The previously developed theory of the supersonic interferometer is extended with the particular view of utilizing it for absorption measurements in gases. It is shown that the mechanical impedance of the interferometer is
Z = Z0 + Z(l)
where
Z0=j(mω − s/ω) + rZ(l)=Acρ/tanh 2αl + (Acρ/sinh 2αl)eiθ=− arc tan sin 2kl sinh 2αlcos 2kl cosh 2αl − 1
.

That is, if reactance is plotted against resistance we obtain an impedance spiral with center (Acρ/tanh 2αl, 0) and radius Acρ/sinh 2αl. The action of the interferometer is studied in terms of the properties of the spiral. Absorption measurements are effected by compensating for the changes in the equivalent series electrical resistance because of changes in l by adjusting a shunt resistance across the crystal so the e.m.f. is held constant, irrespective of l. Absorption in the medium is calculated from the values of shunt resistance for the path lengths of interest. Measurements were taken at three frequencies in the range 899.0 kc to 2514 kc. The quantity 2αλ2 as measured by the interferometric method is not constant but shows a systematic change with frequency.

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© 1933 Acoustical Society of America.
1933
Acoustical Society of America
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