Gregor Lasser

Detectivity enhancement in quantum well infrared photodetectors utilizing a photonic crystal slab resonator.

We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.

Broadband suppression properties of active leaking carrier cancellers

In passive UHF RFID systems backscattering is used for tag to reader communication. This technique relies on a continuous wave signal being transmitted by the reader during the tags data transfer. In order to separate transmission and reception paths circulators, directional couplers or disjoint transmit and receive antennas can be used. Perfect isolation is not achievable with any of those approaches. So a leaking carrier is present at the receiver in any case. It is possible to reduce the interference from this signal by some kind of leaking carrier cancellation. Such a cancellation prevents receiver blocking and reduces the baseband hardwares requirements, depending on the receiver concept. Usually, the narrowband properties of carrier cancellers are studied. This is only sufficient for conventional RFID systems, if the transmitter noise can be neglected. Broadband RFID systems, as recently discussed in literature, also require broadband leaking carrier cancellers. In this paper the broadband suppression properties of carrier cancellers are first investigated theoretically. Further a hardware implementation is presented and characterized. Finally, measurement results are compared to the theoretical findings.

Dual-band channel gain statistics for dual-antenna tyre pressure monitoring RFID tags

In this contribution we analyse the read probability enhancement using two simple dual-antenna techniques for passive RFID tags for Tyre Pressure Monitoring applications. Our analysis is based on real-world channel measurements carried out with a full vehicle body for different antenna and steering angle configurations. Two frequency ranges were analysed: European UHF band at about 866 MHz and 2.45GHz ISM band. Two antenna combining methods were investigated: Antenna selection and power combining. With the latter a read probability enhancement from 49% to 75% is achievable.

Active carrier compensation for a multi-antenna RFID reader frontend

In this paper we present our multi-antenna radio frequency identification (RFID) research and development environment. We show measurement results for an ultra high frequency multi-antenna (one transmitter × two receivers) RFID reader setup using active carrier compensation at the receivers. Moreover, we evaluate the signal to self interference ratio (SSIR) and compare these results with a reference measurement performed without active carrier suppression. By adjusting the active carrier compensation circuits at one single transponder position an SSIR improvement of 73 dB at the tuning position is achieved. For other tag positions, without changing the adjustment, a minimum SSIR gain of 23 dB is observed.

Effect of carbon-fiber composites as ground plane material on antenna performance

The impact of carbon fiber composites (CFC) as a ground plane material on antenna performance is investigated. CFC are lightweight materials that, due to their high mechanical durability, are increasingly used as chassis material for cars. Their electrical characteristics are anisotropic and dependent on the manufactured structure, which is expected to influence the radiation pattern. Simple monopole antennas for 2.45GHz (ISM) and 5.9GHz (ITS G5) are mounted to circular ground planes made of three different CFC and aluminum sheets. The influence on antenna performance is investigated with calibrated gain, return loss and the radiation pattern measurements.

Dual-Band Channel Measurements for an Advanced Tyre Monitoring System

Due to the legal situation in some states and the beneficial effects on vehicular safety, fuel consumption and comfort issues, tyre pressure monitoring systems became very popular in the recent years. Despite this situation, few measurement data about the propagation channel between the sensor units and the vehicles reader antenna are available, especially for frequency bands above 433MHz and for reader antennas mounted on the vehicles bottom plate. In this contribution we present static channel measurements for an advanced tyre monitoring system (ATMS) in the 868MHz and the 2.45GHz bands, carried out with a vehicle equipped with a single dual-band receive antenna at the vehicle bottom. ATM systems obtain sensor data directly in the tyre, so the sensor unit antennas were placed at the tyre sidewalls.

Automatic leaking carrier canceller adjustment techniques

In this contribution, four automatic adjustment algorithms for leakage carrier cancellation in radio frequency identification (RFID) readers are compared: full search, gradient search, fast and direct I/Q algorithms. Further, we propose two enhanced adjustment procedures.First, we analytically calculate the performance of the fast adjustment algorithm in the presence of noise and derive its theoretical bias. We compare the theoretical results with the numerical results from accompanying simulations. Further, we evaluate the performance of these algorithms based on real-world measurements acquired with our RFID testbed.Finally, we propose and discuss the merits of two enhanced adjustment procedures based on the fast adjustment algorithm. The fast adjustment procedure with bipolar probing signals achieves the isolation gain of the (much slower) gradient search algorithm at the expense of a mean penalty of 0.48 dB. We observe that the fast adjustment aided gradient algorithm requires 72% less steps than the gradient search algorithm in our measurements.

Broadband leaking carrier cancellation for RFID systems

Reader systems for passive RFID tags suffer from a strong self generated interferer at the receiver, caused by transmitter to receiver leakage. This problem is often addressed by leaking carrier cancelers which compensate the leaking carrier at a single frequency. In this paper, we present measurements of the leakage channel in an RFID system. Based on the obtained results, we evaluate the leakage reduction that can be achieved by a novel analog broadband leakage canceller in the RF domain. Our proposed method allows for suppression of transmitter noise components. Moreover, it facilitates new broadband technologies, such as precision localisation or chipless RFID.

Gain and efficiency measurement of antennas for an advanced Tire monitoring system

Advanced tire monitoring systems (ATMSs) belong to the most promising future developments in vehicle safety. ATMS expands the possibilities of classical tire pressure monitoring systems (TPMSs) by additionally acquiring sensor data (e.g., tire temperature, contact area, vertical load, slip angle, and street conditions). These systems are composed of wheel units (WUs) mounted in each tire and an on-board unit (OU) located in the car body. Each WU contains sensors and a microchip which is connected to an antenna. The measured tire and road attributes are transmitted to the OU. One of the hardest challenges in developing an ATMS system is the design of an efficient antenna for the WU. In conventional TPMS the WU and its antenna are integrated into the valve [1] or are mounted on the rim of the wheel [2, 3]. To enable the measurement of additional sensor data, the WU in ATMS has to be moved to the tire itself. Thus, knowledge about the tire structure and the dielectric properties of the rubber material are mandatory. Exploration of these parameters can be found for example in [4] and [5]. In this contribution WU antennas – a dipole and a loop – directly attached to the tire rubber are investigated. Significant effects of the tire environment on antenna gain and radiation efficiency, as well as on the radiation pattern have been observed.

Compact low profile UHF switched-beam antenna for advanced tyre monitoring systems

Advanced tyre monitoring systems are based on small sensor units directly embedded into the tyre rubber. In contrast to conventional tyre monitoring systems, more data like vibration information and slip angle are collected at this exposed position, so vehicular safety systems can be further improved. Powering of and communication with these sensor units, could be done with UHF radio frequency identification technology. In this contribution we propose a novel compact switched-beam antenna suitable for UHF frequencies. When mounted below the body floor pan of a vehicle, its directivity of 6 dB and the possibility to switch the main beam direction in 90? steps enables selection of a specific tyre for communication. Finally, we present measurements of the assembled antenna performed in an anechoic chamber.