Abstract
This paper describes a low cost, passive wireless dielectric constant and conductivity sensor using a microfabricated inductor with interdigitated capacitors (IDC). A self-resonant-structure (SRS) is designed by incorporating IDC electrodes in the inter-winding space of the inductor. The distributed capacitance and conductance of the sensor is affected by dielectric constant (ε) and conductivity (σ) of its environment or material under test (MUT). The ε and σ can be used to provide information about the surrounding environment. This serves as an impedance transducer changing the resonant frequency and phase dip of the SRS. The SRS is interrogated using a non-contact inductively coupled reader coil. The change in resonance frequency and phase dip of the SRS is used to detect material properties of the environment/MUT. The relationship between sensor layout and coupling factor between sensor and reader is investigated. Optimizations of the coupling factor based on this relationship are discussed. IDC design trade-offs between the sensor’s sensitivity and coupling factor are also investigated. The sensor’s response to variety of liquid MUTs with a wide range of dielectric constant and conductivity is presented.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Andringa M, Puryear J, Neikirk D, Wood S (2006) Low-cost wireless corrosion and conductivity sensors. Proc SPIE 6174:282–290
FastHenry, http://www.fastfieldsolvers.com/
Gevorgian S, Martinsson T, Linnkr P, Kollberg EL (1996) CAD models for multilayered substrate interdigital capacitors. IEEE Trans Microw Theory Tech 44(6):896–904
Greenhouse H (1974) Design of planar rectangular microelectronic inductors. IEEE Trans Parts Hybrids Packag 10(2):101–109
Igreja R, Dias CJ (2004) Analytical evaluation of the interdigital electrodes capacitance for a multi-layered structure. Sens Actuators A 112:291–301
Kim J, Pasupathy P, Zhang S, Neikirk DP (2009) Measurement of liquid complex dielectric constants using non-contact sensors. IEEE Sensors Conference, 2017–2020. http://dx.doi.org/10.1109/ICSENS.2009.5398291
Mamishev AV, Sundara-Rajan K, Fumin Y, Du Y, Zahn M (2004) Interdigital sensors and transducers. Proc IEEE 92(5):808–845
Mohan SS, del Mar Hershenson M, Boyd SP, Lee TH (1999) Simple accurate expressions for planar spiral inductances. IEEE J Solid State Circuits 34(10):1419–1424
Ong KG, Grimes CA, Robbins CL, Singha RS (2001) Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor. Sens Actuators A 93:33–43
Pausupathy P (2010) Coupled passive resonant circuits as battery-free wireless sensors, PhD dissertation, Department of Electrical and Computer Engineering, The University of Texas at Austin
Yue C, Wong S (2000) Physical modeling of spiral inductors on silicon. IEEE Trans Electron Devices 47(3):560–568
Yvanoff M, Venkataraman J, Fuller L (2008) Impact of multiple tissue layers on an implantable LC sensor. Microw Opt Techn Lett 50(3):783–787
Acknowledgments
This work was supported by the Advanced Energy Consortium. Member companies include BP America Inc., Baker Hughes Inc., ConocoPhillips, Halliburton Energy Services Inc., Marathon Oil Corp., Occidental Oil and Gas, Petrobras, Schlumberger, Shell, and Total. Device fabrication at the UT Microelectronics Research Center was partially supported by the NSF National Nanotechnology Infrastructure Network.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Zhang, S., Pasupathy, P. & Neikirk, D.P. Microfabricated self-resonant structure as a passive wireless dielectric constant and conductivity sensor. Microsyst Technol 18, 885–891 (2012). https://doi.org/10.1007/s00542-011-1403-y
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00542-011-1403-y