. ECEN 5341/4341 Lecture 12 Feb 12,2014. Amplifiers A Space 2.Nonlinear Effects of AC Fields on Cells A Rectification B. Mode Locking C. Coherence D. Minimum Detectable Fields . Amplifiers. 1. Basic Definition
2.Nonlinear Effects of AC Fields on Cells
B. Mode Locking
D. Minimum Detectable Fields
2. A typical transistor amplifier will extract energy from a DC source. Note with a BJT the control signal is separated in energy from the signal to be controlled. With MOSFET they are separated in space.
3. A parametric amplifier extracts energy from an AC source that is at a higher frequency.
4. A stochastic amplifier extracts energy from a noise source.
The membranes are typically 5 to 10nm thick while the cell may range from a few micrometers to a centimeter or so in length. The effective membrane resistance (Rm) per unit area takes on values of 0.14 to 15 Ω/m2in the transverse direction. This corresponds to resistivities in the range of ρm = 107 Ω m to ρm= 10 9 Ω m. The relative dielectric constant for the membrane is typically in the range of 2 to 4. Both the surrounding fluid and the interior of a cell have resistivitiesρf of about ρf= 2 Ω m and a relative dielectric constant of 50 to 80.
Where Jm is the current density through the cell and ρ is the resistivity of the membrane. Typical cell membrane thicknesses are t= 6 to 10 nm, and typical dimensions are 10 to150 µm. Setting L = 100 µm and ρ2t =10Ωm2 V = (10Ωm2+2x10-6Ωm2)Jm
Currents through a membrane.
Note the membrane is a poor rectifier at frequencies
Below approximately 1to 10MHz
At high frequency have not detected nonlinear characteristics at low
Power levels with very sensitive receivers.
Equation and apply a voltage Vm = Vo +V1cos ωt. A Taylor series expansion gives
This give a DC current off set and a second harmonic
Also shows abnormalities in Chick Embryos for 1µT pulses. Add noise and it goes away.
Conservation of energy is