Angel Ramos

Passive Wireless Temperature Sensor Based on Time-Coded UWB Chipless RFID Tags

In this paper, an RF identification sensor system is developed. It comprises passive sensors and an ultra-wideband (UWB) reader. The sensors are based on time-coded chipless tags. They consist of an UWB antenna connected to a delay line that is, in turn, loaded with a resistive temperature sensor. This sensor modulates the amplitude of the backscattered signals as a function of the temperature. The sensor tags are identified by changing the length of the delay line. In this paper, the operation principle and design of time-coded tags is presented and the integration of sensors in these tags is addressed. In addition, two measurement techniques are compared to implement the UWB reader. The first one is based on frequency sweeping and uses a vector network analyzer. The second one is based on a low-cost UWB radar. A full characterization of the sensor system is provided.

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 MEASUREMENT OF TIME-CODED UWB CHIPLESS RFID TAGS

Chipless ultra-wideband (UWB) has been proposed as a low-cost alternative for radiofrequency identiflcation (RFID). In this paper, a comprehensible theoretical introduction to time-domain operation of a UWB RFID tag is described, and a circuit model is proposed. For commercial applications low-cost RFID readers are demanded. To this end, this paper addresses the measurement of time-coded UWB chipless tags for RFID in time domain. Two difierent setups to detect time-coded tags are presented, one based on commercial UWB impulse radar (IR) and the other based on a vector network analyzer (VNA). The experimental results show the feasibility of using an IR-UWB radar as a UWB RFID reader, achieving very good read ranges.

Remote Sensing of Vital Signs Using a Doppler Radar and Diversity to Overcome Null Detection

Vital signs detection by means of several topologies based on Doppler radar are proposed in this paper with the aim of overcoming the problem of null detection. They are based on phase and frequency diversity. The proposed topologies are an alternative to I/Q demodulation and double-sideband transmission. Four topologies are proposed, three of them based on phase diversity and one based on frequency diversity. The first topology is based on using two phase-shifted receivers. The second one is based on a physical antenna displacement between two receivers. A third system with a dynamic phase variation is also presented, which permits to work with only one receiver. The last topology is a radar with frequency diversity within the 2.4 GHz ISM band, which permits a dynamic change of the frequency dynamically in order to place the receiver always in a maximum. A system to empirically characterize nulls is also developed to validate the proposed topologies.

Semi-Passive Time-Domain UWB RFID System

This paper presents a semi-passive time-domain ultra-wideband (UWB) radio identification system. The reader consists of a commercial, low-cost, and integrated impulse-radio radar. The tag is composed of a UWB antenna loaded with a transmission line, which is in turn terminated with a PIN diode. The tag answers to the interrogator by backscattering, modulating the amplitude of the time-domain reflected pulses sent by the radar. A 2.4-GHz downlink channel is used to wake up the tag, in order to increase the lifetime of the battery. The wake-up circuit is based on a diode rectifier and the internal comparator within the tag chip (a microcontroller) without needing additional active devices. Experimental results obtained with a proof-of-concept tag show that read-ranges up to 8.5 m can be achieved.

A Novel UWB RFID Tag Using Active Frequency Selective Surface

This work describes an actively controlled frequency selective surface (FSS) to implement ultrawideband radio identification (RFID) tags. The tag exploits the change in the radar cross section (RCS) of the FSS, which is loaded with switching PIN diodes to modulate the backscattered time-domain response of the tag to an input ultra-wide band pulse. The basic operation theory of the system is explained. An experimental setup based on a ultrawideband radar working as a reader is proposed to measure the modulated radar cross section of the tags. As a proof of concept, a battery-assisted or semipassive tag has been developed.

Active UWB Reflector for RFID and Wireless Sensor Networks

In this paper, we present an active ultra-wideband (UWB) reflector for radio frequency identification (RFID) and wireless sensor applications. The tag is composed of a receiver UWB antenna connected to a broadband amplifier. Its output is connected to a cross-polarized transmit antenna. In order to increase the battery lifetime, an UHF link is used to wake up the microcontroller. It modulates the radar cross section of the tag by turning the amplifier bias on and off. The amplitude of the reflected UWB pulse sent by the UWB reader is modulated as a result. The basic theory of operation of ultra-wideband radio identification systems is explained in this paper. A proof of concept using commercial components and experimental results obtained with an ultra-wideband radar are presented.

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.

Temporal Separation Detection for Chipless Depolarizing Frequency-Coded RFID

This paper studies the detection of chipless frequency-coded tags. The detection exploits a temporal separation that allows obtaining the identification (ID) with only one measurement. In this way, the flexibility of reading of this type of chipless tags is clearly improved, which is highly expected for future real implementation. This temporal separation is possible when the tag presents a long-time signature, longer than the backscattering wave corresponding to the surrounding objects. A technique based on the short-time Fourier transform (STFT) is used to differentiate the useful parts of the signal, which contain the tag ID. Up to now, this was done by using a calibration process based on two measurements at least to remove coupling and clutter contribution. With the proposed approach the acquisition of the tag ID is direct, and it is not necessary to have further information such as the measurement of the environment without the tag. A study on the time duration of several frequency-coded tags is performed based on simulations and measurements. The study shows that this approach can be used with classical depolarizing chipless tags already proposed in the literature. It is proven that the proposed approach is useful to detect the tag response with a single measurement.

Solar-Powered Wireless Temperature Sensor Based on UWB RFID With Self-Calibration

This paper presents a solar-powered wireless temperature sensor based on time-coded ultrawideband (UWB) radio frequency identification. A negative temperature coefficient resistor acts as the sensing element. It controls the current of a PIN diode connected to a UWB scattering antenna. The wireless sensor is self-calibrated using a narrowband tone, making its performance independent of the distance or orientation between the reader and the sensor. A consumption of 82 μA is demonstrated. An error under 0.6 °C within a 35 °C-70 °C temperature range is obtained for most of the cases.