Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a sensitive gas detection technique which requires frequent calibration and has a long response time. Here we report beat frequency (BF) QEPAS ...

Modulation is the act of translating some low-frequency or baseband signal (voice, music, and data) to a higher frequency. Why do we modulate signals? There are at least two reasons: to allow the ...

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Strike a bell, and the bell rings at its resonance modes. Strike it harder and the bell rings at the same tone, only louder. Now imagine a small crack in the bell, perhaps invisible to the eye. We ...

The combination of electric and magnetic fields at right angles produces radio waves. These waves occur at different frequencies, and the range of useful frequencies is called the electromagnetic ...