Microweighing in Vacuo with the Aid of Vibrations of a Thin Band
If a very thin band of elastic material, e.g., polycarbonate plastic is clamped at both ends, and stretched, the natural frequency of transversal vibration depends on both tension and mass distribution. Let us assume that the band is loaded by a thin layer of dust, formed by spraying or electrostatic precipitation. In this case, the natural frequency will be diminished. This is shown in Fig. 1, where the natural frequency of a plastic band with a thickness of about 3 µ,a width of 20 mm, and a length of some centimeters is shown. This frequency is measured by means of a resonance method for several amounts of precipitated dust. The experimentwas carried out in vacuo. Excitation was induced by electrostatic forces and the amplitude of the vibrations was measured by an arrangement similar to a capacitance microphone. By varying the frequency of excitation, the resonance curve could be traced. Without load the peak of the curve was found to be at 1100 Hz, whereas, with a load of 0.2 mg, the peak shifted to 1000 Hz.
KeywordsElectrostatic Force Transversal Vibration Resonance Curve Electrostatic Precipitation Thin Band
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