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Frequently Asked Questions
What is the difference between AMI and X-ray?
AMI and x-ray are complementary techniques that are both frequently found in the same laboratories. They have important differences with regards to what they reveal in a sample. X-rays can be used to see inside a sample based upon material density differences. Dense materials are more opaque to x-radiation and penetration is more limited through metals compared with ceramics or polymers. Since air is not absorbing delaminations, cracks and disbonds cannot be seen unless there is sufficient physical separation of materials. Radiography operates in a through transmission mode that gives a composite image of the entire sample thickness. Radiation from an x- ray source may cause damage or random electrical errors to occur in certain semiconductor devices if they are placed too close to the source for an extended period of time during inspection.

Acoustic waves will penetrate both dense and light solid materials but are very sensitive to the presence of air gaps that can block ultrasound transmission. The integrity of bonding between layers is a unique capability of AMI. In addition to visualizing interior features of samples C-SAM® produces images on a layer by layer basis. Images are made in a reflection mode that requires access to only one surface of a sample, or in transmission that requires access to opposite surfaces (like x-ray).
Will AMI damage my part?
No, the ultrasonic frequencies used for AMI are higher (MHz range) than those used for ultrasonic cleaning (KHz range) and, since cavitation is not produced in this range, there will be no cleaning or agitation to the fragile components.
On what kind of materials can AMI be used?
Ultrasound travels through practically all solid materials as long as there are no air gaps. Porosity in a material will cause sound waves to become attenuated more than if the material is fully densified and this phenomenon can be used to quantify the densification such as for ceramics and powder metallurgy samples. In general the penetration of ultrasound in all solid materials is reduced at higher frequencies.
What is the smallest defect that I can see?
In the “Z” (depth) direction, AMI is sensitive to separations as small as 200 Angstroms. In the X-Y directions, the resolution is based on the ultrasonic frequency and the design of the transducer. Typically the resolution is about 250 microns for 10 MHz, 75 microns for 30 MHz, 25 microns for 100 MHz and 10 microns for 230 MHz. However, a transducer can actually detect defects smaller than its resolution by an order of magnitude. You may not be able to “resolve” the defect, but you can “detect” that it is there.
Do I have to immerse a sample in a fluid to obtain an acoustic micrograph?
Since ultrasound does not travel through air at the frequencies used in AMI a coupling fluid is needed to deliver the ultrasound pulse from the transducer lens to the sample surface.
What coupling fluids can be used?
The most common coupling fluid in use is DI water. Other fluids can be used but chances are that they will absorb more ultrasound than water and at very high frequencies may cause poor signal levels. The instrument operator must choose a fluid that will not harm the sample or the instrument. Alcohols such as IPA are the next most common fluid.
What is the difference between AMI and medical ultrasound?
Medical ultrasound and AMI are based upon the same physics. However, medical ultrasound frequencies are usually in the range of 1-5 MHz whereas AMI are 15- 300MHz. The lower frequencies are needed in the medical environment because of the need to penetrate tissue thicknesses associated with the human body. There is an inverse relationship between penetration and resolution capability (frequency).
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