B.Z. Kaplan

A Versatile Voltage Controlled Three Phase Oscillator

A new method for constructing three phase analog oscillators is suggested and dealt with. The new method is essentially an extension into the three phase domain of methods known previously for the generation of sinewaves in two phases. An electronic realization of the method has resulted in a successful instrument whose performance is tested in the present paper.

Magnetic Anomaly Detection Using a Three-Axis Magnetometer

Magnetic anomaly detection is a good method for detecting ferromagnetic objects, particularly hidden targets. In this work, we address the detection of a moving ferromagnetic target using a static three-axis referenced magnetometer. The analysis and the results are also applicable to the converse case of a static ferromagnetic target and a moving three-axis referenced magnetometer. We use the three magnetometer outputs to build a total magnetic field of the target. This signal is decomposed into a set of orthonormal basis functions, out of which the dominant basis function is chosen as the detector. The detector provides output responses to any target magnetic moment orientation. We support the analysis by a computer simulation and real-world experimental results. The high detection probability and the simple implementation of the proposed method make it attractive for real-time applications.

Processing of magnetic scalar gradiometer signals using orthonormalized functions

This work relates to the detection of hidden ferromagnetic objects with the use of a gradiometer that comprises two scalar sensors and functions as a magnetic anomaly detector (MAD). A hidden object is represented by a magnetostatic dipole. Modeling of the MAD output signal is carried out by its decomposition in the space of orthogonal functions (an orthonormal basis) constructed with the use of Gram-Schmidt algorithm. A set of five functions is found to be sufficient for an accurate signal description in a wide range of distances between the gradiometer and the dipole. The dipole energy signal is introduced in the basis chosen and is found to be a useful function for the data processing algorithm based upon the results of the modeling. It is shown that the use of this function improves either the signal-to-noise ratio or the detection characteristics. Moreover, the dipole energy signal turns out to be independent of the dipole orientation. This leads to the possibility of using an identical signal processing algorithm for all variety of dipole waveforms.

Localization and magnetic moment estimation of a ferromagnetic target by simulated annealing

In many applications, the detection of a visually obscured magnetic target is followed by the characterization of the target, i.e. localization and magnetic moment estimation. Effective target characterization may reduce the detection false alarm rate as well as direct the searcher toward the target. We address the characterization of a static magnetic target by a three-axis fluxgate magnetometer installed on a stabilized mobile platform. The magnetometer readings are contaminated by magnetic noise, which results in a low signal-to-noise ratio. We formulate the problem as an over-determined nonlinear equation set using a magnetic dipole model for the target and use simulated annealing (SA) in order to rapidly find a good approximation to the global optimum of this equation set. Computer simulations demonstrate high accuracy of the SA method in localizing the target and estimating its magnetic moment in the presence of high-level noise. The high accuracy of the SA method is also exemplified in tests employing real-world magnetic signals. In addition to its high accuracy, the SA method is very rapid, making it appropriate for real-time practical applications.

Dynamic stabilization of tuned-circuit levitators

Recent investigations of a relatively new magnetic levitation device are described. This device uses an electromagnet, which is the inductive part of a resonant circuit. If the circuit is properly tuned, static stability is attainable. Levitators built on these lines are simple and reliable. However, it is already well known that a tuned circuit electromagnet on its own is usually not sufficient to maintain levitation for long periods of time, and the suspended object tends to be dynamically unstable. This dynamic instability is prevented by introducing simple electronic or mechanical modifications into the tuned circuit system. Such modifications are described and their investigation is dealt with. The electronic method of stabilization is successfully analyzed by employing the viewpoint of slowly varying quantities. It is believed that the present article is the first to suggest mechanical methods for introducing dynamic stabilization to levitators. It is interesting that mechanical stabilization is achieved without a necessity of employing direct mechanical contact, and the levitated object is suspended freely. The system is stabilized by electromechanically coupling an aluminium solid object to the main levitator circuit.

An ‘improved’ van-der-Pol equation and some of its possible applications

The study of oscillators is complicated and investigators tend to resort to simplified models. One such model is that represented by the van-der-Pol equation. Another model, represented by an ‘improved’ van-der-Pol equation is suggested and investigated in this paper. The latter model is almost as simple as the original one and yet it possesses several advantages which are valuable for the design, investigation, simulation and presentation of real oscillator systems.

Magnetic Anomaly Detection Using High-Order Crossing Method

Magnetic anomaly detection (MAD) is a passive method used to detect visually obscured ferromagnetic objects by revealing the anomalies in the ambient Earth magnetic field. In this paper, we propose a method for MAD employing the high-order crossing (HOC) approach, which relies on the magnetic background nature. HOC is an alternative method for spectral analysis using zero-crossing count, also enabling signal discrimination. Tests with real-world recorded magnetic signals show high detection probability even for low signal-to-noise ratio. The high detection probability, together with a simple implementation and low power consumption, makes the HOC method attractive for real-time MAD applications such as intruder detection and for research on an earthquake magnetic precursor.

Experimental and analytical investigation of synchronization dynamics of two coupled multivibrators

The present paper investigates the dynamic behavior of a system of two coupled multivibrators. The main results are related to the dynamics of synchronization states. The gradual approach of the system to a stable steady synchronization state is explored both analytically and experimentally, and the necessary conditions for maintaining a stable synchronization are successfully stated. The simple analytical treatment yields implicit results without resorting to approximate mathematical methods. The dynamic behavior of coupled multivibrators is of interest because of its relationship to the dynamics of neural systems. The relevance, however, of this dynamic behavior might be broader since it is demonstrated that the investigated system characteristics are similar to those of coupled sinusoidal oscillators, and hence, they may contribute to a better understanding in the general field of coupled oscillators dynamics.

Magnetic anomaly detection using entropy filter

We address the detection of a ferromagnetic target that generates an anomaly in the ambient Earth magnetic field. Detection of an anomaly buried in magnetic noise requires the use of a magnetic anomaly detector (MAD), such as the orthonormal basis functions (OBFs) detector. In contrast to the OBFs detector that relies on target signal waveform ensemble, we propose the adaptive minimum entropy detector (MED) to detect any changes in the magnetic noise pattern. Hence, we have constructed the MED based on the magnetic noise probability density function. The MED was tested on real-world magnetic noise and compared to the OBFs detector. Higher detection rate was exemplified for the MED over the OBFs detector in detecting a ferromagnetic target with low signal-to-noise ratio (SNR). Appreciable advantage of the MED over the OBFs detector is shown, when the target does not move according to the assumed pattern. The low-computational complexity makes the MED appropriate for real time applications.

Biological applications of the “Filtered” Van der Pol oscillator

The present article deals with the development of an oscillatory model, which generates waveforms corresponding to ECG patterns. The present oscillatory system relies on coupling of oscillators derived from the famous VDP oscillator. We demonstrate that inducing a relaxation type of dynamics in the models contributes to their successful generation of ECG like signals. Furthermore, an interesting affinity is found, which associates the present models with a version of the well-known practical Wien Bridge oscillator. The presently discussed system relies on coupled elementary oscillator units. The present coupling is due to merely two units. The model, however, is likely to become even more realistic by coupling in the same manner an assembly of relatively many oscillators.