Multi-band transducer for photoacoustic detection

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.

We claim:  
     
         1 . 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, wherein the improvement comprises: 
 said at least two piezoelectric elements are longitudinal receiver elements for receiving longitudinal waves; and    said first frequency is different from said second frequency.    
     
     
         2 . The transducer as recited in    claim 1    wherein said at least two piezoelectric elements are mounted on a wear plate and contained within a single housing.  
     
     
         3 . The transducer as recited in    claim 2   , wherein said at least two piezoelectric elements are placed independently on said wear plate.  
     
     
         4 . The transducer as recited in    claim 2   , wherein said at least two piezoelectric elements are stacked on said wear plate.  
     
     
         5 . 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 pulsed excitation energy from a laser 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 and at least a second piezoelectric element has a second frequency, wherein the improvement comprises:    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.    
     
     
         6 . The method as recited in    claim 5   , wherein said at least two piezoelectric elements are on a wear plate.  
     
     
         7 . The method as recited in    claim 6   , wherein said at least two piezoelectric elements are placed independently on said wear plate.  
     
     
         8 . The method as recited in    claim 6   , wherein said at least two piezoelectric elements are stacked on said wear plate.  
     
     
         9 . The method as recited in    claim 5   , wherein said at least two piezoelectric elements are on separate wear plates.