P20 - Split-Ring Resonator for measuring low amounts of glutamic acid in pure water
- Event
- 16. Dresdner Sensor-Symposium 2022
2022-12-05 - 2022-12-07
Dresden - Band
- Poster
- Chapter
- Umweltsensorik
- Author(s)
- K. Dehning, A. Gossmann, M. Hitzemann, S. Zimmermann - Leibniz University Hannover, Hannover/D
- Pages
- 132 - 135
- DOI
- 10.5162/16dss2022/P20
- ISBN
- 978-3-9819376-7-1
- Price
- free
Abstract
SRRs are very sensitive to changes in the dielectric properties of a sample at the split capacitor that sets the resonant circuit and can be used as sensitive detectors to measure the properties of liquids. For highest sensitivity, the split capacitor needs to be as large as possible in relation to the parasitic capacitances. Therefore, we use an interdigital finger structure to increase the split capacitance. In addition to the resonance frequency, which is affected by the properties of the split capacitor dielectric and thus the sample at the split capacitor, the attenuation and quality factor, respectively, is also a measure for any sample induced polarization and ohmic losses. Without any liquid sample covering the sensitive region of the SRR, the attenuation mainly depends on the coupling between the two microstrip lines, the losses in the used PCB material (mainly polarization losses), FR4 or Rogers, and on the geometry and material (ohmic losses) of the used microstrip lines. Another effect to be considered is the frequency- dependent skin effect. Due to the skin effect, the ohmic losses in any conductor increase with increasing frequency. At higher frequencies, the conducting cross section of the conductor reduces and the electric current concentrates near the surface. For SRRs, this needs to be considered when the used resonance frequency increases with reduced ring dimensions. For a real measured SRR with an geometric ring length of 48 mm, which corresponds to a SRR resonance frequency of approximate 1.2 GHz (without considering the capacitive extension of the ring length), the skin depth can be calculated with equation 4 with