Airborne non-contact and contact broadband ultrasounds for frequency attenuation profile estimation of cementitious materials

[EN] In this paper, the study of frequency-dependent ultrasonic attenuation in strongly heterogeneous cementitious materials is addressed. To accurately determine the attenuation over a wide frequency range, it is necessary to have suitable excitation techniques. We have analysed two kinds of ultrasound techniques: contact ultrasound and airborne non-contact ultrasound. The mathematical formulation for frequency-dependent attenuation has been established and it has been revealed that each technique may achieve similar results but requires specific different calibration processes. In particular, the airborne non-contact technique suffers high attenuation due to energy losses at the air-material interfaces. Thus, its bandwidth is limited to low frequencies but it does not require physical contact between transducer and specimen. In contrast, the classical contact technique can manage higher frequencies but the measurement depends on the pressure between the transducer and the specimen. Cement specimens have been tested with both techniques and frequency attenuation dependence has been estimated. Similar results were achieved at overlapping bandwidth and it has been demonstrated that the airborne non-contact ultrasound technique could be a viable alternative to the classical contact technique.The authors acknowledge the support from University College Cork (Ireland), Universidad Politecnica de Valencia and the Spanish Administration under grant BIA2014-55311-C2-2-P and Salvador Madariaga's Programme (PR2016-00344/PR2017-00658).Gosálbez Castillo, J.; Wright, W.; Jiang, W.; Carrión García, A.; Genovés, V.; Bosch Roig, I. (2018). Airborne non-contact and contact broadband ultrasounds for frequency attenuation profile estimation of cementitious materials. Ultrasonics. 88:148-156. https://doi.org/10.1016/j.ultras.2018.03.011S1481568

Strategies for Controlled Placement of Nanoscale Building Blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others

Air-coupled ultrasonic testing of materials

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