permanent wave vs wavelet

permanent wave

noun
  • A wave in a moving fluid that does not change shape or position relative to the fluid 

  • A series of waves in the hair produced by means of chemical substances and heat; a perm 

wavelet

noun
  • A small wave; a ripple. 

  • A fast-decaying oscillation. 

How often have the words permanent wave and wavelet occurred in a corpus of books? (source: Google Ngram Viewer )