129 research outputs found
Time-domain equivalent edge currents for transient scattering
Cataloged from PDF version of article.Time-domain equivalent edge currents (TD-EEC) are
developed for the transient scattering analysis. The development
is based on the Fourier inversion of frequency domain equivalent
edge current expressions. The time-domain diffracted fields are expressed
in terms of a contour integral along the diffracting edges
for any arbitrary input pulse shape, thereby yielding finite results
at the caustics of diffracted rays. The approach also eliminates the
need for the evaluation of a convolution integral in the time domain
geometrical theory of diffraction (GTD) analysis. The results are
compared with the first order GTD results for the transient scattering
analysis for a circular disk
Measurement of electromagnetic interference in time-domain
Time-domain EMI measurement systems allow measurement time to be reduced by several orders of magnitude. In this paper a novel real-time operating time-domain EMI measurement system is presented. By the use of several analog-to-digital converters the dynamic range requested by the international EMC standards is achieved. A real-time operating digital signal processing unit is presented. The frequency band that is investigated is subdivided into several sub-bands. A novel implementation of the 9 kHz IF filter for the frequency 150 kHz to 1 GHz is presented. By this way the measurement time has been reduced by a factor of 8000 in comparison to conventional EMI receivers. During emission measurements performed with a modelled IF-bandwidth of 9 kHz the noise floor is decreased to −19 dBµV in the average detector mode by the implemented low noise power splitter. Measurements have been performed with the improved measurement system in the frequency range 30 MHz–1 GHz
Investigation of carbon nanotube antennas using thin wire integral equations
In this paper the characteristics of small carbon nanotube (CNT) dipole antennas are investigated on the basis of the thin wire HallĂŠn integral equation (IE). A surface impedance model for the CNT is adopted to account for the specific material properties resulting in a modified kernel function for the integral equation. A numerical solution for the IE gives the current distribution along the CNT. From the current distribution the antenna driving point impedance and the antenna efficiency are computed. The presented numerical examples demonstrate the strong dependence of the antenna characteristics on the used material and show the limitations of nanoscale antennas
Markovian Dynamics of Josephson Parametric Amplification
In this work, we derive the dynamics of the lossy DC pumped non-degenerate
Josephson parametric amplifier (DCPJPA). The main element in a DCPJPA is the
superconducting Josephson junction. The DC bias generates the AC Josephson
current varying the nonlinear inductance of the junction. By this way the
Josephson junction acts as the pump oscillator as well as the time varying
reactance of the parametric amplifier. In quantum-limited amplification,
losses and noise have an increased impact on the characteristics of an
amplifier. We outline the classical model of the lossy DCPJPA and derive the
available noise power spectral densities. A classical treatment is not
capable of including properties like spontaneous emission which is mandatory
in case of amplification at the quantum limit. Thus, we derive a quantum
mechanical model of the lossy DCPJPA. Thermal losses are modeled by the
quantum Langevin approach, by coupling the quantized system to a photon heat
bath in thermodynamic equilibrium. The mode occupation in the bath follows
the Bose-Einstein statistics. Based on the second quantization formalism, we
derive the Heisenberg equations of motion of both resonator modes. We assume
the dynamics of the system to follow the Markovian approximation, i.e. the
system only depends on its actual state and is memory-free. We explicitly
compute the time evolution of the contributions to the signal mode energy and
give numeric examples based on different damping and coupling constants. Our
analytic results show, that this model is capable of including thermal noise
into the description of the DC pumped non-degenerate Josephson parametric
amplifier
A low-noise high dynamic-range time-domain EMI measurement system for CISPR Band E
In this paper, a broadband time-domain EMI measurement system for
measurements from 9 kHz to 18 GHz is presented that allows for compliant EMI
measurements in CISPR Band E. Combining ultra-fast
analog-to-digital-conversion and real-time digital signal processing on a
field-programmable-gate-array (FPGA) with ultra-broadband multi-stage
down-conversion, scan times can be reduced by several orders of magnitude in
comparison to a traditional heterodyne EMI-receiver. The ultra-low system
noise floor of 6â8 dB and the real-time spectrogram allow for the
characterisation of the time-behaviour of EMI near the noise floor. EMI
measurements of electronic consumer devices and electric household appliances
are presented
TLM modeling and system identification of optimized antenna structures
The transmission line matrix (TLM) method in conjunction with the genetic algorithm (GA) is presented for the bandwidth optimization of a low profile patch antenna. The optimization routine is supplemented by a system identification (SI) procedure. By the SI the model parameters of the structure are estimated which is used for a reduction of the total TLM simulation time. The SI utilizes a new stability criterion of the physical poles for the parameter extraction
Accurate modeling of high frequency microelectromechanical systems (MEMS) switches in time- and frequency-domainc
Abstract. In this contribution we present an accurate investigation of three different techniques for the modeling of complex planar circuits. The em analysis is performed by means of different electromagnetic full-wave solvers in the timedomain and in the frequency-domain. The first one is the Transmission Line Matrix (TLM) method. In the second one the TLM method is combined with the Integral Equation (IE) method. The latter is based on the Generalized Transverse Resonance Diffraction (GTRD). In order to test the methods we model different structures and compare the calculated Sparameters to measured results, with good agreement
Coherent low-energy charge transport in a diffusive S-N-S junction
We have studied the current voltage characteristics of diffusive mesoscopic
Nb-Cu-Nb Josephson junctions with highly-transparent Nb-Cu interfaces. We
consider the low-voltage and high-temperature regime eV<\epsilon_{c}<k_{B}T
where epsilon_{c} is the Thouless energy. The observed excess current as well
as the observed sub-harmonic Shapiro steps under microwave irradiation suggest
the occurrence of low-energy coherent Multiple Andreev Reflection (MAR).Comment: 4 pages, 4 figures, final versio
Mode-Locking in Quantum-Hall-Effect Point Contacts
We study the effect of an ac drive on the current-voltage (I-V)
characteristics of a tunnel junction between two fractional Quantum Hall fluids
at filling an odd integer. Within the chiral Luttinger liquid model
of edge states, the point contact dynamics is described by a driven damped
quantum mechanical pendulum. In a semi-classical limit which ignores electron
tunnelling, this model exhibits mode-locking, which corresponds to current
plateaus in the I-V curve at integer multiples of , with
the ac drive angular frequency. By analyzing the full quantum model at
non-zero using perturbative and exact methods, we study the effect of
quantum fluctuation on the mode-locked plateaus. For quantum
fluctuations smear completely the plateaus, leaving no trace of the ac drive.
For smeared plateaus remain in the I-V curve, but are not
centered at the currents . For rounded plateaus
centered around the quantized current values are found. The possibility of
using mode locking in FQHE point contacts as a current-to-frequency standard is
discussed.Comment: 12 pages, 8 figures, minor change
Microwave Inter-Connections and Switching by means of Carbon Nano-tubes
In this work, carbon nanotube (CNT) based
interconnections and switches will be reviewed,
discussing the possibility to use nanotubes as potential
building blocks for signal routing in microwave
networks. In particular, theoretical design of coplanar
waveguide (CPW), microâstrip singleâpoleâsingleâthrow
(SPST) and singleâpoleâdoubleâthrow (SPDT) devices has
been performed to predict the electrical performances of
CNTâbased RF switching configurations. Actually, by
using the semiconductorâconductor transition obtained
by properly biasing the CNTs, an isolation better than 30
dB can be obtained between the ON and OFF states of the
switch for very wide bandwidth applications. This
happens owing to the shape deformation and consequent
change in the bandâgap due to the external pressure
caused by the electric field. Stateâofâart for other
switching techniques based on CNTs and their use for RF
nanoâinterconnections is also discussed, together with
current issues in measurement techniques
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