Metal cap flexural transducers for air-coupled ultrasonics

Ultrasonic material characterization or inspection for defects is conventionally performed using either liquid coupling (water, usually) or some type of gel or oil in contact-mode coupling. Mechanical waves can be transmitted only through some sound-supporting medium from their source (a transducer) to the object under study, and back again. Using distilled, degassed water to couple ultrasound to an object under test works quite well and has many technical advantages, including relatively low signal loss over laboratory or shop dimensions at typical frequencies, almost zero toxicity, and low cost. For many applications, the use of water is acceptable and preferred. There are, however, certain testing applications for which water can be a disadvantage. These situations include materials that are sensitive to contact with water, such as uncured graphite-epoxy composites or certain electronics. Large objects, whose total immersion is impractical, or objects for which rapid scanning is required might also be unsuitable for water coupling. Recent technological developments are beginning to permit the judicious replacement of water by a far more ubiquitous sound coupling medium—air. Ultrasonic testing in air has been investigated for more than 30 years, but recently there has been an upsurge in interest and application because of the availability of much more efficient sound-generating devices designed specifically for operation in air. In water- or direct-coupled ultrasonics, one typically employs piezoelectric transducers to generate sound waves because they are well suited to the generation of sound in water or in solids because of their high acoustic impedance. In air, however, we need just the opposite. Air is very compliant, so waves from a high-impedance source couple poorly into air. Much effort has been invested in finding suitable impedance matching materials that will render the familiar piezoelectric probe efficient in air-coupled (A-C) ultrasound. The problem, however, is nearly insurmountable because of the large acoustic impedance difference between air and quartz, for example. Quartz has an acoustic impedance of about 15 MRayl, while air’s impedance is about 425 Rayl, a ratio of about 35,000. The challenge is to find a material with an acoustic impedance that nearly equals the geometric average of these two widely disparate values.

Download Full-text

Real-time monitoring of welding process using air-coupled ultrasonics and acoustic emission

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-018-3042-2 ◽

2018 ◽

Vol 101 (5-8) ◽

pp. 1623-1634 ◽

Cited By ~ 4

Author(s):

Lu Zhang ◽

Alexandra Carmen Basantes-Defaz ◽

Didem Ozevin ◽

Ernesto Indacochea

Keyword(s):

Acoustic Emission ◽

Real Time ◽

Welding Process ◽

Real Time Monitoring ◽

Air Coupled Ultrasonics

Download Full-text

Investigation of Discrete Out-of-Plane Waviness in Composite Wind Turbine Blades Using Ultrasonic Nondestructive Evaluation

ASME 2011 Pressure Vessels and Piping Conference: Volume 5 ◽

10.1115/pvp2011-57652 ◽

2011 ◽

Cited By ~ 1

Author(s):

Sunil Kishore Chakrapani ◽

Vinay Dayal ◽

Daniel Barnard ◽

David Hsu

Keyword(s):

Aspect Ratio ◽

Nondestructive Evaluation ◽

Wind Turbine ◽

High Frequency ◽

Turbine Blades ◽

Element Model ◽

Wind Turbine Blades ◽

Out Of Plane ◽

Process Detection ◽

Air Coupled Ultrasonics

With the need for larger and more efficient wind turbine blades, thicker composite sections are manufactured and waviness becomes difficult to control. Thus, there is a need for more effective and field implementable NDE. In this paper we propose a method of detection and quantification of waviness in composite wind turbine blades using ultrasonics. By employing air coupled ultrasonics to facilitate faster and easier scans, we formulated a two step process. Detection was performed with single sided air coupled ultrasonics, and characterization was performed with the help of high frequency contact probes. Severity of the wave was defined with the help of aspect ratio, and several samples with different aspect ratio waves were made. A finite element model for wave propagation in wavy composites was developed, and compared with the experimental results.

Download Full-text

Nondestructive evaluation of bending strength of wood with artificial holes by employing air-coupled ultrasonics

Construction and Building Materials ◽

10.1016/j.conbuildmat.2016.02.020 ◽

2016 ◽

Vol 110 ◽

pp. 24-31 ◽

Cited By ~ 5

Author(s):

Misaki Mori ◽

Masumi Hasegawa ◽

Ji-Chang Yoo ◽

Seog-Goo Kang ◽

Junji Matsumura

Keyword(s):

Nondestructive Evaluation ◽

Bending Strength ◽

Air Coupled Ultrasonics

Download Full-text

PLATE WAVE RESONANCE WITH AIR-COUPLED ULTRASONICS

10.1063/1.3362158 ◽

2010 ◽

Author(s):

H. N. Bar ◽

V. Dayal ◽

D. Barnard ◽

D. K. Hsu ◽

Donald O. Thompson ◽

...

Keyword(s):

Plate Wave ◽

Wave Resonance ◽

Air Coupled Ultrasonics

Download Full-text

Hidden disbond detection in spent nuclear fuel storage systems using air-coupled ultrasonics

10.1117/12.2219482 ◽

2016 ◽

Cited By ~ 2

Author(s):

Homin Song ◽

John S. Popovics

Keyword(s):

Nuclear Fuel ◽

Spent Nuclear Fuel ◽

Storage Systems ◽

Fuel Storage ◽

Disbond Detection ◽

Air Coupled Ultrasonics

Download Full-text

Visualization studies of Lamb wave propagation and interactions with anomalies in composite laminates using air-coupled ultrasonics

10.1063/1.4864942 ◽

2014 ◽

Author(s):

V. S. Sasanka Durvasula ◽

Vivek Madhavan ◽

Janardhan Padiyar M ◽

N. V. Giridharan ◽

Krishnan Balasubramaniam

Keyword(s):

Wave Propagation ◽

Lamb Wave ◽

Composite Laminates ◽

Lamb Wave Propagation ◽

Air Coupled Ultrasonics

Download Full-text

Flaw Investigation in a Multi-Layer, Multimaterial Composite: Using Air-Coupled Ultrasonics

ASME 2011 Pressure Vessels and Piping Conference: Volume 5 ◽

10.1115/pvp2011-57656 ◽

2011 ◽

Author(s):

Richard A. Livings ◽

Vinay Dayal ◽

Dan J. Barnard ◽

Dave K. Hsu

Keyword(s):

Vibration Modes ◽

Main Ingredient ◽

Ceramic Tiles ◽

High Stiffness ◽

Resonance Modes ◽

Air Coupled Ultrasonics ◽

Material Composite

Ceramic tiles are the main ingredient of a multi-layer multi-material composite being considered for the modernization of tank armors. The high stiffness, low attenuation, and precise dimensions of these uniform tiles make them remarkable resonators when driven to vibrate. Defects in the tile, during manufacturing or after usage, are expected to change the resonance modes. The comparison of a pristine tile/lay-up and a defective tile/lay-up will thus be a quantitative damage metric. This study is aimed at examining the vibration modes of the tiles and the composite lay-up and using these vibrations to detect and characterize defects.

Download Full-text