“…Equation (4) is the core of our previous method, for which the scheme in Fig.2 is valid; based on this, R(t) is expanded in a way that every harmonic component of R(t) is a linear combination of the magnitudes B 1 and B 2 , and hence, the ratio B 2 /B 1 can be ideally derived from the frequency components of a series expansion of R(t). However we have found that R(t) can also be expressed as, (9) where SQ 1 (t) is one of the modulating square-waves previously defined (of period 2T b in this case). That is, the response envelope R(t) can be identified with the square-wave modulation of a low-frequency periodic signal r(t) defined as, (10) whose two harmonic components contain, at much lower frequencies, information about the magnitudes, B 1 and B 2 , of the spectral components of the high-frequency response y(t).…”