A Novel Cross-Capacitive Sensor for Noncontact Microdroplet Detection

In this paper, a novel capacitive sensor for noncontact microdroplet detection has been developed and tested successfully. For an accurate and highly repeatable droplet detection, the sensor makes use of a cross-capacitive structure, which is an extension of the Thompson and Lampard theorem. The sensor consists of four identical copper electrodes with infinitesimally small gaps etched out of double-sided copper-cladded polyimide substrate by screen printing and chemical etching process. The sensor prototype has been tested for different sizes of the droplets as well as the droplets from liquids having different dielectric constants and conductivities. The response characteristics of the presented sensor are very accurate, significant, fast, highly repeatable (±0.13%), and drift free. The achieved characteristics of the presented sensor are suitable for employing it for the noncontact microdroplet detection.

[1]  R. Zengerle,et al.  Non-contact optical sensor to detect free flying droplets in the nanolitre range , 2010 .

[2]  H. Le,et al.  Progress and Trends in Ink-jet Printing Technology , 1998, Journal of Imaging Science and Technology.

[3]  Mark A Burns,et al.  Electronic drop sensing in microfluidic devices: automated operation of a nanoliter viscometer. , 2006, Lab on a Chip.

[4]  Roland Zengerle,et al.  A capacitive sensor for non-contact nanoliter droplet detection , 2009 .

[5]  M Rehman,et al.  A novel precision type liquid conductivity measuring system , 1985 .

[6]  F. N. Toth,et al.  A low-cost, stable reference capacitor for capacitive sensor systems , 1996 .

[7]  Pelin Kubra Isgor,et al.  Microfluidic droplet content detection using integrated capacitive sensors , 2015 .

[8]  Paul J. A. Kenis,et al.  Multiplexed electrical sensor arrays in microfluidic networks , 2009 .

[9]  Mart Min,et al.  Contactless sensing of the conductivity of aqueous droplets in segmented flow , 2011 .

[10]  Ferran Reverter,et al.  Interfacing Differential Capacitive Sensors to Microcontrollers: A Direct Approach , 2010, IEEE Transactions on Instrumentation and Measurement.

[11]  William P. Winn.  An Electrostatic Theory for Instruments which Measure the Radii of Water Drops by Detecting a Change in Capacity Due to the Presence of a Drop , 1968 .

[12]  Christoph A. Merten,et al.  Droplet-based microfluidic platforms for the encapsulation and screening of Mammalian cells and multicellular organisms. , 2008, Chemistry & biology.

[13]  Mahfoozur Rehman,et al.  Effect of a symmetrically placed dielectric tube on the capacitance of a cylindrical cross-capacitor , 1982 .

[14]  Tarikul Islam,et al.  A time domain bridge-based impedance measurement technique for wide-range lossy capacitive sensors , 2015 .

[15]  Hongsheng Song,et al.  A droplet-based microfluidic electrochemical sensor using platinum-black microelectrode and its application in high sensitive glucose sensing. , 2014, Biosensors & bioelectronics.

[16]  Yu. P. Semenov,et al.  Precise measurement of the dielectric constants of liquids using the principle of cross capacitance , 2001, IEEE Trans. Instrum. Meas..

[17]  J. Carletta,et al.  Capacitive Coulter counting: detection of metal wear particles in lubricant using a microfluidic device , 2009 .

[18]  W. Heerens.  Application of capacitance techniques in sensor design , 1986 .

[19]  Songjing Li,et al.  Electrical-detection droplet microfluidic closed-loop control system for precise droplet production , 2017 .

[20]  V.G.K. Murti,et al.  An extension and application of the Thompson-Lampard theorem , 1981, Proceedings of the IEEE.

[21]  Q. Fang,et al.  Analytical detection techniques for droplet microfluidics--a review. , 2013, Analytica chimica acta.

[22]  Tarikul Islam,et al.  An Oscillator-Based Active Bridge Circuit for Interfacing Capacitive Sensors With Microcontroller Compatibility , 2016, IEEE Transactions on Instrumentation and Measurement.

[23]  Philippe Schmitt-Kopplin,et al.  The dosage of small volumes for chromatographic quantifications using a drop-on-demand dispenser system , 2007, Analytical and bioanalytical chemistry.

[24]  A. M. Thompson,et al.  A New Theorem in Electrostatics and its Application to Calculable Standards of Capacitance , 1956, Nature.

[25]  A. M. Thompson.  The cylindrical cross-capacitor as a calculable standard , 1959 .

[26]  Mahfoozur Rehman,et al.  A Novel Humidity Sensor Based on the Extension of Thompson and Lampard Theorem , 2015, IEEE Transactions on Electron Devices.

[27]  N. Gavish,et al.  Dependence of the dielectric constant of electrolyte solutions on ionic concentration: A microfield approach. , 2012, Physical review. E.

[28]  Bernd Henning,et al.  Monitoring of droplet growth with nano-litre resolution for liquid flow rate, level or surface tension measurement , 2004 .

[29]  Caglar Elbuken,et al.  Detection of microdroplet size and speed using capacitive sensors , 2011 .