Crystal radio detector ["cat\´s whisker"]: the first wireless device

Summary form only given. The discovery of the crystal detector by Ferdinand Braun in 1874 is briefly discussed. Braun\´s interest in the electrical conductivity of metal salts in solution (electrolytes) ultimately led to his study of metal sulfide crystals and other crystalline solids, which conduct even when not dissolved. After much experimentation, Braun reported in 1874 (Annalen der Physik und Chemie, November 23, 1874) that for many metal sulfides the electrical resistance varies with the magnitude and polarity of the applied voltage. Galena Crystal, composed of lead sulfide, was used in his work. He found this phenomenon to be especially true if at least one of the electrodes was a pointed wire. The device, patented by him in 1899, was made of a single metal wire, fondly called a cat??s whisker, touching against a semiconductor crystal. The result was a "rectifying diode," which lets current through easily one way but hinders flow the other way. In other words, Braun had discovered the point-contact rectifier effect. This effect had no practical application at the time but would be rediscovered over 30 years later in the form of the "cat\´s whisker" crystal radio detector, and it would be instrumental in the point-contact transistor first produced in 1948.