Method and device for detecting a specific acoustic spectral feature
US4577503A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 4, 1984 |
| Grant date | Mar 25, 1986 |
| Priority date | — |
| Expiry date | Sep 4, 2004 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01H3/12
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A method and device for detecting a narrow acoustic spectral feature in a sample as described. The method uses an electrical frequency modulated (FM) signal that is obtained from a voltage controlled oscillator. The Fourier spectrum of this wave is a main frequency f.sub.c with two small sidebands at frequencies f.sub.c .+-.f.sub.s. This whole triplet is slowly swept in frequency by a slow sawtooth generator. The electrical signal is fed into a flat acoustic transducer; the acoustic wave is then transmitted through an acoustically active medium, i.e. the sample, and detected by another flat acoustic transducer which produces an FM signal with a superposed amplitude modulated (AM) signal if one of the sidebands overlaps an acoustic feature. This electrical signal is then demodulated to give a pure AM signal which can be phase sensitive detected by using a lock-in amplifier. By suitable adjustment of the phase setting of the lock-in amplifier both the "in-phase" and "out-of-phase" signals of the detected acoustic signal can be detected.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.