Tomislav Markovic

Microwave heater at 20 GHz for nanoliter scale digital microfluidics

This paper proposes an optimized microwave heater at 20 GHz for nanoliter scale liquid samples in digital microfluidics. The developed measurement setup allows translating of the reflection coefficient of the heater to the temperature change of the water droplet via the temperature dependency of the liquid permittivity, thus avoiding a contact-based temperature measurement. Measurements have been carried out on pure water samples of 500 nL at power levels of 20 and 23 dBm at the probe tips. The measured data agrees very well with multiphysics simulation data. Heating performance has been characterized and high temperature gradients of 30 deg. C per second have been measured.

Temperature controlled measurement setup for permittivity extraction of water up to 40 GHz from 10 to 40 °C

The proposed system in this paper enables the temperature controlled permittivity extraction of liquids up to 40 GHz from 10 to 40 °C. The temperature controlled environment consists of a temperature controlled chuck, probe station and a CPW microwave sensor that is coupled to a miniature T-type thermocouple. A large thermal mass and a platinum wire resistor ensure a precise reference temperature. Challenges in the sensor fabrication and measurements are discussed and further improvements are proposed for higher accuracy measurements. Extracted permittivity of water agrees well with the empirical models available in the literature.

Broadband dielectric spectroscopy calibration using calibration liquids with unknown permittivity

This paper presents a calibration method for broadband dielectric spectroscopy of micro-liter samples of biological liquids with transmission line sensors up to 110 GHz. The method uses water and methanol as calibration liquids to perform a probe-tip-to-liquid calibration without prior knowledge of their complex permittivity. Extracted complex permittivities of the calibration liquids show good agreement with literature values. Furthermore, sensors with different first-tier calibrations and geometries show consistent results.

A 20 GHz microwave heater for digital microfluidic

This paper reports on a microwave heater at 20 GHz for digital microfluidics. It allows rapid heating of nanoliter fluid samples and simultaneous temperature monitoring by correlating the reflection coefficient of the heater with the temperature dependency of the relative permittivity of the lossy fluid under consideration, in this case demineralized water. Microwave heating was performed with power levels of 20 and 23 dBm at the on-wafer probe tips on samples of 500 nL. Temperature measurements were carried out with a miniaturized type K thermocouple, and a platinum resistor to monitor the reference temperature. Microwave and thermal performances have been characterized using multi-physics software, and measurements obtained with a large signal vector network analyzer showed good agreement with simulated data. An average heating rate of 20 °C/s was observed during the first 4 s of the heating process.

Uniplanar microwave heater for digital microfluidics

This paper reports on a 4 GHz microwave droplet heater for digital microfluidics. The uniplanar device was fabricated using a gold-on-quartz process and was optimized for uniform heating within a 1 μL droplet. Microwave measurements show excellent agreement with COMSOL simulations. The uniformity of the induced temperature within the droplet was experimentally validated using fluorescence microscopy using a temperature sensitive fluorophore.

Investigation of thermal effect caused by different input power of biosensor using a novel microwave and optical sensing system for biological liquids

In this paper, we present a novel measurement system combining microwave vector network analysis with high-speed multi-channel fluorescence microscopy. Microwave and fluorescent measurement of 1 mM rhodamine B water solution was accomplished simultaneously with our system. No thermal effect was observed using the temperature dependent fluorescence of rhodamine B when the input power of the device varies from −21.99 dBm to 4.90 dBm. This novel system will enable us to correlate microwave and optical methods for biological characterization.

Characterization of a novel microwave heater for continuous flow microfluidics fabricated on high-resistivity silicon

This paper presents a novel coplanar waveguide transmission line microwave heater, realized on a high-resistivity silicon wafer with etched microfluidic channels that is bonded to a glass wafer. The heater is a 50 Ohm line with variable attenuation constant along the length of the line. This design results in a uniform energy dissipation in water filled channels, and obviates the need for additional matching structures. The heater was measured around the 25.5GHz design frequency and the obtained S21 data agree to within 0.04 dB with COMSOL Multiphysics simulations for liquid temperatures from 20 to 50 °C.

A bottom-up cell modeling strategy using broadband microwave and millimeter wave dielectric spectroscopy

In this paper we introduce a bottom-up microwave and millimeter wave modeling strategy for membrane bound biological systems. The approach is based on the stepwise integration of bulk liquid and membrane dielectric spectroscopy data into 3D biophysical models that are amenable to efficient electromagnetic computation. The purpose of this modeling effort is to develop more understanding of microwave electric field interactions with biological systems from a molecular biology point of view. The proposed strategy allows the systematic study of dielectric interactions within increasingly more complex membrane bound biological systems.