Green's Function Retrieval with Absorbing Probes in Reverberating Cavities.

Area of Science:

• Electromagnetism
• Wave propagation
• Acoustics

Background:

• Diffuse wave field cross-correlation approximates Green's function difference.
• This principle enables passive imaging with ambient noise sources.

Purpose of the Study:

• Investigate Green's function retrieval in electromagnetism.
• Analyze the impact of receiver absorption properties on cross-correlation.
• Determine the feasibility of retrieving causal and anticausal Green's functions.

Main Methods:

• Theoretical modeling based on the fluctuation-dissipation theorem.
• Experimental validation in a reverberation chamber.
• Utilizing a matched antenna for measurements.

Main Results:

• Cross-correlation function is significantly influenced by receiver absorption.
• Experimental confirmation of theoretical predictions.
• Only the anticausal Green's function is retrievable with a matched antenna.

Conclusions:

• Receiver absorption critically affects Green's function retrieval in electromagnetism.
• Matched antenna measurements yield only the anticausal Green's function.
• This outcome is analogous to a time-reversal experiment with an electromagnetic sink.