Metamaterial bricks and quantization of meta-surfaces

Controlling acoustic fields is crucial in diverse applications such as loudspeaker design, ultrasound imaging and therapy or acoustic particle manipulation. The current approaches use fixed lenses or expensive phased arrays. Here, using a process of analogue-to-digital conversion and wavelet decomposition, we develop the notion of quantal meta-surfaces. The quanta here are small, pre-manufactured three-dimensional units—which we call metamaterial bricks—each encoding a specific phase delay. These bricks can be assembled into meta-surfaces to generate any diffraction-limited acoustic field. We apply this methodology to show experimental examples of acoustic focusing, steering and, after stacking single meta-surfaces into layers, the more complex field of an acoustic tractor beam. We demonstrate experimentally single-sided air-borne acoustic levitation using meta-layers at various bit-rates: from a 4-bit uniform to 3-bit non-uniform quantization in phase. This powerful methodology dramatically simplifies the design of acoustic devices and provides a key-step towards realizing spatial sound modulators

Ultrasonic Techniques for Characterization of Manufacturing Defects in Thick Composites

New structural applications of polymer matrix composites require the use of thick sections. The fabrication and use of such thick sections create new needs for flaw detection and characterization which cannot be met adequately by conventional nondestructive evaluation (NDE). These composites are susceptible to manufacturing defects due to thermal gradients and nonuniform resin bleeding during curing.</p

Nondestructive Determination of Elastic Constants of Composite Materials

The anisotropy of fibrous composite materials makes it difficult to determine their elastic constants nondestructively. The unidirectional lamina, which is the basic building block of composite laminates and structures, is treated as a quasi-homogeneous orthotropic material. Determination of material properties of the unidirectional lamina is especially important because this characterization allows prediction of the properties of any multidirectional laminate. In general, the unidirectional lamina is characterized by nine independent elastic constants. Many composite materials, however, have the additional property of transverse isotropy. In such cases the number of independent constants is reduced to five. The objective of this study is to propose a method for determining these constants ultrasonically by measuring phase velocities and critical angles.</p

Characterization of Porosity in Thick Graphite/Epoxy Composites

Porosity, introduced in composites during fabrication, takes the form of dispersed or discrete elongated voids, usually at the fiber-matrix interface. During subsequent loading, these voids act as nuclei of further damage growth resulting in strength degradation. Hence, it is important to determine the void content after fabrication.</p

Characterization of Porosity in Thick Composites Using Ultrasonic Wave Velocity Measurements

Determination of content and distribution of porosity introduced in composites during fabrication, is an important issue in characterizing composite materials, especially thick ones. Dispersed or discrete elongated pores, located at the fiber-matrix or ply interfaces, can act as nuclei of further damage growth during loading of the composite laminate.</p

Defect and Damage Characterization in Composite Materials

Defects may be introduced in composites during processing and fabrication. They include contaminants, porosity, inclusions, delaminations, and nonuniform fiber and matrix distributions. Damage induced in service under loading and environmental variations includes matrix cracking, delamination, fiber breakage, and dispersed defects, such as matrix ageing and degradation.</p

A randomized double-blind study using a laser-guided collimator on dental radiography training

Defects may be introduced in composites during processing and fabrication. They include contaminants, porosity, inclusions, delaminations, and nonuniform fiber and matrix distributions. Damage induced in service under loading and environmental variations includes matrix cracking, delamination, fiber breakage, and dispersed defects, such as matrix ageing and degradation