Analysis and Design of a New Material Sensor Utilizing an Oscillator with a Self-Injection Loop

We present an analysis and design methodology for high-sensitivity material sensors, based on the connection of a long-delay self-injection loop to an existing oscillator. The delay and attenuation of the loop are tuned to ensure that the oscillator operates near a cusp bifurcation, enabling a steep slope with respect to the sensing parameter. The analysis employs a nonlinear semi-analytical formulation capable of predicting the complete evolution of solution curves as the attenuation in the self-injection loop is reduced. In addition, we present a new stability analysis method, which solves the semi-analytical characteristic determinant in terms of a complex frequency. The methods have been applied to the design of an oscillator sensor at 2.4 GHz.