Microwave spectroscopy is a powerful tool for chemical sensing because it detects chemicals on the basis of their rotational transition spectra. A molecule’s rotational transitions are directly related to its physical structure and can be predicted by quantum physics. Therefore, rotational transition spectra are like fingerprints of a chemical, and microwave spectroscopy provides very high specificity that makes it especially useful in chemical identification.
Recent advances of electronic components such as high frequency system in a package, high speed A/D’s, and micropumps, except for the analysis chamber, have removed the barrier that limited conventional microwave spectrometers to a laboratory endeavor.
In this project, in order to achieve the goal of on-site chemical sensing, we focus on developing more compact size analysis chambers that are capable of conducting room-temperature chirped pulse Fourier transform microwave (RT-CP-FTMW) spectroscopy and maintaining the input power at a reasonable level.
We have designed an overmoded waveguide that successfully detects methanol in the frequency range of 9 to 12.5 GHz, shown in Fig. 1.
In addition to the overmoded waveguide spectrometer, we also have designed an overmoded coaxial cable spectrometer and detected methanol rotational spectrum at a frequency as high as 17.9 GHz, shown in Fig. 2.
RT-CP-FTMW spectroscopy has been demonstrated using these spectrometers. The compactness of these spectrometers also proves their potential for being used as chemical sensors.
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