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Electromagnetic Blood Flow Meter Dr. Erdem Topsakal, Advisor Brian McCalebb Taffa Porter Kyle Eubanks Nashlie Sephus

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Electromagnetic Blood Flow Meter Dr. Erdem Topsakal, Advisor Brian McCalebb Taffa Porter Kyle Eubanks Nashlie Sephus. Outline. Problem Statement Solution Introduction/Historical Information Technical Constraints Practical Constraints

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Presentation Transcript
slide1
Electromagnetic

Blood Flow Meter

Dr. Erdem Topsakal, Advisor

Brian McCalebb Taffa Porter Kyle Eubanks Nashlie Sephus

outline
Outline
  • Problem Statement
  • Solution
  • Introduction/Historical Information
  • Technical Constraints
  • Practical Constraints
  • Design Approaches/Tradeoffs

- Testing Apparatus

- Calibration

- Probe

- Electronics

  • Timeline
  • References
problem
Problem
  • The electromagnetic blood flow meters were originally used by the University of Mississippi Medical Center.
  • Obtaining replacements is no longer possible.
  • Other commercially available flow meters proved inadequate.
solution
Solution
  • Reproduce and improve the original probe
  • Reproduce similar results to the original meter
  • Minimum Cost
  • Dependable
  • Easy to use
  • Obtain accurate results
slide5

Electromagnetic Blood Flow Meter

  • What Are Flow Meters?
  • Electromagnetic blood flow meters measure blood

flow in blood vessels

  • Consists of a probe connected to a flow sensor box
electromagnetic blood flow meter
Electromagnetic Blood Flow Meter
  • Why They Are Used?
  • Offers quantitative data during surgical

operations

  • Provides a functional assessment of

newly joined vessels, grafts and organs

  • Used in prosthesis in conjunction with

cardiovascular surgical procedures

  • Most accurate results through both

acute and chronic implants

electromagnetic blood flow meter7
Electromagnetic Blood Flow Meter

How Do They Work?

  • Faraday\'s Law of Magnetic Induction
  • Liquid acts as a conductor
  • Voltage is induced directly related to the average flow velocity
  • “The faster the flow rate, the higher the voltage”
  • Voltage is measured by sensing electrodes mounted in the meter tube
  • Voltage is then sent to the

flow sensor box

outline8
Outline
  • Problem Statement
  • Solution
  • Introduction/Historical Information
  • Technical Constraints
  • Practical Constraints
  • Design Approaches/Tradeoffs

- Testing Apparatus

- Calibration

- Probe

- Electronics

  • Timeline
  • References
measurement accuracy
Measurement Accuracy
  • Affected by:

- Stray magnetic fields detected by electrodes

- Non-uniform magnetic field

- Turbulent fluid flow

- Non-homogenous fluid

  • Accurate to within ±1 cm/s from 0.1-1 m/s

- 10% maximum error at 0.1 m/s

- 1% maximum error at 1 m/s

maximum fluid velocity
Maximum Fluid Velocity
  • Fluid velocities in an aorta

- 89±9.5 cm/s during heart contraction

- 36±6.0 cm/s between contractions

  • Fluid velocity for flow meter

- 1 m/s maximum

  • Importance of low maximum fluid velocity

- Maximizes accuracy for low fluid velocities by

allowing more precision in A/D conversion

conductivity
Conductivity
  • Calibrated conductivity range
    • Conductivity of blood

- 70 Siemens per centimeter

- Varies by up to 20% based on flow rate

    • Acceptable conductivity range of flow meter

- 60–80 Siemens per centimeter

slide13
Size
  • Probe Size
    • 22 mm inner diameter
    • Reasoning

- Requested by sponsor

- Diameter of aorta ranges from 21-35 mm

- Larger aortas taper down to smaller diameters

sustainability
Sustainability
  • Implanted for 2-3 months
  • Protection of wire leads, magnetic core, & wire coil
  • Maintenance of electrodes
ethical
Ethical
  • Designed for cow’s aorta only
  • Not approved or tested for human use
outline17
Outline
  • Problem Statement
  • Solution
  • Introduction/Historical Information
  • Technical Constraints
  • Practical Constraints
  • Design Approaches/Tradeoffs

- Testing Apparatus

- Calibration

- Probe

- Electronics

  • Timeline
  • References
slide21

Testing Apparatus

  • Via Aqua 1800 - $25.00

- 480 GPH, variable flow rate

- 3/4” connections

- Saltwater safe

  • Acrylic tubing - $3.32 / 6ft.

- 7/8” OD, 3/4” ID, 1/16” thickness

- Insulating material

slide22

Testing Apparatus

  • Dialysis tubing - $5.25 / 10ft

- Will be used in future testing

- 22 mm diameter

- 1 mil thickness

- Closely replicates the conductivity of an aorta

- May use multiple layers to adjust the conductivity or increase the water pressure it can withstand

calibration
Calibration
  • Calibration and error can be minimized by selecting the proper voltage source waveform
    • DC

- Voltage drift from polarization of electrodes

    • Sinusoidal AC

- Reduces voltage drift by changing polarity

- Induces emf in electrodes from magnetic flux variation

    • Square-wave AC

- Reduces voltage drift by changing polarity

- Reduces emf in electrodes from magnetic flux variation

slide24

Calibration

  • Why does the output voltage of the probe not directly correlate to the fluid velocity?
      • Ideally, they are directly proportional
      • However, sources of error include:

- Stray magnetic fields picked up by electrodes

- Resistive and capacitive current leakage

- Voltage loss through tubing

- Voltage drift

- Noise

calibration25
Calibration
  • Fundamentals of Calibration
    • Under no flow conditions

- Voltage observed is the combination of all sources of error since no voltage from fluid flow

    • Zero the output waveform

- Cancels out all unwanted voltage contributions

- Output now has a zero baseline voltage

    • Output voltage is now directly proportional to the fluid velocity
calibration26
Calibration
  • Procedure

- The most correct solution is to subtract the entire unwanted waveform

- Requires unnecessary computations

- Sampling occurs at the same place every cycle

- Under no flow, calculate the average voltage at the

desired sampling location for every cycle over some

period

- Subtracting this voltage for every sample gives the voltage contribution due to fluid velocity alone

outline27
Outline
  • Problem Statement
  • Solution
  • Introduction/Historical Information
  • Technical Constraints
  • Practical Constraints
  • Design Approaches/Tradeoffs

- Testing Apparatus

- Calibration

- Probe

- Electronics

  • Timeline
  • References
probe
Probe

Key components

  • Magnetic core
  • Magnet wire
  • Electrodes
probe29
Probe
  • Magnetic cores
    • Permeability

- Describes how much a material is affected by magnetic fields and how strong a field it can generate

    • High permeability results in:

- A stronger magnetic field

probe30
Probe
  • Magnetic cores
probe31
Probe
  • Magnet wire

Key factors

- Thin

- Well-insulated

- Close to range of 34 gauge (commonly used in industrial electromagnetic blood flow meters)

- Availability

- Low cost

probe32
Probe
  • Electrodes

Desirable qualities

      • Low resistance

- More sensitive

      • High capacitance

- Reduces source impedance and signal attenuation

electrodes capacitance
Electrodes - Capacitance

Platinized Platinum

Capacitance (µF)

Frequency (Hz)

electrodes resistance
Electrodes - Resistance

Resistance (kΩ)

Platinized Platinum

Frequency (Hz)

electronics
Electronics

Flow sensor box

references
References

[1] Shercliff, J.A., The Theory of Electromagentic Flow-Measurement. Cambridge: University Press, 1962,pp. 2-4, 125.

[2] Flowmeter Directory. Flowmeter Directory. 2007.

http://www.flowmeterdirectory.com/flowmeter_electromagnetic.html

[3] Tavoularis, S., Measurement in Fluid Mechanics. Cambridge: University Press, 2005, pp. 217.

[4] Omega Engineering. Omega Engineering. 2006. http://www.omega.com/techref/flowcontrol.html

[5] EesiFlo. Eesiflo. 2007. http://www.eesiflo.com/applications.html

[6] Braun, U., and vetJosef, F., “Duplex ultrasonography of the common carotid artery and

external jugular vein of cows,” American Journal of Veterinary Research, vol. 66, no. 6,

pp.962-965, 2005.

[7] Khan, S. R., and Islam, M. N., “Studies on the prospect of bioprostheses by cow aortic valve for human use,” Bangladesh Med Res Counc Bull, vol. 17, no. 2, pp. 75-80, 1991.

[8] Wyatt, D. G., and Phil, D., "Problems in the Measurement of Blood Flow by

Magnetic Induction," Phys. Med. Biol., vol. 5, pp. 369-399, 1961.

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