Analysis and Design of Material Sensors based on Free-Running and Injection-Locked Oscillators

We present novel topologies and analysis procedures for permittivity sensors based on oscillator circuits, operating in both free-running and injection-locked conditions. We analyze the sensing capabilities of oscillators using step-impedance resonators and slow-wave structures, influenced by the material under test (MUT). These structures are connected to the oscillator’s active core, modeled through a numerical nonlinear admittance function extracted from harmonic-balance (HB) simulations. The goal is to achieve high sensitivity with low phase-noise spectral density. When introducing an input signal, the locking band varies with the MUT. This band will be calculated with the aid of a nonlinear current function, obtained through HB. We introduce an innovative system driven by a chirped signal and an injection-locked dual-frequency sensor to enhance robustness. Very good agreement is obtained between simulations and measurements.