Ultrasonic imaging in air using fan-beam tomography and electrostatic transducers

Abstract

Air-coupled ultrasonic capacitance transducers operating at frequencies of up to 1 MHz have been employed in a fan-beam configuration for the cross-sectional tomographic imaging of temperature fields and flow fields in air, and the location of solid objects. Separate transmitter and receiver transducers were manufactured using thin polymer dielectric membranes and polished metal backplates, and used to acquire through-transmission data. The fan-beam reconstruction was developed in LabVIEW â using a re-bin routine combined with a filtered backprojection algorithm and a difference technique to generate the cross-sectional images. The system was first used to reconstruct images showing the locations of solid objects positioned within the scanned region through interpretation of the arrival time of the transmitted ultrasound. The technique was then extended to image the temperature fields produced in air above a small heat source and the flow field produced by a nozzle connected to a regulated compressed air source. Reconstructed temperatures were within 4% of the measured background air temperature and 9% of the air temperature measured above the heat source. Reconstructed images of the flow field above a small nozzle were also presented, showing that the horizontal component of the flow velocity could be resolved using this method. Ó

An ultrasound-based system for temperature distribution measurements in injection moulding: system design, simulations and off-line test measurements in water

“…Using each transducer as receiver and transmitter, it is possible to measure the ultrasound velocity along a large number of sound paths and reconstruct the temperature distribution with appropriate algorithms. Acoustic or ultrasound tomography reconstruction techniques are used for the measurement of temperature distributions in silicon wafers [6], stored grains [7], fine water mist [8], cylindrical steel rods [9] and air [10]. An important requirement for the application of an ultrasound-based tomography system used in injection moulding are temperature (and pressure)-resistant ultrasound probes.…”

Ultrasound tomography

“…In this work temperature variations were imaged in a fluid using multiple hydrophones. Wright and co-workers have imaged the flow velocity and spatial temperature differences in air using electrostatic ultrasound transducers (Figure 9.9) (Ingleby & Wright, 2002;Wright & O'Sullivan, 2003;Wright et al, 1998). During this work they have used different transducer configurations.…”

“…All of their systems operated in the transmission mode and they recorded time of flight and received voltage amplitude data. Ingleby and Wright (2002) were also able to identify solid objects in the air flows using their ultrasound tomography system. Holstein et al (2004) imaged air flow velocity and spatial temperature distribution using a transmission system, as did Jovanovic (2008).…”