An Air Coupled Transmission Mode Acoustic Microscope for On-Line Non-Destructive Evaluation
Abstract
We have demonstrated the feasibility of using a transmission type ultrasonic microscope operating in air in the 1 MHz frequency range. Such systems can be used for in-process evaluation of many structural materials such as composites and green ceramics. Specialized ultrasonic transducers were built that are coupled to air using low acoustic impedance quarter wave plates made of silicone rubber. The feasibility of manufacturing more optimum materials for quarter wave matching was demonstrated. These transducers were capable of being driven at high voltage levels (1500 V) for highest possible transmission efficiency. The minimum insertion loss of these devices is 48 dB, and the 6 dB bandwidth is 6%. Experiments were begun on imaging in transmission mode with two transducers. It has been possible to transmit and receive over distances of up to 8 inches in air. Although no actual imaging was done with the air transducers, the measured signal-to-noise ratio demonstrates that there is sufficient dynamic range to provide useful images of graphite epoxy laminates. A material with close to the correct acoustic impedance for quarter wave matching to air has been made, and further process development will improve its uniformity. Acoustic images.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1989
- Accession Number
- ADA211416
Entities
People
- John D. Fraser