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. 2015 Apr 17;15(4):9078–9096. doi: 10.3390/s150409078

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© 2015 by the authors; licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).

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Ultrasonic surface wave time signals collected with sensor aligned along wave path on concrete; contact accelerometer (left) and with noncontact MEMS (right).