Alois Ascher

A small UHF-RFID transponder with integrated GPS for localization applications

The present publication describes the development of an active UHF RFID localization system concerning small size RFID transponders with an integrated GPS module for fawn saving during pasture mowing. The localization of a conventional active UHF RFID transponder has obvious drawbacks in the needed hardware on the reader side. The transponder sends only its label and no additional position information is available at the reader. Therefore, a direction finding system and a received signal strength (rss) detector for distance estimation in addition to the reader itself is needed. The huge hardware effort required reader side can be prevented by developing a transponder with an integrated GPS Module for localization. Thus, the focus is on a small transponder design, which leads to a trade-off between the requirements of the desired performance and the realization of the localization system, consisting of an active GPS-UHF transponder and the corresponding reader unit. Especially the conditions for the communication between the transponder and the reader related to limited power supply has to be minded. Furthermore, the transponder realization is shown and the considerations were metrological demonstrated.

RSS-based RFID transponder distance estimation for fawn saving

The present publication addresses the RFID transponder distance estimation based on received signal strength (RSS) in the application of fawn saving. During the pasture mowing fawns shall be protected from mowing machines by a RFID transponder localization system. At the moment the localization system is set on direction-of-arrival only. To facilitate the search process the localization capabilities shall be extended by a distance estimation. Two RSS measurement methods are shown and evaluated. The developed measurement hardware and the RFID system are presented. Measurement results in an outdoor environment, with a RFID transponder equipped with a ceramic chip antenna, are shown. Theoretical link budget of the RFID system is derived and can be approved by the measurement results.

An active UHF RFID transponder for fawn saving during pasture mowing

The present publication describes an innovative concept for fawn saving during pasture mowing in spring time. Conventional approaches like scaring by dogs or scarecrows are ineffective and time consuming especially for large areas. Other technical solutions have different drawbacks or insufficient search performance. Within the active UHF RFID localization system the processes of identifying fawns and rescuing them during mowing are separated. To recover them during the mowing sequence the fawns, covered in high and thick grass, are marked with active UHF RFID Transponders. The UHF RFID Transponder is attached to the eavesdropper of the fawn. By using chip antennae an overall size of a one euro coin was achieved despite working within the UHF band. Due to the unknown position of the transponder in high grass the directivity of the chip antennae was measured with consideration of co-and cross-polarization. An efficient power management enables a lifetime of about one month. In addition, the UHF RFID Transponder is supplied with an environment-friendly zinc air battery.

2-D localization of passive UHF RFID tags using location fingerprinting

Localization of UHF RFID tags in an industrial environments is difficult due to signal reflections and multipaths caused by steel and metal objects. Existing solutions have shown decent accuracy for small distances but fail to maintain the accuracy as the distance between the antenna and the tag increases. In this paper, we describe a novel UHF RFID localization approach based on location fingerprinting. The approach uses machine learning to transform localization into a classification problem. Location fingerprints are generated using outputs Bartlett beamformer and MUSIC algorithms that estimate the incoming angle of a signal. We evaluated our approach in an industrial environment, and the results show that we achieve a high classification accuracy and maintain it with the increase of the distance between the tag and the antenna.

3D localization of passive UHF RFID transponders using direction of arrival and distance estimation techniques

The present publication describes a localization concept to determine the 3D Position of passive UHF-RFID transponders. The importance of accurate location information significantly increases with Industry 4.0 in mind. Various applications in production and logistics require the exact location for monitoring the processes and thereby increasing the quality and reliability. The presented system consists of an 8 channel superheterodyne receiver with a connected 2D L-shaped patch antenna array controlled by a standards-compliant UHF reader. The recorded backscattered signal from the transponder gets evaluated by 2D versions of Bartlett Beamforming and MUSIC algorithm using a calculated 2D array manifold. For distance estimation the phase of the backscattered transponder signal gets evaluated for different reader transmission frequencies in the UHF band by applying a modified MUSIC algorithm. By measuring the distance, azimuth and elevation angle a monostatic 3D localization of the passive transponder is possible. For validation the localization concept is examined under ideal conditions in an anechoic chamber and in an industrial environment to show the overall performance.

A solar powered UHF transponder for wildlife and low light applications

Autonomous solar powered transponders or wireless sensor nodes operate well in high sun irradiation whereas in low light conditions the efficiency of the solar cell decreases and full operation is not guaranteed any longer. This is likely to happen in wildlife scenarios particularly in shaded areas or in indoor environments. The presented transponder concept is designed to face exactly these challenging applications. This article describes the characteristic figures that have been evaluated for various different sending intervals of the transponder. The degree of efficiency for the harvested energy is optimized by using an optimum adapted maximum power point for the solar cell and thereby vastly improving the sensitivity of the system. This allows for a single-digit start-up time within minutes in low light conditions and accomplishes operation in lowest light conditions. Therefore, this transponder concept can also be applied in smart industrial indoor environments or any other low light condition scenario.

UHF ceramic chip antenna designs for wildlife applications

In wildlife scenarios UHF transponder can be used to mark and localize animals over a large distance. Therefore, the size of the marking device has to be appropriate besides the wavelength is much bigger than it. Ceramic chip antennae enable a compact design in UHF applications. Due to the unknown position of the transponder in wildlife localization applications an omni-directional radiation pattern is desired in co- and cross-polarization to compensate polarization losses. For this investigation, several linear and circular ceramic chip antenna designs were established. A low co- to cross-polarization suppression show the circular antenna designs. The close proximity of the antenna to the animal body influences the electromagnetic characteristics significantly. A full sphere radiation measurement was performed in an anechoic chamber with and without muscle-like phantom model to characterize the effects of the animal body to the antenna properties. The reflected energy at the dielectric volume is more determent than the absorbed as the antenna was positioned in a cm distance to the phantom model.