Method for eliminating second harmonic distortion based on modulation phase difference in TDLAS technology

Author(s):  
Xu Chong ◽  
Wang Songceng ◽  
Chen Hao ◽  
Wei Bin ◽  
Ju Yu ◽  
...  
2019 ◽  
Vol 1 (2) ◽  
pp. 117-125
Author(s):  
Hyunjo Jeong ◽  
Shu-zeng Zhang ◽  
Xiong-bing Li

Abstract In nonlinear acoustic harmonic generation in solids with stress-free boundaries, such a boundary is known to destructively change the second harmonic generation, and the pulse-echo method is not practically applicable. Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups. This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries. The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields. The phase difference between the two second-harmonic components after reflection from the boundary—that is, the reflected and the newly generated second harmonic—is emphasized. The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.


2010 ◽  
Vol 36 (10) ◽  
pp. 1568-1580 ◽  
Author(s):  
Mirza Pasovic ◽  
Mike Danilouchkine ◽  
Guillaume Matte ◽  
Antonius F.W. van der Steen ◽  
Olivier Basset ◽  
...  

1986 ◽  
Vol 40 (8) ◽  
pp. 1180-1183 ◽  
Author(s):  
F. A. Dethomas ◽  
Cecil Dybowski ◽  
Harvey S. Gold

Lock-in amplification using ac modulation and second-harmonic detection is routinely employed in such techniques as ac polarography, ac voltammetry, and inelastic electron tunneling spectroscopy (IETS). Properties of the modulation source are shown in the present IET studies to limit the obtainable signal-to-noise ratio of a spectrum. A single inelastic electron tunneling junction is used to demonstrate the effect of various commercial modulation sources on the IET spectrum of benzoic acid on alumina. With all other parameters being held constant, the signal-to-noise ratio of the IET spectrum is found to be inversely correlated with the total harmonic distortion of the modulation source.


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