Photon counting based particles detection method and apparatus
Inventors
Sickenberger, David W. • Sickenberger, Richard D.
Assignees
United States Department of the Army • Government of the United States of America
Publication Number
US-8874377-B1
Publication Date
2014-10-28
Expiration Date
2029-02-26
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Abstract
A method for detecting biological aerosols using a photon counting technique to determine the presence of particles is described. A Schmitt trigger is used to prevent over counting of particle events and for greater stability and noise immunity. An alarm determination is made using time-based statistical data derived from the observed fluorescent and scattered photon data.
Core Innovation
The invention described is a method for detecting biological aerosols using a photon counting technique that processes two channels of signals indicative of fluorescent and scattered photon counts. The method involves updating counting variables such as the mean and standard deviation of photon counts across sampling bins, calculating sigma values, performing a Schmitt trigger operation to produce trigger counts, and triggering an alarm when counts exceed specified thresholds. This technique utilizes the statistical properties of photon counts to detect the presence of biological particles.
The problem addressed by the invention arises from challenges in detecting biological aerosols due to background noise, variability across photon detectors, and drift in detector response over time and environmental conditions. Existing peak detection algorithms are prone to over counting particle events and can suffer from instability and noise susceptibility. There is a need for a method that possesses greater noise immunity, compensates for detector variability, and mitigates drift, while preventing over counting when photon signals from a single particle span multiple sampling bins.
Claims Coverage
The patent includes ten independent claims covering methods and computer program products for detecting biological aerosols using photon counting and statistical analysis.
Photon counting with statistical updating and alarm triggering
A method of detecting biological aerosols by receiving fluorescent and scattered photon counts in time-based sampling bins; updating counting variables including sum and sum squared to calculate mean and standard deviation; calculating sigma values; performing a Schmitt trigger operation to produce trigger counts for each channel; calculating mean and standard deviation of these trigger counts; and triggering an alarm when thresholds are met.
Schmitt trigger operation with high and low sigma thresholds
Performing the Schmitt trigger operation by incrementing the trigger count when the sigma value exceeds a high threshold and resetting the trigger state when the sigma value falls below a low threshold, where these thresholds are multiples of the standard deviation over the mean specific to each photon channel.
Distinct alarm conditions for indoor and outdoor detectors
Triggering alarms based on different threshold values for indoor versus outdoor applications, where indoor alarms require higher minimum Schmitt counts and sigma multiples, and outdoor alarms require lower thresholds, with an additional condition based on the ratio between fluorescent and scattered trigger counts exceeding a specified minimum.
Coincident trigger count determination
Calculating a coincident trigger count from simultaneous trigger counts in both the fluorescent and scattered photon channels, and conditioning alarms on thresholds for coincident and fluorescent trigger counts.
Computer program product implementing the photon counting and alarm method
A computer program stored on non-transitory machine readable media comprising instructions to perform the same steps of photon count receiving, statistical updating, Schmitt triggering, and alarm triggering as the method claims.
These inventive features together provide a method and system for biological aerosol detection that uses photon counting with adaptive statistical thresholds and Schmitt trigger logic to robustly detect particle events and trigger alarms conditioned on combined fluorescent and scattered photon data, with modes adaptable to indoor and outdoor environments.
Stated Advantages
Provides greater noise immunity in photon counting detection.
Compensates for variability across different photon detectors of the same model.
Mitigates detector drift caused by time, temperature, and humidity conditions.
Prevents over counting of biological particles when photon signals extend into multiple sampling bins.
Offers stability and reliability in detection using Schmitt trigger logic.
Documented Applications
Detection of biological aerosols in environments with potential biological attacks or industrial accidents.
Long-term continuous monitoring of ambient air for presence of biological particles.
Use in both indoor and outdoor environments with selection of operating mode.
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