The favorable downscaling behavior of photoacoustic spectroscopy has provoked in recent years a growing interest in the miniaturization of photoacoustic sensors. The individual components of the sensor, namely widely tunable quantum cascade lasers, low loss mid infrared (mid-IR) waveguides, and efficient microelectromechanical systems (MEMS) microphones are becoming available in complementary metal–oxide–semiconductor (CMOS) compatible technologies. This paves the way for the joint processes of miniaturization and full integration. Recently, a prototype microsensor has been designed by the means of a specifically designed coupled optical-acoustic model. This paper discusses the new, or more intense, challenges faced if downscaling is continued. The first limitation in miniaturization is physical: the light source modulation, which matches the increasing cell acoustic resonance frequency, must be kept much slower than the collisional relaxation process. Secondly, from the acoustic modeling point of view, one faces the limit of validity of the continuum hypothesis. Namely, at some point, velocity slip and temperature jump boundary conditions must be used, instead of the continuous boundary conditions, which are valid at the macro-scale. Finally, on the technological side, solutions exist to realize a complete lab-on-a-chip, even if it remains a demanding integration problem.
References
[1]
Elia, A.; Lugarà, P.M.; di Franco, C.; Spagnolo, V. Photoacoustic techniques for trace gas sensing based on semiconductor laser sources. Sensors 2009, 9, 9616–9628.
[2]
Miklos, A.; Hess, P.; Bozoki, Z. Application of acoustic resonators in photoacoustic trace gas analysis and metrology. Rev. Sci. Instrum. 2001, 72, 1937–1955.
[3]
Firebaugh, S.; Jensen, K.; Schmidt, M. Miniaturization and integration of photoacoustic detection. J. Appl. Phys. 2002, 92, 1555–1563.
[4]
Holthoff, E.L.; Heaps, D.A.; Pellegrino, P.M. Development of a MEMS-scale photoacoustic chemical sensor using a quantum cascade laser. IEEE Sens. J. 2010, 10, 572–577.
[5]
Gorelik, A.V.; Ulasevich, A.L.; Nikonovich, F.N.; Zakharich, M.P.; Firago, V.A.; Kazak, N.S.; Starovoitov, V.S. Miniaturized resonant photoacoustic cell of inclined geometry for trace-gas detection. Appl. Phys. B 2010, 100, 283–289.
[6]
Karioja, P.; Keraenen, K.; Kautio, K.; Ollila, J.; Heikkinen, M.; Kauppinen, I.; Kuusela, T.; Matveev, B.; McNie, M.E.; Jenkins, R.M.; et al. LTCC Based Differential Photo Acoustic Gas Cell for ppm Gas Sensing. In Optical Sensing and Detection; Berghmans, F., Mignani, A., Hoof, C., Eds.; Spie-Int Soc Optical Engineering: Bellingham, WA, USA, 2010; Volume 7726.
[7]
Rueck, T.; Bierl, R.; Hofmann, M.; Landgraf, F.; Unger, J. Development of a Miniaturized Photoacoustic Multigas Sensing System for Trace Gas Measurement. Proceedings of the 17th International Conference on Photoacoustic and Photothermal Phenomena (ICPPP17), Suzhou, China, 20–24 October 2013.
Carras, M.; Maisons, G.; Simozrag, B.; Garcia, M.; Parillaud, O.; Massies, J.; Marcadet, X. Room-temperature continuous-wave metal grating distributed feedback quantum cascade lasers. Appl. Phys. Lett. 2010, 96, doi:10.1063/1.3399779.
[10]
Carras, M.; Maisons, G.; Simozrag, B.; Trinite, V.; Brun, M.; Grand, G.; Labeye, P.; Nicoletti, S. Monolithic Tunable Single Source in the Mid-IR for Spectroscopy. Proceedings of the SPIE—The International Society for Optical Engineering, San Francisco, CA, USA, 2 February 2013; Volume 8631, pp. 863113:1–863113:7.
[11]
Brun, M.; Labeye, P.; Grand, G.; Hartmann, J.-M.; Boulila, F.; Carras, M.; Nicoletti, S. Low loss SiGe graded index waveguides for mid-IR applications. Opt. Express 2014, 22, 508–518.
[12]
Takahashi, H.; Suzuki, A.; Iwase, E.; Matsumoto, K.; Shimoyama, I. MEMS microphone with a micro Helmholtz resonator. J. Micromech. Microeng. 2012, 22, doi:10.1088/0960-1317/22/8/085019.
[13]
Czarny, J.; Walther, A.; Desloges, B.; Robert, P.; Redon, E.; Verdot, T.; Ege, K.; Guianvarg'h, C.; Guyader, J.L. New Architecture of MEMS Microphone for Enhanced Performances. Proceedings of the IEEE International Semiconductor Conference Dresden Grenoble (ISDSG 2013), Dresden, Germany, 26–27 September 2013.
[14]
Glière, A.; Rouxel, J.; Parvitte, B.; Boutami, S.; Zéninari, V. A coupled model for the simulation of miniaturized and integrated photoacoustic gas detector. Int. J. Thermophys. 2013, 34, 2119–2135.
[15]
Zeninari, V.; Kapitanov, V.A.; Courtois, D.; Ponomarev, Y.N. Design and characteristics of a differential Helmholtz resonant photoacoustic cell for infrared gas detection. Infrared Phys. Technol. 1999, 40, 1–23.
[16]
Baumann, B.; Wolff, M.; Kost, B.; Groninga, H. Finite element calculation of photoacoustic signals. Appl. Opt. 2007, 46, 1120–1125.
[17]
Duggen, L.; Lopes, N.; Willatzen, M.; Rubahn, H.-G. Finite element simulation of photoacoustic pressure in a resonant photoacoustic cell using lossy boundary conditions. Int. J. Thermophys. 2011, 32, 774–785.
[18]
Prokhorov, A.V. Monte Carlo method in optical radiometry. Metrologia 1998, 35, doi:10.1088/0026-1394/35/4/44.
[19]
Bozóki, Z.; Pogány, A.; Szabó, G. Photoacoustic instruments for practical applications: Present, potentials, and future challenges. Appl. Spectrosc. Rev. 2011, 46, 1–37.
[20]
Kreuzer, L.B. Ultralow gas concentration infrared absorption spectroscopy. J. Appl. Phys. 1971, 42, 2934–2943.
[21]
Kreuzer, L.B. The Physics of Signal Generation and Detection. In Optoacoustic Spectroscopy and Detection; Academic Press: London, UK, 1977; pp. 1–25.
[22]
Rothman, L.S.; Gordon, I.E.; Barbe, A.; Benner, D.C.; Bernath, P.E.; Birk, M.; Boudon, V.; Brown, L.R.; Campargue, A.; Champion, J.-P.; et al. The HITRAN 2008 molecular spectroscopic database. J. Quant. Spectrosc. Radiat. Transf. 2009, 110, 533–572.
[23]
Wysocki, G.; Kosterev, A.A.; Tittel, F.K. Influence of molecular relaxation dynamics on quartz-enhanced photoacoustic detection of CO2 at λ = 2 μm. Appl. Phys. B Lasers Opt. 2006, 85, 301–306.
[24]
Colles, M.J.; Geddes, N.R.; Mehdizadeh, E. The optoacoustic effect. Contemp. Phys. 1979, 20, 11–36.
[25]
Zeninari, V.; Tikhomirov, B.A.; Ponomarev, Y.N.; Courtois, D. Photoacoustic measurements of the vibrational relaxation of the selectively excited ozone (ν3) molecule in pure ozone and its binary mixtures with O2, N2, and noble gases. J. Chem. Phys. 2000, 112, 1835–1843.
[26]
Cottrell, T.L.; Macfarlane, I.M.; Read, A.W. Measurement of vibrational relaxation times by spectrophone—Systems CO2 + N2 and N2O + N2. Trans. Faraday Soc. 1967, 63, 2093–2097.
[27]
Petra, N.; Zweck, J.; Kosterev, A.; Minkoff, S.; Thomazy, D. Theoretical analysis of a quartz-enhanced photoacoustic spectroscopy sensor. Appl. Phys. B Lasers Opt. 2009, 94, 673–680.
[28]
Spagnolo, V.; Kosterev, A.A.; Dong, L.; Lewicki, R.; Tittel, F.K. NO trace gas sensor based on quartz-enhanced photoacoustic spectroscopy and external cavity quantum cascade laser. Appl. Phys. B Lasers Opt. 2010, 100, 125–130.
[29]
Kosterev, A.; Tittel, F.; Serebryakov, D.; Malinovsky, A.; Morozov, I. Applications of quartz tuning forks in spectroscopic gas sensing. Rev. Sci. Instrum. 2005, 76, doi:10.1063/1.1884196.
[30]
Holthoff, E.; Bender, J.; Pellegrino, P.; Fisher, A. Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination. Sensors 2010, 10, 1986–2002.
[31]
Morse, P.M.; Ingard, K.U. Theoretical Acoustics; Princeton University Press: Princeton, NJ, USA, 1987.
[32]
Parvitte, B.; Risser, C.; Vallon, R.; Zéninari, V. Quantitative simulation of photoacoustic signals using finite element modelling software. Appl. Phys. B Lasers Opt. 2013, 111, 383–389.
[33]
Joly, N. Finite element modeling of thermoviscous acoustics on adapted anisotropic meshes: Implementation of the particle velocity and temperature variation formulation. Acta Acust. United Acust. 2010, 96, 102–114.
[34]
Malinen, M.; Lyly, M.; Raback, P.; Karkkainen, A.; Karkkainen, L. A Finite Element Method for the Modeling of Thermo-Viscous Effects in Acoustics. Proceedings of the European Congress on Computational Methods in Applied Science and Engineering (ECCOMAS 2004), Jyvaskyla, Finland, 24–28 July 2004.
[35]
Karniadakis, G.E.; Beskok, A. Micro Flows: Fundamentals and Simulation; Springer: Berlin, Germany, 2002.
[36]
Gad-el-Hak, M. MEMS: Introduction and Fundamentals; CRC Press: Boca Raton, FL, USA, 2010.
[37]
Kuusela, T.; Kauppinen, J. Photoacoustic gas analysis using interferometric cantilever microphone. Appl. Spectrosc. Re. 2007, 42, 443–474.
[38]
Spagnolo, V.; Patimisco, P.; Borri, S.; Scamarcio, G.; Bernacki, B.E.; Kriesel, J. Part-per-Trillion Level Detection of SF6 Using a Single-Mode Fiber-Coupled Quantum Cascade Laser and a Quartz Enhanced Photoacoustic Sensor. In Quantum Sensing and Nanophotonic Devices X; Razeghi, M., Tournie, E., Brown, G.J., Eds.; Spie-Int Soc Optical Engineering: Bellingham, WA, USA, 2013; Volume 8631.
