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AIR COUPLED ULTRASONIC TESTING (ACUT)
26 November 2021, Chennai
Ultrasonic testing (UT) is a non-destructive test (NDT) method based on the propagation of ultrasonic waves through the sample. There are many ways to generate ultrasound for NDT purposes, this includes but not limited to; electromagnetic, laser and the most common piezoelectric method. A typical piezoelectric UT system consists of a piezoelectric transducer connected to pulser-receiver electronics and the output is often displayed in an oscilloscope or a data acquisition system connected to a computer. A wide variety of engineering materials such as metals, composites, polymers, and ceramics can be inspected using UT. However, some materials (example: wood and paper products) cannot be inspected using the conventional ultrasound method as it requires liquid couplant, which inadvertently affects the sample or could contaminate it.
To overcome this problem, air coupled ultrasonic testing (ACUT) can be a promising contactless ultrasonic measurement alternative. In recent years, ACUT has been gaining significant traction, particularly starting with the aerospace industry for inspecting composites, the applications have been extended to automotive components (clutch facings, brake pads), graphite-epoxy sandwich panels, asphalt concrete, honeycomb sandwiches, foam sandwich panels and solar panels, to name a few. Sensitive inspections for defects such as internal cracks, voids, delamination, and air inclusions can be investigated for the material under test.
Based on different applications, ACUT can be performed using through transmission or pulse-echo method, as illustrated in figure below. Pulse echo method requires a single transducer which acts as both transmitter and receiver, projecting an ultrasound beam into the sample and receiving the echoes reflected from the back surface and from any discontinuity lying in the path of the beam. Through transmission mode requires access to the sample from both sides. One transducer act as a transmitter and other as a receiver. The presence of an internal defect is indicated by a reduction in signal amplitude and less sound energy is attenuated in this method.
This method requires neither immersion tank as in ultrasonic immersion technique and consequently requires minimal part preparation. Also, as no external coupling medium is required, it is suitable for inspecting water sensitive materials and/or during production process such as composite layups. Since the contact pressure is eliminated, amplitude fluctuations or damage to the surface of the component is avoided and speedup the measurement process. All these advantages make ACUT an ideal testing method for low acoustic impedance materials such as composites, paper, textile, etc. ACUT generally operates at frequencies below 1 MHz, above this frequency transmission of sound in the air reduces and scattering loss increases in many materials.
If you have any questions regarding ACUT (or) would like to discuss using Azeriri’s ACUT solutions for your application, please feel free to drop us an email at info@azeriri.com
- Pooja R , Experimental Scientist at Azeriri
References:
· Air-coupled Ultrasound – A Millennial Review – Joe Buckley, Sonatest Plc – ndt.net
· Air-coupled Ultrasound – Emerging NDT Method – Wolfgang Essig, Yannick Bernhardt, Daniel Döring, Igor Solodov, Tobias Gautzsch, Mate Gaal, Daniel Hufschläger, Ryan Sommerhuber4, Matthias, Torben Marhenke, Jörg Hasener, Artur Szewieczek, Wolfgang Hillger – ndt.net
· Review of the use of air-coupled ultrasonic technologies for nondestructive testing of wood and wood products – Yiming Fang, Lujun Lin, Hailin Feng, ZhixiongLu, Grant W.Emms
what is non destructive testing (NDT)?
7th August 2021, Chennai
Non-destructive testing (NDT) is a testing and analysis technique used to evaluate the properties, acceptability, or fitness of a material, component, structure, or system without permanently affecting the item under test.
Specifically, this procedure may include:
· Detect internal or external defects
· Determine structure, composition, or material properties
· Measure geometric characteristics
Depending on the extent of analysis carried out on the outcome of the inspection (Go/No-Go, Accept/Reject, quantitative assessment, life assessment, remaining life, fitness-for-service, etc) the other terms commonly used to describe this technology are Non-Destructive Examination/Evaluation (NDE), and Non-Destructive Inspection (NDI). It supplements destructive testing, which is carried out typically to determine the strength of structures by methods such as breaking, peeling, etc – which is both time consuming and wasteful.
As no harm occurs to the items under test during NDT, it is a very valuable technique used for product evaluation, research and problem solving which can save both time and money. NDT is used widely in all areas of engineering, aerospace, defense, oil & gas, power generation, automotive, medicine and even art and cultural heritage preservation. NDT could employ any (or a combination of) techniques including Visual Inspection, Eddy Current, Fluorescent Penetrant, Flux Leakage, Magnetic Particle, Radiographic, Tap Testing, Thermography, Ultrasonics and several more – all based on different physics principles.
A multidisciplinary profession cutting across domains where physics, chemistry, materials science, mechanics, electronics instrumentation, computer science, etc. synergize in several ways to realize the end objectives. NDT can and should be used in all phases, from raw materials to product's design and manufacturing process (including materials selection, research and development, quality assurance and production) and while in service till end-of-life; leading to being termed as a cradle-to-grave technology!
If you are new to the field of NDT, please visit our "Whitepapers" page to download your FREE NDT Resources Guide and FREE NDT Societies Guide where we have listed some useful resources to give you a good introduction to this topic.
Happy reading!
welcome message
Message from Prof. Krishnan Balasubramanian
7th August 2021, Chennai
Ultrasonic Technologies is pervasive now-a-days. Every day, we encounter the magic of Ultrasonics while, reversing your car, parking, using cell phones, using a fingerprint biometrics, …….and many more.
Did you know that Ultrasonics is also a part of your daily routine as a fluid level or flow sensor in your water or gas pipes?
Ultrasonic sensor technology also keeps us healthy through biomedical imaging and diagnostics, destroys your kidney stones, keeps us safe via nondestructive testing-based quality control and through in-service inspection, keep our infrastructure operating beyond its design life by continuous structural assessment.
Recently, low-cost Ultrasonic Technologies are also becoming relevant in the COVID world by providing touchless communication, for augment and virtual reality applications and in everyday robots, all of that redefines our lifestyles.
AZERIRI is a deep-research deep-tech startup company, backed by 100 years of international professional experience of the founding team, that will help make the ultrasonic technologies more relevant, more affordable, more sustainable by focusing on the state-of-the-art transducers that will be the key ingredient to any ultrasonic system. Incubated by the best academic startup eco-system in India, located in the IIT Madras Research Park, with support from the #1 ranked university in India, AZERIRI aspires to disrupt the supply chain of ultrasonic applications and products.
Best wishes to AZERIRI for achieving its vision and its goal of becoming a gamechanger in the ultrasound world.
“The beginning is the most important part of the work.”
― Plato, The Republic
Prof. Krishnan Balasubramanian
IIT Madras and Azeriri Co-Founder