Method and device for frequency response measurement
A method is provided for measuring a frequency response of an object, the method involving: generating an excitation signal having relatively fast changing frequency, defined by a time-domain function; generating at least one reference signal, having a waveform corresponding to the excitation signal; introducing the excitation signal into the object, receiving a response signal from the object; analyzing said response signal in a signal analyzer by correlating the response signal with at least one reference signal during a relatively short sliding time-domain window.
1. A method for measuring a frequency response of an object, the method comprising:
generating an excitation signal having relatively fast changing frequency, defined by a time-domain function;
generating at least one reference signal, having a waveform corresponding to said excitation signal;
introducing said excitation signal into the object,
receiving a response signal from said object;
analyzing said response signal in a signal analyzer by correlating said response signal with said at least one reference signal during a relatively short sliding time-domain window.
2. The method as in claim 1 , wherein said relatively short sliding time-domain window is divided into several time-domain sub-windows.
3. The method as in claim 1 , wherein the length of said relatively short sliding time-domain window is variable and determined by running frequency value.
4. The method as in claim 1 , wherein the beginning and the end of said relatively short sliding time-domain window are chosen at zero-crossings of said excitation signal.
5. The method as in claim 1 , wherein said excitation signal is generated as a sinusoidal wave.
6. The method as in claim 1 , wherein the excitation signal is generated as non-sinusoidal wave.
7. The method as in claim 6 , wherein said excitation signal is a square wave signal.
8. The method as in claim 1 , wherein the excitation signal is generated as a chirp signal.
9. The method as in claim 8 , wherein said chirp signal is a linear chirp signal.
10. The method as in claim 8 , wherein said chirp signal is a nonlinear chirp signal.
11. The method as in claim 10 , wherein said nonlinear chirp signal is selected from the group consisting logarithmic, exponential and arbitrarily formulated chirp signal.
12. The method as in claim 1 , comprising analyzing said response signal in at least two consecutive steps, while using adaptively results of an earlier step for determining the parameters of said excitation signal or at least one analysis window for a subsequent step.
13. The method as in claim 12 , wherein in said previous step the parameters of the excitation signal or of at least of one analysis window for the subsequent step are defined to minimize the effect of noise or measurement inaccuracy.
14. The method as in claim 12 , wherein in said previous step the parameters of said excitation signal or of at least one analysis window for the subsequent step are defined to classify said object.
15. The method as in claim 1 , wherein said reference signals are convolved in complex arithmetic in said short time-domain window by said response signal for calculation of the real and imaginary parts of the response signal, to be used for calculation of the real and imaginary parts of the object's transfer coefficient as a function of the frequency.
16. The method as in claim 1 , wherein a first reference waveform corresponding to said excitation signal, is used to determine real and imaginary parts of a transfer coefficient by correlating it in the short-time window by complex representation of said response signal, given by Hilbert Transform of the acquired response signal.
17. A device for measuring of the frequency response of an object, comprising:
a unit of signal generation and data acquisition for generating an excitation signal with a fast changing frequency to be introduced into said object and
a response-signal analyzer adapted to receive a response signal from said object,
said response-signal analyzer working in a short time window, wherein the analyzer comprises a first unit adapted to generate a first reference waveform that is in phase with the excitation signal, and a second unit adapted to generate a second reference waveform that is in quadrature with the excitation signal,
wherein the waveforms of the first and second excitation signals are defined by said excitation signal waveform, and means for correlating said response waveform with the first reference waveform and with the second reference waveform in a short time-domain window.