Multiple-pulse Modulation Research Articles

Transient absorption microscopy setup with multi-ten-kilohertz shot-to-shot subtraction and discrete Fourier analysis.

Recording of transient absorption microscopy images requires fast detection of minute optical density changes, which is typically achieved with high-repetition-rate laser sources and lock-in detection. Here, we present a highly flexible and cost-efficient detection scheme based on a conventional photodiode and an USB oscilloscope with MHz bandwidth, that deviates from the commonly used lock-in setup and achieves benchmark sensitivity. Our scheme combines shot-to-shot evaluation of pump-probe and probe-only measurements, a home-built photodetector circuit optimized for low pulse energies applying low-pass amplification, and a custom evaluation algorithm based on Fourier transformation. Advantages of this approach include abilities to simultaneously monitor multiple pulse modulation frequencies, implement the detection of additional pulse sequences (e.g., pump-only), and expand to multiple parallel detection channels for wavelength-dispersive probing. With a 40 kHz repetition-rate laser system powering two non-collinear optical parametric amplifiers for wide tuneability, we find that laser pulse fluctuations limit the sensitivity of the setup, while the detection scheme has negligible contribution. We demonstrate the 2-D imaging performance of our transient absorption microscope with studies on micro-crystalline molecular thin films.

Lightweight multi-hop VLC using compression and data-dependent multiple pulse modulation.

Particulate matter (PM) has a diameter of few micrometers, which causes different illnesses. We used visible light communication (VLC) to transfer PM data to a user monitoring terminal in real-time. To reduce the time and power required for communication, we compressed the PM data. Subsequently, these compressed data were transmitted using a modulation technique called data-dependent multiple pulse position modulation (DDMPPM). We evaluate the performance of DDMPPM for multi-hop communication in VLC through practical experiments. For the same data set, DDMPPM utilizes a lesser frame to transfer PM data. Using DDMPPM, we achieved a total communication distance of 48 m.

Artificial Neural Network Controller for Performance Optimization of Single Phase Inverter

Thyristorised Power control provides high efficiency. However, generated harmonics cause a nuisance in power system operation. The work presented here, deals with reduction of harmonics (3 rd -11 th ) by using Multiple Pulse Modulation technique. Traditional numerical methods do not yield accurate pulse-positions as non-linearity is involved in computation. In this paper, a continuous Hopfiled Neural Network is designed for Harmonic minimization in a 1Φ inverter output voltage. Results show considerable improvement in voltage spectrum if trigger pulses are generated at the ANN positions as harmonic contents are reduced with significant improvement in fundamental voltage resulting in reduction in device ratings. The ANN controlled voltage is used to drive a 1Φ Induction motor in MATLAB simulation and is compared with SPWM controlled VSI driving the same motor load. The quantitative analysis is given in tabular form. This shows feasibility of design of a controller for optimized performance of a single phase VSI.

Measurements of the acoustic field of a turbulent vortex ring

Turbulent vortex rings are one of the few examples of nearly stable flow structures in high Reynold's number flows. An investigation of their pressure and flow field characteristics could contribute to our understanding of the processes that couple (dilitational) acoustic fields and rotational flow fields. For this study an electromagnetic method for generating vortex rings of highly repeatable form was developed. The propagating rings were visualized by means of laser sheet illumination and aerosol seeding of the flow. The velocity field associated with a vortex ring was measured by multiple pulse modulation of the illuminating laser beam and direct photographing of the observed particle motions. The pressure field associated with the ring was measured with an array of membranes. Numerical data processing methods were employed to distinguish the acoustic component of the total flow field at various distances from the turbulent core of the vortex ring. Some possible implications of the results for low‐wavenumber components of turbulent boundary layer flow will also be discussed. [Research sponsored by ONR.]Turbulent vortex rings are one of the few examples of nearly stable flow structures in high Reynold's number flows. An investigation of their pressure and flow field characteristics could contribute to our understanding of the processes that couple (dilitational) acoustic fields and rotational flow fields. For this study an electromagnetic method for generating vortex rings of highly repeatable form was developed. The propagating rings were visualized by means of laser sheet illumination and aerosol seeding of the flow. The velocity field associated with a vortex ring was measured by multiple pulse modulation of the illuminating laser beam and direct photographing of the observed particle motions. The pressure field associated with the ring was measured with an array of membranes. Numerical data processing methods were employed to distinguish the acoustic component of the total flow field at various distances from the turbulent core of the vortex ring. Some possible implications of the results for low‐wav...

On certain possibility of comparison of different methods of multiple pulse modulation with the help of integral square error criterion

SUMMARY The main aim of this paper is to show that well known definition of integral square error /ISE/ may be a criterion of comparative analysis of modulation procesees. The effect of analysis of ISE property is that the comparison of pulse signal with model signal by their integrals gives an estimation of shape of the signal which is aiequate to current on the output of inverters. Simultaneously, this ISE is the measure which is corresponding to additional losses in an inverter load caused by deformation of current. As an example of the application of this criterion the results of numerical calculations of ISE versus amplitude of the first harmonic for choosed forms of modulation are given in the paper. The possibility of making synthesis of pulse modulation by minimizing the ISE is also pointed.

Multiple Pulse Modulation in Static Inverters Reduces Selected Output Harmonics and Provides Smooth Adjustment of Fundamentals

It is the problem of the inverter designer to design a unit whose cost is low and whose reliability is high, consistent with all other application requirements. This suggests that a minimum of major switching elements be used, that conservatively rated components be employed, and that circuit redundancy be incorporated in the design. Another major problem facing the inverter designer is that of maintaining the output voltage of the inverter within an allowable band of values. This problem arises due to the normal voltage drops within the inverter. It also is aggravated by the voltage drops in the rectifier supplying power to the inverter or by the battery voltage variation. Multiple pulse modulation provides more than one polarity reversal per half-cycle. The amplitude of the input voltage to the inverter is equal to that of the source and is essentially fixed for small intervals of time. The freedom to reverse polarity is the freedom to change the harmonic structure of the output. By selecting the number and location of the reversals in polarity, the fundamental amplitude may be varied while eliminating low-order harmonics. This technique offers a unique utilization of power handling components.