초록 ▼

In a method of controlling or measuring layer thicknesses, wherein a continuous frequency-modulated ultrasonic signal that periodically scans a frequency band is transmitted and wherein the resultant signal is evaluated. The frequency bandwidth is selected large enough that a multiple of the interfe

In a method of controlling or measuring layer thicknesses, wherein a continuous frequency-modulated ultrasonic signal that periodically scans a frequency band is transmitted and wherein the resultant signal is evaluated. The frequency bandwidth is selected large enough that a multiple of the interference interval is covered. The spectral maxima or minima which periodically recur in the frequency spectrum of the received signal are evaluated. At a fixed modulation rate of the transmitted signal, an unambiguous interrelation exists between the repetition frequency of the maxima or minima in the spectrum and the thickness of the layer under examination. The repetition frequency increases with increasing layer thickness. According to an alternative embodiment of the invention, a ratio of harmonic amplitudes corresponding to the layer thickness is evaluated. The harmonics are produced by selecting a narrow frequency band, so that only part of the interference interval is covered. The repetition frequency of modulation is determined as a function of the desired measuring range.

대표청구항 ▼

An apparatus to determine a thickness of a material layer, comprising: (a) a sweep generator to generate an ultrasonic signal which covers a multiple of an interference interval, the sweep generator has: (i) an adjustable band width; and (ii) an adjustable modulation rate; (b) an amplifier to amplif

An apparatus to determine a thickness of a material layer, comprising: (a) a sweep generator to generate an ultrasonic signal which covers a multiple of an interference interval, the sweep generator has: (i) an adjustable band width; and (ii) an adjustable modulation rate; (b) an amplifier to amplify the generated signal; (c) a transmitting transducer to transmit the amplified signal into the material layer wherein the transmitted signal is reflected from surface interfaces of the material layer resulting in interference signals; (d) a receiving transducer to receive the interference signals from the material layer; (e) an amplitude demodulator to demodulate the received signals; and (f) a means to analyze frequencies of the demodulated interference signal and correlate the frequencies of the interference signal to a thickness measurement of the material layer.