Cantilever enhanced photoacoustic spectroscopy enables the detection of small amount of
trace gases which is vital in many applications.
Photoacoustic spectroscopy is one of the most sensitive optical detection schemes. It is based on detecting a gas specific
acoustic wave
Acoustic waves are a type of energy propagation through a medium by means of adiabatic loading and unloading. Important quantities for describing acoustic waves are acoustic pressure, particle velocity, particle displacement and acoustic intensit ...
generated that originates from the absorption of light in the medium. The sensitivity of the traditional membrane microphones is limited by electrical noise and the nonlinearity of the displacement of the mechanical sensor at high optical power levels. Conventional membrane microphones can be replaced with optically measured micromechanical cantilevers to enhance sensitivity.
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Characteristics
The novel MEMS cantilever approach detects pressure changes in a photoacoustic cell. High sensitivity is achieved by using a cantilever pressure sensor that is over hundred times more sensitive compared to a membrane, which is conventionally used in photoacoustic spectroscopy. A laser-based readout interferometer is able to accurately measure displacement from well under a
picometer up to
millimeters
330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter.
The millimetre (American and British English spelling differences#-re, -er, ...
.
Technology
An extremely thin
cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
portion moves like a flexible door due to the pressure variations in the surrounding gas. The displacement of the cantilever is measured with an accurate interferometric readout system. This way the "breathing effect" can be avoided. The so-called breathing effect occurs in capacitive measurement principle where the other electrode damps the movement of the sensor and restricts the dynamic range.
Cantilever sensor
The cantilever sensor is made out of single crystal SOI-silicon with a specially developed
dry-etching process that leads to a highly stable and robust component; this is why the sensor is practically totally immune to temperature and humidity variations. In addition, the sensor does not suffer from wearing. The sensor and readout can be isolated in terms of temperature allowing heated gas cell which enables applications that require gas analysis at elevated temperatures such as chemical emissions monitoring and process control.
Applications
Cantilever enhanced photoacoustics measuring technology can be used e.g. in detection and analysis of gases, liquids, and solid materials in applications of research, industry, environmental, safety, and security.
[{{Cite web, url=http://www.gasera.fi/technology/, title=Photoacoustic spectroscopy - Gasera, website=Gasera, language=en-US, access-date=2016-06-22]
References
Spectroscopy