Elastic wave thermal fluctuations, ultrasonic waveforms by correlation of thermal phonons

Richard L. Weaver, Oleg I. Lobkis

Research output: Contribution to journalArticlepeer-review


It is widely recognized that acoustic degrees of freedom coupled to a thermal bath have amplitudes which fluctuate with a mean square proportional to temperature; this is the basis for the Debye theory of the heat capacity of insulating solids. It is shown here that these elastic wave thermal phonons have correlation functions identical to the system's ultrasonic Green's function, and furthermore that thermal noise in ultrasonic detectors should have correlation functions equivalent to conventional waveforms obtained by active transmission and reception. This suggests the possibility of doing ultrasonics without a source. Theory for the identity is presented, and several room temperature laboratory confirmations are conducted in the frequency range 0.1-1.0 MHz. The thermal nature of the origin of these correlations is established by comparing their strength with theoretical expectations. Applications are discussed.

Original languageEnglish (US)
Pages (from-to)2611-2621
Number of pages11
JournalJournal of the Acoustical Society of America
Issue number5
StatePublished - May 1 2003

ASJC Scopus subject areas

  • Arts and Humanities (miscellaneous)
  • Acoustics and Ultrasonics


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