Time-Domain Dielectric Spectroscopy Using a Miniaturized Contact-Based UWB System

This paper presents a miniaturized contact-based system for dielectric spectroscopy using time-domain (TD) technique in ultrawideband (UWB) frequency range. The system consists of a miniaturized UWB transmitter, a planar sensor having direct contact with a liquid material under test (MUT), and a high-speed oscilloscope receiver. In the transmitter, a baseband (BB) pulse with 3.5-GHz bandwidth is generated from a square-wave input signal by employing a step recovery diode and a short-circuited stub. Then, the BB pulse is upconverted by a UWB mixer with 6.5-GHz local oscillator frequency, creating a 3-10-GHz passband pulse. After being amplified, the passband pulse excites the miniaturized sensor, including two stages of microstrip open-circuited stub between meander inductors. This sensor has a small area, requires only 0.3 μL of liquid MUT for accurate sensing, and responds to both ε' and ε" properties. The sensor output is captured by the oscilloscope in TD and then converted to frequency domain (FD) by the fast Fourier transform operation. Considering ε' and ε" of MUT simultaneously affect both phase and magnitude of output signal in FD, the behavior of the system is described by testing 12 reference MUTs. From the behavioral model of the system, three unknown MUTs are characterized with errors less than 0.1|ε*| in both ε' and ε" from 3.28 to 10 GHz.