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  • 8/3/2019 Us Lab En

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    Open Diploma Thesis:

    Laboratory system for ultrasonic measurements of distance and speedDescription:Ultrasonic sensors are used in a large variety of applications such as the measurement of

    distance and speed, the detection of objects and object situations, object identification, non-destructive testing or medical imaging. Owing to their excellent characteristics, which includehigh range resolution, high precision and good reproducibility, high mechanical robustness andlong-term stability, a large measuring range that is adjustable with simple means, and a

    relatively low price. For communication and object detection under water (sonar), ultrasonicwaves are used almost exclusively due to the large attenuation of electromagnetic waves. Boththe basic metrological principles and signal processing methods are very similar for ultrasonicand radar measurement technology. Thus, for example, for many applications of non-contacting distance and speed determination, pulse echo methods are employed. The object

    distance to be determined is proportional to the roundtrip time of the emitted, reflected andreceived pulse-shaped wave packet; the object speed is the difference between thetransmission and receiving frequencies (Doppler shift). Drawbacks of the simple pulse echomethod (low exploitation of transmission power and thus limitation of range, restriction ofrange resolution and measurement precision due to pulse duration) can be eliminated byapplying what is referred to as pulse compression, using transmission pulses with a high time-bandwidth product, e.g. frequency-modulated pulses (termed chirps).

    Activities and objectives:Based on an existing prototype, a modern measuring site will have to be planned and set upwhich includes the measuring instruments needed to evaluate and quantify possibilities and

    limits of distance and speed measurements by means of ultrasound as well as importantparameters influencing measurement ranges and spatial resolution. This measuring set-up shall

    be suitable for use e.g. in studies carried out as part of lab classes. For two modes of operation(pulse echo and pulse compression methods), echo signals are to be recorded as a function ofthe distance, size, number, speed and surface characteristics of different reflectors, employingseveral commercial ultrasonic transducers varying with respect to their operating principles,

    resonance frequencies and bandwidths, directional characteristics etc. All parameters of thetransmission signal (mean frequency, bandwidth and/or pulse width, pulse shape, amplitude,repetition frequency) should be adjustable by the operator. In order to achieve almost uniformsensitivity throughout the coverage area, echo signals must be amplified by a suitableamplification unit, depending on their roundtrip times and amplitudes. The required signal

    processing routines may be implemented either with the help of a microprocessor or a PC;system control and visualization shall be realized by means of a GUI (graphical user interface)

    in Matlab/ LabView.Desirable know ledge and requirements:Ultrasonic sensor technology, experience in electronic circuit design and hardware set-up,programming in LabView or MatLab, basic knowledge of (digital) signal processing.

    Contact:Dr.-Ing. Heinrich Ruser; [email protected]

    Division of Sensor Technology andMeasurement Systems (SMS)Univ.-Prof. Dr. Christian KargelInstitute for Measurement and AutomationDepartment of Electrical and Computer Engineering

    transducer

    objectsexcitation

    echo analysis

    usable object

    echo detection