We show that emissivities in the near infrared can be determined relative to a reference surface employing the photoacoustic effect. The photoacoustic cell is equipped with two windows and a… Click to show full abstract
We show that emissivities in the near infrared can be determined relative to a reference surface employing the photoacoustic effect. The photoacoustic cell is equipped with two windows and a pair of synchronously moving chopping wheels so that the cell alternately views the test and the reference surface. The acoustic signals produced in the cell are detected with a microphone and that output is fed to a lock-in amplifier. The temperature of the test surface is varied to produce a null in the lock-in amplifier, which permits determination of a relative emissivity. Results of measurements for several plastic and metal surfaces are reported.
               
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