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Sensors 2019, 19(6), 1373; https://doi.org/10.3390/s19061373

Application of Fresnel Zone Plate Focused Beam to Optimized Sensor Design for Pulse-Echo Harmonic Generation Measurements

1
Department of Mechanical Engineering, Wonkwang University, Iksan, Jeonbuk 54538, Korea
2
School of Traffic and Transportation Engineering, Central South University, Changsha 410075, China
*
Author to whom correspondence should be addressed.
Received: 1 December 2018 / Revised: 12 February 2019 / Accepted: 13 March 2019 / Published: 19 March 2019
(This article belongs to the Special Issue Ultrasound Transducers)
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Abstract

In nonlinear acoustic measurements involving reflection from the stress-free boundary, the pulse-echo method could not be used because such a boundary is known to destructively change the second harmonic generation (SHG) process. The use of a focusing acoustic beam, however, can improve SHG after reflection from the specimen boundary, and nonlinear pulse-echo methods can be implemented as a practical means of measuring the acoustic nonlinear parameter (β) of solid specimens. This paper investigates the optimal sensor design for pulse-echo SHG and β measurements using Fresnel zone plate (FZP) focused beams. The conceptual design of a sensor configuration uses separate transmission and reception, where a broadband receiver is located at the center and a four-element FZP transmitter is positioned outside the receiver to create a focused beam at the specified position in a solid sample. Comprehensive simulations are performed for focused beam fields analysis and to determine the optimal sensor design using various combinations of focal length, receiver size and frequency. It is shown that the optimally designed sensors for 1 cm thick aluminum can produce the second harmonic amplitude and the uncorrected nonlinear parameter corresponding to the through-transmission method. The sensitivity of the optimal sensors to the changes in the designed sound velocity is analyzed and compared between the odd- and even-type FZPs. View Full-Text
Keywords: focused beam; second harmonic generation (SHG); nonlinear parameter; Fresnel zone plate (FZP); pulse-echo method focused beam; second harmonic generation (SHG); nonlinear parameter; Fresnel zone plate (FZP); pulse-echo method
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Jeong, H.; Shin, H.; Zhang, S.; Li, X.; Cho, S. Application of Fresnel Zone Plate Focused Beam to Optimized Sensor Design for Pulse-Echo Harmonic Generation Measurements. Sensors 2019, 19, 1373.

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