Rectangular Pulse Shape Research Articles

Evaluation of novel stimulus waveforms for deep brain stimulation

Deep brain stimulation (DBS) is an established therapy for the treatment of a wide range of neurological disorders. Historically, DBS and other neurostimulation technologies have relied on rectangular stimulation waveforms to impose their effects on the nervous system. Recent work has suggested that non-rectangular waveforms may have advantages over the traditional rectangular pulse. Therefore, we used detailed computer models to compare a range of charge-balanced biphasic waveforms with rectangular, exponential, triangular, Gaussian and sinusoidal stimulus pulse shapes. We explored the neural activation energy of these waveforms for both intracellular and extracellular current-controlled stimulation conditions. In the context of extracellular stimulation, we compared their effects on both axonal fibers of passage and projection neurons. Finally, we evaluated the impact of delivering the waveforms through a clinical DBS electrode, as opposed to a theoretical point source. Our results suggest that DBS with a 1 ms centered-triangular pulse can decrease energy consumption by 64% when compared with the standard 100 µs rectangular pulse (energy cost of 48 and 133 nJ, respectively, to stimulate 50% of a distributed population of axons) and can decrease energy consumption by 10% when compared with the most energy efficient rectangular pulse (1.25 ms duration). In turn, there may be measureable energy savings when using appropriately designed non-rectangular pulses in clinical DBS applications, thereby warranting further experimental investigation.

A laser interferometry instrumental complex for recording the velocity of moving surfaces in explosive experiments

The instrumental complex described is intended for recording the velocity of motion of the surface of a sample under study exposed to impact-explosion loading in gas-dynamic investigations of properties of structural materials. The velocity is determined from the Doppler wavelength shift of reflected radiation of the probing laser measured by the interferometry method. A solid-state laser with a pulse duration of >50 μs, an average power of at least 50 W, and a system for controlling the resonator quality factor, which ensures radiation stabilization for maintaining an almost rectangular pulse shape, is used as the probing-radiation source.

Symbol duration blind estimation of OFDM signals with low SNR

To explore the parameters estimation of OFDM (Orthogonal Frequency Division Multiplexing) signals in cognitive radio systems,the symbol duration blind estimation of OFDM signals was achieved through the cycle spectrum.Firstly,the cyclostationarity of the OFDM signals with cyclic prefix and rectangular pulse shape was demonstrated.Then based on the cycle spectrum of single-carrier signal and the orthogonality of OFDM subcarriers,the cycle spectrum expressions of OFDM signals were derived on the condition of no noise and low SNR.Finally,the computer simulation results of both the continuous signals and discrete signals are the same,which can estimate the symbol duration of OFDM signals blindly with low SNR through the cycle spectrum.

Development of 60 kV, 300 A, 3 kHz Pulsed Power Modulator for Wide Applications

In this paper, a novel pulsed power generator based on IGBT stacks is proposed for wide pulsed power applications. Because it can generate high voltage pulsed output without any step-up transformer or pulse forming network, it has advantages of fast rising time, easiness of pulse width variation, high repetition rate and rectangular pulse shapes. Proposed scheme consists of multiple power stages which were charged parallel from series resonant power inverter. Depending on the number of power stages it can increase maximum voltage up to 60 kV or higher with no limits of power stages. To reduce component for gate power supply, a simple and robust gate drive circuit which delivers gate power and gate signal simultaneously by way of one high voltage cable is proposed. For gating signal and power a full bridge inverter and pulse transformer generates on-ofi signals of IGBT gating with gate power simultaneously and it has very good characteristics of protection of IGBT switches over arcing condition. It can be used for various kinds of pulse power application such as plasma source ion implantation, sterilization, water and gas treatment which requires few kHz pulse repetition rate with few to ten of microseconds pulse width.

Analysis of Clock-Jitter Effects in Continuous-Time $\Delta \Sigma $ Modulators Using Discrete-Time Models

This paper proposes a simple discrete-time (DT) modeling technique for the rapid, yet accurate, simulation of the effect of clock jitter on the performance of continuous-time (CT) DeltaSigma modulators. The proposed DT modeling technique is derived from the impulse-invariant transform and is applicable to arbitrary-order lowpass and bandpass CT DeltaSigma modulators, with single-bit or multibit feedback digital-to-analog converters (DACs) employing delayed return-to-zero (RZ) or non-return-to-zero (NRZ) rectangular pulses. Its accuracy is independent of both the power spectrum of the clock jitter and the loop transfer function of the DeltaSigma modulator. The proposed DT modeling technique is validated (for both independent and accumulated clock-jitter errors) against accurate simulations in SIMULINK, using behavioral blocks developed to directly simulate RZ or NRZ DACs with clock jitter. It is subsequently applied to various CT DeltaSigma modulator architectures (low- pass and bandpass, with single-bit and multibit DACs) to study the relative effectiveness of different feedback-DAC pulsing schemes (NRZ, RZ, RZ with fixed on-time, and RZ with fixed off-time) in minimizing the modulator sensitivity to clock jitter. The performance of each architecture is compared as a function of clock jitter, thereby offering a valuable reference for selecting a rectangular feedback-DAC pulse shape when designing CT DeltaSigma analog-to-digital converters.

Characterisation of a parallel optical all pass filter for chromatic dispersion equalisation in 10 Gb/s system

The chromatic dispersion (CD) that occurs in single mode fibres (SMFs) is an important issue that needs to be addressed in long-haul optical communication links. The effect of CD is pulse spreading which in turn leads to inter-symbol interference, thus resulting in the deterioration of the bit error rate (BER) performance of the system. An alternative CD compensation technique that utilises a parallel optical all pass filter (p-OAPF) is presented, where the p-OAPF design is based on the inverse phase response of the SMF. The p-OAPF is based on a class of all-pass filter. Simulation results of the proposed technique show an increase in the repeater-less length of a point-to-point optical communication system by up to three and four times using a non-return-to-zero data format with a rectangular and Gaussian pulse shape, respectively, at error-free condition (BER < 10 -9 ). The results also show that the p-OAPF is robust in performing dispersion equalisation at a wide range of SMF lengths to attain error-free communication.

On chip pulse shape design for precise synchronization of DS‐CDMA systems

AbstractIn this work, a methodology is established to design optimum chip pulse shapes which are absolutely bandlimited, their energy mainly concentrated in the chip duration, and which minimize the variance of the time‐delay estimation error of an unbiased estimator. The low‐complexity optimization method is based on the prolate spheroidal wave functions. Thus, the variational problem at hand can be transformed into a tractable parametric optimization problem. It is shown that the designed optimum chip pulse shapes significantly improve the synchronization performance of direct sequence code‐division multiple access systems by minimizing the Cramer–Rao lower bound (CRLB). The time‐delay estimation bias under the presence of multipath is compared with the conventionally used bandlimited rectangular chip pulse shape. Copyright © 2007 John Wiley &amp; Sons, Ltd.

In-process monitoring and adaptive control for gap in micro butt welding with pulsed YAG laser

A gap is one of the most important issues to be solved in laser welding of a micro butt joint, because the gap results in welding defects such as underfilling or a non-bonded joint. In-process monitoring and adaptive control has been expected as one of the useful procedures for the stable production of sound laser welds without defects. The objective of this research is to evaluate the availability of in-process monitoring and adaptive control in micro butt welding of pure titanium rods with a pulsed neodymium : yttrium aluminium garnet (Nd : YAG) laser beam of a 150 µm spot diameter. It was revealed that a 45 µm narrow gap was detected by the remarkable jump in a reflected light intensity due to the formation of the molten pool which could bridge the gap. Heat radiation signal levels increased in proportion to the sizes of molten pools or penetration depths for the respective laser powers. As for adaptive control, the laser peak power was controlled on the basis of the reflected light or the heat radiation signals to stably produce a sound deeply penetrated weld reduced underfilling. In the case of a 100 µm gap, the underfilling was greatly reduced by half smaller than those made with a conventional rectangular pulse shape in seam welding as well as spot welding with a pulsed Nd : YAG laser beam. Consequently, the adaptive control of the laser peak power on the basis of in-process monitoring could reduce the harmful effects due to a gap in micro butt laser welding with a pulsed laser beam.

A Simplified Illustration of Arbitrary DAC Waveform Effects in Continuous Time Delta-Sigma Modulators

In this paper a straight-forward approach to extract the equivalent loop-gain of a continuous time Delta-Sigma modulator with an arbitrary DAC waveform in z-domain is presented. In this approach the arbitrary DAC waveform is approximated by the infinite number of rectangular pulse shapes. Then simply using the transformations available in literatures for a rectangular DAC pulse shape and applying superposition on each rectangular pulse shape, the loop-gain of the system is derived in z-domain.

Surface temperature evolution in pulsed laser action of millisecond range

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001–1.573 μm, 50 μs acquisition time for each photodiode, 800 μm spatial resolution, 900–3500 °C brightness temperature range) is used to measure brightness temperature under the pulsed action of Nd:YAG laser (HAAS–HL62P) on stainless steel (INOX 304L) substrates. Specially developed “notch” filters (10−6 transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored on the basis of method of multi-colour pyrometry. The accuracy of brightness temperature measurements is examined by comparing the temperature evolution for pulses with different durations but with the same value of energy density flux. The influence of the following parameters is studied keeping the remaining ones constant: pulse duration (6–20 ms, rectangular pulse shape), energy per pulse (10–33 J, rectangular pulse shape), pulse shape (three types of triangulars and one rectangular). Finally the evolution of surface temperature for pulses with more complex shapes but with the same pulse duration and energy per pulse is compared.

Coherent manipulation of coupled Josephson charge qubits

We have analyzed and measured the quantum coherent dynamics of a circuit containing two-coupled superconducting charge qubits. Each qubit is based on a Cooper pair box connected to a reservoir electrode through a Josephson junction. Two qubits are coupled electrostatically by a small island overlapping both Cooper pair boxes. Quantum state manipulation of the qubit circuit is done by applying non-adiabatic voltage pulses to the common gate. We read out each qubit by means of probe electrodes connected to Cooper pair boxes through high-Ohmic tunnel junctions. With such a setup, the measured pulse-induced probe currents are proportional to the probability for each qubit to have an extra Cooper pair after the manipulation. As expected from theory and observed experimentally, the measured pulse-induced current in each probe has two frequency components whose position on the frequency axis can be externally controlled. This is a result of the inter-qubit coupling which is also responsible for the avoided level crossing that we observed in the qubits’ spectra. Our simulations show that in the absence of decoherence and with a rectangular pulse shape, the system remains entangled most of the time reaching maximally entangled states at certain instances.

A Highly Efficient Generalized Teager-Kaiser-Based Technique for LOS Estimation in WCDMA Mobile Positioning

Line-of-sight signal delay estimation is a crucial element for any mobile positioning system. Estimating correctly the delay of the first arriving path is a challenging topic in severe propagation environments, such as closely spaced multipaths in multiuser scenario. Previous studies showed that there are many linear and nonlinear techniques able to solve closely spaced multipaths when the system is not bandlimited. However, using root raised cosine (RRC) pulse shaping introduces additional errors in the delay estimation process compared to the case with rectangular pulse shaping due to the inherent bandwidth limitation. In this paper, we introduce a novel technique for asynchronous WCDMA multipath delay estimation based on deconvolution with a suitable pulse shape, followed by Teager-Kaiser operator. The deconvolution stage is employed to reduce the effect of the bandlimiting pulse shape.

Porosity Formation by Laser Welding in Rectangular Pulse Shape

Porosity Formation by Laser Welding in Rectangular Pulse Shape

Numerical investigation on laser transformation hardening with different temporal pulse shapes

A 3-D numerical model for pulsed laser transformation hardening (LTH) is developed using the finite element method. In this model, laser spatial and temporal intensity distribution, temperature-dependent thermophysical properties of material, and multi-phase transformations are considered. The influence of laser temporal pulse shape on connectivity of hardened zone, maximum surface temperature of material and hardening depth is numerically investigated at different pulse energy levels. Results indicate that these hardening parameters are strongly dependent on the temporal pulse shape. For the rectangular temporal pulse shape, the temperature field obtained from this model is in excellent agreement with analytical solution, and the predicted hardening depth is favorably compared with experimental one. It should be pointed out that appropriate temporal pulse shape should be selected according to pulse energy level in order to achieve desirable hardening quality under certain laser spatial intensity distribution.

Capacity Bounds for Power- and Band-Limited Optical Intensity Channels Corrupted by Gaussian Noise

We determine upper and lower bounds on the channel capacity of power- and bandwidth-constrained optical intensity channels corrupted by white Gaussian noise. These bounds are shown to converge asymptotically at high optical signal-to-noise ratios (SNRs). Unlike previous investigations on low-intensity Poisson photon counting channels, such as some fiber optic links, this channel model is realistic for indoor free space optical channels corrupted by intense ambient light. An upper bound on the capacity is found through a sphere-packing argument while a lower bound is computed through the maxentropic source distribution. The role of bandwidth is expressed by way of the effective dimension of the set of signals and, together with an average optical power constraint, is used to determine bounds on the spectral efficiency of time-disjoint optical intensity signaling schemes. The bounds show that, at high optical SNRs, pulse sets based on raised-quadrature amplitude modulation (QAM) and prolate spheroidal wave functions have larger achievable maximum spectral efficiencies than traditional rectangular pulse basis sets. This result can be considered as an extension of previous work on photon counting channels which closely model low optical intensity channels with rectangular pulse shapes.

Closed-Form for Infinite Sum in Bandlimited CDMA

A closed-form expression is presented for an infinite sum that appears in the theoretical analysis of works in code-division multiple access (CDMA) that assume root-raised-cosine pulse shaping instead of rectangular pulse shaping. The expression derived is sufficiently general to work for arbitrary values of the roll-off factor. The expression is expected to contribute to the simplification of the analysis of CDMA systems with realistic pulse shaping.

Linear dynamical systems under random trains of non-overlapping, arbitrary-shape pulses: generalized approach

The excitation considered is a train of non-overlapping pulses, defined as a train of alternate random pulse durations and time gaps between the consecutive pulses. The time gaps and durations are assumed to be independent, continuous random variables. In this model the pulses are not only non-overlapping, but they are also non-adjoining, i.e. they can only adjoin with probability zero. All durations are assumed to be characterized by one common, Erlang (or integer parameter gamma) type, probability distribution. Likewise, the time gaps are all identically, Erlang distributed, but the probability distributions of the durations and of the time gaps have different parameters. Pulse shapes are given by an arbitrary, deterministic function and pulse heights are given by independent, identically distributed random variables. The mean value and autocorrelation function of the pulse train are evaluated analytically and are shown to be expressed in terms of the renewal densities of the renewal process governing the pulse arrivals. It is shown that for rectangular pulses with equal, deterministic heights these expressions reduce to the ones obtained independently with the aid of another approach, where the mean value and autocorrelation function are given in terms of Markov ‘on’ state probabilities. The mean value and variance of the response of a linear oscillator are obtained via a time domain analysis. Illustrative numerical analysis is carried out for example trains of pulses with parabolic and rectangular pulse shapes.

High-power long-pulse second harmonic generation and optical damage with free-running Nd: YAG laser

Frequency doubling with a free-running long-pulse Nd:YAG laser and LBO or KTP nonlinear crystals yields conversion efficiency of up to 17.5% and 162 W peak power in the second harmonic. This efficiency is obtained for a TEM/sub 00/ beam with rectangular temporal pulse shape of 50 to 400 μs. To our knowledge, this is the highest second-harmonic generation (SHG) efficiency reported for the long-pulse free-running configuration. The efficiency is limited by optical damage with much lower threshold than in the Q-switch domain. The damage is preceded by a saturation effect of the SHG efficiency. Both wavelengths (fundamental and second-harmonic) are necessary for the creation of the catastrophic damage. We present first evidence for a mechanism that involves creation of transient absorption centers by the second-harmonic radiation due to multiphoton absorption. Absorption of the fundamental wave at these centers leads to local heating and ultimately catastrophic damage.

Multiuser receivers that are robust to delay mismatch

We investigate a new robust multiuser signal detector for asynchronous code-division multiple-access uplink channels under delay mismatch. We first formulate a robust decorrelating detector by dividing each user into two virtual users with rectangular chip pulse shapes. To increase the system capacity, a multistage version of the robust decorrelating detector is derived, which can achieve capacity of up to M/(M+1) of the spreading factor, where M is the observation block length. We further propose a robust successive interference cancellation (SIC) implementation. The proposed robust SIC detector adds only a residual error estimation procedure onto the standard SIC detector, so its computational complexity is of the same order of that of the SIC. Performance is investigated via analysis and simulation. Computer simulation results showed that our proposed robust SIC detector outperforms the conventional decorrelating detector when delay estimation error is present, and its performance is close to that of the decorrelating detector with perfect time-delay information. Finally, we generalize the robust SIC detector to the case of nonrectangular chip pulse shapes.

Generation of triggerless silicon shunting plasma and ion extraction

The electrical characteristics of a pulsed silicon ‘shunting plasma’ are described and compared with carbon and niobium shunting plasmas. The plasma development occurs in three phases. Initially the solid material is heated by the discharge current, followed by a surface discharge during a glow-like phase, and finally the main plasma is formed as an arc by joule heating of the chosen solid material. The time at which the surface discharge bridges over the silicon plate corresponds to an abrupt decrease in voltage across the plate. Both streamer plasma bridging and an abrupt voltage decrease initiate the arc discharges as the final phase of the plasma formation process. Observations of optical emission spectra indicate that the plasma is composed of the original chosen solid material. Ion current is extracted from the plasma to a nearby target by application of a pulsed voltage to the target. The extracted current depends on the ambient gas pressure in the target region. For a pressure of 2.7 Pa a sharp current peak occurs upon application of voltage, while for a pressure of 133 Pa a rectangular current pulse shape is formed, similar to the shape of the applied voltage pulse. This may be a result of the formation of a matrix sheath surrounding the target that is immersed in the shunting plasma.