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Ultrasonic Oxygen Sensing

Ultrasonic Oxygen Sensing

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Ultrasonic Oxygen Sensing

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  1. Ultrasonic Oxygen Sensing Logan Sammons

  2. Method of Oxygen Delivery • Steps of operation of oxygen concentrator • Take in atmospheric air • Run through a zeolite filter to remove nitrogen • Exhaust Nitrogen • Deliver 90-95% pure oxygen via onboard compressor

  3. Purpose of Gas Sensing Medical Applications • Assure that patient is receiving close to pure oxygen • Sound alarm when oxygen falls below an acceptable level Water Sanitation • Assure the proper amount of Ozone is being produced • Measureable level of water sanitation Airline Applications • Reduce the risk of hauling pressurized oxygen bottles • Space and weight considerations

  4. Method of Oxygen Sensing Transducer used with two ultrasonic speakers that operate at 25 kHz. • Transmit speaker excited with pulse from microprocessor • Piezoelectric transmit speaker produces acoustic wave turning electrical energy to mechanical energy • Acoustic wave travels through medium filling transducer body • Transmitted waveform impinges onto piezoelectric receive speaker turning mechanical energy into electrical energy • Time calculations made to determine what medium flowing through transducer

  5. How a Piezoelectric Speaker Works Contains a heavy polarized piezoelectric crystal material with an anode connection and cathode connection • When a electric field is present these polarized atoms align resulting in the creation of dipoles • When the dipoles are created the physical structure of the thin metal that makes up the speaker resulting in an acoustic wave at a set frequency

  6. Calculations Velocity of propagation (Vp) of an ultrasonic wave through a gas can be represented as shown below, where k is the ratio of specific heats and R is the gas constant. Oxygen: k = 1.40 and R = 259.8 Atmospheric Air: k = 1.40 and R = 287 Once Velocity is known the time of travel for an ultrasonic wave through a fixed distance is calculated as shown below, where R is the length of the transistor (1.254 inches = 31.85 mm). • Calculating these values for oxygen it is shown that: • Calculating these values for atmospheric air it is shown that:

  7. Results When Using Separate Transmit and Receive Speaker AtmosphericAir Oxygen

  8. Signal Processing Find zero crossover using two timers, Analog to Digital converter, and system clock to calculate time taken to travel down transducer. Calibration necessary due to manufacturing differences. Atmospheric Air Oxygen

  9. Future Plans Use a single speaker for transmit and receive by reflecting acoustic wave off far end of transducer.

  10. Calculations Being that now the wave has to travel down the transducer and back the time of travel will change. • Using the following equation the time of travel can be calculated, where a factor of 2 was included in the numerator to account for round trip time. Oxygen: Atmospheric Air:

  11. Possible Issues Length of time of transmitted wave is greater than the time of round trip travel (.

  12. Possible Fixes to Issues • Ground the transmit speaker to dictate length of transmit pulse with enough zero crossovers to allow for calibration. • Increase frequency of transmit and now receive speaker to obtain more zero crossovers.

  13. References