Method and apparatus for sensing or determining one or more properties or the identity of a sample

A method for sensing or determining a characteristic feature of a sample, the method comprising the steps of:

• (a) selectively utilizing electromagnetic radiation whose optical character is changed by said sample due to an optical effect which is at least one of optical interference, absorption, or scatter;
• (b) causing said electromagnetic radiation to be directed to said sample, said radiation including at least three components having respectively different properties;
• (c) measuring the relevant transmittance or reflectance of said sample for each of said radiation components to derive respective measured values;
• (d) providing known model values of relevant transmittance or reflectance as an output from at least one mathematical model into which is input (i) known values relating to the properties of the radiation components, and (ii) different magnitudes of the characteristic feature to be sensed or determined, said model taking account of the relevant absorption and interference and/or scatter;
• (e) correlating said measured values with said output model values;
• and
• (f) selecting the output model values having an optimum correlation with said measured values, the selected output model values representing the characteristic feature of the sample which is sensed or to be determined.

A method for sensing or determining a characteristic feature of a sample comprising the steps of:

• (a) selectively utilizing electromagnetic radiation whose optical character is changed by said sample due to an optical effect which is at least one of optical interference, absorption, or scatter;
• (b) causing electromagnetic radiation to be directed to said sample, said radiation including at least three components having respectively different properties;
• (c) measuring the relevant transmittance or reflectance of said sample for each of said radiation components to derive respective measured values;
• (d) computing model values on the basis of a differential function of a mathematical model to which are input (i) known values relating to properties of the radiation components, and (ii) different magnitudes of the characteristic feature to be sensed or determined and from which said model values are output;
• (e) correlating said measured values with said computed output model values;
• (f) determining optimum correlation from a zero correlation value in the correlation between said measured values and said computed output model values;
• and
• (g) selecting the computed output model values at which the correlation is optimum as the values which represent the characteristic feature of the sample which is sensed or to be determined.

A method for sensing or determining a characteristic feature of a sample comprising the steps of:

• (a) selectively utilizing electromagnetic radiation whose optical character is changed by said sample due to an optical effect which is at least one of optical interference, absorption, or scatter;
• (b) causing electromagnetic radiation to be directed to said sample, said radiation including two or more groups of radiation components, each group including at least three components having respectively different properties;
• (c) measuring the relevant transmittance or reflectance of said sample for each of said radiation components to derive respective measured values;
• (d) providing known model values of relevant transmittance or reflectance as an output from at least one mathematical model into which is input (i) known values relating to the properties of the radiation components, and (ii) different magnitudes of the characteristic feature to be sensed or determined;
• (e) computing correlation coefficients between said measured values and said output model values for said two or more groups of radiation components;
• (f) determining the highest correlation coefficient for each of said groups of radiation components over a limited range of known magnitudes;
• (g) deriving the highest correlation coefficients from the latter step (f) and using them to compute the magnitudes at which peaks occur in the correlation coefficients for each of said groups;
• and
• (h) selecting the output model values at the known magnitudes where the correlation coefficient peaks are coincident, or most nearly coincident.

Apparatus for sensing or determining a characteristic feature of a sample utilizing electromagnetic radiation selected to be subject to an optical effect which is at least one of optical interference, absorption, or scatter, the apparatus comprising:

• (a) means for causing said electromagnetic radiation to be directed to said sample, said radiation including at least three discrete components selected from a spectral range so that at least one of said components is subjected to said optical effect so that the optical character of said component is changed;
• (b) means for receiving the relevant transmitted or reflected radiation components and for providing corresponding measurement values;
• (c) means for providing different known values of relevant transmittance or reflectance, said different known values representing different values of known characteristic features of a known material;
• (d) means for determining the correlation between said measured values and said known values and for selecting the known values having an optimum correlation with said measured values, the selected known values representing the characteristic feature of the sample which is sensed or to be determined.

Apparatus for sensing or determining a characteristic feature of a sample utilizing electromagnetic radiation selected to be subject to an optical effect which is at least one of interference, absorption, or scatter, the apparatus comprising:

• (a) means for causing said electromagnetic radiation to be directed to said sample, said radiation including at least three components having respectively different properties;
• (b) means for receiving the relevant transmitted or reflected radiation components in order to provide measurement values and for converting said measurement values into digital form;
• (c) computing means programmed (i) with at least one mathematical model to which is input known values relating to the properties of the radiation components and different magnitudes of the characteristic feature to be sensed or determined in order to output model values, (ii) to compute correlation coefficients between said measured values and said output model values for two or more groups of said radiation components, (iii) to determine the highest correlation coefficient for each group of said radiation components over a limited range of known magnitudes, (iv) to derive the highest correlation coefficients from the latter step and to use them to compute the magnitudes at which peaks occur in the correlation coefficients for each of said groups, and (v) to select the output model values at the known magnitudes where the correlation coefficient peaks are coincident, or most nearly coincident.