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| The '''Sauerbrey equation''' was developed by G. Sauerbrey in 1959 as a method for correlating changes in the oscillation frequency of a [[piezoelectric]] [[crystal]] with the mass deposited on it. He simultaneously developed a method for measuring the characteristic frequency and its changes by using the crystal as the frequency determining component of an oscillator circuit. His method continues to be used as the primary tool in [[quartz crystal microbalance]] experiments for conversion of frequency to mass and is valid in nearly all applications. | | The author's title is Andera and she believes it sounds quite good. He is an information officer. Ohio is where her home is. It's not a typical thing but what she likes doing is to perform domino but she doesn't have the time recently.<br><br>Feel free to visit my webpage ... [http://www.youronlinepublishers.com/authWiki/AdolphvhBladenqq are psychics real] |
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| The equation is derived by treating the deposited mass as though it were an extension of the thickness of the underlying quartz.<ref name="Sauerbrey">{{Citation
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| | last = Sauerbrey
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| | first = Günter
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| | title = Verwendung von Schwingquarzen zur Wägung dünner Schichten und zur Mikrowägung
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| | journal = Zeitschrift für Physik
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| | volume = 155
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| | issue = 2
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| | pages = 206–222
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| |date=April 1959
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| | doi = 10.1007/BF01337937 |bibcode = 1959ZPhy..155..206S }}</ref>
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| <ref name="QCM">QCM100 – Quartz Crystal Microbalance Theory and Calibration, Stanford Research Systems.</ref> Because of this, the mass to frequency correlation (as determined by Sauerbrey’s equation) is largely independent of electrode geometry. This has the benefit of allowing mass determination without calibration, making the set-up desirable from a cost and time investment standpoint.
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| The Sauerbrey equation is defined as:
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| :<math>\Delta f = -\frac{2f_0^2}{A \sqrt{ \rho_q \mu_q } }\Delta m</math>.
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| Equation 1 – Sauerbrey’s equation
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| :<math>f_0</math> – [[Resonant frequency]] (Hz)
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| :<math> \Delta f</math> – Frequency change (Hz)
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| :<math> \Delta m </math> – Mass change (g)
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| :<math> A </math> – [[Piezoelectric effect|Piezoelectrically]] active crystal area (Area between electrodes, cm<sup>2</sup>)
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| :<math> \rho_q</math> – [[Density]] of quartz (<math> \rho_q</math> = 2.648 g/cm<sup>3</sup>)
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| :<math> \mu_q </math> – [[Shear modulus]] of quartz for AT-cut crystal (<math> \mu_q </math> = 2.947x10<sup>11</sup> g/cm.s<sup>2</sup>)
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| Because the film is treated as an extension of thickness, Sauerbrey’s equation only applies to systems in which the following three conditions are met: the deposited mass must be rigid, the deposited mass must be distributed evenly and the frequency change <math> \Delta f /f </math> < 0.02.<ref>A. K. Srivastava and P. Sakthivel, J. Vac. Sci. Technol. A 19(1),97-100 Jan/Feb 2001</ref>
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| If the change in frequency is greater than 2%, that is, <math> \Delta f /f </math> > 0.02, the Z-match method must be used to determine the change in mass.<ref name="QCM"/>
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| The formula for the Z-match method is:<ref name="QCM"/>
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| :<math> \frac{\Delta m}{A}\ = \frac{N_q \rho_q}{\pi Z f_L}\tan^{-1} \left [ Z\tan \left ( \pi \frac{f_U-f_L}{f_U} \right ) \right ] </math>
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| Equation 2 – Z-match method
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| :<math> f_L </math> – Frequency of loaded crystal (Hz)
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| :<math> f_U </math> – Frequency of unloaded crystal, i.e. Resonant frequency (Hz)
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| :<math> N_q </math> – Frequency constant for AT-cut quartz crystal (1.668x10<sup>13</sup>Hz.Å)
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| :<math> \Delta m </math> – Mass change (g)
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| :<math> A </math> – Piezoelectrically active crystal area (Area between electrodes, cm<sup>2</sup>)
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| :<math> \rho_q </math> – Density of quartz (<math> \rho_q </math> = 2.648 g/cm<sup>3</sup>)
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| :<math> Z </math> – <math> Z = \sqrt{ \left ( \frac{\rho_q\mu_q}{\rho_f\mu_f}\ \right ) } </math>
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| :<math> \rho_f </math> – Density of the film (Varies: units are g/cm<sup>3</sup>)
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| :<math> \mu_q </math> – Shear modulus of quartz (<math> \mu_q</math> = 2.947x10<sup>11</sup> g/cm.s<sup>2</sup>) | |
| :<math> \mu_f </math> – Shear modulus of film (Varies: units are g/cm.s<sup>2</sup>)
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| == Limitations ==
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| The Sauerbrey equation was developed for oscillation in air and only applies to rigid masses attached to the crystal. It has been shown that quartz crystal microbalance measurements can be performed in liquid, in which case a [[viscosity]] related decrease in the resonant frequency will be observed:
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| :<math>\Delta f = { -\ f_0^{3/2} ( \eta_l \rho_l / \pi \rho_q \mu_q )^{1/2} } </math>
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| where <math>\rho_l</math> is the density of the liquid and <math>\eta_l</math> is the viscosity of the liquid (Kanazawa and Gordon 1985).
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| ==References==
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| {{reflist}}
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| ==Further reading==
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| * K.K. Kanazawa and J.G. Gordon, Analytical Chemistry, '''57'''(1985) 1770-1771
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| [[Category:Electrical phenomena]]
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| [[Category:Transducers]]
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| [[Category:Weighing instruments]]
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