Pulse Time Modulation Research Articles

Stroking through Electrolyte: Liquid Metal Droplet Propulsion through Pulse Time Modulation

AbstractActive droplets play important roles in microfluidics, robotics, and micro‐electromechanical systems. As a special class of active droplets that are conductive, reactive, and of high surface tension, liquid metal droplets (LMDs) can be driven by electric‐field‐induced surface (Marangoni) flows to function as reconfigurable components in actuators, sensors, catalytic reactors, and antennas. Stimulating LMDs using an electric field induces concurrent electro‐hydrodynamic flows and electrochemical surface oxidation (passivation). It is however difficult to decouple these two effects which brings complexity in controlling LMD motions. To address this challenge, pulse time modulation (PTM) signals are used. PTM enables controlled LMD displacement by propelling the droplets forward during the voltage‐on phases and facilitating surface recovery from oxidation during the voltage‐off phases. Counterintuitively, by taking such intermittent “rests”, the LMDs effectively inhibit the unfavorable impact of oxidation, granting high motion controllability. Combining high‐speed imaging, motion tracking, machine learning, and electrochemical analysis, the study reveals how electro‐hydrodynamic flows and surface oxide formation/dissolution interplay to generate well‐defined motion regimes. The study further develops a quasi‐analytical model to describe droplet motions and designs a rotary LMD motor to showcase the versatility of the approach. This work provides the fundamental framework and viable strategy for designing innovative liquid metal‐based systems.

Error performance analysis for chaotic pulse width position modulation in free space optical communication system

Abstract In this paper, a pulse time modulation method called chaotic pulse width position modulation (CPWPM) is studied for free space optical communication system. This is a digital modulation technique that combines pulse position modulation and pulse width modulation with chaos. In this scheme, the binary information is carried by both the position and width of the pulses, which are modulated by a chaotic signal. Hence, on a single pulse, two bits of information are encoded, which results in higher bit rates, better privacy, and larger effective bandwidth as compared to chaotic pulse position modulation (CPPM) and chaotic pulse width modulation (CPWM) techniques. Probability of error is investigated for different FSO scenarios, i.e., varying turbulence conditions and link lengths for CPWPM scheme. Finally, the performance of CPWPM-FSO system is compared with a commonly used differential chaos shift keying (DCSK) scheme. CPWPM-FSO system shows comparable results as DCSK-FSO system (for probability of error, P e = 10−4 average signal-to-noise ratio (SNR) required for DCSK and CPWPM scheme is 40 dB and 41 dB, respectively, for same length and system conditions), while data rate is doubled in latter, and this verifies the validity of using CPWPM in FSO communication system.

Transport control of dust particles by pulse-time modulated RF in dusty plasmas

Transport of dust particles was studied in radio frequency (RF) plasmas. Dust particles of two sizes were injected in the plasmas. The plasmas were generated by applying a pulse-time modulated RF voltage. The pulse-time modulation made it possible to change the electron temperature in the plasmas. The electron temperature dominates the charges of the dust particles and the electric fields around the sheath where the dust particles are levitated. The equilibrium position of the dust particles can be determined by forces on them derived from the charges and the electric fields. In this research, it was clearly shown to change the position of the dust particles and drop them from the plasmas by the pulsed-time modulation. Furthermore, the modulated RF plasma worked as sieves of the dust particles. It was possible to drop larger dust particles from the plasma, while smaller ones remain in the plasmas.

Gate-control of spin-motive force and spin-torque in Rashba SOC systems

The introduction of a strong Rashba spin–orbit coupling has been predicted to enhance the spin motive force (SMF) (see Kim et al 2012 Phys. Rev. Lett. 108 217202). In this work, we predict further enhancement of the SMF by time modulation of the Rashba coupling , which induces an additional electric field . When the modulation frequency is higher than the magnetization precessing frequency, the amplitude of this field is significantly larger than previously predicted results. Correspondingly, the spin torque on the magnetization is also effectively enhanced. We also suggest a biasing scheme to achieve rectification of SMF, i.e., by application of a square wave voltage at the resonant frequency. Finally, we numerically estimate the resulting spin torque field arising from a Gaussian pulse time modulation of .

Design and Implementation of PCM-to-PWM Data Converter

Pulse width modulation (PWM), a member of pulse time modulation (PTM) techniques, has been found advantageous for transmission of digital signals over optical fiber links. Most of the data is often found in Pulse Code Modulated (PCM) form and therefore needs to be converted into Pulse width modulation. A simple and low-cost circuit for the conversion of pulse code modulation (PCM) to Pulse Width Modulation (PWM) is proposed. The circuit has been tested in hardware and the experimental results are quite satisfactory. The circuit for the conversion of PWM to corresponding PCM is also proposed.

Characteristics of SiO2 etching by using pulse-time modulation in 60 MHz/2 MHz dual-frequency capacitive coupled plasma

60 MHz pulsed radio frequency (rf) source power and 2 MHz continuous wave rf bias power, were used for SiO2 etching masked with an amorphous carbon layer (ACL) in an Ar/C4F8/O2 gas mixture, and the effects of the frequency and duty ratio of the 60 MHz pulse rf power on the SiO2 etch characteristics were investigated. With decreasing duty ratio of the 60 MHz pulse rf power, not only the etch rate of SiO2 but also the etch rate of ACL was decreased, however, the etch selectivity of SiO2 over ACL was improved with decreasing the duty ratio. On the other hand, when the pulse frequency was varied at a constant duty ratio, no significant change in the etch rate and etch selectivity of both materials could be observed. The variation of the etch characteristics was believed to be related to the change in the gas dissociation characteristics caused by the change in the average electron temperature for different pulsing conditions. The improvement in the etch selectivity with the decrease of duty ratio, therefore, was related to the decreased gas dissociation of C4F8 by the decrease of average electron temperature and, which resulted in a change in composition of the fluorocarbon polymer on the etched materials surface from C–C rich to CF2 rich. With decreasing the duty ratio, not only the etch selectivity but also the improvement in the SiO2 etch profile could be observed.

A Chaotic Pulse‐Time Modulation Method for Digital Communication

We present and investigate a method of chaotic pulse‐time modulation (PTM) named chaotic pulse‐width‐position modulation (CPWPM) which is the combination of pulse‐position‐modulation (PPM) and pulse‐width modulation (PWM) with the inclusion of chaos technique for digital communications. CPWPM signal is in the pulse train format, in which binary information is modulated onto chaotically‐varied intervals of position and width of pulses, and therefore two bits are encoded on a single pulse. The operation of the method is described and the theoretical evaluation of bit‐error rate (BER) performance in the presence of additive white Gaussian noise (AWGN) is provided. In addition, the chaotic behavior with tent map and its effect on average parameters of the system are investigated. Theoretical estimation and numerical simulation of a CPWPM system with specific parameters are carried out in order to verify the performance of the proposed method.

Effect of iodotrifluoromethane plasma for reducing ultraviolet light irradiation damage in dielectric film etching processes

Iodotrifluoromethane (CF3I) gas is one of the environmentally conscious perfluorocarbon gases because it has a very low global warming potential. The authors have found that CF3I gas plasma drastically reduces ultraviolet (UV) photon irradiation of ∼4.0 eV, which corresponds to the excitation energy at silicon dioxide (SiO2)/silicon (Si) interfaces, in comparison with octafluorocyclobutane (C4F8) gas. This results in reducing UV irradiation damage in dielectric film etching processes, which was experimentally confirmed by evaluating charge-pumping currents in metal insulator semiconductor field effect transistors fabricated by using CF3I gas etching. They have also demonstrated that a novel etching method using pulse-time modulation of CF3I gas plasma for the first time further reduced UV light irradiation damage.

Adherent octacalciumphosphate coating on titanium alloy using modulated electrochemical deposition method

Our aims in this study were (1) to develop an electrochemical method of depositing adherent octacalciumphosphate (OCP) and other calcium phosphate coatings on titanium alloy (Ti6Al4V) substrates of different shapes and surface preparations, (2) to determine the properties of the coating (composition, morphology, thickness, dissolution), and (3) to observe transformation of OCP to carbonatehydroxyapatite (CHA) in simulated body fluid (SBF). Titanium (Ti)-alloy plates, tensile bars with four types of surfaces (grit-blasted with apatitic abrasive, chemically textured, arc-deposited, and Co-Cr-beaded) and dissolution cylinders were electrochemically coated with the use of modulated pulse time electric fields programmed with a custom-made dual microprocessor. Modulated electrochemical deposition (MECD) was carried out with pH and temperature conditions favorable for OCP formation. Coatings were characterized using X-ray diffraction, FT-IR, scanning electron microscopy, tensile strength tests, and solubility tests. XRD and FT-IR analyses showed that pure, uniform OCP coatings were produced on Ti6Al4V surfaces with coating-to-substrate tensile strengths greater than 7,000 psi. Coatings on Ti arc-deposited surfaces, chemically textured surfaces, and Co-Cr-beaded surfaces all gave tensile strengths ranging from 5,000 to 7,000 psi, with no coating shadows in the crevices. Dissolution of OCP coating in 100 mL of 0.1 M Tris buffer solution was determined from the amount of calcium (Ca) released onto the buffer, which was 7.7 +/- 1.0 ppm Ca at pH 7.3 after 4 h, and 22 -/+ 1.4 ppm Ca at pH 3 after 2 h. We found that OCP crystal size can be controlled by the current density and relative pulse time modulation. Our study demonstrated the following: (1) Highly adherent calcium phosphate (e.g., OCP) coating of uniform compositions (e.g., OCP) on Ti-alloy substrates can be obtained at low temperatures with the use of MECD by optimizing pulse time modulation of the electric field, reaction pH, temperature, and electrolyte composition; and (2) OCP readily transforms to CHA when exposed to SBF.

Pulse-time modulation of mutually coupled arrays of oscillators

This paper specifies the coupling parameters for multioscillator arrays (2 in number) such that nondegenerate symmetric and antisymmetric states may be sequentially accessed by electronic control of the coupling parameters. A requirement of this coupling configuration is that, when mutually locked, the oscillator amplitudes are identical to one another. Thus, when the oscillator signals are combined with a series of magic-T's, the output power is the sum of the oscillator powers in the array minus some small loss in the coupling circuit for the symmetric state and zero for the antisymmetric state. Switching from one state to the other is accomplished by control of the feedback phase delay between oscillators. Ideal oscillator cases are analyzed for two, four, and higher numbers of oscillators by induction. By this electronic-mode control of mutually locked oscillators, we have been able to generate pulse-time modulation (PTM) signals which are useful for communication systems. We describe some results of an X-band PTM signal generator.

Method of generating precision amplitude-modulated signals by triangular modulation of the time parameters of rectangular pulses of the carrier

A method of synthesizing amplitude-modulated signals by triangular pulse-time modulation of the pulses of a carrier with subsequent narrow-band filtering is proposed and investigated. Expressions are obtained for the amplitude-modulation coefficient for four forms of pulse-time modulation.

Optical fibre transmission of a broadband subcarrier multiplexed signal using PTM techniques

Subcarrier multiplexing (SCM) is an attractive multiplexing technique to deliver broadband services over optical fibres. The majority of existing systems employ an analogue signal for optical transmission and therefore the performance of these systems are limited. This paper proposes to improve SCM system performance by converting the analogue SCM signal into a pulse time modulated signal for optical transmission. The pulse time modulation techniques investigated are pulse frequency modulation and square wave frequency modulation. System measurements and theoretical predictions were obtained and they are in close agreement. We have improved the dynamic range and optical power budget considerably, compared to conventional systems.

Digital pulse interval and width modulation

This article investigates the implementation of a new digital pulse-time modulation (PTM) technique based on a digital pulse internal and width modulation (DPIWM) scheme. Original expressions are presented for code characterization, channel capacity, and power spectral density. These illustrate the advantages of this scheme compared with conventional pulse-code modulation (PCM). Both theoretical and simulated spectral results are given, and are shown to be in close agreement.

A new modulation technique based on digital pulse interval modulation (DPIM) for optical‐fiber communication

AbstractA novel digital pulse time modulation (PTM) technique called digital pulse interval modulation (DPIM) is presented, in which the input signal information is transmitted by the time intervals between two succeeding pulses. DPIM has simplicity of circuit configuration combined with other attractive features of digital pulse position modulation (DPPM) for optical‐fiber communications. This article derives theoretical expressions for transmission capacity, code characteristics, and power spectral density (PSD), and the analytical results are compared with experimental data. © 1995 John Wiley & Sons, Inc.

Squarewave frequency modulation techniques

Transmission of high-quality analogue sourced signals over copper or optical fibre links and networks demands a critical choice of modulation format to achieve both high performance and to avoid unnecessary bandwidth overhead penalties. Pulse time modulation (PTM) techniques are being increasingly employed to overcome many of the problems associated with traditional analogue and digital methods. Among the family of pulse time modulation techniques squarewave frequency modulation (SWFM) is particularly well suited to the transmission of high-quality wideband instrumentation and video signals, such as high definition TV, due to its attractive combination of performance and simplicity. This paper presents theoretical and practical aspects of SWFM and describes a number of experimental SWFM systems capable of transmitting signals from DC to 30 MHz. >

Pulse time modulation techniques for optical communications: a review

The principal factor in realising a high-performance bandwidth-efficient fibre communication system at an acceptable cost is the choice of modulation format on the optical carrier. In this context, pulse time modulation (PTM) techniques represent an attractive alternative to purely digital or analogue methods. The PTM family is reviewed, a classification system is proposed and their potential for use in high-speed fibre systems intended for the transmission of analogue data is examined.

Towards human brain near infrared imaging: time resolved and unresolved spectroscopy during hypoxic hypoxia.

Near infrared (IR) spectroscopy (NIRS) on animals and humans originated from the work of Jobsis (1977). Early cerebral and muscle NIRS measurements using multi-wavelength photometers were only qualitative. Fast scanning spectrophotometry has been utilized for a better spectral analysis and quantification purposes (Ferrari et al., 1989). Only pulse time and phase modulation spectroscopies can calculate pathlength in brain and muscle. Optical imaging in the near IR using these time-resolved methods is currently pursued by different groups (Chance, 1991 for a review). There are however significant technical and clinical problems related to the imaging technique yet to be solved before it can become truly a routine clinical tool.

Analogue optical fibre communications

* Chapter 1: Subcarrier multiplexing in optical communication network * Chapter 2: Coherent techniques in analogue signal transmission * Chapter 3: Analogue intensity modulation for optical-fibre video transmission * Chapter 4: Pulse time modulation techniques for optical fibre communications * Chapter 5: Soliton pulse position modulation * Chapter 6: Optical fibre digital pulse position modulation * Chapter 7: Performance assessment of subcarrier-multiplexed optical systems * Chapter 8: Optoelectronics for millimetre-wave radio over fibre systems * Chapter 9: Optical generation and delivery of modulated mm-waves for mobile communications * Chapter 10: Optical receiver design for optical-fibre SCM systems * Chapter 11: Optical fibre amplifiers and WDM

Analogue multiplier using compound pulse-time modulation

A new four-quadrant analogue multiplier based on compound pulse-time modulation formats is proposed. A particular type using pulse-width modulation (PWM) has been analysed and verified experimentally.

Pulse-time modulation and frequency modulation using the step recovery diode

Pulse-time modulation and frequency modulation using the step recovery diode