Understanding Electricity
The Basic principles of Electromagnetism
Figure 1: Water Analogy for Basic Electromagnetic Properties
In order to safely and effectively perform electro-acupuncture, an understanding of the basic principles of electromagnetism is necessary. The water analogy illustrated in Figure 1 has proven to be very helpful in understanding the basic properties for those without a technical background. A, the height of water in a dam, is analogous to Voltage. The higher the water in the dam, the stronger the force pushing water through pipe B. Similarly, the higher the voltage, the more pressure there is to “push” electrons through a wire. Voltage is measured in Volts (V). In electro-acupuncture we are using microvolts (billionths of a volt). Whereas in TENS or CES we are using microvolts (thoousants of a volt. And when you are using electricity to contract a muscle you are typically using 10s of millivolts. The difference is the resistance in the circuit.
Pipe B is analogous to Resistance. Just as the size of the pipe restricts the amount of water that can flow through it, the resistance of an object (ex. a resistor) restricts the number of electrons that can flow through it. Resistance is measured in Ohms (Ω). Metals, because of the abundance of free or loosely bound electrons in their molecular structure,metals allow electrons to flow relatively freely through them and thus have a low resistance. Some metals conduct electricity better than others. Gold is the best conductor, then Silver, then copper. Because gold does not tarnish, it is preferred for electrical connections. The tarnish that eventually develops on silver or copper connections increases the resistance through the connection and can lead to faulty or intermittent connections. Materials such as most plastics, rubbers, ceramics and other non-metallic materials are generally poor conductors of electricity. Because most water has lots of minerals in it, water, especially in the body, is vey conductive. Whereas the tissues in the body provide resistance.
C, the amount of water flowing through the pipe, is analogous to Current. Current is the measure of the flow of electrons through an object or substance. It is measured in Amperes (amps or A for short). In biological systems, we will usually be talking in terms of microamps (uA, or 1 x 10-6 amps), or milliamps (mA, or lx 10-3amps). The variable used to express current is I (for example I = 16 uA). Current Density is the amount of current flowing through a unit area, i.e. amps/meter2. In electrostimulation, the higher the current and current density, the stronger the sensation.
For current to flow, there has to be a complete circuit. That is why you have to have 2 point of contact on the body to perform electro-acupuncture. That way electrons can flow between the positive and negative poles of the voltage source.
D, a pond or reservoir, is analogous to a Capacitor. A capacitor stores electrons somewhat akin to a battery. Capacitance is the measure of the ability of an object (such as a capacitor) to store a charge. It is analogous to how large the pond or reservoir stores water. It is measured in Farads (F) and its variable is C. Skin has both resistance and capacitance.
E, the water wheel, is analogous to an Inductor. A typical inductor consists of a coil wound around an iron core. Just as the water wheel transforms the energy of the flowing water into the rotational energy of the water wheel, an inductor transforms the energy of the current flowing in the coil into a magnetic field. Also, just as the water wheel depends on the continuous flow of water to keep it turning, an inductor depends on the continuous flow of current to maintain the presence of the magnetic field. Inductance is the measure of the ability of an object (such as an inductor) to store energy in the form of a magnetic field. Its variable is L and it is measured in Henrys (H). The inductance is directly proportional to the number of turns of wire in the inductor. The more turns, the stronger the magnetic field.
here are other basic principles or definitions that are also useful to know:
The Right-Hand Rule
refers to the relationship between an electric current and magnetic field. Essentially it refers to the fact that if the thumb of the right hand is pointing in the direction of current flow, the four fingers point in the direction of circular rotation of the resulting magnetic field. This is the principle by which an inductor produces a magnetic field. Electromagnetism is how an electric motor works.
Magnetic Flux Density
The measure of the strength (flux) of a magnetic field per unit area. The unit of measure is Tesla. The strength of a magnet is more commonly measured in Gauss. 1 Tesla = 104 Gauss.
Ohm’s Law
The definition of the relationship between voltage and current in an electrical circuit. It is given by the formula V = I R, where V is in Volts, I is in Amps and R is in Ohms. For example, to find the voltage across a resistor of resistance 1kΩ with a current flowing through it of 1mA, then V = 1mA x 1kΩ = 1 Volt. So for a fixed resistance, increasing the voltage will increase the current.
Electric Charge
A fundamental phenomenon in nature first described through experiments in static electricity. There are two kinds of charge, positive and negative. Like charges repel and unlike charges attract. Negative charge is associated with an overabundance of free electrons, while positive charge is due to a lack of electrons relative to the number of protons in a substance. The unit of charge is the Coulomb, and its variable is q. It is defined as the amount of charge that flows through a given cross-section of wire in one second if there is a steady current of one Ampere in the wire. The force F between two point charges a distance r apart is given in the formula F = / 4πϵ0r2 (Coulomb’s Law). Thus, the force is inversely proportional to the square of the distance.
Ion
An atom or group of atoms that contain an electric charge.
Conductor
A substance that can conduct electricity by allowing electric charges (generally electrons) to move freely through the material. Typically, a “wire”.
Insulator
A substance that impedes the flow of electricity by restricting the movement of electrons in the material. Also called a dielectric. Typically, the plastic coating on a wire.
Breakdown Voltage VBR
Breakdown Voltage i.e. the voltage a which point the substance’s resistance goes from it’s original value to a lower value. This sometimes happens when doing electro-acupuncture. As you turn it up, suddenly the sensation can get stronger all of a sudden. This is why some machines modify the wave-shape. Instead of just a square-wave, it is modified to be 1/2 square wave and 1/2 a pulse. the pulse is designed to get you past the breakdown voltage.
Resistor
A Resistor is a power-consuming device whose electrical behavior can be completely characterized by its voltage-current (v-I) curve. The simplest resistor is a linear time-invariant (LTI) type, which has a linear v-I curve that doesn’t vary with time. Other kinds of resistors are the Linear time-variant (LTV), and the nonlinear resistors. Examples of an LTV resistor would be a stepped resistor and a potentiometer. Examples of nonlinear resistors are an incandescent lamp and a semiconductor diode. Resistors dissipate the power in the form of heat. In the case of a normal light bulb, the filament in the bulb gets so hot it glows, giving off light.
Diode
A nonlinear resistor whose typical v-I curve is shown above. The most significant characteristic of a diode is that it allows current to flow in one direction but resists it in the other. Ion pumping cords consist of a diode connected to two alligator clips.
Conductance
Is the inverse of resistance (I/R) and is thus the measure of an object’s or substance’s ability to conduct current. The units of measure are Mhos. It is not used much. But you might run into it.
Alternating Current (AC)
Direct Current (DC)
Describes a steady state voltage or current (polarized).
Polarized Waveform
A waveform that results in a net Polarized movement of current in one direction in the circuit. It is used intentionally in iontophoresis, where ions of a substance are electrically impregnated into the tissues. Polarized waveforms are also used to actively change the charge concentrations in various areas of the body(i.e. to treat inflammation or degeneration).
Power
The ability to do work. In electricity, it is expressed in Watts and is calculated by the formula P = 12R = VI.
Frequency
Often confused with pulse repetition rate. Strictly, frequency refers to the pulse repetition rate of a pure sinusoidal signal. Non-sinusoidal waveforms contain a mix of frequency components. Frequency is measured in Hertz (Hz), and its variable is f.
Pulse Repetition Rate
The rate at which a cyclical waveform repeats itself, measured in cycles per second (cps). Its variable is cps but most people also use f. From a practical point of view, frequency and pulse repetition rate can be used interchangeably but be sure you understand the difference. The higher the Pulse Repetition Rate or frequency, the more the sensation typically because the signal is “on” more often or more frequently.
Spectral Analysis
The determination of the frequency components in P(Watts) of a waveform. This is determined by a mathematical calculation called a Fourier Transform.
Spectrum Analyzer
An electronic device which performs a Fast Fourier Transform on whatever waveform is input into the machine. The output is shown on a TV or computer screen in the form of an x-y graph, with the frequency on the x-axis and the power (intensity of that frequency component) on the y-axis.
Period
The length of time it takes a cyclical waveform to repeat itself. It is also the inverse of frequency or 1/f. Its variable is T.
Duty Cycle
The percentage of time a cyclical signal is “on”. For example, the square wave shown at right has an “on” time of ton and a period of T. Therefore, the Duty Cycle = ton/ T.
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