Miki.m

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function [beta]=Miki(freq,k0,sigma,h)
% Miki impedance model see [Miki 1990] and [Kirby 2014]

    if sigma >= 100000 
        beta = zeros(size(freq));         % perfecty flat and rigid
    else
        Zc = 1+5.50*(freq./sigma).^(-0.632)+1i*8.43*(freq./sigma).^(-0.632); % characteristic impedance // Z0
        kc = k0.*(1+7.81*(freq./sigma).^(-0.618)+1i*11.41*(freq./sigma).^(-0.618)); % characteristic wavenumber
        
        Zs = thickness(Zc,h,kc);  % surface impedance

        beta = 1./Zs;
    end
    
end