Measurement of porous film

1. A method for measuring radiation scattered by a first sample of a material, the method comprising:

determining a first and second wavelength at which the material exhibits substantially no absorption;

measuring a transmission of the first sample at the first wavelength;

measuring a transmission of the first sample at the second wavelength; and

calculating, based on the transmissions of the first sample at the first and second wavelengths, a first parameter, S, of the first sample using a first multivariate regression model comprising first regression coefficients, wherein the first parameter is a parameter which affects a total amount of radiation scattered by the first sample at the first and second wavelengths.

2. The method as claimed in claim 1 , wherein measuring the transmission of the first sample at the first wavelength comprises illuminating the first sample with incidence radiation including the first wavelength and measuring an intensity of radiation transmitted by the first sample at the first wavelength.

3. The method as claimed in claim 1 , wherein:

measuring the transmission of the first sample at the first wavelength comprises filtering radiation at the first wavelength; and

measuring the transmission of the first sample at the second wavelength comprises filtering radiation at the second wavelength.

4. The method as claimed in claim 3 , wherein filtering radiation at the first wavelength is performed on at least one of radiation incident on the first sample or radiation transmitted by the first sample at the first wavelength.

5. The method as claimed in claim 3 , wherein filtering radiation at the second wavelength is performed on at least one of radiation incident on the first sample or radiation transmitted by the first sample at the second wavelength.

6. The method as claimed in claim 1 , wherein measuring the transmission of the first sample at the second wavelength comprises illuminating the first sample with incidence radiation including the second wavelength and measuring an intensity of radiation transmitted by the first sample at the second wavelength.

7. The method as claimed in claim 1 , wherein the first and second wavelengths each comprise at least one of a visible wavelength, an infra-red wavelength, a near-infrared wavelength, or a mid-infrared wavelength.

8. The method as claimed in claim 1 , wherein at least one of the first wavelength or the second wavelength is a scatter-affected wavelength.

9. The method as claimed in claim 1 , wherein an amount of scatter exhibited by the first sample at the first wavelength is different from an amount of scatter exhibited by the first sample at the second wavelength.

10. The method as claimed in claim 1 , wherein the first parameter, S, is a parameter related to at least one of a porosity or a density of the first sample.

11. The method as claimed in claim 1 , wherein the first multivariate regression model is a first linear multivariate regression model.

12. The method as claimed in claim 1 , further comprising:

calculating the first regression coefficients by:

measuring transmissions of a second sample and a third sample of the material at the first wavelength;

measuring transmissions of the second and third samples at the second wavelength;

measuring the first parameter, S, of the second and third samples; and

calculating the first regression coefficients of the first multivariate regression model,

wherein the transmissions of the second sample at the first and second wavelengths are independent variables and the corresponding first parameter measurement of the second sample is a dependent variable of a first equation of the first multivariate regression model, and

wherein the transmissions of the third sample at the first and second wavelengths are independent variables and the corresponding first parameter measurement of the third sample is a dependent variable of a second equation of the first multivariate regression model.

13. The method as claimed in claim 12 , wherein:

the first parameter, S, is porosity; and

measuring the first parameter, S, of the second and third samples comprises calculating the porosity of the second and third samples using a formula,

S= 1−(sample density/material density),

wherein the sample density is a density of a sample, measured by dividing a mass per unit area of the sample by sample thickness, and the material density is a known density of a material with no pores.

14. The method as claimed in claim 1 , wherein the first and second wavelengths are determined by spectroscopy.

15. The method as claimed in claim 1 , further comprising:

calculating a second parameter, A, of the first sample using a second multivariate regression model comprising second regression coefficients, wherein the second parameter is a parameter related to a mass per unit area, g/m 2 , of the first sample.

16. The method as claimed in claim 15 , further comprising:

determining a third wavelength and a fourth wavelength, at which an amount of absorption exhibited by the first sample at the third wavelength is different from an amount of absorption exhibited by the first sample at the fourth wavelength;

measuring a transmission of the first sample at the third wavelength including filtering radiation at the third wavelength; and

measuring a transmission of the first sample at the fourth wavelength including filtering radiation at the fourth wavelength.

17. The method as claimed in claim 16 , further comprising:

calculating the second regression coefficients by:

measuring transmissions of a fourth sample and a fifth sample of the material at the third wavelength;

measuring transmissions of the fourth and fifth samples at the fourth wavelength;

measuring the second parameter, A, of the fourth and fifth samples; and

calculating the second regression coefficients of the second multivariate regression model,

wherein the transmissions of the fourth sample at the third and fourth wavelengths are independent variables and the corresponding second parameter measurement of the fourth sample is a dependent variable of a first equation of the second multivariate regression model, and

wherein the transmissions of the fifth sample at the third and fourth wavelengths are independent variables and the corresponding second parameter measurement of the fifth sample is a dependent variable of a second equation of the second multivariate regression model.

18. The method as claimed in claim 17 , wherein the second parameters of the fourth and fifth samples are measured by weighing samples of a predetermined area.

19. The method as claimed in claim 16 , wherein at least one of the third or fourth wavelength is the same as at least one of the first or second wavelength.

20. The method as claimed in claim 16 , wherein at least one of the fourth or fifth sample is the same as at least one of the second or third sample.

21. The method as claimed in claim 16 , wherein the first parameter, S, is used as a scatter-correction factor for the transmission measurements at the third and fourth wavelengths.

22. The method as claimed in claim 15 , the method further comprising:

combining the calculated first parameter, S, of the first sample with the calculated second parameter, A, of the first sample to calculate at least one of a thickness, a mass per unit area, a density, or a porosity of the first sample.

23. The method as claimed in claim 22 , wherein combining the calculated first parameter, S, of the first sample with the calculated second parameter, A, of the first sample comprises multiplication or division.

24. The method as claimed in claim 22 , wherein combining the calculated first parameter, S, with the calculated second parameter, A, comprises calculating at least one of the thickness, the mass per unit area, the density or the porosity (T) of the first sample using an equation selected from the group comprising:

T=a [( Sb+c )( Ad+e )]+ f;

T=a [( Sb+c )/( Ad+e )]+ f;

T=a [( Ad+e )/( Sb+c )]+ f ; and

T=a{A [( Sb )+ c]}+d

wherein a, b, c, d, e and f are empirically-calculated constants.

25. The method as claimed in claim 1 , wherein the material is at least one of a battery separator film or a lithium-ion battery separator film.

26. A method, for measuring a first sample of a material, comprising:

calculating a first parameter, S, of the first sample of the material by:

determining a spectrum for the material associated with an absorption by the material to radiation;

obtaining a transmission of the first sample at the determined spectrum;

determining, based on the transmission of the first sample, scatter correction parameters for the first sample using a scatter correction model;

using the scatter correction parameters to calculate the first parameter, S;

calculating a second parameter, A, of the first sample, wherein the second parameter is a parameter related to a mass per unit area of the first sample; and

combining the calculated first parameter, S, of the first sample with the calculated second parameter, A, of the first sample to calculate at least one of a thickness, the mass per unit area, a density, or a porosity of the first sample.

27. The method as claimed in claim 26 , wherein determining the spectrum for the material comprises at least one of:

averaging measured spectra of a plurality of samples of the material; or

employing a rolling time average measurement of the spectrum measured on a moving sample of the material.