Public Address systems that include a setup with at least one microphone and speaker can suffer from acoustic feedback. This results in an annoying howling effect which can damage hardware and human hearing. To solve this issue, an adaptive filter that estimates the feedback path and uses this estimate to cancel the feedback can be designed. However, because the adaptive filter receives signals from both the microphone and the feedback, and because sound signals are generally correlated over time, the estimate becomes biased. To reduce this bias, the speaker signal can be decorrelated from the input. In this thesis several options to decorrelate these signals are explored, and they are evaluated based on decorrelation performance and effect on audio quality. Frequency shifting is selected as the best decorrelation method as it provides the most decorrelation while retaining audio quality. Finally it is shown that using Frequency Shifting to decorrelate the microphone and speaker signal indeed improves the estimation of the feedback path.

This report is written as part of the Bachelor Graduation Project in the third year of the Electrical Engineering Bachelor programme at the Delft University of Technology. This report is made by a subgroup that is part of a larger project dedicated to finding a solution to frequency feedback in electroacoustic systems, also known as the Larsen effect.

This problem has a long history of literature and many solutions to this problem have been presented. For this project, the focus lies on the application of Adaptive Feedback Cancellation (AFC). This technique uses estimations of the Room Impulse Response (RIR) to minimise the feedback component. This report focuses on estimating such a RIR in the case of a PA system. Several methods will be discussed and compared by implementing and testing them in a simulation environment built in Matlab. The different methods are subjected to a set of performance measurements that provide the necessary information to see for each method and situation if and how the results measure up against a set of predetermined system requirements. From the researched algorithms, one is chosen as the one to be implemented in the final design of the group. At last, some considerations and recommendations are given for implementing one of the algorithms into software and hardware components.

The most promising method for acoustic feedback control in public address systems is adaptive feedback cancellation (AFC). This approach is based on making an estimation of the room impulse response, which is used to subtract an estimate of the feedback from the microphone signal. A postfilter is often used to improve the performance of such an AFC system by reducing residual feedback or increasing stability. The postfilter implemented in this thesis focuses on the latter. It consists of two modules: howling detection and howling suppression. The final design makes use of the peak to harmonic power ratio criterion (PHPR) and second order digital Butterworth notch filter respectively. Simulation measurements show a successful suppression of howling as long as the loudspeaker signal does not
get saturated.

This report discusses one part of a project consisting of three parts. The goal of the project is to design a battery less sensor powered by RF energy fields present in an office environment. The sensor is able to measure temperature and is able to communicate wirelessly using a low power communication protocol. In this project the use case of a building is explored. In this thesis the possibilities of low power sensing, processing and communicating are investigated. Different options for sensing, processing and communication chips are discussed. Measurements in terms of communication range and power consumption are performed on the system. A TMP-102 temperature sensor, an ATtiny84A microcontroller and an SX1272 LoRa module are chosen. Roughly 4 mJ is needed to perform a measurement and transmit it. Further research is needed to reduce the energy consumption even further.

This report discusses one part of a project consisting of three parts. The goal of the project is to design a battery less sensor powered by RF energy fields present in an office environment. The sensor is able to measure the temperature and is able to communicate wirelessly using a low power communication protocol.In this report the energy conversion and storage of the system will be discussed. A high-frequency signal coming from an antenna must be converted to an output signal which is functional for the communication module. Therefore a steady 3.3 V DC output needed to be created with a rectifier circuit. In order to achieve maximum power transfer to the load, a matching circuit with the RF energy harvesting antenna needed to be designed. The main challenges were to achieve a high enough input voltage to reach the threshold voltage of the diodes of the rectifier and to rectify the AC input as efficient as possible. To tackle these challenges a design with a Greinacher rectifier with low-threshold Schottky diodes and a DC/DC booster is presented.

This report discusses one part of a project consisting of three parts. The goal of the project is to design a battery less sensor powered by RF energy fields present in an office environment. The sensor is able to measure the temperature and is able to communicate wirelessly using a low power communication protocol. In this project the use case of a building is explored. This thesis treats the RF energy harvesting part, which scavenges the RF power out of the ether and delivers it to the rectifier to convert and store the energy. First the spectrum has been analyzed to determine the most suitable frequency band. An antenna has been designed to harvest as much power at the chosen frequency. To make the power transfer from the antenna to the rectifier as efficient as possible, a matching circuit for matching the impedances is implemented. In this report, a Planar Inverted-F Antenna is designed to meet all the given requirements.

This bachelor thesis is written as part of the curriculum for the bachelor Electrical Engineering at the Delft University of Technology. The thesis is part of the course EE3L11 - Bachelor Afstudeer Project and took place from April 2017 until July 2017.

This document describes the development of a system that is able to drive electric drum brakes, the brake control unit (BCU). The BCU is a subsystem of a larger project; a braking system that minimizes the force between a trailer and a car when braking. The ultimate goal is to let the trailer completely brake for itself.

To achieve this, two other subgroups have designed a control algorithm and a force sensor readout circuit that measures the force. The BCU receives a desired braking force from the control algorithm that should be exerted in order to eliminate the force between car and trailer.
This input force covers a certain range, so the BCU should be designed such that the braking force of the brakes can be regulated. For this purpose a power supply, current controller and lookup table are designed.

The developed power supply is able to provide a constant voltage to the solenoids inside the electric brakes. The power supply consists of a DC/DC converter, which is powered from a car battery. As a consequence, the input voltage of the DC/DC converter is dependent on the state of charge of the battery. Nevertheless, the output of the designed converter is able to provide a constant DC voltage with a maximum current of 8 A.

The designed current controller makes use of a PWM driven current source, which controls the output current of the DC/DC converter. Besides this source, an algorithm that estimates the duty cycle of the PWM signal is derived, based on the desired current through the solenoid.

Last, a lookup table is implemented that determines which current is needed for specific input forces. The table makes use of inter- and extrapolation between measured test results to calculate the right current for every input force.