page_title: Crystal detector
section_title: Pickard: first commercial detectors
hierarchical_section_title: Crystal detector / History / Pickard: first commercial detectors
caption_attribution_description: English: Photo of a carbon detector or "microphone detector" from 1909, a primitive coherer radio wave detector used in the first radio receivers. It was used from about 1900 to 1910 to receive Morse code radiotelegraphy transmissions from the first spark radio transmitters . The microphone detector was invented by David Edward Hughes, who stumbled on radio wave communication in 1879 while he was experimenting with carbon microphones. It consists of a steel needle resting across two sharp edged carbon blocks. One carbon was connected to the aerial and the other was connected to ground, so the radio waves from the antenna were applied across the needle contact. With no radio signal the device had a large resistance (megohms) but the radio wave altered the steel-carbon contact causing its resistance to drop. An earphone in series with a battery was connected across the carbons, so when the needle conducted electricity it made a hissing noise in the earphone. Greenleaf Whittier Pickard first observed radio wave rectification in 1902 with a similar detector. A semiconducting layer of corrosion on the needle which caused the device to act like a diode may have been responsible for the rectification. This was the first semiconductor diode. Information from Douglas, Alan&#32;(April 1981).&#32;"The Crystal Detector". IEEE Spectrum&#32;18&#32;(4): 64–69. DOI:10.1109/MSPEC.1981.6369482. ISSN 0018-9235.
context_page_description: 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 and was employed as a detector to extract the audio modulation 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 whisker detector, which consisted of a piece of crystalline mineral, usually galena, 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.
context_section_description: Greenleaf Whittier Pickard may be the person most responsible for making the crystal detector a practical device.  Pickard, an engineer with the American Wireless Telephone and Telegraph Co. invented the rectifying contact detector, discovering rectification of radio waves in 1902 while experimenting with a coherer detector consisting of a carbon block resting across two steel knife edge contacts.  On 29 May 1902 he was operating this device, listening to a radiotelegraphy station.  Coherers required an external current source to operate, so he had the coherer and telephone earphone connected in series with a 3 cell battery to provide power to operate the earphone. Annoyed by background "frying" noise caused by the current through the carbon, he reached over to cut two of the battery cells out of the circuit to reduce the current
  The frying ceased, and the signals, though much weakened, became materially clearer through being freed of their background of microphonic noise.  Glancing over at my circuit, I discovered to my great surprise that instead of cutting out two of the cells I had cut out all three; so, therefore, the telephone diaphragm was being operated solely by the energy of the receiver signals.  A contact detector operating without local battery seemed so contrary to all my previous experience that ... I resolved at once to thoroughly investigate the phenomenon.
  The generation of an audio signal without a DC bias battery made Pickard realize the device was acting as a rectifier.  During the next four years, Pickard conducted an exhaustive search to find which substances formed the most sensitive detecting contacts, eventually testing thousands of minerals, and discovered about 250 rectifying crystals.  In 1906 he obtained a sample of fused silicon, an artificial product recently synthesized in electric furnaces, and it outperformed all other substances.  He patented the silicon detector 30 August 1906.  In 1907 he formed a company to manufacture his detectors, Wireless Specialty Products Co., and the silicon detector was the first crystal detector to be sold commercially.  Pickard went on to produce other detectors using the crystals he had discovered; the more popular being the iron pyrite "Pyron" detector and the zincite–chalcopyrite crystal-to-crystal "Perikon" detector in 1908, which stood for "PERfect pIcKard cONtact".
caption: "Microphone" coherer detector from 1909 similar to one Pickard discovered rectification with, widely used in the first receivers.  It consists of a steel needle resting on two carbon blocks. A semiconducting corrosion layer on the steel may have been responsible for the rectification.
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