OOK Harmonic Rectifier-Modulator for Self-Aligning Wireless IoT Sensor Nodes With Uncompromised Efficiency

This paper presents a harmonic based on-off keying (OOK) rectifier-modulator (HRM) for energy efficient battery-less self-aligning wireless sensor nodes. The proposed HRM efficiently converts the incident fundamental power to DC and simultaneously backscatters an OOK-modulated second-harmonic (2f0) signal, thereby enabling straightforward localization and data communication with the wireless power transfer (WPT) transmitter. The OOK harmonic control network (HCN) modulates the 2f0f signal without disturbing the diode’s fundamental-band impedance, thus maintaining high power conversion efficiency (PCE). Fabricated on a 0.79-mm Taconic TLC-32 substrate, the prototype preserves virtually identical peak PCEs of 72.7% and 73.8% for the ON and OFF states, respectively, at 27 dBm input and achieves conversion gains (CG) of −11.1 dB at 11 dBm, respectively. A measured on-off isolation of 23 dB, exceeding 10 dB at 2.3–2.6 GHz, confirmed robust OOK modulation. System-level tests with patch antennas at 2.45/4.9 GHz further verified stable direct current (DC) harvesting and harmonic backscatter under spatial misalignments, demonstrating a compact passive solution that merges high efficiency energy harvesting with self-beam alignment in practical WPT links. These features make the tag suitable for distributed wireless IoT sensor nodes, for which battery replacement is impractical.