Saw vapor sensor apparatus and multicomponent signal processing

• US 5,465,608 A
• Filed: 06/30/1993
• Issued: 11/14/1995
• Est. Priority Date: 06/30/1993
• Status: Expired due to Fees

• Current Assignee: Hamilton Sundstrand Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Orbital Sciences Corporation (Northrop Grumman Corporation)
• Inventors: Tracy, David H., Lokshin, Anatole, Burchfield, David E.
• Primary Examiner(s): NOLAND, THOMAS
• Application Number:
  US08/085,604
• Time in Patent Office: 867 Days
• Field of Search: 73/24.01, 73/24.06, 73/23.2, 73/31.01, 73/31.02, 73/579, 364/498
• US Class Current: 73/24.01
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/02845 Humidity, wetness
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects
• CPC Class Codes: G01N 29/326 compensating for temperature variations

Abstract

A method and apparatus for the identification and quantification of a vapor, or a number of vapors, in air mixtures is discussed. The method includes calibration of a vapor responsive sensor, or a plurality of vapor responsive sensors, to known concentrations of the vapors of interest or to known concentrations of potential interfering vapors. The calibrations result in sensor response vectors which are derived from the transient signals observed as the vapors are sorbed and desorbed on the sensors. Detection of vapors in complex mixtures is effected by subjecting the apparatus to the mixture and measuring the sensor response, or plurality of sensor responses, and then applying multidimensional statistical analysis or filtering methods to this data, using the precalibrated response vectors as the basis set for deconvolution. The sensors disclosed are Surface Acoustic Wave sensors (SAWs), and include variations of temperature programmed SAWs, SAWs with various combinations of chemically selective coatings, and arrays of temperature programmed and coated SAWs.

Claims

1. A method for detecting and determining the concentration of at least one target compound in a vapor mixture of compounds of unknown concentrations comprising the steps of:

providing a pair of vapor responsive sensors whose average one cycle frequency response to a unit concentration of a selected vapor is known;

subjecting said vapor responsive sensors to a mixture of compounds of unknown concentrations which provide a frequency shift from said average frequency response to a second frequency response as a result of said mixture on said vapor responsive sensors; and

processing this frequency shift by multidimensional statistical methods to detect the target compound and determine its concentration.

2. The method of claim 1 wherein the step of processing the frequency shift comprises:

constructing a calibration matrix comprising vectors that represent the average one cycle frequency response of said vapor responsive sensor per unit concentration of each target compound;

constructing a response matrix comprising the one cycle frequency shift of said vapor responsive sensor to said vapor mixture; and

operating on said response matrix by said calibration matrix to calculate the concentration of each target compound.

3. The method of claim 2 wherein the step of operating on said response matrix comprises multiplying said response matrix by the pseudo inverse of said calibration matrix.

4. The method of claim 3 wherein the step of providing a pair of vapor responsive sensors comprises providing a surface acoustic wave sensor.

5. A method of detecting and determining the concentration of a target compound in a vapor mixture containing unknown concentration of the target compound and interferants, comprising the steps of:

providing a surface acoustic wave sensor which has been calibrated to produce a signal which is an average one cycle response per unit concentration of the target compound;

exposing this calibrated sensor to said vapor mixture to produce an output signal; and

mathematically processing this output signal to identify the target compound and its concentration in the mixture.

6. The method of claim 5 wherein the step of mathematically processing the output signal of said sensor comprises:

constructing a calibration matrix comprising vectors that represent the average one cycle response of the sensor per unit concentration of the target compound;

processing the output signal of said sensor and said calibration matrix by multidimensional statistical methods to detect the target compound and determine its concentration.

7. The method of claim 6 wherein the step of processing the output signal of said sensor and said calibration matrix includes forming weighting vectors from said calibration matrix and multiplying said weighting vectors by said output signal to obtain a vector representing the concentrations of said target compound in said vapor mixture.

8. A method of detecting at least one target compound and its respective concentration in a vapor mixture having one or more target compounds and interferants, comprising the steps of:

directing sample mixtures containing known concentrations of said target compounds through each of an array of surface acoustic wave sensors to produce output signals which are each processed to provide a set of vectors representing the average one cycle response per unit concentration for each of the target compounds;

constructing a matrix with each of the vectors of target compound response forming the columns of the matrix;

exposing said sensor array to a mixture containing unknown concentrations of one or more of said target compounds to produce an output signal;

mathematically processing this output signal to identify any one or more of the target compounds and their concentrations.

9. The method as claimed in claim 8 wherein the last mentioned step includes forming weighting vectors from the target compound response matrix and using this vector to extract the concentrations of the identified target compounds.

10. The method of claim 9 wherein the step of processing the output signal of said sensor array further comprises multiplying said weighting vectors by said output signal to obtain a vector representing the concentrations of said target compounds in said vapor mixture.

11. The method of claim 8 wherein the step of mathematically processing the output signal of said sensor array to identify target compounds comprises:

processing the output signal of said sensor array to obtain a vapor mixture response matrix comprising a vector for each sensor in said sensor array representing the response of said sensor to the exposure of said vapor mixture; and

determining the presence and concentration of target compounds in said vapor mixture by mathematical operations on said vapor mixture response matrix by said target compound response matrix.

12. The method of claim 11 wherein determining the presence and concentrations of said target compounds comprises multiplying said vapor mixture response matrix by the pseudo inverse of said target compound response matrix.

13. The method of claim 8 wherein the step of directing known concentrations of said target compounds through each sensor of said sensor array comprises:

recording the response of each sensor to the known concentration of said target compound; and

scaling this response data to obtain a set of vectors representing the average one cycle response of said sensor to a unit concentration of said target compound.