Patent ID: 8677823

Claim:
Method for operating an electroacoustic device configured to operate in a gas filled space and from a first side of an object to be measured for making a non-contact ultrasonic thickness measurement of said object or for making a non-contact ultrasonic characterization of a medium located on an opposite side of said object, the method including providing said device comprising an electro acoustic transducer device, an electronic transceiver device connected to the electro acoustic transducer device and being configured to excite the electroacoustic transducer device to emit an acoustic signal towards said object and to receive an acoustic response signal therefrom, and a signal processor configured to process the response signal and to determine on basis of the acoustic response signal the thickness characteristic of said object to be measured, the electroacoustic transducer device having an acoustic transducer-to-gas interface, and providing the transceiver device being configured to drive the electroacoustic transducer device to emit into a gas filled space between the electroacoustic transducer device and said object to be measured an acoustic broadband pulse towards said object and to receive an acoustic resonance response signal in the acoustic response signal at a level allowing acquisition of the resonance response signal above a predetermined signal/noise level, the method further comprising: outputting from the transceiver said received acoustic response signal as a digitized time vector of a series of real numbers corresponding to voltages being output from the transducer device and representing the acoustic response signal, providing said signal processor with an input for said time vector and an input for input parameters, performing in the signal processor a time frequency analysis on basis of the time vector for identifying the time of the maximum energy and from this and a length of time window for spectral estimation determining the start time of the resonance tail, and a matrix of power, a vector of times, and a vector of frequencies, and to generate a thickness estimate on basis of the vector of time, input parameters and an output from the time frequency analyses, by preforming in the signal processor the steps of: a) identification of primary echo, b) spectral estimation by estimating frequency power contents of the time signal, c) identification of resonance frequency by identification of harmonic frequencies and assigning the correct harmonic order to them, and d) characterization of the object by computing object thickness on basis of the speed of sound in said object, the integer indicating the harmonic order, and the resonance frequency of the harmonic order, and averaging.