Photoacoustic method for measuring concentration of chemical species

• US 6,244,101 B1
• Filed: 06/01/1999
• Issued: 06/12/2001
• Est. Priority Date: 06/01/1999
• Status: Expired due to Fees

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Battelle Memorial Institute
• Inventors: Autrey, S. Thomas, Posakony, Gerald J., Amonette, James E., Foster-Mills, Nancy S.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US09/322,910
• Time in Patent Office: 742 Days
• Field of Search: 73/240.2, 73/240.1, 73/614.5, 73/614.9, 73/617.5, 73/617.9, 356/432, 356/437, 250/343, 250/351, 250/339.12, 250/339.13, 250/338.5
• US Class Current: 73/61.45
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids

Abstract

The present invention is a transducer for photoacoustic detection having at least two piezoelectric elements wherein at least a first piezoelectric element has a first frequency and at least a second piezoelectric element has a second frequency. The improvement according to the present invention is that at least two piezoelectric elements are longitudinal elements for longitudinal waves; and the first frequency is different from said second frequency. In other words, the invention is a multi-frequency longitudinal transducer for photoacoustic detection.

Claims

1. In a mixture containing at least two chemical species, a method for identifying and measuring concentration of said at least two chemical species, comprising the steps of:

passing electromagnetic energy through said mixture thereby creating a photoacoustic signal;

receiving said photoacoustic signal with at least two piezoelectric elements, wherein at least a first piezoelectric element has a first frequency, at least a second piezoelectric element has a second frequency,

said at least two piezoelectric elements are longitudinal elements for longitudinal waves, and

said first frequency is different from said second frequency; and

fitting four parameters with said first and second frequencies.

2. The method as recited in claim 1, wherein said at least two piezoelectric elements are on a wear plate.

3. The method as recited in claim 2, wherein said at least two piezoelectric elements are placed independently on said wear plate.

4. The method as recited in claim 2, wherein said at least two piezoelectric elements are stacked on said wear plate.

5. The method as recited in claim 1, wherein said at least two piezoelectric elements are on separate wear plates.

6. The method as recited in claim 1, wherein said electromagnetic energy is pulsed excitation energy from a laser.