• Hæggström, Edward
• Karppinen, Timo
• Salmi, Ari

Abstract

An affordable acoustic method to estimate mechanical film characteristics with in-plane shear and longitudinal waves was developed. A 23 kHz (24% FBW,-3 dB) signal was excited into thin plate-like samples with a piezoceramic pickup (Ronette ST105/ Tonar) and received with an inductive pickup (Shure M92E). Signal-to-noise ratios of 12-27 dB were obtained corresponding to a two-way insertion loss of-105.5,-94.5 dB (shear, long). From the time-of-flight the phase velocity of the wave was estimated. This actuation-detection scheme can excite in-plane acoustic waves in the sample. An in-plane mode purity of-45 dB was recorded. Laser Doppler vibrometry showed that the waves were truly in-plane. The method showed good repeatability with a standard deviation of 2 m s-1 (0.17%) for shear and 5 m s-1 (0.22%) for longitudinal waves. Elastic and shear moduli as well as the Poisson ratio were determined for 174 +/- 2 mu m thick Mylar((R)) and 184 +/- 2 mu m thick (795 +/- 10 kg m(-3)) coated paper samples (24 +/- 0.5 degrees C and 40 +/- 5% RH). The estimated in-plane moduli for the Mylar((R)) showed a 30% offset, but exhibited the same ratio, compared to the sample manufacturer values (ASTM D 882 test). The effect of heating the sample (140 +/- 1 degrees C) was studied and changes in the dynamic mechanical moduli of the samples on the order of 3% were detected.

Topics

• phase