Impedance/Admittance
What is the formula for admittance?
Y^2=B^2+G^2
Where is conductance plotted?
On the abscissa.
What is impedance?
The vector sum of resistance and reactance. When an alternating force is applied to a mechanical system, the following apply: -Force is minimal when velocity is maximal and vice versa, velocity leads force by 90 degrees. -Force is minimal when velocity of the mass is maximal and vice versa, velocity lags force by 90 degrees. -Force in a frictional (spring-less & mass-less) system is at the same value as velocity.
T of F: resistance is independent of frequency
True
What is the formula for impedance?
Z^2=R^2+X^2
As frequency increases, stiffness reactance....
decreases
As frequency decreases (or mass decreases), mass susceptance....
increases
As frequency increases (or stiffness decreases, stiffness susceptance....
increases
As frequency increases, mass reactance....
increases
Why must impedance be plotted as a vector?
-Because maximum velocity for each component (stiffness reactance, mass reactance and resistance) occurs at different points in the force cycle.
660 Hz probe tones are good for what?
Identifying mass-loaded pathologies like ossicular discontinuity.
Stiffness reactance can be decreased by....
-Decreasing stiffness or -Increasing frequency
When does notching occur?
-In B, G, and Y tymps as probe tone increases. Patterns include: 1B-1G, 3B-3G, 5B-3G.
Mass reactance can be increased by....
-Increasing mass or -Increasing frequency
In polar notation, two numbers represent what?
-One number represents that admittance vector and the other represents the phase angle of the admittance vector. (1 angle, 1 end of vector)
Where are resistance and reactance plotted?
-Resistance is on the X, reactance is on the Y -Stiffness is negative because velocity leads force
When is a system in resonance?
-at the frequency where mass and stiffness reactance are equal.
A normal tymp must meet these requirements:
-extrema must not exceed 5B-3G -distance in dap a between outermost G maxima must be smaller than distance between B maxima -distance between outermost maxima must not exceed 75 dapa for tymps with 3 extrema and must not exceed 100 for tymps with 5 extrema
Ossicular discont. is associated with what 3 things on a tymp?
-more peaks than the model -a distance between outermost maxima >75 dapa (3 extrema) or 100 dapa (5 extrema) -distance between the G outermost maxima > susceptance outermost maxima
Acoustic admittance can be expressed in what 2 ways?
-rectangular notation -polar notation
What is admittance?
-the reciprocal of impedance. It represents the ease of energy flow. The relationship between velocity and force is the opposite of impedance.
Explain 3B-3G.
ME is mass dominated and at 0 dapa, but stiffness dominated at pressure extremes; absolute value of ME resistance at 0 dapa is greater than mass reactance, and at pressure extremes, stiffness reactance is greater than ME resistance
Explain 5B-3G.
ME is mass dominated at 0 dapa, but stiffness dominated at pressure extremes; mass reactance is greater than resistance at 0 dapa, and at pressure extremes, stiffness reactance is greater than resistance.
Explain 1B-1G.
ME stiffness is dominated and ME resistance is less than the absolute value of the stiffness reactance.
What is a mechanical system?
Mass, elasticity and resistance
Which ordinates are stiffness susceptance (+BS) and mass susceptance (-BS) represented on?
Stiffness susceptance=positive ordinate Mass susceptance= negative ordinate
Explain 3B-1G.
ME resistance is greater than the absolute value of the stiffness reactance at 0 dapa and when the ME resistance is less than the stiffness reactance at the pressure extremes.
