The complex natural resonances (CNR) of the target are extracted from the time domain impulse response using a matrix pencil method and can be correlated with the target's physical properties. An automated E‐pulse scheme has been used to discriminate changes in the physical properties of target. The discrimination performance is calculated quantitatively by using an energy discrimination number (EDN) and discrimination ratio (DR). This technique can ultimately be used as a diagnostic tool in detection and discrimination of an unknown target inside a half‐space.

Study of a band‐notched double printed dipole antenna

AbstractIn this article, a double‐printed dipole antenna with band‐notched function for UWB applications is proposed and investigated. The band‐notched characteristic is achieved by inserting two U‐shaped slots on the dipole. Experimental and numerical results show that the proposed antenna meets the requirement of 3.1–10.6 GHz UWB systems with VSWR < 2, while avoiding the interference with the 5 GHz WLAN band. Transmitting antenna transfer function, receiving antenna transfer function, and antenna system function are used to describe the antenna performance. The impulse responses in time domain were calculated using inverse Fourier transform. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2986–2989, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23816

Simulation of ultrasound two-dimensional array transducers using a frequency domain model

Ultrasound imaging with two-dimensional (2D) arrays has garnered broad interest from scanner manufacturers and researchers for real time three-dimensional (3D) applications. Previously the authors described a frequency domain B-mode imaging model applicable for linear and phased array transducers. In this paper, the authors extend this model to incorporate 2D array transducers. Further approximations can be made based on the fact that the dimensions of the 2D array element are small. The model is compared with the widely used ultrasound simulation program FIELD II, which utilizes an approximate form of the time domain impulse response function. In a typical application, errors in simulated RF waveforms are less than 4% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/35 of those incurred using FIELD II. The 2D model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, dynamic receive focusing, and 3D beam steering can also be simulated.

TU‐C‐332‐05: Simulation of Ultrasound Two‐Dimensional Array Transducers Using a Frequency Domain Model

Purpose: Ultrasound imaging with two‐dimensional (2D) arrays has garnered broad interest from scanner manufacturers and researchers for real time three‐dimensional (3D) imaging. Previously we described a frequency domain B‐mode imaging model applicable for linear and phased array transducers. In this study, we extend this model to incorporate 2D array transducers. Method and Materials: The pressure field for a 64×64 square array with element dimension of 0.15 mm and center‐to‐center spacing of 0.2 mm was calculated by applying the paraxial approximation to solve the 2D Rayleigh integral. We assume a rigid baffle, no apodization, a 2.5 MHz center frequency, and a speed of sound of 1540 m/s. A single transmit focus at 30 mm and dynamic receive focus with an F‐number of 2 was utilized. The 2D array model is compared with the widely used ultrasound simulation program FIELD II, which utilizes an approximate form of the time domain impulse response function. Results: Discrepancies between waveforms computed using our model and FIELD II are less than 4%, regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/35 of those using FIELD II. Modern beam‐forming techniques such as apodization, dynamic aperture, dynamic receive focusing and 3D beam steering can also be simulated. The simulated beam patterns and point spread function images allow evaluation of beam properties for specific transducer parameters. Simulations of B‐mode images provide vivid demonstrations of the ability of 2D arrays with specific imaging parameters to detect lesions of a given backscatter contrast and size. Conclusion: The frequency domain approach provides an effective and feasible tool to model transmitted and pulse‐echo fields as well as B‐mode images for 2D array transducers.

Time-Domain Measurement of the Frequency-Dependent Delay of Broadband Antennas

We present a new time-domain technique for direct measurement of the frequency-dependent delay of broadband antenna structures. By utilizing a series of fixed-bandwidth, variable center frequency waveforms synthesized in a photonics-based electromagnetic pulse shaper, we perform high time resolution (~54 ps over ~10 ns) measurements of several broadband antenna structures. Our results show excellent agreement with the delay extracted via time-domain impulse response measurements, however, compared to conventional impulse response measurements, our method ensures a higher signal-to-noise ratio because it relies on several relatively narrowband measurements as opposed to a single broadband measurement. In addition, the delay uncertainty in our technique (~54 ps) is significantly below that of impulse response measurements (~300 ps) where numerical differentiation of noisy data leads to substantial errors. Our technique is well suited as a diagnostic tool for future variable-frequency fixed-bandwidth systems.

Approximation of the impulse response of an ultra-wide band antenna

Ultra-wide band antennas can be characterized by the time-domain impulse response. This paper introduces an approximate form of the impulse response that can be calculated by applying the method of moments to the Freedholm integral equation of convolution. Numerical results are compared to those obtained using the traditional frequency-domain approach. The validity of the approximate impulse response and the application constraints are also discussed. It is shown that the time-domain approach is faster than the frequency-domain approach while the accuracy is preserved.

Compensation of the effects of antenna dispersion on UWB waveforms via optical pulse-shaping techniques

To our knowledge, we present the first experimental demonstration of compensation of antenna dispersion effects on impulsive ultra-wideband (UWB) signals. By extracting the RF spectral phase from a time-domain impulse response measurement of a pair of ridged TEM horn antennas, we utilize a photonic-synthesis technique for arbitrary electromagnetic signal waveforms to generate a signal ''matched'' to the antenna pair. We demonstrate that the received waveform is compressed and exhibits reduced ringing levels, as compared to the impulse response of the system. Our technique is reprogrammable and we believe the technique will be applicable to a variety of antennas operating in the UWB communications band of 3.1-10.6 GHz.

Design and hybrid realization of FIR Nyquist filters with quantized coefficients and low sensitivity to timing jitter

A design of finite impulse response (FIR) Nyquist filters with zero intersymbol interference (ISI) and low sensitivity to timing jitter is presented. Using an affine scaling linear programming algorithm, a near-optimum quantized coefficient set can be obtained in a feasible computational time. By varying a parameter, the design provides a tradeoff between the tail energy of the impulse response in the time domain and the stopband of the magnitude response in the frequency domain. We also present a pipelined multiplier-free FIR filter realization with periodically time-varying (PTV) coefficients based on a hybrid form. The realizations exploit the coefficient symmetry to reduce the hardware by about one half. By placing most of the shifts followed by addition toward the back end of the structure, hardware is reduced due to the shorter wordlength of the adders. The proposed structure has a provision to increase the speed by adjusting a design parameter but at the expense of more hardware.

A State Space Method for Modal Identification of Mechanical Systems from Time Domain Responses

A new state space method is presented for modal identification of a mechanical system from its time domain impulse or initial condition responses. A key step in this method is the identification of the characteristic polynomial coefficients of an adjoint system. Once these coefficients are determined, a canonical state space realization of the adjoint system and the system′s modal parameters are formulated straightforwardly. This method is conceptually and mathematically simple and is easy to be implemented. Detailed mathematical treatments are demonstrated and numerical examples are provided to illustrate the use and effectiveness of the method.

Lossy transmission line simulation based on closed-form triangle impulse responses

Analytical frequency-domain expressions for single and coupled transmission lines with triangular input waveforms are first developed. The inverse Fourier transform is then used to obtain an expression for the time-domain triangle impulse responses for frequency-independent transmission line parameters. The integral associated with the inverse Fourier transform is solved analytically using a differential-equation-based technique. Closed-form expressions for the triangle impulse responses are given in the form of incomplete Lipschitz-Hankel integrals (ILHI) of the first kind. The ILHI can be efficiently calculated using existing algorithms. Combining these closed-form expressions for the triangle impulse responses with a time-domain convolution method using a triangle impulse as a basis function, provides an accurate and efficient simulation method for very lossy transmission lines embedded within linear and nonlinear circuits.

LiNbO3-based integrated optical network analyser for vectorial structure characterisation of fibre Bragg gratings

A LiNbO3-based integrated optical network analyser for polarisation-resolved longitudinal structure characterisation of optical fibre Bragg gratings is reported. The frequency-dependent complete reflectance Jones matrix is measured by interferometry and transformed into the time-domain impulse response. From the impulse response matrix the vectorial grating structure is determined by inverse scattering. Local dichroic reflectivity and birefringence were derived from this data. Knowledge of the vectorial nature of refractive index modulation depth and phase should allow an improvement of the ultraviolet (UV) illumination process and an effective correction of phase mask errors by longitudinally selective UV light post-processing, in order to fabricate chirped and/or apodised gratings which require the highest fabrication accuracy.

Impulse scattering processes of an elastic sphere

The ‘‘movable rigid sphere’’ scattering model of Hickling and Wang [J. Acoust. Soc. Am. 39, 276–279 (1966)] incorporates the translational ‘‘rebound’’ response of the scatterer to the incident field. However, as a physically unrealizable object, the rigid sphere has limited applicability. Recently, it was shown [J. Acoust. Soc. Am. 106, 553–564 (1999)] that both the movable rigid sphere and Anderson’s fluid sphere model [J. Acoust. Soc. Am. 22, 426–431 (1950)] are limiting cases of Faran’s elastic sphere scattering theory [J. Acoust. Soc. Am. 23, 405–418 (1951)]. In this paper, the time domain impulse response is used to demonstrate the three dimensional scattering of an elastic sphere and its special cases. The critical factor is the shear rigidity modulus. For normal elastic values of the modulus, shear waves dominate the scattering response. When the rigidity is high, the shear waves travel more rapidly through the sphere, and its motion becomes increasingly characterized as a rebound translation without change of shape. Wave conversion at the boundary is also inhibited. For low or vanishing rigidity, only compressional waves are supported, and these determine the scattering response. The presentation will be illustrated by movie animations. [Work supported by ONR.]

A frequency domain model for generating B-mode images with array transducers

A frequency domain B-mode imaging model applicable to linear and phased array transducers was developed for simulating ultrasound images of random media. Computations are based on an approximation that is less restrictive than the Fresnel approximation. The model is compared with the exact time domain impulse response method, regarded as the "gold standard". In a typical application, errors in simulated rf waveforms are less than 1% regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/150 of those using the exact method. This model takes into account the effects of frequency-dependent attenuation, backscattering, and dispersion. Modern beam-forming techniques such as apodization, dynamic aperture, elevational focusing, multiple transmit focusing and dynamic receiving focusing also can be simulated.

Buried thermoplastic layer diagnostics by the use of combined frequency-domain and impulse response photo-thermo-mechanical radiometry

A photothermal approach to the problem of characterizing the thermoplastic layer thickness sandwiched between two metal foils used in heat-sealed food containers is described. Real-time signal acquisition instrumentation for the photothermal radiometric signal based on impulse-response fast Fourier transform (FFT) processing via chirped laser-beam modulation and cross-correlation spectral analysis, instead of the conventional point-by-point discrete frequency scans with a lock-in amplifier has been introduced. A theoretical frequency-domain model for the signal generation due to laser heating, which contains both a thermal component and a mechanical component due to the thermal expansion of the thermoplastic layer, is presented. The time domain impulse response theoretical data have been obtained by a numerical FFT of the frequency-domain theoretical data. The total signal was measured via radiometric detection in both domains and was fitted to the theory to obtain thermal transport properties of the three-layered system. The thickness of the thermoplastic layer has been extracted with better than 5% precision.

Time Resolved Measurements Which Isolate the Mechanisms Responsible for Terahertz Glory Scattering from Dielectric Spheres

The surface-wave scattering processes responsible, in part, for the optical glory have never been compared with theoretical predictions. Here, THz impulse ranging is used to measure the time domain impulse response of spherical targets with sufficiently high temporal resolution to permit the surfacewave contribution to the total impulse response to be isolated. The first direct experimental comparison for the surface wave with Mie theory as well as the surface-wave approximation of van de Hulst is performed. Interference of the surface waves from a dielectric sphere is shown to lead to the frequency and angular intensity dependence of the THz glory. [S0031-9007(97)04970-3] PACS numbers: 42.25.Fx