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A. Schröder, M. Kupnik, P. O´Leary, E. Benes, M. Gröschl:
"A capacitance ultrasonic transducer for fast flow-measurements in hot pulsating gases";
in: "Proc. IEEE Sensors 2004", D. Rocha, P.M. Sarro, M. Vellekoop (Hrg.); IEEE, 2004, S. 240 - 243.

A novel high-temperature resistant capacitance transducer
is presented. It is designed for an ultrasonic transit-time
flowmeter (UFM) and meets two main requirements not fulfilled
by common piezoelectric transducers: Firstly, a special
construction based on an oxidized and patterned silicon
backplate combined with a metallic membrane enables
transducer operation at elevated gas temperatures of up to
600 °C. Secondly, the geometry and material parameters
were chosen to obtain a broad-band device allowing for
high signal slew rates and pulse repetition rates. As proven
by measurements in a test bed environment, this new transducer
suits for internal combustion engine exhaust flow
measurements in between the catalytic converter and the
end of the exhaust pipe. Preliminary results for the exhaust
mass flow (up to 160 kg/h) of a typical automotive engine
measured with these novel transducers are given and compared
to the mass flow calculated from fuel consumption
and air/fuel ratio ( ?).

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