Muhammad B. Akbar

Modulation and sensitivity limits for backscatter receivers

This paper discusses how a low-powered RFID tag or sensor motes backscatter modulation scheme - limited in ways that conventional digital wireless systems are not - may be adapted to the peculiar non-white noise properties of a backscatter receivers radio frequency electronic chain to maximize detection. The analysis and results in this paper enable longer-range operation of todays passive, or semi-passive RFID tags as well as future backscatter sensor links that operate in higher frequency bands.

Range improvement of backscatter radio systems at 5.8GHz using tags with multiple antennas

This paper presents an improvement of the read range, radar cross section (RCS) and reliability of radio frequency identification (RFID) tags using multiple antennas. Measurements were performed using custom built, semi-passive RFID tags with co-planar segmented-loop antennas. Results show an increased read range as compared to RFID tag with single segmented-loop antenna.

Malevolent object detection using microwave RFID tags

Radio Frequency Identification (RFID) tags are gaining popularity in sensing applications. Common implementations rely on backscattering digitally encoded sensor data from an RFID tag to a reader. This paper discusses a unique capability of RFID technology to detect objects in a tags near vicinity by observing trends in the magnitude and phase of backscattered signal, irrespective of the information encoded in the data. Computational results and measurements are presented, and demonstrate how to improve sensitivity for object detection near a tag.

Amplitude and phase difference estimation bounds for multisensor based tracking of RFID Tags

Localization and tracking (L&T) are some of the most important applications of radio frequency identification (RFID) technology. One method of achieving this is by approximating the position of an object from the measured backscattered signal parameters and backscattered data. A comprehensive analysis of the backscattered signal parameters, such as received signal amplitude and phase, is necessary to establish their effect on the accuracy of L&T. In this context, this paper investigates the probability density functions (PDFs) of the received signal amplitude and phase for RFID systems. It was observed that both PDFs converge to Gaussian distributions in high signal-to-noise ratio scenarios. Moreover, the Cramer Rao Lower Bound (CRLB), which serves as an established reference for unbiased estimation, is also derived for the estimated received signal amplitude and phase difference. It was noticed that the CRLBs are inversely proportional to the number of observations taken for the parameter estimation. Finally, it is pertinent to mention that if multiple types of sensed information are fused to perform L&T, it results in millimeter-level accuracy. For RFID, one such technique which employs multiple sensed parameters for L&T is Hybrid Inertial Microwave Reflectometry (HIMR). This paper also presents a simulation and experimental analysis of HIMR. HIMR-based RFID tracking scheme results in tracking accuracy in the range of 1-10 mm.

Long range and low powered RFID tags with tunnel diode

In this paper, we present a 5.8 GHz RFID tag equipped with a high gain, low power reflection amplifier based on a tunnel diode. Experimental results show that the realized prototype achieves gains above 40 dB and requires only 29 μW of biasing power. The tag detects very low RF signals (<; -90 dBm) and provides read ranges up to 2 km. Long communication ranges and Manchester encoding are achieved by biasing on and off the tunnel diode.

Hybrid Inertial Microwave Reflectometry for mm-Scale Tracking in RFID Systems

This paper proposes a new fine-scale (millimeter level) radio localization and tracking scheme-Hybrid Inertial Microwave Reflectometry-for radio frequency identification and other wireless systems. The scheme combines the backscattered radio frequency signal properties, such as received signal strength and received signal phase, along with reflected inertial data from a tag-mounted accelerometer sensor. Experimental results yield a mean error of 2 mm in ranging accuracy, with a 90% confidence interval of ±1 mm, while tracking a tag moving at a maximum speed of 1.4 m/s.

Analysis of Ε-patch antenna performance over various dielectric materials at 2.4 GHz

Antenna detuning can be used for a variety of sensing applications. In this paper, the performance of an E-patch and a conventional patch antenna was evaluated in the presence of dielectric materials. The gain penalty and the reflection coefficient of both the antennas were simulated and measured using a vector network analyzer. The performance of the E-patch antenna was evaluated to be much better than a normal patch antenna over each dielectric material. This analysis is useful for environmental monitoring, rescue, and surveillance applications.

Omnidirectional loop antenna for a 5.8 GHz microwave backscatter RFID tag

A novel miniaturized printed circular loop antenna with perimeter of nearly one wavelength is designed for operation with a radio-frequency identification (RFID) tag at 5.8 GHz. RFID tags and RFID-enabled sensors which operate at this frequency offer many benefits over traditional UHF and LF tags, such as smaller footprints and increased bandwidth. The loop is broken into conducting segments that alternate on either side of a substrate for capacitive loading needed to maintain a constant current and generate a near omni-directional radiation pattern. The performance of the loop antenna is measured in-situ with the tag and the reader configured as a microwave backscatter radio communication system at 5.8 GHz. An overview of the RFID tag design is presented along with measured backscattered pattern.

Broadband backscatter based technique to identify the presence of skimming electronics on payment terminals

This paper presents a broadband, RF backscatter-based sensing method to identify the presence of payment terminal tampering, particularly using small, unwanted electronics such as payment skimmers in close proximity to a 5.8 GHz RFID tag. The broadband nature of this methodology makes it resilient to false alarms from interfering RF signals. Consistent detection of a conductive object is achieved by tracking long term changes in both magnitude and phase of the backscattered signal. In laboratory measurements, the presence of thin metal wires was determined for distances up to two wavelengths from the tag.

Orientation sensing using backscattered phase from multi-antenna tag at 5.8 GHz

Object localization is one of the most important applications of RFID technology. In this paper, we demonstrate how fine-scale orientation can be estimated from a multi-antenna backscatter tag. Three basic orientation changes - tag roll, pitch and yaw - were considered, where roll and pitch maneuvers were successfully identified from the direction of phase rotation. Moreover, an inclination of 5° in roll and pitch maneuvers was successfully identified by measuring the phase difference with 15% and 8% error respectively. The analysis can be extended to any amount of inclination.