Recent Advances and Applications of Passive Harmonic RFID Systems: A Review.

Harmonic Radio Frequency Identification (RFID) systems have attracted significant interest over the last decade as it provides many benefits over the conventional RFID systems. Harmonic RFID is desired over conventional RFID systems due to reduced self-jamming, location accuracy from dual frequency, and higher phase noise immunity. In a harmonic RFID system, the tag receives instructions from the reader at an RF carrier frequency and replies back at the harmonic of the RF frequency. A nonlinear element consuming very low power at the tag is required to generate the harmonic carrier for the battery-less system. In this review article, a detailed contrast between conventional and harmonic RFID systems is presented. This is followed by different circuit design techniques to generate harmonics and integration techniques to form a fully operable passive harmonic RFID tag. Also, a wide range of applications, especially sensor integration with harmonic RFID's, along with the future trends are presented.

Wireless Battery-Free Harmonic Communication System for Pressure Sensing.

In this paper, an efficient passive wireless harmonic communication system is proposed for the real-time monitoring of the pressurized pipelines. A pressure sensor is fabricated using the additive manufacturing technique and a harmonic radio frequency (RF) tag is designed to operate at the fundamental frequency (fo) of 2 GHz that shifts the phase of the back reflected RF signal according to the applied pressure ranging from 0 to 20 psi. A power efficient phase modulation with virtually no losses is achieved using a hybrid coupler-based phase shifter that efficiently reflect back the incoming signal using an end coupled reactive impedance element/sensor. The phase delay introduced by the reactive element gets doubled with the second harmonic communication, which increases the sensitivity by a factor of two. The concept of harmonic backscattering is exploited to reduce the effects of multi-path interference and self jamming, as well as improving the signal-to-noise ratio (SNR).

Printed Diodes: Materials Processing, Fabrication, and Applications.

Printing techniques for the fabrication of diodes have received increasing attention over the last decade due to their great potential as alternatives for high-throughput and cost-effective manufacturing approaches compatible with both flexible and rigid substrates. Here, the progress achieved and the challenges faced in the fabrication of printed diodes are discussed and highlighted, with a focus on the materials of significance (silicon, metal oxides, nanomaterials, and organics), the techniques utilized for ink deposition (gravure printing, screen printing, inkjet printing, aerosol jet printing, etc.), and the process through which the printed layers of diode are sintered after printing. Special attention is also given to the device applications within which the printed diodes have been successfully incorporated, particularly in the fields of rectification, light emission, energy harvesting, and displays. Considering the unmatched production scalability of printed diodes and their intrinsic suitability for flexible and wearable applications, significant improvement in performance and intensive research in development and applications of the printed diodes will continuously progress in the future.

AuNP-RF sensor: An innovative application of RF technology for sensing pathogens electrically in liquids (SPEL) within the food supply chain.

Rapid detection techniques of pathogenic bacteria in the liquid food supply chain are of significant research interest due to their pivotal role in preventing foodborne outbreaks, and in maintaining high standards of public health and safety. Milk and dairy products are of particular interest due to their widespread consumption across the globe. In this paper, a biosensor for detecting pathogenic bacteria in milk using dextrin-capped gold nanoparticles (d-AuNP) as labels decoded at microwave frequencies is presented. The SPEL (sensing pathogens electrically in liquids) biosensor consists of a 3D printed vial and uses an RF reader and an RFID (radio-frequency identification) compatible Split Ring Resonator (SRR) based tag. The SPEL biosensor is capable of detecting bacteria at 5 log CFU/mL within 75 min, with the possibility of testing multiple concurrent samples. Detection is based on impedance loading of SRR by d-AuNP bound to pathogenic bacteria. Spectrophotometry, along with carbohydrate-functionalized magnetic nanoparticle (MNP) cell capture, is used to verify the sensitivity of the SPEL biosensor with respect to d-AuNP presence. The proof-of-concept device, along with challenges and opportunities for commercialization, are also outlined.

A Triaxial Applicator for the Measurement of the Electromagnetic Properties of Materials.

The design, analysis, and fabrication of a prototype triaxial applicator is described. The applicator provides both reflected and transmitted signals that can be used to characterize the electromagnetic properties of materials in situ. A method for calibrating the probe is outlined and validated using simulated data. Fabrication of the probe is discussed, and measured data for typical absorbing materials and for the probe situated in air are presented. The simulations and measurements suggest that the probe should be useful for measuring the properties of common radar absorbing materials under usual in situ conditions.

Self-calibrating technique for terahertz time-domain material parameter extraction.

This manuscript introduces a self-calibrating technique for terahertz (THz) time-domain material characterization in transmission mode. The self-calibrating technique utilizes the relations between the multiple transmissions of a transient plane wave through a sample under test in order to extract its material properties. The method presented in this paper is particularly useful in reducing the time required for simultaneous imaging and spectroscopy scans, since existing characterization methods require the knowledge of the waveform of both the plane wave transmitted through a reference sample and the waveform of the plane wave transmitted through the sample under test. The technique presented also ameliorates the problem caused by differences between sample and reference signals due to power and time drifts inherent in a THz system, hence reducing artifacts in the characterization results.