| Title |
Pulse compression for long spread spectrum signals application in air-coupled ultrasonic thickness resonance spectroscopy |
| Authors |
Svilainis, Linas ; Tayyib, Muhammad |
| DOI |
10.1109/TIM.2026.3676189 |
| Full Text |
|
| Is Part of |
IEEE Transactions on instrumentation and measurement.. Piscataway, NJ : IEEE. 2026, vol. 75, art. no. 6506714, p. 1-14.. ISSN 0018-9456. eISSN 1557-9662 |
| Keywords [eng] |
inverse filter ; matched filter ; non-contact resonance ultrasound spectroscopy ; pulse compression ; spread spectrum signals |
| Abstract [eng] |
Interfering reflections occur due to air impedance mismatch from sample and transducer in non-contact resonance ultrasound spectroscopy (NC-RUS) measurements. The transducer is in close vicinity to the sample in order to ensure low attenuation in the air and flat wavefront. Therefore, interfering reflections are at 30-100 μs distance from the useful signal. Pulse excitation is used to avoid the overlap that can distort the measurement. A short pulse is required to ensure a broadband excitation, but such a pulse is low energy. Air-to-sample impedance mismatch further reduces signal energy and SNR. Therefore, very high voltage excitation and averaging is required. High voltage excitation increases nonlinearity effect in air, averaging increases measurement time. Long spread spectrum (SS) signals can achieve high SNR, avoid distortion in air, and expand the bandwidth available for analysis. However, long SS signals will overlap. Here it was demonstrated that the pulse compression (PuC) using matched filter is not suitable: the correlation sidelobes overlap with interfering reflections and bias errors of NC-RUS measurements increase. Solution proposed for PuC uses inverse filter. Such compressed signal corresponds to ideal pulse excitation (uniform spectrum) and has no sidelobes. If the spectral content of the SS needs to be preserved, then the PuC result can be gated and decompressed back. It was demonstrated that errors can be significantly reduced in such a case. For example, 0.008% sample density estimation bias error is achieved in case of 350 μs long excitation compared to 2.42% when using matched filter or 2.1% in case of mismatched filter, a 300 times reduction. |
| Published |
Piscataway, NJ : IEEE |
| Type |
Journal article |
| Language |
English |
| Publication date |
2026 |
| CC license |
|
