Halt extremely body mike has volume small, structure is simple, electroacoustic function the characteristic with good, low price, in be being used extensively at box type recorder, radio microphone and sound to accuse to wait for circuit.
Halt extremely body mike is alternated by acoustical report changeover and impedance two parts are comprised. The crucial element that acoustical report changes is to be stationed in extremely body vibration film. It is a paper-thin plastic diaphragm, amid one side evaporates a bullion is filmy. Next electric field of repass high pressure is stationed in extremely hind, two sides is stationed in respectively have opposite sex charge. The evaporate gold face of diaphragm is outward, connect with metallic crust photograph. Of diaphragm additional
With thin insulation line encircles segregation to leave between one side and metallic plate. Such, evaporate forms a capacitance between golden film and metallic plate. Should be stationed in extremely when body diaphragm encounters sound wave vibration, cause capacitance the electric field of two end produces change, produced what change and change along with sound wave to hand in thereby change voltage. Be stationed in extremely the capacitance between body diaphragm and metallic plate is smaller, it is a few PF commonly. Its output impedance cost is very consequently high (1 ／ of Xc ＝ 2~tfc) , make an appointment with above of a few Europe. So tall impedance cannot match with frequency amplifier directly. Receive dynatron of crystal of effect of a knot field to undertake impedance alternates inside mike so. The characteristic that field effect is in charge of is input impedance coefficient of extremely tall, noise is low. Common field effect is in charge of active pole (S) , grid (G) and leakage extremely (D) 3 extremely. What use here is interiorly between source pole and grid again compound the canal of special field effect of a diode. The purpose that receives diode is attendant effect protective effect has when the canal suffers strong signal to pound. The grid that field effect is in charge of accepts metallic plate. Such, halt extremely the output line of body mike has 3. Namely source pole S, use blue model line commonly, leakage pole D, use gules and plastic wire and join metal case commonly braid screen line.
Halt extremely of body mike and circuit receive a law to have two kinds: Source pole output and leakage extremely output. The ejaculation that source pole outputs similar crystal dynatron extremely output. Need to use 3 derivative lines. Leakage pole D receives power source anode. One resistor Rs is received to offer source pole voltage between source pole S and ground, signal by the source extremely output of classics capacitance C. Braid action of the screen since line ground connection. The output impedance that source pole outputs is less than 2k, circuit is stabler, dynamic range is big. But output signal compares leakage pole output is little. Leakage pole outputs the common emitter of similar crystal dynatron to be put. Require two derivative lines only. Leakage pole D and power source anode leak secondhand extremely resistor RD, signal by leakage extremely output of C of D classics capacitance. Source pole S and braid a line one case ground connection. Leakage pole output has voltage gain, when consequently mike sensitivity compares source pole to output, want tall, but circuit trends limits slightly small.
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