Ultrasonics without a source: thermal fluctuation correlations at MHz frequencies.

Area of Science:

• Acoustics
• Solid-state Physics
• Signal Processing

Background:

• Ultrasonic receiver circuits typically disregard noise from transducers and amplifiers.
• Acoustic thermal fluctuations are generally considered a nuisance, not a source of data.
• Previous research has not explored the informational content of thermal noise in ultrasonic systems.

Purpose of the Study:

• To demonstrate that acoustic thermal fluctuations contain significant ultrasonic information.
• To establish a link between noise autocorrelation functions and direct pulse/echo measurements.
• To confirm the thermal origin of elastodynamic noise in ultrasonic systems.

Main Methods:

• Analyzing the noise autocorrelation function of ultrasonic receiver circuits.
• Conducting experiments comparing direct pulse/echo measurements with noise correlation functions.
• Performing absolute measurements of noise strength to determine sample temperature.

Main Results:

• The noise autocorrelation function directly corresponds to the waveform obtained from pulse/echo measurements.
• Experimental comparisons validated the theoretical prediction.
• The strength of the elastodynamic noise was measured, confirming its thermal origin and relationship to temperature.

Conclusions:

• Acoustic thermal fluctuations are a rich source of ultrasonic information, not merely noise.
• The noise autocorrelation function provides an alternative method for ultrasonic measurements.
• Understanding thermal noise is crucial for advancing ultrasonic receiver circuit design and application.