David Victor Thiel

A robotic system to locate hazardous chemical leaks

Tracing leaks of airborne radioactive, poisonous or flammable materials is a potentially dangerous activity that could be undertaken by robotic systems. This paper describes a practical investigation of the possibility of developing simple, low cost, autonomous robots to perform this task. It is envisaged that these robots would be used in large numbers. This would improve reliability through redundancy and provide large area coverage from a wide distribution of robots. Failure of a single unit would not jeopardise the overall sensing operation. Sensing and control techniques developed to perform leak location in a simplified laboratory environment are described and experimental results are presented.

Base-station tracking in mobile communications using a switched parasitic antenna array

Base-station tracking in mobile communications benefits from a directional antenna and so requires direction finding technology. A novel technique for electronically directing the radiation pattern of an antenna array employs a directional array with only one active element and three parasitic elements operating near resonance. Three different methods of direction finding are assessed; a coarse angular location method, a precise angular location method assuming one incident beam, and a precise angular location method with multiple incident beams. An array with n elements, if used in conjunction with a relatively simple controller, can be used to resolve n-1 signals. This technology can be implemented using both wire and patch antenna-array elements and either linear or circular polarization can be used, lending the technology to applications in both terrestrial and satellite communications systems.

A mechanism for the production of electromagnetic radiation during fracture of brittle materials

The feasibility of the charge separation model as the source of electromagnetic radiation received from the fracture of brittle materials is demonstrated. An analytical expression and a finite difference method enable the calculation of currents flowing around the tip of a crack. Results from the model compare favourably with fracture events recorded from ice samples. Changes in material conductivity affect pulse shape although changes in crack surface conductance and not crack apex conductance cause most variation in the received signal.

Consensus Clock Synchronization for Wireless Sensor Networks

Wireless sensor networks (WSN) are emerging as a valuable tool in many fields of science and industry. Time synchronization is an important issue for WSNs due to the collaborative and distributed nature of the tasks they perform. This paper describes a new technique for clock synchronization in WSNs called consensus clock synchronization that provides internal synchronization to a virtual consensus clock. It is sensitive to the limited resources available to sensor nodes and is robust to many of the challenges faced in dynamic ad-hoc networks. Simulations are presented to analyse the effectiveness of the synchronization protocol in a mesh network.

The synthesis of surface reactance using an artificial dielectric

A thin artificial dielectric layer consisting of a rectangular array of closely spaced, thin conductive cylinders (pins), was constructed above a perfectly conducting ground plane. The reactance of the surface was measured at 4.8 GHz for a variety of pin heights and dielectric embedding material by measuring the height-gain profile of a transverse magnetic (TM) surface wave launched across it. Design equations using the theories of artifical dielectrics and propagation in anisotropic media are given. These can be used to predict the surface reactance providing a correction factor accounting for fringing fields at the tops of the pins is included. Using an embedding dielectric tends to reduce this fringing effect.

Electronically steerable Yagi-Uda microstrip patch antenna array

This paper describes a dual-frequency circularly polarized electronically steerable microstrip patch antenna array suitable for land-mobile communications. Based on a four-element Yagi-Uda (1928) patch antenna, the four antennas forming the array are located radially from a single square reflector patch on a double-sided printed circuit board. The main lobe of the array covers the elevation angles from 20 to 70/spl deg/ with a peak gain of 8.4 dBi at 1.54 GHz and 11.7 dBi at 1.62 GHz. Full azimuthal coverage is possible by electronically switching between the four elements.

Switched parasitic antenna on a finite ground plane with conductive sleeve

A switched parasitic monopole antenna on a finite ground structure with a conductive sleeve attached to a small, circular ground plane controls the vertical radiation direction. The antenna was designed using a genetic algorithm and finite element (FEM) solver. At 1.575 GHz, the constructed antenna exhibited a front to back ratio of 10.7 dB and gain of 6.4 dBi with no elevation from the horizontal. The switched parasitic nature of the antenna allowed it to steer a directional beam through 5 locations in the azimuth. Incremented from 0/spl lambda/ to 0.45/spl lambda/, the sleeve was observed to linearly depress the main lobe elevation with little influence on other antenna characteristics such as gain and S/sub 11/.

Odor Sensing for Robot Guidance

There is no generally applicable technique for finding the position of an autonomous mobile robot operating in an un structured or varying environment. This article describes a project to investigate the use of short-lived navigational mark ers consisting of olfactory chemicals to guide mobile robots and to help them search and explore efficiently. Such a method of laying a trail to mark the path of a robot provides differ ential navigational information relative to the starting point and starting direction. Many insects employ olfactory cues as navigation aids and to improve their efficiency when searching for food. Three scenarios are proposed in which navigational markers can be of assistance to a mobile robot. The design and characteristics of an adsorbed mass olfactory sensor are described. This sensor was designed to be mounted on a mo bile robot and is suitable for detecting and tracking olfactory chemicals. The performance of this sensor is described together with preliminary results of using it to track an odor trail.

Sensing odour trails for mobile robot navigation

By monitoring or following trails layed on the ground a mobile robot can perform several useful navigation tasks. An example would be following a trail layed on an outward journey in order to later find the way back to the starting point. This paper describes the latest stage in the development of a robot navigation system based on laying down and detecting trails of volatile chemicals. Previously a prototype olfactory sensor was developed which showed the feasibility of having a mobile robot follow an odour trail on the floor. This prototype sensor has now been improved by managing airflow in the vicinity of the sensor. This has decreased the sensor response time and improved rejection of spurious odour signals carried by airflow in the room. A simple and effective applicator has also been developed for laying odour trails.<<ETX>>

Antenna Efficiency Calculations for Electrically Small, RFID Antennas

Radio frequency identification (RFID) antenna efficiency is an important component of link budget design. A method of moments technique based on the summation of segment currents compares favorably with two different results obtained using the finite element method (radiation pattern integration and Wheeler cap). The efficiency of a resonant dipole was found to be proportional to the inverse square root of the conductivity. For a typical RFID meander line antenna in free space the relationship is more severe