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Fig. 15. Model of scraper–file interactions and their relation to sound. (A)
Hypothetical file segment and scraper region. Note the increments in
inter-tooth distances (in the direction of scraper movement) indicated with
blue dotted lines and letters; the structures of the scraper involved are also
labelled. The sound cycle, shown below, was generated when the scraper was
released from T2 (tooth 2) and crossed the region with distance D1. Note that
the scraper has been released and is moving forwards, travelling over D1 to
find the following tooth (T3). HPZ and LPZ, higher and lower pressure zones of
the sound wave, respectively. (B) The scraper hits T3, generating a reaction
of the system at its natural frequency (
5 kHz for P.
pallicornis). The oscillatory reaction is shown in the diagram with a red
outline (half a cycle), which is added before the previous cycle, indicated in
A, decays. The impact will also generate a vibration of high frequency (see
Bennet-Clark and Bailey,
2002), represented with a red asterisk but not indicated in the
oscillation of the diagram. The scraper is temporarily trapped by T3 but, as
the forewings continue in motion, the scraper regions bend upwards. In this
model, the initial deflection of the oscillator is upward, to generate the
higher pressure zone (maximal amplitude of the sound cycle, see A); scale bar,
0.11 ms. (C) The motion of the wings causes the scraper to dislodge while the
first half of the oscillation is completed. (D) The distorted adjacent
membranes temporarily recover their original shape, passing through
equilibrium. The adjacent membranes and the rest of the oscillator of the
right tegmen continue their vibration downward to generate lower pressure
zone, completing the second half of the cycle (red outline). The scraper
completely dislodges from T3, generating a click sound also of high frequency
(blue asterisk), and travels over D2. Scale bar, 0.22 ms. (E) The scraper
travels D2 and strikes T4 before the previous oscillation decays; this action
repeats over and over. Note that the time spent by the scraper to go from one
tooth to the next is equal to the period of 5 kHz (0.22 ms 
1/5
kHz).
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