alpha_n alphaM(0,freq) "Normal incidence absorption coefficient"
alpha_ran integrate(alphaM(q,freq)*sin(2*q),q,0,pi/2) "Random incidence absorption coefficient"
Zn_n ReZnM(0,freq)+1i*ImZnM(0,freq) "Normal incidence surface impedance"
Zn_ran ReZnM(53[deg],freq)+1i*ImZnM(53[deg],freq) "Random incidence surface impedance"