); [EMAIL_ADDRESS] (V.M.N.P.) M. N. Passaro  
2 Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (V.M.N.P.) M. N. Passaro  
2 Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [PERSON].M. ); [PERSON]M.D.G. ); [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (V.M.N.P.) M. N. Passaro  
2 Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (V.M.N.P.) [PERSON] Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [PERSON]M.); [EMAIL_ADDRESS] (V.M.N.P.) [PERSON] Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (V.M.N.P.) [PERSON] Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (V.M.N.P.) [PERSON] Department of Electrical and Information Engineering, Politecnico di Bari, 70126 Bari, Italy; [EMAIL_ADDRESS] (G.M. ); [PERSON]D.G. ); [EMAIL_ADDRESS] (G.M. ); vittorioby stress field spatial inhomogeneity leading to temperature fluctuations [12]. The main loss mechanisms depend upon the prong size and the resonance mode of the QTF. Another parameter affecting the QEPAS signal is the radiation-to-sound conversion efficiency of the gas, namely, the efficiency of the gas to convert the modulated absorbed light into sound, which is mainly determined by the non-radiative relaxation dynamics of the excited molecules [13]. Lowering the modulation frequency, i.e., the QTF resonance frequency, is essential when dealing with slow relaxing molecules (with relaxation times of few microseconds) to allow a complete release of the absorbed energy during each oscillation period. Thus, QTFs with resonance frequencies lower than \(\sim\)20 kHz and a quality factor as high as possible are an interesting choice for QEPAS detection. To follow these guidelines, a new geometry with T-shaped QTF prongs was introduced in [14]. Compared with a rectangular shape, T-shaped prongs allow a lower resonance frequency without affecting the \(Q\)-factor, as well as an increased stress field generated on the prong surface while the QTF is vibrating. The QTF is usually coupled with a pair of resonator tubes, allowing an enhancement of the QEPAS SNR [15; 16]. The acoustic system composed of a QTF and a pair of resonator tubes is usually referred to as a spectrophone. In a spectrophone, an additional dissipation phenomenon can become limiting due to the interaction between the prong surface and the tubes' transversal section squeezing damping. The influences of air pressure in the resonance properties of classic shape QTFs have been reported in the literature through analytical models, and a good agreement with experiments has been demonstrated [17; 18; 19]. In [14], a new geometry of QTF was introduced that may not be modelled in a similar manner. This work aims to analyze the influence of air pressure on the resonance properties both of a bare T-shaped QTF, and of the same QTF when acoustically coupled with two resonator tubes. A theoretical model was developed to predict the influence of air pressure both on the frequency and quality factor of the fundamental resonance mode of the QTF. The model was validated with experimental results. Furthermore, the QTF was assembled in a spectrophone with two resonator tubes. The influence of resonator tubes on the spectrophone resonance properties was investigated and compared with those of the bare QTF. The same analysis was performed on the QTF tubes at two different distances.