Limited sensitivity and sensing range are arguably the greatest challenges in microwave sensor design. Recent attempts to improve these properties have relied on metamaterial (MTM)-inspired open-loop resonators coupled to transmission lines (TLs). Although the strongly resonant properties of the resonator sensitively reflect small changes in the environment through a shift in its resonance frequency, the resulting sensitivities remain ultimately limited by the level of coupling between the resonator and the TL. This paper introduces a novel solution to this problem that employs negative-refractive-index TL MTMs to substantially improve this coupling so as to fully exploit its resonant properties. A MTM-infused planar microwave sensor is designed for operation at 2.5 GHz, and is shown to exhibit a significant improvement in sensitivity and linearity. A rigorous signal-flow analysis of the sensor is proposed and shown to provide a fully analytical description of all salient features of both the conventional and MTM-infused sensors. Full-wave simulations confirm the analytical predictions, and all data demonstrate excellent agreement with measurements of a fabricated prototype. The proposed device is shown to be especially useful in the characterization of commonly available high-permittivity liquids as well as in sensitively distinguishing concentrations of ethanol/methanol in water.

This paper presents a novel dual-band microstrip patch antenna that employs a metamaterial-based electromagnetic bandgap (MTM-EBG) integrated into its radiating edges to support two distinct operating frequencies. The resulting antenna is compact, uniplanar, completely printable, and via-free. Dispersion engineering of the MTM-EBG unit cell through a rigorous multiconductor transmission-line analysis allows simple, systematic design for two or more arbitrary frequencies. Additionally, a novel approach is taken to employ the same MTM-EBG to impedance-match the antenna to an inset microstrip feed at both operating frequencies. A dual-band MTM-EBG antenna designed to radiate at 2.4 and 5.0 GHz is simulated and tested, and experimental results demonstrate radiation performance comparable to the corresponding conventional patch antennas in excellent agreement with simulations, while also affording some degree of miniaturization at lower frequencies.

In this article, a novel batteryless wireless sensor design is proposed and demonstrated. The proposed passive wireless sensor node integrates a ultrahigh-frequency (UHF) radio-frequency identification (RFID) chip, a filter, and a reactive sensor to enable the reading of environmental conditions wirelessly, without increasing the complexity of a typical RFID chip and substantial loss of the read range. The sensor changes the phase of the reflected RFID signal based on the sensed parameter; whereas, the filter helps in resolving any phase ambiguity that may arise due to the placement of the node at different distances. The phase change is detected at the reader using a noncoherent IQ demodulator. The design can easily integrate any type of sensors, such as temperature, humidity, and water-level sensor. A flood sensor and a temperature sensor were used to demonstrate the performance of the proposed design in a home and office environment.

We present a survey on battery-less Radio Frequency Identification (RFID-based wireless sensors that have emerged in the past several years. We discuss the evolution of RFID turning into wireless sensors. Moreover, we talk about different components of these battery-less RFID-based wireless sensors, five main topologies that transform a simple RFID chip into a battery-less wireless sensor, and state-of-the-art implementations of these topologies. In battery-less wireless sensors, the read range is of key importance. Hence, we discuss how each component of the sensor plays its role in determining the read range and how each topology exploits these components to optimize read range, complexity, and/or cost. Additionally, we discuss potential future directions that can help provide improvements in RFID-based wireless sensor technology.

This work presents the design and fabrication of a novel uniplanar microstrip patch antenna that is simultaneously dual-band and dual-polarized. By embedding a carefully designed metamaterial-based electromagnetic bandgap structure (MTM-EBG) into the edges of a conventional square patch, operation with orthogonal linear polarizations at both 3.6 GHz and 5.8 GHz is achieved. The design is fully printed, compact, low-profile, and pin-fed using a shielded microstrip configuration, and it is 17% smaller than a conventional square patch at the lower operating frequency. The presented antenna shows a reflection coefficient better than -16 dB at each frequency and over 24 dB of port-to-port isolation. Radiation patterns are patch-like in both operating bands, with broadside gains of 6.4 dBi and 5.3 dBi at the lower and higher operating frequencies, respectively. The antenna is fabricated using conventional PCB manufacturing methods, and measurement results are in very good agreement with simulations.

A novel miniaturized printed folded dipole antenna has been designed for narrowband sensing applications. It is shown that the antenna may be systematically engineered to achieve matching to a practical source impedance at frequencies well below its half-wavelength resonance using series-LC loading and asymmetrical arm widths. This approach is used to design an inherently well-matched antenna that does not require an external matching network and demonstrates approximately 75% miniaturization, excellent co- to cross-polarization separation, over 24 dB higher realized gain, and strongly improved radiation efficiency relative to an unloaded folded dipole of the same electrically small size. Experimental validation of a fabricated prototype demonstrates excellent agreement with simulations.