Answer the following questions (if you are working in groups, each group member
ID: 1716904 • Letter: A
Question
Answer the following questions (if you are working in groups, each group member must submit his or her own answers). To answer questions, use this lab, lecture notes, your textbook, and so on. Please reference any sources you use, and please answer the following in your own words. Answers should be well researched, thoughtful, and in complete sentences.
Define bioamplifier.
What are bioamplifiers used for?
Give four examples of different physiological signals in which bioamplifiers are used.
For each of these physiological signals, what is the approximate magnitude of the signal (millivolts, microvolts, etc.)?
What is the bioamplifier gain needed for each of the above-mentioned physiological signals?
Choose one of the physiological signals researched above.
List at least three challenges to acquiring a good signal.
How does a bioamplifier attempt to rectify these challenges?
Bioamplifiers are almost always used in conjunction with some sort of filter(s).
Why are filters necessary when acquiring a physiological signal?
Are the filters used before or after the signal is acquired?
Explanation / Answer
Definition and usage
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. It may be an independent unit, or integrated into the electrodes.Multiple physiological signals are such as ECG, EEG, GSR and EMG
ECG voltage signal is very low in magnitude (few millivolts) and has relatively low frequency content i.e., less than 100muV = 0.3 to 2mV
EMG ranges from 0.1 to 2000 mV
GSR made conductance with the measure of design in the circutary
EEG voltage signal is very low in magnitude (few microvolts) and has relatively low frequency content i.e., 0.024muV(for 35Hz bandwidth) and 0.13muV(for 70Hz bandwidth)
Bio-amplifier gain for
ECG ---- 80db
EEG ,EMG ,GSR ---- 100db
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. Types of electrode materials and the mount position of electrodes affect the acquirement of the signals. Multielectrode arrays are also used, in which multiple electrodes are arranged in an array. Electrodes made with certain materials tend to perform better by increasing surface area of the electrodes.Electrodes have less surface area than those made with other materials. More surface area results in reducing impedance of electrode, then neurons signals are obtained easier.
Digital amplifiers and filters are produced small enough nowadays to be combined with electrodes, serving as preamplifiers. The need for preamplifiers is clear in that the signals that neurons (or any other organs) produce are weak. Therefore, preamplifiers preferably are to be placed near the source of the signals, where the electrodes are adjacent to. Another advantage for having preamplifiers close to the signal source is that the long wires lead to significant interference or noise. Therefore, it is best to have the wires as short as possible.
They should be lightweight, waterproof, not scratching skin or scalp from parts that they need to mount themselves, and they should dissipate heat well. Heat dissipation is a big issue, because extra heat may cause in the temperature of nearby tissue to rise, potentially causing a change in the physiology of the tissue. One of the solutions to dissipate heat is the usage of the Peltier device. A Peltier device actively pumps the heat from one side to the other side of the device, consuming electrical energy.
Conventional cooling using compressed gases would not be a feasible option for cooling down an individual integrated circuit, because it needs many other devices to operate such as evaporator, compressor and condenser. Overall, a compressor-based system is more for a large-scale cooling jobs, and is not viable for small-scale system like bioamplifiers. The passive cooling, like heat sink and fan, only limits the rise of temperature above the ambient condition, while Peltier devices can actively pull heat right out of a thermal load, just like compressor-based cooling systems. Also, Peltier devices can be manufactured at sizes well below 8 mm square, therefore they can be integrated to the bioamplifiers without making them to lose mobility.
filtering
Filtering of the signal is important; it is used to focus on a narrow band of electrical energy that is of interest to us rather than all the electrical signals at the sensors will pick up. It enables us to remove noise and artifact.It is used to transport electrical energy and is emitted into the recording environment by devices such as florescent lights , computer power supplies etc. Primarily EMG signals occur within the range of 0 –500Hz, however artifact can be introduced at the low frequency end of this range by sources such as the heart and electrical equipment. This EMG signal was measured in close proximity to the heart, the heart’s electrical activity can clearly be seen as spikes in activity approximately every second.The choice of the band should be a cautious one as it is a trade off between over filtering and under filtering the signal.
Filters employed before the signal is acquired.