Sensors and methods for high-sensitivity optical particle counting and sizing

A method of deconvoluting a pulse height distribution PHD derived from particles of unknown size flowing along different trajectories through a non-uniform light field of a single-particle optical sizing device for sizing particles in a fluid suspension, comprising:

• setting up a matrix having a plurality of columns, each containing a basis vector comprising a pulse height distribution of particles of a substantially known size corresponding to the response of a photo-detector of said device to said particles of known size, each successive column containing a basis vector for particles of successively larger sizes, said matrix also having a like plurality of rows, each corresponding to a successive pulse height channel, each channel including a range of pulse heights, successive rows corresponding to successively larger pulse heights, each column having a maximum count pulse height value at a location for a row which relates to a pulse height corresponding to said particle of known size associated with said column, said maximum count pulse height values for successive columns being arranged on a diagonal of said matrix;
• and
• implementing a successive subtraction algorithm comprising the steps of:
• starting with the basis vector with its maximum count value in the largest row number;
• scaling a column basis vector by a factor corresponding to the value of the row in the PHD that matches the column number;
• subtracting said scaled basis vector from the PHD to form an element of a deconvoluted PHD (dPHD), leaving an intermediate PHD vector with a smaller number of total particles;
• and
• repeating this process using the remaining basis vectors until the entire PHD has been consumed and all the elements of the deconvoluted dPHD have been formed.

A method of optically sizing particles in a fluid suspension, comprising:

• establishing a flow of said suspension through a physically well-defined measurement flow channel of a single-particle optical sizing sensor apparatus wherein a beam of light, having an axis, is directed through said measurement flow channel to form an optical sensing zone within said measurement flow channel, said beam of light and said optical sensing zone being of such size relative to the size of said measurement flow channel that said sensor apparatus responds to only a fraction of the total number of particles flowing through said measurement flow channel, whereby said sensor apparatus will respond effectively to a relatively concentrated fluid suspension, said beam having a maximum intensity portion in said beam and a continuum of lesser intensities for positions in said beam spaced transversely from said axis, whereby some of said particles have a trajectory through said maximum intensity portion, others of said particles have trajectories through said lesser intensity positions, and still others of said particles may have trajectories outside said zone;
• detecting light from said zone to provide pulse height signals, each responsive to a particle flowing through said zone, said pulse height signals being functions of the sizes and trajectories of detected particles, said pulse height signals collectively forming a pulse height distribution PHD;
• and
• mathematically deconvoluting and processing said PHD to extract from said PHD a particle size distribution PSD of said particles in said fluid suspension, wherein said step of deconvoluting and processing said PHD comprises setting up a matrix having a plurality of columns, each containing a basis vector comprising a pulse height distribution of particles of a known size corresponding to the response of a photo-detector of said device to said particles of known size, each successive column containing a basis vector for particles of successively larger sizes, said matrix also having a like plurality of rows, each corresponding to a successive pulse height channel, each channel including a range of pulse heights, successive rows corresponding to successively larger pulse heights, each column having a maximum count pulse height value at a location for a row which relates to pulse heights corresponding to said particle of known size associated with said column, said maximum count pulse height values for successive columns being arranged on a diagonal of said matrix;
• modifying said matrix by setting all terms corresponding to pulse height values greater than said maximum count pulse height value in a column to zero;
• and using a deconvolution algorithm to perform matrix inversion and vector multiplication of said pulse height distribution and said inverted matrix as modified.

A method of optically sizing particles in a fluid suspension, comprising:

• establishing a flow of said suspension through a physically well-defined measurement flow channel of a single-particle optical sizing sensor apparatus wherein a beam of light, having an axis, is directed through said measurement flow channel to form an optical sensing zone within said measurement flow channel, said beam of light and said optical sensing zone being of such size relative to the size of said measurement flow channel that said sensor apparatus responds to only a fraction of the total number of particles flowing through said measurement flow channel, whereby said sensor apparatus will respond effectively to a relatively concentrated fluid suspension, said beam having a maximum intensity portion in said beam and a continuum of lesser intensities for positions in said beam spaced transversely from said axis, whereby some of said particles have a trajectory through said maximum intensity portion, others of said particles have trajectories through said lesser intensity positions, and still others of said particles may have trajectories outside said zone;
• detecting light from said zone to provide pulse height signals, each responsive to a particle flowing through said zone, said pulse height signals being functions of the sizes and trajectories of detected particles, said pulse height signals collectively forming a pulse height distribution PHD;
• and
• mathematically deconvoluting and processing said PHD to extract from said PHD a particle size distribution PSD of said particles in said fluid suspension, wherein said step of mathematically deconvoluting said PHD comprises using a deconvolution algorithm to provide a deconvoluted pulse height distribution dPHD, and said method further comprising providing a calibration curve of the relationship of pulse height and diameter, and using said calibration curve to translate each deconvoluted pulse height value in the dPHD into a unique particle diameter associated with this pulse height value yielding a “raw” particle size distribution (PSD), and converting said raw PSD into a final PSD by renormalizing said raw PSD by multiplying by the value 1/Φd, where Φd is the fraction of particles actually detected by said device for particles of each size, d.