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.

Using a combination of 3D printing and thin-film processes, a compact microwave front-end module is designed and fabricated. An ultra-wide-band Vivaldi antenna with a structurally embedded receive module is demonstrated. The receive module is placed in a packaging cavity that is formed in the unused region of the antenna structure. The measurements of this 3D printed system is compared to a traditional ridged horn antenna with an identical receive module. This novel system-on-antenna (SoA) front-end module shows 5 dB more receive power when compared to the ridged horn antenna based design. Integrated transmit and receive modules play a critical role in the overall cost and performance of phased-array systems, and the process presented demonstrates an emerging technique for meeting these challenges.

This paper presents the design, fabrication, and characterization of aerosol jet printed quasi-optical components for operation in the terahertz (THz) spectral range. Performance of each of these components is compared to their counterpart fabricated by a lithographic process. Two band-stop filters, one designed for operation at 250 GHz and another at 550 GHz, as well as a band-pass filter designed for operation at 250 GHz, are designed and characterized. Additionally, polarizing screens are presented, demonstrating high-resolution capabilities of the aerosol printing concept. Enhancement of printed structures by means of an electroless metal plating process is demonstrated using an aerosol jet printed seed layer.

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.

In this paper, a hybrid RFID tag and reader system is proposed for wireless and batteryless automotive sensors. The hybrid RFID tag operates in dual mode, which includes conventional RFID operation, and tag active transmission. The reader provides the carrier in conventional RFID communication, using which the tag performs backscatter modulation. In tag active transmit mode, the reader does not provide any carrier, and the tag synthesizes its own carrier for communication. The hybrid tag can communicate with the reader for a range of 21 in. A commercial seat belt sensor was integrated with the tag and a working prototype of the complete system was demonstrated. Time response is a critical parameter for the whole system to work coherently and hence the operational states were modeled for time estimation and address the key parameters. Individual subsystems within the tag and reader circuits are presented in detail to capture the complete system. The proposed system can reduce the effective on-time of the reader significantly and the analysis shows that the reader transmit time can be reduced as much as 90% compared to the conventional RFID reader. The system was validated by designing, fabricating, and testing of the tag and reader circuits within a lab environment.

In this paper, a detailed transient analysis is performed on modified Dickson charge pump circuit, widely used as an energy harvester in RFID and wireless sensor tags at UHF. An analytical model was developed and experimentally validated to capture the transient response of a multi-stage charge pump circuit at any arbitrary capacitive and resistive load. The detailed analysis addresses the effect of stage number, and matching network on the steady state output DC voltage, efficiency, and charging rise time. The analysis shows that the steady state voltage varies in proportionate to √n and the rise time varies in proportionate to n at no load condition, where n is the number of stages.