Airborne ultrasound phased arrays

This work shows the development and the characterization of an air-coupled ultrasonic phased array using a 3D-printed waveguide. The waveguide allows an element distance of λ/2 with existing ultrasonic transducers exceeding λ/2 dimension. With an element distance of λ/2, a grating-lobe-free radiation characteristic is realized. In addition to the improved radiation characteristic, the spatial separation of transducers and the acoustically active aperture is achieved. This allows the free arrangement of the ultrasonic transducers in the design space and the use of larger and more powerful ultrasonic transducers, since the transducer size is not limited by the element arrangement. Apart from the design of the waveguide, phased array electronics is presented which enables transmit and receive beamforming of ultrasonic signals. Furthermore, the required signal processing architecture for receive beamforming is presented. The signal processing uses GPU-acceleration to achieve an immediate evaluation of the received signals. Different applications are demonstrated with the built up system. The first application is a gas flow metering based on the the time-of-flight-principle. By exploiting the electronic beam steering, the measurable velocity range is extended compared to conventional single transducers. Furthermore, the imaging based on pulse echo localization is demonstrated. This method is state of the art in medical imaging as well as in sonar systems under water. In this thesis, this method is transferred to air-coupled ultrasound. For this, a characterization with different measurement series is carried out. It was possible to demonstrate ranges up to 6 m. The achievable lateral resolution for separating two adjacent objects is at least 12°. Furthermore, successive objects can be resolved with an axial resolution of 200 mm. In another experiment the beamforming of sound waves is made visible with the help of schlieren photography. The necessary image processing is presented. The schlieren images are used for the comparison between simulation and the real beamforming behavior. The developed platform enables the evaluation of additional ultrasonic applications. These include non-destructive testing using Lamb waves, which are the subject of current research at the Measurement and Sensor Technology Group at the Technische Universität Darmstadt. Furthermore, the field monitoring for robotic applications is already being investigated using the array and compared with established sensor systems. In addition to these ultrasound applications, the developed platform is a model system for various questions of signal processing and communication technology