A Miniaturized Contactless UWB Microwave System for Time-Domain Dielectric Spectroscopy

A miniaturized time-domain (TD) dielectric spectroscopy system for contactless material characterization over the ultra-wideband (UWB) microwave range is presented in this paper. The proposed system includes a transmitter, a compact contactless sensing unit, and a receiver. A picosecond pulse generator unit in the transmitter delivers a quasi-monocycle pulse with 3.5-GHz 10-dB bandwidth to an up-converter and then an amplifier. The generated pulse provides the capability to perform the material characterization in a fast pure TD fashion. The transmitter unit provides the 3-10-GHz excitation pulse based on utilizing a direct up-conversion architecture. The excitation pulse is transmitted to the receiver through the sensing unit. Two Vivaldi antennas are coupled to each other in their radiative near field to construct the sensing unit, while the material-undertest (MUT) is placed in between. A custom-designed Quartz-Glass cuvette is utilized with optimized MUT volume of -.5 mL. The TD data are captured for each MUT using DSA91304A infiniium oscilloscope as the receiver, and finally the fast Fourier transform of the measured data is extracted in MATLAB. A calibration procedure is discussed to achieve a behavioral model of the system using seven calibration MUTs. From there, the ε' and ε'' characterization of three unknown MUTs are carried out. The system shows the worst case mean-squared error (MSE) of 1.92% for ε' and 3.84% for ε'' characterization. Furthermore, binary mixture detection based on E' accomplished with the MSE of 2.74%.