ECE 405 Final Exam Qualitative Notes

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Classification of Devices (3 types)

Classification of Devices (3 types)

Diagnostic, Therapeutic, Assistive

Examples of diagnostic devices

temperature, blood pressure, ECG

Examples of therapeutic devices

defibrillators, electrocautery, radiation therapy

Examples of assistive devices

artificial limbs, cochlear implants

Sensor (definition)

a device that converts an environmental condition into an electrical signal

Actuator (definition)

a device that converts a control signal (usually electrical) into mechanical action (motion)

Resistive Temperature Devices (RTDs) (definition)– materials whose resistance changes in accordance with temperature, have a positive temperature coefficient

Thermistors (definition)

semiconductor materials, negative temperature coefficient

Thermocouples (definition)

pair of dissimilar metals joined at one end, so when there is a temperature difference between the joined ends and the open ends, a thermal EMF is generated and measured at the open ends

Temperature transducers (3 types)

Thermoresistor, thermocouple, thermistor

Pros and Cons of temperature transducers

Thermoresistor (linear, low cost, but low temperature coefficient, i.e. low sensitivity), thermocouple (ultra small but low sensitivity), thermistor (high sensitivity, small, but non-linear)

Other methods of temperature transduction (4 types)

infrared radiation, liquid crystals, MRI, ultrasound thermometry

Radiation thermometry

relationship between surface temperature and radiant power, non-contact temperature measurement

What is measured in radiation thermometry

total radiant power (area under the curve)

Pros and Cons of LCD Thermograph

low cost (pro), poor sensitivity and requires contact (cons)

Glaucoma

raised intraocular pressure that causes vision disturbances and ultimately blindness

Bed sores

ulcers that develop because of excessive pressures applied to skin for extended period

Maximum sustained skin pressure

40 mmHg (only exception is the soles of the feet)

Intraocular pressure measurement

tonometer uses indentation and flattening to measure pressure in eye by using a puff of air

Laplace’s Law

pressure differential of cylinder (vessel): T/r pressure differential of sphere: 2T/r where T is tension in the wall/barrier

Imbert Fick Law

if the wall of a sphere is locally flattened, the pressure is force/area

Direct methods to measure blood pressure

intravascular: fiber optic, fluid filled catheter extravascular: strain gauge

Indirect methods to measure blood pressure

auscultation, oscillometry, tonometry

Auscultation

indirect method to measure blood pressure using Korotkoff method (pressure cuff and stethoscope)

Oscillometry

indirect method to measure blood pressure in cuff

Tonometry

indirect method to measure blood pressure by measuring the pressure required to flatten the vessel wall

Kortokoff method

blood pressure decrease, hear faint tapping sounds (kortokoff sounds) heart at systolic pressure, sounds become muffled at diastolic pressure

Ventricles during systole

contract

Ventricles during diastole

relaxed and full

Pathway of blood through the heart

from the body, into heart via vena cava, right atrium, tricuspid valve, right ventricle, pulmonary artery, lungs, pulmonary veins, left atrium, bicuspid valve, left ventricle, aorta, delivered to the body

Poiseuille’s Law

relates pressure differential and flow rate to the viscosity and tube size (gives resistance formula)

Fick’s first law

JD = -D*dC/dx where JD is the diffusion flux, and D is the diffusion coefficient

Osmotic pressure

water molecules will want to diffuse across concentration gradient, pressure created due to concentration gradient across a membrane

Osmolarity

concentrations of dissociate particles

Van’t Hoff Equation

pi=RT([C1]-[C2])

Causes of Biologic Charge Separation

positive/negative ions, diffusion, mobility coefficients, semipermeable membranes

Passive membrane channel properties

nongated channels, responsible for resting membrane potentials, ion specific, bidirectional

Active membrane channel properties

voltage gated channels, responsible for action potentials, ion specific, bidirectional

Nodes of Ranvier

regions of axon not insulated by myelin, allows for generation of rapid electrical impulse along the axon (called saltatory conduction)

Automaticity (definition)

automatic nature of the heartbeat, heart will beat if myocardial cells remain alive

Sinoatrial node

only region in heart that demonstrates spontaneous electrical activity, cells don’t maintain a resting membrane potential

Pacemaker potential

slow spontaneous depolarization of the SA node during diastole, from -60 to -40 mV threshold

Resting membrane potentials of myocardial cells

-90 mV

Conduction of Impulse from SA node

spreads quickly to the atria, slowly to the AV node, time delay between excitation of atria and ventricles, rapid spread in Purkinje fibers

How does electrocardiogram work

action potentials spreads from atria to ventricles, voltage measured between these two will vary in a way that provides a picture of the electrical activity of the heart

Two types of ECG leads

bipolar (record voltage between electrodes placed on wrists and legs) unipolar (record voltage between a single exploratory electrode and ground electrode built into the electrocardiograph)

How many leads for a standard ECG

12 leads

Distinct ECG waves (3 types)

P, QRS, T waves represent changes in potential between two regions (not action potentials)

P-wave physical meaning

spread of atrial depolarization

QRS-wave physical meaning

spread of depolarization into ventricles

T-wave physical meaning

repolarization of ventricles

Dipole model of the heart

superposition of dipole moments of each individual cardiac cell for a net dipole moment

Einthoven’s Triangle

three limb leads form an equilateral triangle with dipole located at the center

Augmented Terminal Reference Limb Leads (3 types)

aVR, aVL, and aVF

12-lead electrocardiogram

3 standard leads, 6 precordial leads, 3 augmented leads (Wilson’s central terminal)

Ideal properties of amplifier

infinite gain, infinite bandwidth, infinite input impedance, infinite CMRR, zero output impedance, zero noise

4 rules of Op Amp

no current can enter the terminals, output voltage is gain times differential input voltage, V+=V- via virtual ground property, opamp needs two rail voltages to power it

Comparator Op Amp Application

detection of QRS complex in ECG

Voltage follower Op Amp Application

interfacing high impedance sensors such as microelectrodes or microphones

Properties of instrumentation amplifier

differential amplification, very high gain, very high input resistance, common-mode rejection

EEG (definition)

electroencephalography, uses 10-20 standard lead system, used to identify sources of brain activity

Sources of noise when measuring biopotentials

power lines, other biopotentials, motion artifacts, electrode noise, circuit noise, common mode noise

Power rating of electrical outlets

110V AC with respect to center tap

Wall socket contacts (3 types)

Hot (black), Neutral (white), and Green (ground, center tap)

Ground faults (definition)

short circuit between the hot conductor and ground, injects large currents into the grounding system

Bioelectric Stimulation depends on

current density

Macroshock

lightning, instruments, externally applied currents spread throughout the body via contact with skin (dry skin has high resistance, limits current flow through body)

Microshock

implantable catheters leakage, internally applied current flows through the heart (low tissue impedance below the skin, takes less to do serious damage/kill)

Grounding Philosophy 1

if every object is maintained at ground potential, subject can never have voltage drop across body (not foolproof, e.g. ground faults)

Grounding Philosophy 2

eliminate use of grounds in system/environment, everything is at same potential

Double insulation technique

enclose circuit/system in an insulating chasis which is grounded

Ground fault circuit interpreters

use an electrical circuit to monitor current flow through hot and neutral wires of outlet, if there is a difference between the currents, it trips the circuit breaker and removes the power

Transformer isolation

power supply and instrument are “connected” via transformers, not direct contact so power supply is isolated

Optical isolation

used in simple circuit designs, electronic component that transfers electrical signals between two isolated circuits using light

Piezoelectricity (definition)

piezoelectric materials generate an electric potential when mechanically strained or electric potential and cause physical deformation of the material

Piezoelectric effect

converts mechanical energy (deformation of crystal) into electrical energy

Inverse Piezoelectric Effect

converts electrical energy (electric potential) into mechanical energy (deformation of crystal)