Elena Cocherova

Investigation of self-temperature-sensing of SC-Cut with simultaneous excitation of two higher overtones in dual-mode crystal oscillator

This paper deals with evaluation of self-temperature-sensing of stress compensated (SC) quartz resonator with simultaneous excitation of two higher overtones - the slow thickness-shear modes (i.e. the c-modes) in dual-mode crystal oscillator (DMXO). Two different combinations of overtones simultaneously excited in the standard 10-MHz 3rd overtone SC-cut resonator are compared here: - the 5th overtone excited together with the 3rd overtone; - and the 7th overtone excited together with the 3rd overtone. Possible applications of the self-temperature-sensing include: stabilization of the SC-cut resonatorpsilas temperature with excellent accuracy; as well as precise compensation for frequency shifts due to the variations of the temperature in the SC-cut resonator surrounding.

Dependence of the RF field absorption on the human body dimensions

In this paper, the dependence of radio-frequency (RF) field absorption on human body dimensions is investigated. The resonance properties of an ellipsoidal homogeneous human model have been investigated in frequency range from 10 MHz to 500 MHz with assistance of CST Microwave Studio program environment. In the article, the simulation of RF field absorption in the ellipsoidal body model has been performed for three various body heights, as well as three widths for a given body height.

RF Field Orientation Influence on the Specific Absorption Rate in a Biological Object

The influence of radio-frequency (RF) field orientation on specific absorption rate (SAR) in a human body is investigated in this paper. Three basic field orientations have been simulated: electric field vector, magnetic field vector and Poynting vector parallel to the longitudinal axis of a human body. The influence has been investigated in frequency range from 10 MHz to 2450 MHz with assistance of CST Microwave Studio program environment. Here the homogeneous ellipsoid, as a human body model, is irradiated by plane wave, representing far-field zone of antenna.

Tissue Parameters Influence on the Microwave Energy Absorption in Biological Objects

This article is devoted to an investigation of electrophysical parameters of biological tissue influence on its absorption of microwave energy. The specific absorption rate (SAR) is the dosimetric quantity for evaluation of microwave energy absorbed in biological tissue. Many parameters have effect on the SAR value, such as geometry of the part of the body, which is exposed to microwave energy, electrical parameters of body tissues, distance between the source of energy and surface of body, geometry of the antenna etc. In this article, homogeneous spherical model of the human head is modeled in CST Microwave Studio program environment. The tissue parameters variation influence on SAR values is evaluated for 900 MHz, 1800 MHz and 2450 MHz frequencies utilized in communication, medical and other applications.

Spectrum of counts computation for HRV analysis

Heart rate variability (HRV) analysis provides noninvasive way for assessment of neural activity that control cardiovascular system. Contributions of sympathetic and parasympathetic autonomous nervous system that modulate instantaneous heart rate are studied by means of spectral analysis. The objective is to recover modulating signal spectrum from beat occurrence times. In this paper, properties of so called spectrum of counts with respect to artifact arising in practical application of this method are described. Specifically, spectral leakage and beat time detection precision are discussed. Phenomena are analyzed on theoretical basis of integral pulse frequency modulation (IPFM). Computer simulations and recommendations for artifact rejection are presented.

The critical radius of stimulation electrode related to heart activation

This article examines the dependence of stimulation current threshold on stimulation electrode radius and other cardiac tissue parameters. The dependence was evaluated on a homogeneous slab model of the heart wall, with local membrane properties determined by modified FitzHugh-Nagumo model. Simulation results reveal that stimulation current density threshold depends proportionally on diffusivity related to tissue conductivity and on membrane excitation threshold. It is also inversely proportional to stimulation electrode radius. The critical radius of the stimulation electrode for the given model parameters estimated to be 0.8 mm was compared with simulation results. Stimulation electrodes with smaller radius are ineffective in eliciting excitation in the cardiac tissue.

On the existence of steady state oscillations in closed-loop feedback systems

This paper examines modification of an oscillator with parallel LC resonant circuit, in order to confirm that the Barkhausen criterion is a necessary, but not sufficient condition for steady state oscillations existence in closed-loop feedback systems. Up to now, only oscillators with different RC circuits in their feedback loop have been analyzed. In this study, we examine an oscillator circuit with parallel LC resonant circuit where self-sustained steady state oscillations do not occur even when the Barkhausen condition is satisfied.

Observability of Spectral Components beyond Nyquist Limit in Nonuniformly Sampled Signals

Identification of a signal component with the frequency exceeding the Nyquist limit is a challenging problem in signal theory as well as in some specific applications areas like astronomy and biosciences. A consequence of the well-known sampling theorem for a uniformly sampled signal is that the spectral component above the Nyquist limit is aliased into lower frequency range, making a distinction between true and aliased components impossible. The nonuniform sampling, however, offers a possibility to reduce aliased components and uncover information above the Nyquist limit. In this paper, we provide a theoretical analysis of the aliased components reduction in the nonparametric periodogram for two sampling schemes: the random sampling pattern and the sampling pattern generated by the integral pulse frequency modulation (IPFM), the latter widely accepted as the heart rate timing model. A general formula that relates the variance of timing deviations from a regular scheme with the aliased component suppression is proposed. The derived relation is illustrated by Lomb-Scargle periodograms applied on simulated data. Presented experimental data consisting of the respiration signal derived from the electrocardiogram and the heart rate signal also support possibility to detect frequencies above the Nyquist limit in the condition known as the cardiac aliasing.

Design and verification of thermostat with peltier thermoelectric modules

In the paper we deal with design, modeling and verification of thermostat with particularly thermally insulated chamber, based on Peltier thermoelectric modules (elements). A prototype of the designed thermostat has been realized. Parameters of the regulated system were obtained experimentally. We have developed the reliable model of the complete thermostat with the PSD regulation in the Matlab environment, as well. The model helps to optimize the parameters of the regulator according to desired temperature profiles inside the chamber. Measurements show a good agreement between the model and realized prototype of the thermostat.

Nonminimal-phase feedback circuits in oscillators

This article is intended to compare some nonminimal and minimal-phase (MPS) RC feedback systems from their argument (phase vs. frequency) characteristics point of view. There will be shown the nonminimal-phase systems (NPS) as feedback circuits with active element (e. g. OPAMP), which are able to generate periodic (quasisinusoidal) signals when some differences of MPS have been concerned and fulfilled.