A Bioamplifier is an electrophysiological device, a variation of the instrumentation amplifier, used to gather and increase the signal integrity of physiologic electrical activity for output to various sources.
In 1887, Augustus Waller, a British physiologist, successfully measured the electrocardiograph of his dog using two buckets of saline, in which he submerged each of the front and the hind paws.
The electrocardiograph was impractical to use until Willem Einthoven, a Dutch physiologist, innovated the use of the string galvanometer for cardiac signal amplification.
[2] Significant improvements in amplifier technologies led to the usage of smaller electrodes that were more easily attached to body parts.
The typical requirements for the amplifiers to be used in ECG include:[1] Electromyography (EMG) records the electrical activity produced by skeletal muscles.
It records various types of muscle signals from simple relaxation by using placing electrodes on the subject's forehead, to complex neuromuscular feedback during stroke rehabilitation.
The temporal and spatial resolutions and signal to noise ratios of EEG have always lagged behind those of comparable intracortical devices, but it has the advantage of not requiring surgery.
Since the sweat glands are controlled by the sympathetic nervous system, the skin conductance is crucial in measuring the psychological or physiological arousal.
[1] Electrocorticography (ECoG) records the cumulative activity of hundreds to thousands of neurons with a sheet of electrodes placed directly on the surface of the brain.
In addition to requiring surgery and having low resolution, the ECoG device is wired, meaning the scalp cannot be completely closed, increasing the risk of infection.
It is limited in the amount of information it can provide, however, because the electronics it uses to transmit its signal (based around differential amplifiers) require so much space on the scalp that only four can fit on a human skull.
He demonstrated that they are capable of controlling assistive technology devices, suggesting that less invasive techniques can be used to restore functionality to locked-in patients.
It has been implanted in a human for over two years and consists of 100 conductive silicon needle-like electrodes, so it has high resolution and can record from many individual neurons.
The amplification process does not only depend on the performance and specifications of the amplifier device, but also closely binds to the types of electrodes to attach on the subject's body.
For instance, Indium tin oxide (ITO) electrodes have less surface area than those made with other materials, like titanium nitride.
In terms of digital amplifiers, a lot of works that the laboratories do are feeding back signals to the networks in closed loop, real-time.
[13] The trend with the development in electrodes and amplifiers has been reducing its size for better transportability, as well as making them implantable on the skin for prolonged recording of the signals.