Ultra-wideband Pulse Propagation Research Articles

An experimental research of the ultra-wideband pulse propagation in a transdirectional coupler based on coupled striplines

An experimental research of the ultra-wideband pulse propagation in a transdirectional coupler based on coupled striplines

FREQUENCY RESPONSE OF UWB SIGNAL IN A BEATING HEART

The measurement, monitoring of heartbeat and its rate are necessary to know the health of the heart of human beings. In addition, they are needed for extended applications like criminal investigation, law enforcement, defense and military usage, search, rescue operation, etc. The ultra-wideband (UWB) radars found growing interest in recent years as they are able to overcome the limitations of continuous-wave (CW) Doppler radars in detecting human heartbeat. Modeling and analysis of the UWB pulse propagation behavior through a human body is important before developing a practical UWB radar. Several researchers have estimated the reflected signals to study if their variations correlate with the heartbeat rate. However, the reflected signal strength carrying Doppler information received at the radar after a two-way propagation of the RF signal was found to be too weak for detection. This paper presents (i) a model for UWB wave propagation through a human thorax and (ii) estimation via simulation, of transmission coefficient at various frequencies in the UWB range 1–10[Formula: see text]GHz using CST Microwave Studio. The study clearly indicates that the variation of power transmission coefficient of UWB signal has a strong correlation to the instantaneous dimension of the heart in a cardiac cycle, a feature that can be exploited in detecting cardiac activity of human being using radar-based principles.

An experimental research of the ultra-wideband pulse propagation in a transdirectional coupler based on coupled striplines

The propagation of short picosecond pulses in coupled strip lines with a phase velocity ratio of odd and even modes of 3:1 is considered. The feature of the separation of the input pulse between the three output ports without significant loss of energy due to reflection from the input in transdirectional couplers based on coupled strip lines is experimentally shown. As a result of the analysis, it was found that the spectral components of the pulse are separating between the ports of the transdirectional coupler.

The Combined Method of Ray Tracing and Diffraction and Its Application to Ultra-wideband Pulse Propagation

In this study the scattered-filed computation using the combined method of ray tracing and diffraction (CMRD) is revisited but with an extension to the backscattering computation. The concept of the equivalent phase object is considered as the key part in the developed CMRD method, and is analyzed mathematically with accurately derived expressions for its amplitude and phase function. A formulated CMRD method for the backscattering computation is developed in this work, which is then used in the forward modeling and numerical computations for ultra-wideband pulse propagation and backscattering from a perfectly conducting circular cylinder. The numerical simulation indicates that reasonable and good agreements can be achieved for comparisons between our CMRD method and exact eigenfunction expansion approach. It is expected that the theoretical model and method of backscattering calculation using CMRD can be applied to the image processing and target identification with measurements of backward-scattered electromagnetic and acoustic waves.

Optimal pulse penetration in Lorentz-Model dielectrics using the Sommerfeld and Brillouin precursors.

Under proper initial conditions, the interrelated effects of phase and attenuation dispersion in ultrawideband pulse propagation modify the input pulse into precursor fields. Because of their minimal decay in a given dispersive medium, precursor-type pulses possess optimal penetration into that material at the frequency-chirped Lambert-Beer's law limit, making them ideally suited for remote sensing and medical imaging.

Study of RF Signal Attenuation of Human Heart

A study of ultrawideband pulse propagation modeling through human body for all frequencies from 0.1 to 10.5 GHz is presented. Reflection coefficient and signal attenuation are computed from the model considering the variation of heart dimension with respect to time unlike a fixed dimension of heart used in earlier models. The performance of cardiac activity is studied from the change of signal attenuation. This estimation may help in the design of a noninvasive diagnostic system using ultrawideband of frequencies.

Experimental Results on UWB Pulse Propagation in Low-Voltage Power Cables With Different Cross Sections

The paper presents some experimental results on unusual propagation of an ultrawide band (UWB) pulse in low-voltage three-conductor power cables. For cables of flat cross section, the results confirm the possibility of modal decomposition of the pulse into two low level pulses. However, this phenomenon does not occur in cables of circular cross section.

Ultrawideband pulse propagation through a homogeneous, isotropic, lossy plasma

We investigate a linearly polarized, plane wave electromagnetic step function modulated sine wave pulse traveling through an isotropic, homogeneous, lossy plasma with dielectric permittivity described by the Drude model. The results of this investigation extend the useful frequency domain below the plasma cutoff frequency. An asymptotic method of analysis is used to provide a closed‐form approximation to the integral representation of the propagated pulse that is valid for all input carrier frequencies. This closed‐form expression is the sum of its three asymptotic component fields: the Sommerfeld precursor, the Brillouin precursor and the signal contribution. These expressions reveal that, because of conductivity, each field component attenuates exponentially with distance at its own characteristic rate and that, for sufficiently large propagation distance, the Sommerfeld precursor will be the dominant contribution to the field. However, a study of the penetration capability of each field component shows that, for a large enough propagation distance with carrier frequencies below cutoff, the Brillouin precursor decays algebraically as z−2 with a minimal exponential attenuation with propagation distance while the Sommerfeld precursor decays at a rate that approaches a z−3/4 algebraic decay. Optimal signal penetration through a finite distance of a lossy plasma medium, for either radar imaging, remote sensing, or communication applications, may then be realized by using an appropriately constructed sequence of Brillouin precursor pulses.

A New CMOS Multilayer Electromagnetic Band-Gap Microstrip Line and Experimental Investigation of UWB Pulse Propagation

We report on the development of a new microstrip line and Its experimental results on ultra-wideband pulse propagation. The transmission line employs electromagnetic band-gap (EBG) structures and is implemented in the multilayer metal stack of a 0.25-mum CMOS process. The inductance and capacitance per unit length of the new microstrip line can be independently adjusted to achieve various slow-wave factors for different characteristic impedances by properly selecting the dimensions of the EBG cells, their respective locations, and the CMOS metal layers. Experimental time-domain investigation of the pulse propagation reveals an interesting phenomenon of pulse compression. This unique property of the new CMOS multilayer EBG microstrip line can be exploited to help generate pico-second pulse as well as to compensate for the loss and dispersion of transmission lines, hence effectively retaining or enhancing the pulse propagation characteristics in UWB impulse circuits.

Nonstationary waveguide equations for investigation of ultrawideband pulses in irregular waveguides

Nonstationary waveguide equations for investigation of the processes of excitation and propagation of ultrawideband pulses in irregular electromagnetic waveguides are derived. The equations allow direct calculation of the electric-field intensity of the pulses as a function of the spatial coordinates of the observation point and time. The intensity of the magnetic field is determined at the next stage after additional calculations. The equations proposed are a supplement to and a generalization of the equations derived earlier.

Uniform Asymptotics Applied to Ultrawideband Pulse Propagation

A canonical problem of central importance in the theory of ultrawideband pulse propagation through temporally dispersive, absorptive materials is the propagation of a Heaviside step-function signal through a medium that exhibits anomalous dispersion. This problem is rich in the use of asymptotic theory. Sommerfeld and Brillouin provided the first (qualitatively accurate but quantitatively inaccurate) closed-form approximations of the dynamic evolution of this waveform through a single-resonance Lorentz model dielectric based upon Debye's method of steepest descent. An improved approximation has since been provided by Oughstun and Sherman using modern, uniform asymptotic methods that rely upon the saddle-point method. An accurate, uniform asymptotic approximation describing the dynamical evolution of the unit step-function modulated sine wave signal through a single-resonance Lorentz model dielectric is presented here based upon their work. This refined asymptotic description results in a continuous evolution of the propagated field for all space-time points.

The time-frequency interpretation for transient evolution of wave propagation through dispersive medium

The propagation of electromagnetic waves in a linear, dispersive Lorentz medium is calculated using the finite-difference time-domain (FDTD) method; their time-frequency (TF) characteristics are studied using the Gabor extension. Numerical results show that the TF spectrum gives a clear interpretation for transient evolution of ultra wideband pulse propagation through a Lorentz medium.

Failure of the group-velocity description for ultrawideband pulse propagation in a causally dispersive, absorptive dielectric

The accuracy of the group-velocity description of dispersive pulse propagation in a double-resonance Lorentz model dielectric is shown to decrease monotonically as the propagation distance increases, whereas the accuracy of the asymptotic description increases monotonically as the propagation distance increases above a single absorption depth in the medium at the pulse carrier frequency.