Miniaturised photoacoustic gas sensor based on patented interferometric readout and novel photonic integration technologies (MINIGAS project #224625, FP7)

             High-sensitivity gas sensors measure the presence of trace gases. They have a wide range of applications. Finnish SME Gasera has recently developed a MEMS-based mechanism for detecting the pressure waves created in photo-acoustic cells. This innovation can be used to realize infrared gas sensors of extreme sensitivity. Instead of the usual microphone (membrane with capacitive readout) the Gasera cell contains a “free-standing” silicon cantilever. The mechanical movement of the free end of the cantilever is 100x larger than the centre of a fixed membrane. Furthermore, the movement of the cantilever is detected interferometrically not capacitively. The resulting improvement in sensitivity by these innovations is about three orders of magnitude over the prior art. Three international patent applications are pending. Whereas other optical gas detection methods can not be miniaturized because of the long optical pathlengths needed for high sensitivity, theoretical analyses predict that the cantilever PA cell can be miniaturized. The goal is to build and demonstrate a miniaturised sensor sub-system that achieves two or three orders of magnitude better sensitivity (on sub-ppm level!) than other optical measurement methods could achieve at similar package volume. A much lower cost and wider temperature range of operation are also predicted.

Schematic of the PA sensor placed on the right hand                Microimmersion lens LED with 1 mm lens

Photoacoustic effect induced by negative luminescence device

T. Kuusela,¹, J. Peura^,1 B. A. Matveev^,2 M. A. Remennyy,² and N. M. Stus’²

¹Department of Physics and Astronomy, University of Turku, FIN-20014 Turku, Finland

²Centre of Nanoheterostructure Physics, Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia

Received 31 March 2010; accepted 25 May 2010; published online 8 July 2010_

JOURNAL OF APPLIED PHYSICS 108, 014903 (2010)

© 2010 American Institute of Physics. _doi:10.1063/1.3456499_

            The cantilever enhanced photoacoustic trace gas detection technique has been combined with mid-infrared light emitting diodes LEDs producing significant negative luminescence at a reverse bias. In contrast to normal positive photoacoustic phenomenon the negative luminescence of the LED creates wavelength specific cooling of the gas under study and pressure drop in the photoacoustic sample cell, which can be detected by a cantilever microphone. In experiments a LED operating at 5.5 μm wavelength range was used to detect acetone vapor.

LED view                                                                        Schematic of the PA experiments

Photoacoustic gas detection using a cantilever microphone and III–V mid-IR LEDs

T. Kuusela ^a, J. Peura ^a, B.A. Matveev ^b, M.A. Remennyy ^b, N.M. Stus’ ^b

^a Department of Physics and Astronomy, University of Turku, FIN 20014 Turku, Finland

^b Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia

Vibrational Spectroscopy 51 (2009) 289–293

 The cantilever enhanced photoacoustic trace gas detection in the mid-infrared 3–7 μm wavelength range has been combined with light emitting diode (LED) technology. Mid-IR LED output power was modulated by pulse driving current with frequency high enough to avoid acceleration and acoustical noise. Methane (CH₄), propane (C₃H₈), carbon dioxide (CO₂) and sulphur dioxide (SO₂) gases have been used for preliminary evaluation of the method sensitivity. The lowest detection limit of 6 ppm was observed for propane employing a LED with a center wavelength 3.3 μm and with 1 s sample integration time.

Sensitive and Fast Gas Sensor for Wide Variety of Applications Based on Novel Differential Infrared Photoacoustic Principle

Ismo Kauppinen, Arto Branders, Juho Uotila, Sauli Sinisalo, Jyrki Kauppinen, and Tom Kuusela 

Technisches Messen: Vol. 79, No. 1, pp. 17-22.

doi: 10.1524/teme.2012.0173

A modular sensor concept for various gas measurement applications requiring high sensitivity and fast response time is presented. The proposed differential photoacoustic detection combines the selectivity of the traditional absorption method and the high sensitivity of the novel cantilever enhanced photoacoustic detector. High precision is achieved using short optical path length resulting in fast response time and wide dynamic measurement range. An example realization for greenhouse gas flux measurement is presented.

Read More: http://www.oldenbourg-link.com/doi/abs/10.1524/teme.2012.0173

Keywords: photoacoustic, gas detection, greenhouse gas flux, cantilever sensor, leak detection