Aleksander Burd

Analysis of some basic properties of multicavity photoacoustic Helmholtz cells

The paper presents results of comparative analysis of some basic properties of multicavity photoacoustic Helmholtz cells. The analysed cells were three-cavity Helmholtz resonators formed from a standard dual-cavity photoacoustic Helmholtz cell with an additional cavity connected by means of a capillary with the sample cavity of the cell at the other end. Influence of change of the volume of the additional cavity as well as diameter and length of the connecting duct on the microphone signal vs. frequency was studied. Analysis was based on computer simulations in which a modified transmission line model was used. The model was improved by introducing of additional damping factors which values were extracted from measurements of number of practically implemented dual-cavity photoacoustic Helmholtz cells. The analysis showed that additional cavity makes it possible to improve shape of the frequency response of the cell. In particular it is possible to extend range of frequencies in which resonance properties of the cell can be used for the purpose of photoacoustic signal amplification. It should be noticed that choice of the cell dimensions must be careful, as some combinations decrease resonance properties of the cell.

Influence of skin-effect on TDR-based diagnosis of transmission line

The paper illustrates an essential influence of skin effect on results of time-domain reflectometry technique applied to diagnosis of DSL transmission line. Skin effect (frequency-dependent ohmic losses dependent on geometry and material of the wire) appeared to be a phenomenon mainly responsible for transmission degradation. Skin effect significantly reduces possibilities of wide-band digital data transmission along telephone lines. It also limits TDR measurement system resolution and accuracy, which is shown in numerous measurement and computer simulation results.

Non-noise instabilities in oscilloscope trigger circuits

The paper discusses two phenomena called tremor, which result in incorrect operation of the oscilloscope trigger circuits. Both of them change delays introduced by the trigger circuit, resulting in horizontal shifts of traces on the screen, but the origins of the two phenomena are different. Both kinds of tremors in the oscilloscope trigger circuits produce images on the screen, which often are similar to those resulting from the noise jitter. Hence, limited knowledge of tremor may be a source of improper interpretation of the oscilloscope measurements. On the other hand tremor can be considered as a different approach to the problem of flip-flop circuits metastability.

Low-cost trigger circuit for sampling oscilloscope

The paper presents a low-cost trigger circuit for use in sampling oscilloscope with bandwidth in order of hundreds of MHz. The presented dual-step trigger circuit provides relatively high bandwidth because of significant reduction of possibility of incorrect turning on in trigger circuit flip-flop (caused by circuit instability called tremor or - describing the same phenomenon by other means - its metastability. The paper presents a circuit structure, principle of operation and its physical realization.

A novel method of measurement of LC circuits Q-factor

This paper presents a new method of measurement of quality factor of inductors and resonance circuits with usage of the effect of the formation of oscillations in sine wave oscillator. The article presents two different hardware realizations for parallel and series LC resonators.

Electromagnetic Obstacle Detection in Close Distance

The main topic is the electronic system, designed and built to help car drivers during parking. It uses electromagnetism phenomena for making an estimation of arrangement of obstacles. The device works with close distance (about 5-15cm), depending on the material from which the obstacle is made.

Temperature compensation of step recovery diode in fast sampling circuits

The paper concerns temperature compensation of time delay in ultra fast sampling circuits, used in digital oscilloscopes of gigahertz bandwidth. The main source of thermal instability appears to be step recovery diode used for sampling pulses generation, so the effort was taken toward assuring invariance of its delay regardless of operating temperature. The idea was successfully tested in the proposed circuit for diode polarisation and compensation.

Precise low-current source for sub-nanosecond pulse measurements

This paper presents the precise low current source circuit for use in a time measurement system with a time expansion. The circuits design and structure are shown, with a special attention brought to the problems during the system construction. The results of essential measurements are also shown. These results confirm the value of presented solution.

Low-cost fast ramp circuit for sampling oscilloscope

The paper presents a low-cost fast ramp circuit for use in sampling oscilloscope. A structure and a principle of operation of the circuit are described. The way of realisation and results of measurements are announced too. Usefulness of the circuit for fast sampling oscilloscopes is estimated.

The linearity measurements of the time-base circuit for random repetitive sampling oscilloscope

The paper presents design of a random repetitive sampling oscilloscope time-base circuit. The measurement system based on the pulse generator wih the precise pulse width control functionality is shown. The linearity measurements were performed and employed to verify the time-base circuit design.