Low-profile FSS design methodology to increase isolation between vehicle-borne multifrequency antennas

The present work describes a new approach for the design of a Frequency-Selective Surface (FSS) in the context of frequency filters to increase isolation between two vehicle-borne antennas. A compact FSS design based on nested square meandered resonators is optimized for multifrequency operation. Furthermore, a design workflow is proposed. In general, the measurement of low-profile FSS does not correspond to simulation through Floquet modes based on periodic boundary conditions due to the lack of uniformity of mutual coupling among the FSS unit cells. The proposed method demonstrates the agreement between the infinite simulation and the measurement of the finite prototype once a convenient scale factor is applied, which facilitates the design workflow. In this case, an FSS is used as an efficient filter to increase the isolation between antennas by 6 dB in three representative bands (3GPP, WiFI I and II). In this way, multifrequency antennas can be placed at approximately half their actual distance with the same performance in spatial-constrained vehicular environments

Design and Implementation of Subcutaneous UHF Band Antennas for Smart Implants using a Novel Characterization Procedure.

Smart implants enable the wireless transfer of physiological parameters gathered inside the human body. In this research work two broadband antennas for implanted smart central venous catheters (SCVC) are designed, implemented and characterized using a novel characterization procedure. The design of implanted antennas involves several challenging aspects such as miniaturization because of the very limited space, high efficiency despite the highly lossy environment in the near field of the antenna, adaptability to the given shape of the implant as well as insulation from the surrounding tissue. These constraints in mind, the electromagnetic specifics of body tissues are studied. This knowledge is required for a profound simulation and analysis of antenna topologies suitable for smart implants. According to two different scenarios for SCVC applications, two different antenna topologies are proposed. A planar round-shaped broadband UHF antenna for passive RFID is designed for mounting on the top of a smart CVC reservoir placed in a subcutaneous position in the chest. This printed monopole-strip antenna operated at 868 MHz is suitable for near field applications. Alongside a virtual body phantom of the chest, near field simulations as well as simulations in the close far field up to 1 meter distance are run. Since the actual working range turns out to be narrower than anticipated, another topology is projected answering the purpose of higher performance in the far field. This dual-band CVC antenna is 3-D conformal to a truncated cone and scheduled for 402-405 MHz MICS band and 2.4 GHz ISM band. The corresponding smart CVC is battery powered to provide a wide working range. Measurement environments imitating the properties of the human body are prepared and the antenna prototypes are implemented in a test bed. Measurements inside a body phantom are carried out, yet, the results do not reveal conclusive data. Simulations of the antenna in the test bed detect an influence of the test bed feeding cables on the radiation properties. This observation anticipates the insight that simulation and measurement cannot be regarded separately, but need to be interpreted in common. Only a procedure that comprehends a combination of both is a viable way to accurately characterize antenna properties for a selected application despite all manipulating factors. In order to resolve the observed mismatch, an uncertainty factor is calculated taking into account the measured and the simulated maximum gain. The obtained results, again, are used to adapt the dual-band UHF antenna to the smart implant prototype. Finally, the performance of the system is examined by running functional tests. These prove that the link budget calculation reliably enables the evaluation of possible application scenarios and, in particular, the maximum operating distance of the future system in certain positions even before a working smart implant prototype is manufactured. The results of the study state that the presented novel characterization procedure is suitable to verify obtained property data. Consequently, the limits of measurement set ups can be compensated and realistic and comparable antenna characterization can be assured

Reader Arquitecture Characterization for Chipless Wireless Sensors Applications.

The main goal of this project is to design, implement and characterize a portable chipless reader for resonator chipless tags by comparing it with a non-portable chipless reader. In laboratory settings, test equipment such as Vector Network Analyzers (VNAs), Signal Analyzers and Digital Storage Oscilloscopes (DSO) are used. However, it is not economical to use these expensive and heavy laboratory pieces of equipment for the real-world applications of chipless RFID systems. Therefore, apart from reducing the cost by using chipless technologies, it is essential to develop a low-cost reader device that makes the system even more inexpensive. This is basically done by replacing the large and bulky equipment with some commercial components that make the device light and portable. Concretely, the design of the reader presented in this document, implements a Wideband Synthesizer with Integrated VCO in order to replace the Signal Generator. The most challenging task is the correct synchronization of the new device with the rest of the elements of the reader. This is achieved by a new computer software specifically programmed to control the whole reader, which is based on a previous version. The system’s performance is tested with several chipless tags; resonators with different resonance frequencies. The obtained results are compared to the measurements taken with a VNA and with a previous version of the reader composed by laboratory instruments. The measurements are made with a gain/phase detector that sends its data to an Arduino. Moreover, the information is processed by a Visual Studio project written in C Language that also contains the software with the user interface to control the synthesizer from the computer and all the data processing and visualization algorithms. The aim of the project is to describe the characterization of a reader based on frequency domain detection techniques and obtain the most accurate and effective performance of it to improve the previous version of the system and approach to an applicable device

Design and Implementation of Subcutaneous UHF Band Antennas for Smart Implants using a Novel Characterization Procedure.

Smart implants enable the wireless transfer of physiological parameters gathered inside the human body. In this research work two broadband antennas for implanted smart central venous catheters (SCVC) are designed, implemented and characterized using a novel characterization procedure. The design of implanted antennas involves several challenging aspects such as miniaturization because of the very limited space, high efficiency despite the highly lossy environment in the near field of the antenna, adaptability to the given shape of the implant as well as insulation from the surrounding tissue. These constraints in mind, the electromagnetic specifics of body tissues are studied. This knowledge is required for a profound simulation and analysis of antenna topologies suitable for smart implants. According to two different scenarios for SCVC applications, two different antenna topologies are proposed. A planar round-shaped broadband UHF antenna for passive RFID is designed for mounting on the top of a smart CVC reservoir placed in a subcutaneous position in the chest. This printed monopole-strip antenna operated at 868 MHz is suitable for near field applications. Alongside a virtual body phantom of the chest, near field simulations as well as simulations in the close far field up to 1 meter distance are run. Since the actual working range turns out to be narrower than anticipated, another topology is projected answering the purpose of higher performance in the far field. This dual-band CVC antenna is 3-D conformal to a truncated cone and scheduled for 402-405 MHz MICS band and 2.4 GHz ISM band. The corresponding smart CVC is battery powered to provide a wide working range. Measurement environments imitating the properties of the human body are prepared and the antenna prototypes are implemented in a test bed. Measurements inside a body phantom are carried out, yet, the results do not reveal conclusive data. Simulations of the antenna in the test bed detect an influence of the test bed feeding cables on the radiation properties. This observation anticipates the insight that simulation and measurement cannot be regarded separately, but need to be interpreted in common. Only a procedure that comprehends a combination of both is a viable way to accurately characterize antenna properties for a selected application despite all manipulating factors. In order to resolve the observed mismatch, an uncertainty factor is calculated taking into account the measured and the simulated maximum gain. The obtained results, again, are used to adapt the dual-band UHF antenna to the smart implant prototype. Finally, the performance of the system is examined by running functional tests. These prove that the link budget calculation reliably enables the evaluation of possible application scenarios and, in particular, the maximum operating distance of the future system in certain positions even before a working smart implant prototype is manufactured. The results of the study state that the presented novel characterization procedure is suitable to verify obtained property data. Consequently, the limits of measurement set ups can be compensated and realistic and comparable antenna characterization can be assured

Time–temperature excursion monitoring using chipless RFID tags and organic oils.

A food-safe cost-effective time-temperature indicator (TTI) sensor for cold chain disruption detection at the item level is proposed. The sensor is based on the radar cross section (RCS) readout from a chipless square split ring resonator (SSRR) exposed to organic oils with customizable melting temperatures and defined flow paths. The inclusion of several oil mixtures into the same sensor allows for the determination of a range of configurable temperatures/times. The same sensor has two modes of operation: one for threshold detection and another for gradual change detection. These modes depend on the orientation of the sensor on the packaging and the influence of gravity. The provided design, along with a convenient signal conditioning strategy, accurately detects four time exposure thresholds in the 7-30 min range when placed in upright position at ambient temperature, while it exhibits linear response between 10 and 30 min just by turning it by 90 degrees. Prospective future directions are also discussed

Low-profile FSS design methodology to increase isolation between vehicle-borne multifrequency antennas

The present work describes a new approach for the design of a Frequency-Selective Surface (FSS) in the context of frequency filters to increase isolation between two vehicle-borne antennas. A compact FSS design based on nested square meandered resonators is optimized for multifrequency operation. Furthermore, a design workflow is proposed. In general, the measurement of low-profile FSS does not correspond to simulation through Floquet modes based on periodic boundary conditions due to the lack of uniformity of mutual coupling among the FSS unit cells. The proposed method demonstrates the agreement between the infinite simulation and the measurement of the finite prototype once a convenient scale factor is applied, which facilitates the design workflow. In this case, an FSS is used as an efficient filter to increase the isolation between antennas by 6 dB in three representative bands (3GPP, WiFI I and II). In this way, multifrequency antennas can be placed at approximately half their actual distance with the same performance in spatial-constrained vehicular environments

Chipless wireless sensor coupled with nachine learning for oil temperature monitoring.

Temperature monitoring is essential in several industries driving the need for sensors. Chipless radio frequency identification (RFID) technology has emerged as a cost-effective solution, enabling wireless detection without the need for a power supply or electronics embedded in the sensor tags. However, a significant challenge lies in wirelessly monitoring temperature within liquid environments using chipless RFID tags as resonances vanish due to energy absorption in liquids. This work presents a chipless RFID sensor for wireless detection of oil temperature in a glass container. The temperature monitoring is based on the characterization of the permittivity of oil samples with different concentrations of total polar compounds (TPCs). After evaluating two chipless RFID tag designs, we propose to use a complementary ring resonator (CRR) tag as it exhibits a robust response to oil liquid volume, improving the detection of temperature in low-loss liquids and offering higher sensitivity. When the measurement results are coupled with machine learning (ML), we demonstrate that the response of the proposed tag as a wireless sensor can be used to estimate the temperature of oil samples with different quality (TPC) with an average test RMSE of 4 degrees C (standard deviation < 2 degrees C), in the approximate range 22 degrees C-95 degrees C

SDR-based monostatic Chipless RFID Reader with Vector Background Subtraction Capabilities

This article presents a high-performance frequency-domain chipless RFID reader with vector background subtraction capabilities, implemented in a software-defined radio (SDR) for the first time. The proposed reader is low-cost, compact size, and versatile. It is implemented in a USRP N210 paired to a modified CBX-40 daughterboard, enabling magnitude and phase data acquisition in a monostatic (one antenna) set up. The reader can perform a vector background subtraction operation between two complex measurements (with and without a chipless tag) to suppress the self-interference (SI) that hinders the response of the tag and provide 40 dB of dynamic range. To demonstrate the performance of the reader, the spectral signatures of three frequency-coded (FC) tags with four resonant frequencies are captured over the 1.5-4-GHz band scanned with 10-MHz resolution in 251 ms, obtaining comparable measurements to those of an expensive laboratory vector network analyzer (VNA) from 20 to 40 cm. The detected resonant frequency offset between both devices is Delta f(r) <= 4.18% . It is also demonstrated that the proposed reader can track a resonant frequency shift and therefore be used in real-time sensing applications

A 5.8-GHz-Direction of an arrival localization radio system with a reconfigurable monopole antenna array.

This article presents the design of a complete radio system receiver to detect, in real time, the direction of arrival (DOA) of an incoming industrial, scientific, and medical (ISM)-band signal at 5.8 GHz. When a transmitter continuously sends a binary phase-shift keying (BPSK), modulated pseudo-noise (PN) code, the receiver estimates the DOA based on the received signal strength (RSS) and performs the channel sounding. The device that we describe includes a pattern-reconfigurable monopole antenna array, a front end, and a systemon-module (SOM). The SOM controls the antenna's main lobe direction by positive-intrinsic-negative (p-i-n) diode switching, configures the front-end modules, completes the data acquisition, and performs the digital signal processing (DSP) for the DOA estimation. The system has an average DOA resolution of 90° in the horizontal plane, with a success rate higher than 90%. It is presented as an educational platform for electrical engineering undergraduate and M.S. degree students

Chipless RFID tag implementation and machine-learning workflow for robust identification

In this work, we describe a complete step-by-step workflow to apply machine-learning (ML) classification for chipless radio-frequency identification (RFID) tag identification, covering: 1) the tag implementation criteria for circular ring resonator (CRR) and square ring resonator (SRR) arrays for ML interoperability; 2) the data collection procedure to get a sufficiently representative dataset of real measurements; 3) the ML techniques to visualize the data and reduce its dimensionality; 4) the evaluation of the ML classifier to ensure high-accuracy predictions on new measurements; and 5) a thresholding scheme to increase the certainty of the predictions. The differences in the tags' frequency responses are maximized by optimizing the Hamming distance between the tag identifiers (IDs) and by controlling each resonator array's radar cross section (RCS) level. We show that the proposed workflow achieves perfect accuracy for the identification of four tags at a fixed distance of 160 cm. We also evaluate the performance of the proposed workflow to identify up to 16 tags within a flexible range (up to 140 cm), showcasing the tradeoff between the number of tags that can be correctly classified based on the reading range