R. Villarino

Chipless UWB RFID Tag Detection Using Continuous Wavelet Transform

The basic theory of operation of ultra wideband radio identification systems is explained in this letter. An experimental setup based on an ultrawideband radar working as a reader is proposed to measure time-coded tags. A method based on the Continuous Wavelet Transform is developed in order to overcome detection problems associated to a low signal-to-noise ratio at the receiver. Experimental results obtained with the ultrawideband radar and using an ultrawideband antenna connected to a delay line to emulate a tag are presented. A good improvement is achieved with this processing method.

Time-Domain UWB RFID Tag Based on Reflection Amplifier

This letter describes an active ultrawideband (UWB) tag for radio frequency identification (RFID) and wireless sensor applications. The tag is composed by a UWB antenna connected to a one-port reflection amplifier. A UWB impulse radar is used as the reader. The reader sends a short pulse, and its echo is amplified and reflected back due to the return gain of the tag amplifier. The amplitude of the reflected pulse is modulated by controlling the amplifier bias. The basic theory of ultrawideband operation applied to the time-domain RFID system is described. Experimental results with a proof-of-concept tag using commercial components are presented.

Signal Processing Techniques for Chipless UWB RFID Thermal Threshold Detector Detection

This letter presents signal processing techniques to detect a passive thermal threshold detector based on a chipless time-domain ultrawideband (UWB) radio frequency identification (RFID) tag. The tag is composed by a UWB antenna connected to a transmission line, in turn loaded with a biomorphic thermal switch. The working principle consists of detecting the impedance change of the thermal switch. This change occurs when the temperature exceeds a threshold. A UWB radar is used as the reader. The difference between the actual time sample and a reference signal obtained from the averaging of previous samples is used to determine the switch transition and to mitigate the interferences derived from clutter reflections. A gain compensation function is applied to equalize the attenuation due to propagation loss. An improved method based on the continuous wavelet transform with Morlet wavelet is used to overcome detection problems associated to a low signal-to-noise ratio at the receiver. The average delay profile is used to detect the tag delay. Experimental measurements up to 5 m are obtained.

Time-coded chipless RFID temperature sensor with self-calibration based on a Vivaldi antenna

This paper proposes a radio frequency identification (RFID) sensor based on an ultra-wide band (UWB) Vivaldi antenna loaded with two transmission lines. The time-domain response is composed by a structural and two tag (or antenna) mode reflections. Each transmission line generates its own tag mode. One tag mode is used to sense temperature, and the other is used to calibrate the sensor. Experimental results obtained with two reader approaches are presented to validate the system.

Diversity Study of a Frequency Selective Surface Transponder for Wearable Applications

This communication presents a semipassive radio frequency identification system in the 2.45-GHz Industrial, Scientific and Medical band. The transponder (or tag) is based on a modulated frequency selective surface (FSS). The FSS is composed of dipoles loaded with varactor diodes that modulate the radar cross section. The FSS transponder is designed to work for wearable and on-body applications and is used for reading and transmitting information from different sensors placed on the body. Experimental results locating the FSS at different positions in real scenarios and also at different places on the body are provided. Multiple FSSs have been used to explore spatial and polarization diversity techniques in order to mitigate the deep fadings that can happen during communication. Noticeable diversity gain has been obtained in both the cases without using antenna diversity in the reader. Finally, this communication describes a proof-of-concept experiment of the communication where two FSSs send digital data using a frequency shift keying modulation.

Backscatter tag based on frequency selective surface for FMCW radar applications

FMCW radar has been proposed in the literature as a reader for long distance transponders for wireless local positioning systems and sensing. One of the major challenges for positioning and for RFID systems are the disturbances due to multipath propagation. In addition, low-cost FMCW radars are often based on homodyne receivers, where the minimum measurement distance is limited by the transmitter coupling and the phase noise interference in the low-frequency band of the spectrum. To mitigate these problems, backscatter transponders have been proposed. This works presents an actively-controlled frequency selective surface (FSS) to implement a backscatter transponder at X band. The FSS is composed by dipoles loaded with PIN diodes which act as switching elements. The transponder exploits the change in the radar cross section (RCS) of the FSS to modulate the field illuminated by the FMCW radar. This change is performed varying the bias of the diodes. The basic operation theory of the system will be described. An experimental setup based on a commercial 9.25–10.75 GHz FMCW radar working as a reader is proposed to measure the transponders. The transponder response can be distinguished from the interference of non-modulated clutter, modulating the transponders RCS. Some FSS with different number of dipoles are studied, as a proof of concept. Measurements at several distances are provided with a 10 dipoles prototype. The tag distance can be obtained from the frequency offset between the peaks around the modulating frequency. The standard deviation error is 12 cm.

Active Backscatter Transponder for FMCW Radar Applications

This letter presents a low-cost wideband active backscatter transponder at X-band suitable for frequency-modulated continuous-wave (FMCW) radar applications. In order to maximize its read range, the radar cross section (RCS) of the transponder is increased by means of a two-stage amplifier based on high electron mobility transistors (HEMT), which is connected between two (one receiver and one transmitter) bowtie antennas. To distinguish the transponder response from stationary clutter it modulates the level of its RCS modifying the bias of the transistors. The backscattered response of the transponder is collected using a FMCW commercial radar. The transponder achieves a bandwidth of 7-12 GHz, with a gain between 18-22 dB, and a power consumption of 75 mW. Theoretical operation and experimental results are presented.

A wearable, wireless, and long lifetime device to detect sleep disorder diseases

Sleep disorder disease (SDA) and sleep apnoeas are, at this moment, very common pathologies that affect at least 25% of the worldwide population. The method to investigate this disease is expensive, complicated, and needs hospitalization of patients. For these reasons, most cases remain undiagnosed. A comfortable wireless device has been designed to detect the main parameters of SDA as respiration rate (RR), time of apnea (TA), and activation of the autonomous central nervous system (SNA). The device consists of two simple sensors; a thermistor placed close to the nose, which detects the changing in airflow during breathing, and a galvanic skin response (GSR) sensor, which measures the conductivity of the skin. The information is extracted by a low power microcontroller, which calculates RR, TA and the activation of the SNA. The information is collected by a smartphone using the low energy Bluetooth feature to guarantee a long lifetime to the device that uses a small coin battery. Different algorithms are described to minimize the payload on the connection, and therefore power consumption too. The amount memory used to store data on the smartphone is approximately 0.01% compared to a continuous recording.

Wireless Sensors Using Semi-passive UWB RFID

This chapter presents the implementation of some wireless sensors with the semi-passive time-coded UWB RFID systems presented in Chapter 4. Four implementations are presented: – a temperature sensor using the analog semi-passive UWB RFID system, using a PIN diode at the end of the transmission line, and powered by solar energy;

Indoor Localization with Smart Floor Based on Time-coded UWB RFID and Ground Penetrating Radar

RFID can be used to locate or guide autonomous entities, such as robots or people, within a defined surface. To this end, tags are scattered in a given space and then an RFID reader is placed on the mobile subject in order to identify the position inside that space, based on a previous tag mapping of the environment. This concept is often referred to as smart floor. Several RFID approaches have been investigated for this application and low-cost passive tags are preferred.