  The next generation of ultra-dense connected and automated wireless sensor
networks (WSN) requires proximity intelligence for many of its applications,
especially for identification and localization. This work presents the first
bidirectional circuitry for Internet of Things (IoT) transponder that
reciprocally generates harmonics and subharmonics, dual-band frequencies. A
multi-band or wideband localization system is essential for future intelligent
WSN to mitigate the influence of multipath signals for indoor dense
environment. The proposed frequency generation circuitry is based on the novel
nonlinear ring resonator (NRR) operating based on standing wave resonation. The
proposed NRR generates two sustainable oscillation frequencies based on the
periodicity of the nonlinear circuit in the ring configuration. Due to the
symmetry and reciprocity of the ring layout, the two bidirectional ports can
excite the circuit at the two opposite nodes while maintaining the required
boundary conditions for oscillation. The sustainable resonance conditions occur
by creating zero, short impedance, or pole, infinite impedance, at subharmonic
and harmonic excitation ports. The NRR circuit consumes zero DC power and
covers two communication frequency plans interchangeably, which makes it a
premier technique compared to the conventional ultra-wideband (UWB)
localization system and conventional single-band nonlinear passive circuitry.
The latter is narrowband due to the tunning limitation of the nonlinear
varactor while the former is power-hungry approach with complex hardware
requirements.
