A crystal detector is an obsolete electronic component used in some early 20th century radio receivers that consists of a piece of crystalline mineral which rectifies the alternating current radio signal. It was employed as a detector (demodulator) to extract the audio modulation signal from the modulated carrier, to produce the sound in the earphones. It was the first type of semiconductor diode, and one of the first semiconductor electronic devices. The most common type was the so-called cat's whisker detector, which consisted of a piece of crystalline mineral, usually galena (lead sulfide), with a fine wire touching its surface.
The "asymmetric conduction" of electric current across electrical contacts between a crystal and a metal was discovered in 1874 by Karl Ferdinand Braun. Crystals were first used as radio wave detectors in 1894 by Jagadish Chandra Bose in his microwave experiments. Bose first patented a crystal detector in 1901. The crystal detector was developed into a practical radio component mainly by G. W. Pickard, who began research on detector materials in 1902 and found hundreds of substances that could be used in forming rectifying junctions. The physical principles by which they worked were not understood at the time they were used, but subsequent research into these primitive point contact semiconductor junctions in the 1930s and 1940s led to the development of modern semiconductor electronics.
The unamplified radio receivers that used crystal detectors are called crystal radios. The crystal radio was the first type of radio receiver that was used by the general public, and became the most widely used type of radio until the 1920s. It became obsolete with the development of vacuum tube receivers around 1920, but continued to be used until World War II and remains a common educational project today thanks to its simple design.
The contact between two dissimilar materials at the surface of the detector's semiconducting crystal forms a crude semiconductor diode, which acts as a rectifier, conducting electric current well in only one direction and resisting current flowing in the other direction.
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In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it. This is in contrast to an ordinary resistor in which an increase of applied voltage causes a proportional increase in current due to Ohm's law, resulting in a positive resistance. While a positive resistance consumes power from current passing through it, a negative resistance produces power.
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The course will cover the physics of particle detectors. It will introduce the experimental techniques used in nuclear and particle physics. The lecture includes the interaction of particles with matt
Ce cours est une introduction aux principes physiques des composants à semiconducteurs (transistors bipolaires, MOSFET et autres) et à leur modèlisation. Les performances électriques (digitales et ana
The course presents the detection of ionizing radiation in the keV and MeV energy ranges. Physical processes of radiation/matter interaction are introduced. All steps of detection are covered, as well
While domain adaptation has been used to improve the performance of object detectors when the training and test data follow different distributions, previous work has mostly focused on two-stage detec