
%
%   re_thin_plate_free.m  ver 1.1  by Tom Irvine
%
%   radiation efficiency thin plate all edges free
%
%    a = smallest of length & width
%    b = largest of length & width
%    c = speed of sound
%    fcr = critical frequency
%
%   with Fahy-like correction at low frequencies

function [rad_eff] = re_thin_plate_free(freq,fcr,a,b,c)

P = 2*a + 2*b;
S = a*b;

fb = fcr + 5*c/P;

% --- user choice: slope exponent ---
n = 1.5;   % 1 → 3 dB/oct, 1.5 → 4.5 dB/oct, 2 → 6 dB/oct

% --- value at fb (for continuity) ---
sigma_b = 1/sqrt(1 - (fcr/fb));

if(freq <= fb)
    rad_eff = sigma_b * (freq/fb)^n;
else
    rad_eff = 1/sqrt(1 - (fcr/freq));
end

% --- optional cap (prevents unrealistic spikes near fc) ---
rad_eff = min(rad_eff, 3);   % typical cap 2–5

end