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The analysis presented in this article shows that the Great Seal bug has a well-coupled eigenmode around 1800 MHz, which is consistent with some of the references. This was probably one of the harmonics of the illumination source, as a high transmit power at the lower frequency would have been easier to generate. In addition, the interaction between acoustically introduced vibrations of the diaphragm would generate an AM signal that could be detected remotely.
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Brooker et al. (2013) studied this question.
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