MRI as a medical diagnostics tool is still unavailable to the majority of the developing world. Therefore the design and development of new low-cost hardware are essential. The design of gradient coils corresponding to this hardware is necessary for conventional imaging and reconstruction methods to be used. The target field method, which was originally developed to deal with longitudinal main magnetic fields, is applied to a transverse field, as produced by a Halbach permanent magnet array. Using this method current densities for gradient fields in the three spatial directions are derived. Subsequently, using stream functions, wire patterns for the three gradient coils are determined. These are verified using a commercial magneto-static solver. Furthermore, one of the gradients is constructed to validate the performance of the method. The measured fields are in good agreement with the simulations and their prescribed target fields. This confirms that the proposed method provides a reliable way to design and manufacture gradient coils for various requirements. Based on the experimental review of the constructed coil three optimized gradients are proposed for the low field MRI system developed at the LUMC in cooperation with the TU Delft. The method can also be readily generalized to other geometries and requirements due to the robust fundamental physical basis and accuracy with respect to computer simulations.

Internet of things (IoT) applications become more and more prominent in our modern society. IoT has the potential to improve business processes and change the ways we live. KPN New Business has a high affinity with IoT projects and supplied the problem definition that this project builds on. The project has been done in close collaboration with KPN.

This document describes the design process for a stand-alone obstruction detection system for supermarket environments. The focus lies on obstructions near emergency exits, where they pose safety threats and obstructions in shopping aisle, where they hinder customers. The system should detect obstructions and communicate the presence of an obstruction to a central server. The communication is however not within the scope of this design report.

Five sensing techniques were considered for the detection system, ultrasonic ranging sensor were deemed the most suitable for this application. Ultrasonic sensors lend themselves well for IoT applications as they are easy to implement, cheap and operate on low power.

A MaxBotix MB1300 sensor was chosen for the implementation of the prototype as it offers an Analog Envelope (AE) output of the measurements. This allows for multiple objects to be detected in a single measurement. Furthermore, the MB1300 sensor has the largest beam width in the AE product line and can thus cover the most surface area.

The processing of the measurements in the prototype is done using an Arduino Mega 2560. The Arduino board allows for easy prototyping and has sufficient memory on-board to store and process the measurements. The measurements are sampled using the built-in ADC of the Arduino at a sampling frequency of approximately 8.93 kHz. The sampling frequency is a trade-off between the spatial resolution of the system and the memory required to store the measurements.

An algorithm is developed for the detection of objects from the sampled measurements. The process involves the windowing of the measurements to only look at relevant samples. A background subtraction is performed to avoid the detection of scenic objects, and the objects are detected using a threshold.

A data structure was created in order to store the detected objects. An algorithm was developed to check whether detected objects remain static. If an object is repeatedly detected it is marked as an obstruction. If an object goes unseen for a certain period, the object is removed from the memory. Thresholds for when an object is marked as an obstructions, the deletion of objects and measurement intervals are suggested for emergency exits and shopping aisle systems. These should however be verified in further development.

The performance of the system was evaluated in testing environments for the emergency exits and shopping aisles. Testing results showed that the system performs well on most design criteria. The area covered by a single sensor was however below expectations. This could be problematic for the implementation of the system in shopping aisles, as lots of sensors would be required to cover entire shopping aisles. Also some false positives occurred in the detection of obstructions. This could however easily be solved with minor changes to the detection algorithm.

Based on the testing results the conclusion is drawn that the design goals are partially met. The system is able to detect obstructions, but does not yet operate as a stand-alone unit. This design goal was however considered in every design choice. Power consumption of the prototype remains to be tested, this however is also dependant on the communication system.

Recommended is to further look into the power consumption of the system, the implementation of a multi-sensor system to cover more floor area in shopping aisles, and to reconsider CCTV images for the detection of obstructions in shopping aisles.