Square-wave Waveforms are used extensively in circuits for clock and timing control signals as they are symmetrical waveforms of equal and square duration representing each half of a cycle and nearly all digital logic circuits use square wave waveforms on their input and output gates.
Unlike sine waves which have a smooth rise and fall waveform with rounded corners at their positive and negative peaks, square waves, on the other hand, have very steep almost vertically up and downsides with a flat top and bottom producing a waveform which matches its description, – “Square” as shown below.
Units of periodic time, ( T ) include Seconds ( s ), milliseconds ( ms ) and microseconds ( μs ).
For sine wave waveforms only, the periodic time of the waveform in either degrees or radians, as one full cycle is equal to 360o ( T = 360o ) or in Radians as 2pi, 2π ( T = 2π ), 2π radians = 360o.
When taking the reciprocal of the period, ( 1/T ) the number of times a period or cycle repeats itself in one second or cycles per second, is known as Frequency with units of Hertz, (Hz). Hertz is
defined as “cycles per second” (cps) and 1Hz is exactly equal to 1 cycle per second.
Both period and frequency are mathematical reciprocals of each other and as the periodic time of the waveform decreases, its frequency increases and vice versa with the relationship between Periodic time and Frequency given as.
Symmetric Biphasic Rectangular pulse
Description Alternate current with positive and negative rectangular
Pulse Frequency 1-200 Hz
Phase duration 50-300 µsec
Current, Amplitude 0-50 mA into 500 ohm
Voltage, max ±60V Peak
Waveform Duty Cycle 20% max
Output Mode Normal, Modulation, Burst
The square-shaped electrical waveforms are symmetrical in shape as each half of the cycle is identical, the time that the pulse width is positive must be equal to the time that the pulse width is negative or zero. When square wave waveforms are used as “clock” signals in digital circuits the time of the positive pulse width is known as the “Duty Cycle” of the period.
The square wave waveform positive side is “ON” time and equal to the negative or “OFF” time. The duty cycle must be 50%, (half of its period). As frequency is equal to the reciprocal of the period, ( 1/T ) it defines the frequency of a square wave waveform as:
Rectangular Waveforms are similar to the square wave waveform above, the difference being that the two pulse widths of the waveform are of an unequal time period. Rectangular waveforms are therefore classed as “Non-symmetrical” waveforms as shown below.
The example shows that the positive pulse width is shorter in time than the negative pulse width. Equally, the negative pulse width could be shorter than the positive pulse width, either way, the resulting waveform shape is a rectangular waveform.
Triangular Waveforms are generally bi-directional non-sinusoidal waveforms that oscillate between a positive and a negative peak value. Although called a triangular waveform, the triangular wave is actually more of a symmetrical linear ramp waveform because it is simply a slow rising and falling voltage signal at a constant frequency or rate. The rate at which the voltage changes between each ramp direction is equal during both halves of the cycle as shown below.
The positive-going ramp or slope (rise), is the same time duration as the negative-going ramp (decay) giving the triangular waveform a 50% duty cycle. Any given voltage amplitude, the frequency of the waveform determine the average voltage level of the wave.
Sawtooth Waveforms the shape of the waveform resembles the teeth of a saw blade. Sawtoothed waveforms can have a mirror image of themselves, by having either a slow-rising but extremely steep decay, or an extremely steep almost vertical rise and a slow-decay as shown below.
The Sawtooth waveform consists of a fundamental frequency ( ƒ ) and all its integer ratios of even harmonics only, 1/2, 1/4, 1/6 1/8 … 1/n etc. it is rich in harmonics.
Although technically Triggers and Pulses are two separate waveforms, when combined them as a “Trigger” it is basically a narrow “Pulse”. The difference is that a trigger can be either positive or negative in direction whereas a pulse is only positive in direction.
A Pulse Waveform or “Pulse-train” is a type of non-sinusoidal waveform that is similar to the Rectangular waveform. A Pulse is a waveform or signal in its own right. It has very different Mark-to-Space ratio compared to a high-frequency square wave clock signal or even a rectangular waveform. The purpose of a “Pulse” and that of a trigger is to produce a very short signal to control the time at which something happens.
The Russian Current waveform delivers medium frequency current in alternating pulses or bursts of energy. This type of stimulation generates a motor response which can be used to strengthen muscles and muscular re-education. A study published in the International Journal of Rehabilitation and Science found that Russian current used in addition to physical therapy increased quadriceps strength in burn patients more than patients that received physical therapy alone. To add to its versatility, Russian Current can also be used to stimulate an analgesic effect in the muscles, making it effective in reducing pain as well as increasing muscular strength.
Interferential Current (also referred to as IFC) is used to address chronic, post-surgical and post-trauma acute pain in patients. IFC works at a higher frequency meaning the energy crosses the skin with less stimulation. Because of its ease in reaching deep into pain sites and the increased tolerance for patients. Additionally, the IFC waveform offers deep tissue penetration over a larger volume of tissue.
Premodulated Current also referred to as “period”. With premod current, a single channel is used to mix the frequencies prior to delivery of the current through the electrode of the body (using two electrodes rather than four). This is beneficial when treating areas of the body that have less space available for electrode placement. It is the best choice to use on smaller muscle groups and joints such as the elbow, ankle, foot, and hands. For example, a premodulated current would be effective in treating pain associated with tennis elbow. In literature, it is constantly connected to Interferential Current.
“Biphasic” refers to two phases, or pulses, of 2 different intensities alternating with each other during treatment. Biphasic current is considered the most versatile of the stimulation therapy waveforms because most devices feature settings that allow control of amplitude (intensity), stimulation (voltage), current, and duration of each pulse. Biphasic current e-stim can be used to:
• strengthen muscles
• re-educate muscles
• increase circulation
• decrease swelling
Biphasic treatment is used to treat both acute and chronic pain, muscular and disc syndromes in the back and neck, arthritis, shoulder syndromes, neuropathies, etc.
High Voltage electrical stimulation uses polarity (positive or negative) to stimulate the tissue. This type of stimulation can be used to decrease pain, edema or facilitate in wound healing. Because of its ability to aid in circulation, High Voltage can be used to great effect in healing wounds in patients with circulatory issues such as diabetes. Additionally, this waveform can be used to relieve muscle spasms.
Microcurrent utilizes micro-size, pulsating current to resonate with the body’s own bio-electrical exchanges that take place at the cellular level. When microcurrent is applied, it triggers impulses to facilitate a chemical reaction to activate the release of adenosine triphosphate (ATP) at the cellular level, which is used to facilitate wound or tissue healing. Microcurrent is considered sub-sensory, implying that the intensity does not cause any visual jolting muscular movement, so it’s more comfortable for patients.