How to determine phase shift

I have obtained phases (In degrees) for two different material at different frequences. How do i calculate the phase shift between the two. I have attached the data. Initially i just subtracted the two values but i think that approach is wrong. Any help will be appreciated.

Kind regards

Answer 1

[Star Strider]

Subtracting them is likely appropriate, however unwrapping them first will likely produce the correct result.

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/780738/DATA.xlsx', 'VariableNamingRule','preserve')

T1 = 201×3 table
     Freq(Hz)     MAT1(DEG)    MAT2(DEG)
    __________    _________    _________

         3e+05      32.728        25.08 
    2.2798e+07      10.427        164.8 
    4.5297e+07      86.034       9.4404 
    6.7796e+07      159.68       169.17 
    9.0294e+07      74.432       162.38 
    1.1279e+08         152       108.78 
    1.3529e+08      22.797       -92.03 
    1.5779e+08     -31.374      -170.59 
    1.8029e+08     -5.1939         -116 
    2.0279e+08      29.483       81.739 
    2.2528e+08     -22.492      -57.782 
    2.4778e+08     -67.007       113.04 
    2.7028e+08     -137.61      -3.1447 
    2.9278e+08     -46.927       53.483 
    3.1528e+08     -58.902       144.16 
    3.3778e+08      174.11       31.828 

Fv = T1.('Freq(Hz)');
MAT1 = T1.('MAT1(DEG)');
MAT2 = T1.('MAT2(DEG)');

figure
plot(Fv, MAT1,    Fv, MAT2)
grid

MAT1r = deg2rad(MAT1);
MAT1ru = unwrap(MAT1r);
MAT2r = deg2rad(MAT2);
MAT2ru = unwrap(MAT2r);

figure
yyaxis left
plot(Fv, MAT1ru,    Fv, MAT2ru)
ylabel('Unwrapped Phase (rad)')
yyaxis right
plot(Fv, MAT1ru-MAT2ru)
ylabel('Phase Difference (rad)')
grid
legend('MAT_1','MAT_2','Difference', 'Location','best')
xlabel('Frequency (Hz)')

It is necessary to convert them to radians before unwrapping them. I kept them as radians here, so use the rad2deg fucntion to convert them back to degrees if desired.

.