This paper presents a fully reconfigurable and reliable PXIe-567X software defined interrogation signal generator for SAW-based passive RFID. Contrary to most commercial SAW RFID readers that operate only at a unique predefined frequency, the proposed Vector Signal Generator is aimed to operate at any frequency defined by the user, from 85 MHz to 6.6 GHz, including the 902 MHz -928 MHz and 2.45 GHz ISM bands. The PXIe-567X-based signal generator can accurately generate not only conventional OOK modulated or "pulsed BPSK" modulated SAW RFID interrogation signals, but also completely user-defined interrogation signals. A custom LabVIEW user interface that allows to control the carrier frequency, the power and the waveform of the interrogation signal has been designed. The operator can switch between custom waveforms without resetting and reprogramming the whole system. The proposed RFID request signal generator has been validated using a complete measurement setup. Time domain and frequency domain validation tests of OOK modulated and wideband "pulsed BPSK" modulated signal generation have been conducted at 170 MHz, 340 MHz, 915 MHz and 2.45 GHz. Very accurate results have been obtained. The PXIe-567X-based RFID interrogator has been tested with a fabricated 3-bit SAW RFID tag. The operability of the entire SAW RFID system has been demonstrated.
In this work, a novel microwave sensor fully based on Substrate Integrated Waveguide (SIW) technology filled with nanofibrillated cellulose for humidity detection is presented for the very first time. The proposed structure consists of a circular SIW cavity resonator perturbed by the inclusion of nano-fibrillated cellulose inside the cavity. Due to the presence of humidity, the relative permittivity of the eco-friendly dielectric, which is known as a humidity sensitive material, changes, leading to a shift of the resonance frequency of the Substrate Integrate Cavity Circular Resonator (SICCR). The proposed humidity sensor structure operates between 4.28 to 4.32 GHz and exhibits a frequency shift of around 20 MHz for relative humidity in the range of 11.7% to 91% RH. The proposed sensing device operates with very low-cost sustainable and renewable material, is simple to manufacture, co-integrates with existing microwave planar circuits and has the advantage of demonstrating high sensitivity performance.
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