Use Of Amplitude Modulation Research Articles

Amplitude modulated feed-forward thermal drift compensation for linear and nonlinear current sensors

The linear and nonlinear temperature responses restrict the application of Hall current sensors operating in thermal power plants and industries. The rise in temperature of electron device-based measurement causes a significant error, leading to undesirable consequences for plant operation and relay coordination. This paper investigates four Hall current sensor types with linear and nonlinear temperature responses. The Hall current sensor, which receives the magnetic excitation from the permanent magnet, exhibits a linear temperature response, and the wire-wound design exhibits a nonlinear temperature response in the temperature range of 306–376 K. The solution scheme with amplitude modulation and thermal sensor integration with interdigitated electrode design having graphene and ZnO–KMnO4 compounds as the dielectric is also proposed. The use of amplitude modulation achieves input frequency immunity with a 0.03% K−1 improvement in the temperature response of the capacitive thermal sensor. Experimental observations confirm the validity of the thermal drift compensation scheme with a 20%–99% reduction of thermal drift error with a suitable choice of a thermal sensor.

Frequency-modulation Kelvin probe force microscopy under tapping mode operation for surfaces with large protrusions

Kelvin probe force microscopy (KPFM) is a useful technique for simultaneously visualizing topography and contact potential difference (CPD). Although frequency-modulation (FM) KPFM has high spatial resolution and sensitivity, it is not readily applicable to measuring large protrusions owing to the instability of the feedback condition. Here we investigate the combined use of amplitude-modulation and FM for tip-sample distance control and electrostatic force detection, respectively. The proposed method enabled simultaneous acquisition of topography and CPD images of gold nanoparticles on a Nb-doped TiO2(100) surface. The effect of the tip shape and tilt angle on the CPD images is also discussed.

Amplitude modulation schemes for enhancing acoustically-driven microcentrifugation and micromixing.

The ability to drive microcentrifugation for efficient micromixing and particle concentration and separation on a microfluidic platform is critical for a wide range of lab-on-a-chip applications. In this work, we investigate the use of amplitude modulation to enhance the efficiency of the microcentrifugal recirculation flows in surface acoustic wave microfluidic systems, thus concomitantly reducing the power consumption in these devices for a given performance requirement-a crucial step in the development of miniaturized, integrated circuits for true portable functionality. In particular, we show that it is possible to obtain an increase of up to 60% in the acoustic streaming velocity in a microdroplet with kHz order modulation frequencies due to the intensification in Eckart streaming; the streaming velocity is increasing as the modulation index is increased. Additionally, we show that it is possible to exploit this streaming enhancement to effect improvements in the speed of particle concentration by up to 70% and the efficiency of micromixing by 50%, together with a modest decrease in the droplet temperature.

Acoustic-Emergent Phonology in the Amplitude Envelope of Child-Directed Speech.

When acquiring language, young children may use acoustic spectro-temporal patterns in speech to derive phonological units in spoken language (e.g., prosodic stress patterns, syllables, phonemes). Children appear to learn acoustic-phonological mappings rapidly, without direct instruction, yet the underlying developmental mechanisms remain unclear. Across different languages, a relationship between amplitude envelope sensitivity and phonological development has been found, suggesting that children may make use of amplitude modulation (AM) patterns within the envelope to develop a phonological system. Here we present the Spectral Amplitude Modulation Phase Hierarchy (S-AMPH) model, a set of algorithms for deriving the dominant AM patterns in child-directed speech (CDS). Using Principal Components Analysis, we show that rhythmic CDS contains an AM hierarchy comprising 3 core modulation timescales. These timescales correspond to key phonological units: prosodic stress (Stress AM, ~2 Hz), syllables (Syllable AM, ~5 Hz) and onset-rime units (Phoneme AM, ~20 Hz). We argue that these AM patterns could in principle be used by naïve listeners to compute acoustic-phonological mappings without lexical knowledge. We then demonstrate that the modulation statistics within this AM hierarchy indeed parse the speech signal into a primitive hierarchically-organised phonological system comprising stress feet (proto-words), syllables and onset-rime units. We apply the S-AMPH model to two other CDS corpora, one spontaneous and one deliberately-timed. The model accurately identified 72–82% (freely-read CDS) and 90–98% (rhythmically-regular CDS) stress patterns, syllables and onset-rime units. This in-principle demonstration that primitive phonology can be extracted from speech AMs is termed Acoustic-Emergent Phonology (AEP) theory. AEP theory provides a set of methods for examining how early phonological development is shaped by the temporal modulation structure of speech across languages. The S-AMPH model reveals a crucial developmental role for stress feet (AMs ~2 Hz). Stress feet underpin different linguistic rhythm typologies, and speech rhythm underpins language acquisition by infants in all languages.

Dielectrophoresis force spectroscopy for colloidal clusters

Optical trapping-based force spectroscopy was used to measure the frequency-dependent DEP forces and DEP crossover frequencies of colloidal polymethyl methacrylate spheres and clusters. A single sphere or cluster, held by an optical tweezer, was positioned near the center of a pair of gold-film electrodes where alternating current elecroosmosis flow was negligible. Use of amplitude modulation and phase-sensitive lock-in detection for accurate measurement of the DEP force yielded new insight into dielectric relaxation mechanisms near the crossover frequencies. On one hand, the size dependence of the DEP force near the crossover frequencies indicates that the dominant polarization mechanism is a volume effect. On the other hand, the power-law dependence of the crossover frequency on the particle radius with an exponent of -2 indicates the dielectric relaxation is more likely because of ionic diffusion across the particle surface, suggesting the dominant polarization mechanism may be a surface polarization effect. Better theories are needed to explain the experiment. Nevertheless, the strong size dependence of the crossover frequencies suggests the use of DEP for size sorting of micron-sized particles.

Low Frequency Modulation properties of Thyristor circuits

Load voltage waveforms corresponding to symmetrical phase-angle triggering and integral-cycle triggering in single-phase thyristor circuits, and also the waveform due to half-wave rectification, are all discrete forms of amplitude modulation. In each case the modulated output voltage is obtained from a sinusoidal (supply) carrier signal by use of a rectangular modulating function, dependent on thyristor switching. The use of amplitude modulation (AM) techniques for frequency conversion in high power applications is subject to certain severe restrictions of performance. These restrictions can be largely overcome by the use of phase modulation (PM) methods which involve two channels of AM in each electrical supply line. Appropriate waveforms may be realised by the use of controlled switching of thyristors. These are arranged in combinations of inverse-parallel connected pairs forming subtractor modulators. Certain thyristor commutation problems arise in PM systems at high power levels. These problems can be overcome by producing so-called AM/PM waveforms that combine the separate advantages of AM and PM systems.

A UHF mobile telephone system using digital modulation: Preliminary study

A UHF mobile telephone system using digital modulation is described. The system uses on-off keying of an 836-MHz carrier, the code being supplied by an adaptive delta coder with a clock frequency of 50 kHz. The maximum audio baseband signal-to-noise ratio is approximately 30 dB. The mobile receiver employs space diversity in a maximal-ratio combiner. Due to the use of amplitude modulation of the carrier rather than exponential modulation, the diversity receiver is very simple. The system was tested in the laboratory and in the field. Field tests were made in suburban and urban areas. For the four-branch system, threshold occurred at an average IF signal-to-noise ratio of approximately 12 dB.

Amplitude Modulation Method for Producing Sidebands in NMR Experiments

The use of amplitude modulation for the generation of sidebands offers certain advantages in NMR experiments, particularly when relatively large modulation frequencies (say above 1 kc) are required. For the Varian 40- and 60-Mc high resolution spectrometers, minor circuit modifications are described by means of which usable sideband signals are produced for modulation frequencies up to 70 kc, with amplitude reasonably constant from 200 cps to 40 kc.

Recent developments in mobile radio in Britain

The paper outlines briefly the development of v.h.f. mobile radio in Great Britain, its past history, its present development, and its future planning. The predominant use of amplitude modulation is discussed, particularly in relation to the introduction of 25 kc/s channel spacing which is now being used. Equipment has also been developed to work on channel spacings as close as 12.5 or 15 kc/s. Future trends and the possibility of introducing single-sideband with or without carrier, are briefly discussed.

Polyphase broadcasting

THE universal use of amplitude modulation in radio broadcasting service has led to several formidable problems in the design of broadcast transmitting equipment. Improvements in technique which permitted the complete modulation of a carrier (100 per cent modulation) raised new problems in connection with the conversion efficiency of the final radio-frequency amplifier stage. Continued research has resulted in such developments as the high-level plate-modulated amplifier, the high-efficiency linear amplifier, outphasing modulation, and others.

Polyphase Broadcasting

THE universal use of amplitude modulation in radio broadcasting service has led to several formidable problems in the design of broadcast transmitting equipment. Improvements in technique which permitted the complete modulation of a carrier (100 per cent modulation) raised new problems in connection with the conversion efficiency of the final radio-frequency amplifier stage. Continued research has resulted in such developments as the high-level plate-modulated amplifier, the high-efficiency linear amplifier, outphasing modulation, and others.