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THE DEVELOPMENT OF A NOVEL INTEGRATED SUPER HIGH FREQUENCY (SHF) NON CONTACT DETECTOR UNIT FOR MOBILITY DETECTION AND SPEED MEASURMENT

Final Report Summary - WAVESHIFT (The development of a novel integrated super high frequency (SHF) non contact detector for mobility detection and speed measurement)

Our first objective was to scientifically characterise and determine the optimum parameters for the short range motion and movement direction detection unit, exploring methodologies for enhancing detection accuracy in a variety of environments and ensuring resolution capabilities to enable the full characterisation of a commercially viable detector.

The next goal was to define the substrate for the printed circuit board and on the basis of it, design and build microstrip antennas meeting the requirements defined in the theoretical, technological review. We have chosen the substrate to be Rogers 4003, RO4003 is available in 0.2 mm and 0.5 mm thickness, the dielectric constant is nominally 3.38 and the loss tangent is 0.0027 at 10 GHz. We continued with the development of a beam switching mechanism based on a novel PIN diode switching model. The prototype was designed and tested. The proposed reconfigurable antenna array has been developed.

The next objective was to create a multi layered printed circuit board in which the antenna system constitutes the whole of one side and the other side is used to accommodate the microwave electronics. A groundplane layer was buried within the printed circuit board. Our next aim was to design and build the microwave mixer. Having investigated the possible technologies, we have decided that we would design two types of mixers, an active mixer based on a field effect transistor (FET) and a passive mixer based on single ended and single balanced Shottky diode mixers.

The next goal was to evaluate different system configurations, followed by bench testing to confirm radiation pattern characteristics against reference designs. In all cases, the antenna arrays that were developed exhibited good return loss characteristics within the operational band. Overall the measured parameters for the developed antenna arrays for the 24 GHz motion detection sensor are consistent with the specification and therefore the antennas are suitable for use in the application.

The next part of work we have conducted was the development of a thermally improved prototype housing. This housing was designed to achieve a number of criteria to ensure that the motion and direction sensor was thermally stable while ensuring the required shielding parameters were met. We have studied several different possible manufacturing techniques for the housing. The main categories of materials that can be used for the housing are plastic or metallic materials. Plastic material alone does not provide the necessary electromagnetic shielding so post-processing is required. The additional process in this situation was metal plating of the housing. Manufacturing the housing from metallic materials is a novel and innovative approach. We also carried out studies on the thermal conductivity. It was discovered that there is no difference in the thermal conductivity between plastic materials with and without stainless steel fibres. We continued to investigate different materials, fillers and coating to manufacture the housing. An existing housing geometry was selected to perform the shielding tests and the thermal stability tests with an existing sensor. A prototype mould was built to inject different kind of materials (acrylonitrile butadiene styrene (ABS), glass fibre reinforced PA6 and PC) with and without conductive fillers (stainless steel fibres) for the electromagnetic (EM) shielding properties. Some of these prototypes were coated with a conductive layer. Different kinds of coating were tested (electroplating of Cu-Ni, physical vapour deposition of Al and conductive painting). Furthermore, two metallic prototypes were machined from aluminium (Al) and magnesium (Mg) blanks. The EM shielding properties and the evaluation of the thermal stability of all these housings were carried out by MSL. A prototype mould was built to inject several thermoplastic materials. The selected materials for testing are given on the following table. Some of these materials were combined with conductive fillers (stainless steel fibres) and / or a conductive coating.

The EM shielding properties of the housing are difficult to predict because they depend on a variety of parameters such as operating frequency, the nature of the emitting source, the housing material, the wall thickness and the geometry. In our case (near field, small distance from the source), we have a high wave impedance (electric field higher than magnetic field). For this reason, we decided to test the effect of conductive fillers in the housing material.

After successful completion of the development of all independent elements of the detector we moved to integration and testing. The main goal was to develop a working prototype of the motion and direction sensor and to benchmark its parameters. We began by manufacturing a multilayer board with chips. All the partners involved in this part of the project put effort into successful production of different variants of the multilayer board integrated with antenna. After production, the circuit boards were assembled by hand and a variety of tests were performed to establish the integrity of the circuit design. Here are exemplary photos of validated prototypes of different modules for motion and direction sensor module.

Next, we assembled the complete motion and direction detector for security applications and automatic door openers, i.e. assembled the printed circuit with chips inside the housing. Finally, we performed prototype testing.

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