Ultrasonic band gaps and negative refraction.

Area of Science:

• Materials Science
• Acoustics
• Condensed Matter Physics

Background:

• Periodic structures, or phononic crystals, can control wave propagation.
• Ultrasonic band gaps are crucial for wave manipulation and localization.
• Previous studies focused on theoretical aspects or different material systems.

Purpose of the Study:

• To review the experimental observation of ultrasonic band gaps in novel bidimensional composite materials.
• To demonstrate the capability of these structures to localize ultrasonic waves.
• To explore potential applications in ultrasonic waveguides and negative refraction devices.

Main Methods:

• Fabrication of aluminum alloy plates with periodic cylindrical mercury-filled holes.
• Experimental observation of ultrasonic wave propagation and band gap formation.
• Investigation of defect structures (linear and point) for wave localization.
• Design and testing of twinned-square structures for wave bending and splitting.
• Theoretical analysis of a composite slab with an epoxy wedge for negative refraction.

Main Results:

• Experimental confirmation of the first ultrasonic band gaps in periodic bidimensional composites.
• Observation of ultrasonic wave localization in linear and point defects.
• Achievement of a 90-degree ultrasonic waveguide.
• Demonstration of 45-degree wave bending and splitting using twinned-square structures.
• Experimental observation of anomalous refraction at grain boundaries.
• Theoretical evidence for negative refraction in a specific composite configuration.

Conclusions:

• Periodic bidimensional composites offer effective control over ultrasonic wave propagation.
• These materials enable the creation of functional ultrasonic devices like waveguides and beam splitters.
• The findings suggest potential for developing ultrasonic metamaterials with novel properties, including negative refraction.