Ultrasonic gas analyzer and method to analyze trace gases

Abstract

An ultrasonic gas analyzer includes an acoustic cavity through which an air sample is drawn by a low speed air pump or other mechanism. The cavity has a pair of ultrasonic wave transmitters/receivers on opposite sides of the acoustic cavity. An electronic circuit controls the transmitters/receivers so that a high frequency ultrasonic wave is propagated across the cavity and thereby through the gas flowing through the cavity. This ultrasonic wave reflects back and forward across the acoustic cavity and the transmitters/receivers receive this wave and supply a signal indicative of the wave to an electronic circuit. Based on the time of flight data for the ultrasonic wave being reflected in a gas/air mixture and in air and the amplitude of those reflected ultrasonic waves, a determination is made as to the gases within the gas/air mixture. This determination then can be displayed and an audio signal can be generated depending on the amount of detected gases. In one embodiment of the gas analyzer, a switch valve is used to selectively provide the gas/air mixture or air through the acoustic cavity. In another embodiment of the gas analyzer, two acoustic cavities are provided with a double concave reflector lens separating the cavities and each with a transducer at an opposite end from the lens. Air is drawn through one of the acoustic cavities and the gas/air mixture is drawn through the other of the acoustic cavities