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Vol: 54(68) No: 4 / December 2009 Square Wave Generator with DC Control for High-field Asymmetric Ion Mobility Spectrometers (FAIMS) C. Feştilă Technical University of Cluj-Napoca, Department of Automation, Cluj-Napoca, Romania, e-mail: Clement.Festila@aut.utcluj.ro E. H. Dulf Technical University of Cluj-Napoca, Department of Automation, Cluj-Napoca, Romania, e-mail: Eva.Dulf@aut.utcluj.ro R. Cordos Technical University of Cluj-Napoca/ Department of Management and System Engineering, Cluj-Napoca, Romania, e-mail: Roxana.Cordos@mis.utcluj.ro Keywords: square wave generator, DC control, High-field Asymmetric Ion Mobility Spectrometers. Abstract The problem of ion separation or ion detection has applications in many fields, like: nuclear technology, detection of contraband products and explosives, security and military domain. There are two categories of devices able to separate /detect some species of ions: with weak and with strong electric field. In weak electric field, the ratio of the ion-speed (v) over the electric field strengths (E) in a transport (drift) gas at atmospheric pressure has a typical value for each ion with the given mass (m) and electric charge (e). This ratio, known as mobility (K) can be measured using the “time of flight (t*)” over a given distance (d*) and by a constant field level (E*). Reciprocal, if a certain time of flight was found, that indicates the presence of some substance, even by very small concentration in transport gas. By stronger electric field, mobility (K) changes drastically, rising in high level of field. If a ion is carried through the plates of a small capacity, using a drift (transport) gas, an AC voltage applied to the plate of the capacitor moves the ion to one plate or to other, alternating the direction of the speed. If the positive and negative maxima of the voltage (at the same time period) are different, a ion motion toward one plate or other is generated and the ion is neutralized, so the AC electrical field is called “dissipative voltage DV”. Another DC smaller voltage: the “compensation voltage CV” may ensure the avoidance of the plate contact and the ion may traverse the plate distance. Of course, only the ion with certain physical properties – hence belonging to the certain substance – may pass, giving a small ion current. The paper deals with the possibility to generate the dissipative and compensation field in accord to some performance specifications: accuracy, energetic efficiency, etc. A lot of performance specifications can be fulfilled only by the use of a closed loop control system. References [1] R. Guevremont, High-field Asymmetric Waveform Ion Mobility Spectrometry, Canadian Journal of Analytical Science and Spectroscopy, pp.105-113, 2004. [2] B. V. Bocos-Bintintan Modern Techniques in Trace-Analysis, (in Romanian), Universitar-Press, Cluj, 2004. [3] E. V. Krylov, “Differential Mobility spectrometer: model of operation”, Mass Spectrometry International Journal, 266, pp.76-85, 2007. [4] R. C. Dorf, R. Bishop, Modern Control Systems, Pearson Prentice Hall, 2005. [5] Cl. Festila, Power Electronics in Automatic Control, Mediamira Publishing House, Cluj-Napoca, 2003. |