Low-frequency Electrical Signal Research Articles

Proposals for the ISS: «Reliability» Experiment Influence of low-frequency atmospheric electrical processes and near-space electromagnetic signals on the central nervous system functional condition of a man maintaining space systems

Proposals for the ISS: «Reliability» Experiment Influence of low-frequency atmospheric electrical processes and near-space electromagnetic signals on the central nervous system functional condition of a man maintaining space systems

Transmission of stress induced electric signals in dielectric media

The conditions under which pressure (stress) variations on solids, containing charged defects, can lead to the emission of transient electric signals, are discussed. The resulting electric field E varies as 1/d3 (where d denotes the distance from the emitting source), in the simple case when the surrounding medium is homogeneous and isotropic. We show that this behavior changes to 1/d when studying the electric field within a cylindrical channel of radius R and infinite length having conductivity appreciably larger than that of the host medium; this holds up to a certain (reduced) distance d/R, which increases versus the conductivity ratio. We also investigate the variation of the electric field, versus the distance, inside a layer of width w and infinite extent having conductivity appreciably larger than that of the host medium; we then find that the electric field decreases as 1/d2, in a wide range of distances up to a certain value of d/w, which is controlled by the conductivity ratio. In both conductive paths, i.e., cylinder and layer, the electric field approaches the 1/d3 behavior, but only at very large values of d/R and d/w, respectively, reaching the value that would be measured if the host medium was solely present. This implies a high current density inside the path. The case, when the highly conductive path terminates within the host medium, is also discussed; it is found that the “edge effects” play a prominent role in electric field values measured within the host medium, but close to the outcrop of the path. It is shown that a simplified calculation could erroneously obtain electric field values that are several orders of magnitude smaller than those calculated in this article. As an example, the transmission of low frequency electric signals in the earth is discussed. It is concluded that charged-defect generation mechanisms lead to electric field values that are measurable at large distances.

Hearing aid having plural microphones and a microphone switching system

A hearing aid apparatus is disclosed that employs both an omnidirectional microphone and at least one directional microphone of at least the first order. The electrical signals output from the directional microphone are supplied to an equalization amplifier which at least partially equalizes the amplitude of the low frequency electrical signal components of the electrical signal with the amplitude of the mid and high frequency electrical signal components of the electrical signals of the directional microphone. A switching circuit accepts the signals output from both the omnidirectional microphone and the directional microphone. The switching circuit connects the signal from the omnidirectional microphone to an input of a hearing aid amplifier when the switching circuit is in a first switching state, and connects the output of the equalization circuit to the hearing aid amplifier input when the switching circuit is in a second switching state. The switching circuit may be automatically switched in response to sensed ambient noise levels.

A novel optical fibre technique to calibrate the frequency response of optical detectors

An optical fibre interferometer is used to generate a modulated light beam. The interferometer is scanned with a piezoelectric tube driven by a low-frequency electrical signal. The technique ensures an amplitude modulation of the light independence of the frequency. The actual experimental arrangement covers the frequency range 1 kHz to 45 MHz.

Triangular phase-modulation approach to an open-loop fiber-optic gyroscope

A new approach to an open-loop, all-fiber gyroscope with a wide dynamic range and a linear scale factor is described. For signal processing, the Sagnac phase shift is converted into a phase shift in the low-frequency electrical signal by using a triangular phase-modulation waveform followed by gate switching. The basic principle of this technique and experimental results are reported.

Deep phase-modulation approach to an open-loop fiber optic gyroscope

A new approach to an open-loop, all-fiber gyroscope with a wide dynamic range and linear scale factor is described. For signal processing, the Sagnac phase lift is converted into a phase shift in the low-frequency electrical signal by using a deep sinusoidal phase-modulation waveform followed by gate switching. With the duty cycle of the gating signal selected to be in the range between 20 and 70%, the scale factor is stable with respect to change in the amplitude of the phase modulation signal by as much as 15%. The basic principle of the technique and experimental results are reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sources of electromagnetic radiation from fracture of rock samples in the laboratory

Rock, when fractured in the laboratory, emits electrical signals with a broad maximum in the power density spectrum in the band from 900 Hz to 5 kHz. Quartz‐free basalt rocks radiate both light and low‐frequency electrical signals as intensely as quartz‐bearing rocks, suggesting that the piezoelectric effect of quartz is at most a minor contributor to the total power radiated. Newly created rock surfaces acquire a local net charge distribution when exoelectrons are expelled and removed from the vicinity of the new surfaces by collisional and other processes. The rotational, vibrational, and linear motion of rock fragments with charged surfaces is the major contributor to the observed power density spectrum of the low‐frequency electrical signals. Neither optical spectral lines nor high‐frequency electromagnetic radiation, characteristic of electric discharges, occur at fracture. Exoelectron bombardment of the ambient fluid surrounding the sample, not electric discharge, is the excitation source for the light emitted at fracture.

Low-Frequency Electrical Signal Measurement by Electrooptical Methods

An analog system for the optical telemetry of voltage or current information using light-emitting diodes (LED) is described. Errors resulting from variations in the optical coupling efficiency are minimized because the light emitted by the LED contains the signal to be measured superimposed on a fixed intensity beam controlled by a reference zener diode. The nonlinearity of the LED is overcome by using part of its emitted light to control the feedback current to an operational amplifier that supplies the signal to the LED. The prototype system developed has a total error of approximately 0.2 percent of the input signal.

Sensory feedback from electroreceptors to electromotor pacemaker centers in gymnotids

Sensory feedback from electroreceptors to electromotor pacemaker centers in gymnotids