The PolySense team has just published a new article on Analytical Chemistry reporting on a the realization of a QEPAS sensor for simultaneous dual gas detection of Methane/Nitric Oxide and water vapor with sensitivity down to few ppbs, by simultaneously exciting two in-plane flexural vibrational mode of a custom QTF. The following link provide access to the article.
http://polysense.poliba.it/wp-content/uploads/2019/09/109_analytical-chem_-dual-gas-Qepas_2019.pdf