International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
Development of EMG Sensor for Transfemoral
Amputation (Knee Flexor and knee Extensor)
Kirtan P. Parekh#1, Jignesh B. Vyas*2
#*Department of Biomedical Engineering, Govt. Engineering College, Sec-28, Gandhinagar-382028, Gujarat, India.
Abstract— The electromyogram, the electrical activity of skeletal
muscle – finds useful applications in many fields, such as
biomechanics, rehabilitation medicine, neurology, gait analysis,
pain management, orthotics, even unvoiced speech recognition,
prosthetic device control and man-machine interfaces. This
paper shows that how the development of EMG Sensor which is
use in Transfemoral Amputation which is specially used in knee
flexor and knee extensor. This paper gives the best solution for
the EMG Acquisition for the amputee people who was suffered
from Transfemoral (above knee) amputee.
Keywords— EMG Sensor, Surface Electromyography(SEMG),
Transfemoral Amputee, knee joint.
I. INTRODUCTION
Small electrical currents are generated by the muscle fibres
prior to the production of muscle force. These currents are
generated by the exchange of ions across muscle fibre
membranes, a part of the signalling process for the muscle
fibres to contract. The signal called the electromyogram
(EMG) can be measured by applying conductive element or
electrodes to the skin surface, or invasively within the muscle.
Surface EMG is the more common method of measurement,
since it is non-invasive and can be conducted by personnel
other than Medical Doctors, with minimal risk to the subject.
Surface electromyography (SEMG) signals provide a noninvasive tool for investigating the properties of skeletal
muscles. The bandwidth of the recorded potentials are
relatively narrow (40Hz-1 KHz), and their amplitude is low
(50 µV - 5 mV). These signals have been used not only for
monitoring muscle behaviour during rehabilitation programs,
but also for the mechanical control of prostheses. In this
context, it is important to be able to correctly predict which
movement is intended by the user. The SEMG signal is very
convenient for such application, because it is non-invasive,
simple to use, and intrinsically related to the user’s intention.
The SEMG signals are acquired by surface electrodes
placed on the skin over muscle(s) of the user. The signals
originating from the electrodes are pre-amplified to
differentiate the small signals of interest, and then are
amplified, filtered and pre-amplified. Finally, the information
is transferred to a myoelectric controller.
This Paper will provide the concept and development of the
EMG sensor for those people who are suffering from the
Transfemoral amputee. And also this paper is used for the
manufacturer, Neuro surgeon, doctors, scientists and
Developer who can work on the EMG Signal processing and
work on the Transfemoral amputees.
ISSN: 2231-5381
II. IMPORTANCE OF KNEE JOINT
The knee joint is one of the most complex synovial joints
that exist in the human body whose main functions are to
permit the movement during the locomotion, and to allow the
static stability. The mobility associated with the knee joint is
indispensable to human locomotion and it helps correct foot
orientation and positioning in order to overcome the possible
ground irregularities. In the knee articulation, there are three
types of motion, namely, flexion, rotation, and sliding of the
patella. The knee joint includes three functional compartments,
medial, lateral, and patello-femoral, which make the knee
quite susceptible to injures and chronic disease, such as
displacement, arthritis, ligaments rupture, and menisci
separation. In fact, the greatest number of human ligament
injuries occurs in ligaments of the knee. The knee joint is
surrounded by a joint capsule with ligaments strapping the
inside and outside of the joint (collateral ligaments) as well as
crossing within the joint (cruciate ligaments).
Fig 1The Human leg muscles that caused flexion/extension knee joint
The muscles of the lower limb are larger and more
powerful than those of the upper limbs. These muscles can be
divided into three groups and they are shown in fig 1:
 Muscles that move the thigh.
 Muscles that move the leg.
 Muscles that move the foot and toes.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
Here, we considered only muscle that the move the leg. It
means the principal knee movements are flexion and
extension.
III. PROPOSED SYSTEM
Aimed at improving the quality of life for amputees, this
paper is providing the development of EMG sensor for
Transfemoral amputation. Two channels of MES are collected
from the thigh using gelled surface electrodes. Electrodes are
placed equidistant at thigh for knee flexors and knee extensors.
The two MES channels are fed through instrumentation
amplifier (AD620), with the limited gain. Outputs of the preamplifiers are fed into amplifiers with the bandwidth set at 50
Hz to 1 kHz. These filtered signals are than rectified and this
signal seen on CRO or DSO.
Fig 2 Generalized Block Diagram of EMG Acquisition System
A. EMG Characteristics
A motor unit action potential, or MUAPs, is a summated
action potential as detected from all the muscle fibers in the
same motor unit. It is the summation of all the MFAPs
produced by fibers of the MU. The shape and characteristics
of a MUAP are shown in Figure 3. Now the characteristics of
EMG or the O/P from MUAP can be summarized. The
following characteristics will be covered: Duration,
Amplitude, no. of turns / Area / the Area to Amplitude Ratio
(AAR) [Thickness] / Size Index Firing Rate / Firing Rate per
Motor Unit (FR/MU) / # of Phases / % Polyphasic MUAPs / #

of Turns.


(abnormal) cases, but can vary between reduced and very high
for neuropathic cases. Amplitude also has correlations with
other characteristics that may make it valuable to graph it on a
two dimensional scatter plot with another characteristic.
Amplitude and Duration are positively correlated. Amplitude
and AAR are negatively correlated which leads to more
separable data distributions when the two are plotted together.
B. Real EMG Signal Measurement
There are two types of electrodes for obtaining EMG signals,
inserted (invasive) electrodes and surface (non-invasive)
electrodes. The ease of use of surface electrodes makes their
implementation for this project preferable. Surface electrodes
come in many varieties, with most characterized by the
number of contacts. Some different types of surface electrodes
are monopolar, bipolar, tripolar and multipolar, all of whose
geometry is described by their name. For the purpose of this
paper a multichannel bipolar electrodes are used along with a
reference electrode in order to implement the differential
amplifier.
Electrode placement is important when using any of the
electrode types described above. With the bipolar electrode
the optimal position of the electrodes is parallel to the muscle
fibers in order to maximize the probability of reading the same
signal. Here to mimic the natural leg movement myoelectric
signals are collected from knee flexor and extensor since these
muscle groups are directly responsible for the knee movement
of interest. Two differential myoelectric signal channels were
recorded using surface electrodes. One channels were used to
record potentials for flexors and the other one are used to
record for extensor. The desired position for electrodes is on
the belly of the muscle and not on the outer edge of the
muscle where other muscles could interfere with the muscle
under examination.
The data for this experiment is recorded with single channel,
and patient’s weight is 58Kg and his height is 168cm.
Here, we were taking EMG in four places in patient’s body.
This four muscle names are given below:
1. Rectus Femoris
For Extensors
2. Vastus Medialis
3. Biceps Femoris (Short Head)
For Flexors
4. Semimembranosus
There are many important parameters that must be taken
under consideration in the measurement process. The most
important parameter in the measurement process is selecting a
position for electrodes and clinical information of the job.
Fig 2 Characteristics of an EMG Signal
Now the simple explanation will present classification. The
amplitude is consistently reduced or normal in myopathic
ISSN: 2231-5381
1) Position of Electrodes: There are nine muscles up and
down of the knee joint affecting the movements of the knee.
From the clinical information and practice experiential, the
best position of electrodes is to recognize the maximum
amplitude for flexion/extension knee joint.
Fig 3 (A to D) represents practice experiment to select the
position for two electrodes to get the EMG signal at the
movements of joint. In this paper we used four muscles that
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
have min effect for flexion/extension knee joint. The EMG
signal is recorded by using SEMG electrodes therefore four
electrodes must be used at the same moment (i.e. four
channels recorded).
Fig 3 Location of SEMG on Human Leg
2) Recording of SEMG Data: In this project the real SEMG
signals were recorded by the following Procedure:

Record the signal with relax and no movement in the
knee joint (spontaneous case).

Record the signal from full extension to full flexion
of knee joint with time (3 sec) (i.e. slow motion of
leg).
Record the signal from full extension to full flexion
of knee joint with time (1 sec) (i.e. fast motion of
leg).
Record the signal from full flexion to full extension
of knee joint with time (3 sec) (i.e. slow motion of
leg).


S Muscle
r Name
.
N
o
1 Rectus
Femoris
2 Vastus
Medialis
3 Semimembra
nosus
Biceps
4 Femoris
(Short
head)

In According to Table 1, data gives result for main four
muscles which responsible minimum movement of
flexion/extension of knee joint.
For Flexions,
1. Rectus Femoris’s amplitude range is 46µV to 149µV.
2. Vastus Medialis’s amplitude range is 47µV to 184µV.
For Extensions,
1. Semi-membraneous’s range is 82µV to 211µV.
2. Biceps Femoris (Short Head)’s amplitude range is
41µV to 145µV.
C. High CMRR Instrumentation Amplifier
The preferred method of amplification for this application is
differential amplification using a bipolar electrode and
instrumentation amplifier. It is this methods ability to remove
electromagnetic noise that the body has picked up that make it
the most attractive for this application.
The main specification that must be considered when
selecting an instrumentation amplifier for this task is its
CMRR or common mode rejection ratio. In the case of EMG
amplification the common signal is most commonly noise so
this specification plays a critical role in acquiring an accurate
signal.
Readin
g1
Readin
g2
Readin
g3
Readin
g4
Readin
g5
113µV
46µV
51µV
149µV
134µV
Fig 4 Instrumentation Amplifier
47µV
73µV
184µV
162µV
58µV
111µV
147µV
82µV
90µV
211µV
82µV
71µV
145µV
41µV
106µV
Here the instrumentation amplifier AD620 of Analog
Devices is selected for this design due to its high CMRR at
high gain. The AD620 is a low cost, high accuracy
instrumentation amplifier that requires only one external
resistor to set gains of 1 to 10,000.Here Limited gain of
approximately 25 is designed as we don’t want to amplify
noise with the signal.
Record the signal from full flexion to full extension
of knee joint with time (1 sec) (i.e. fast motion of
leg).
TABLE I
READING OF SEMG DATA ON MUSCLES WHICH RESPONSIBLE FOR MAXIMUM
MOVEMENT OF KNEE FLEXION/EXTENSION
D. Band Pass Filter (40 Hz - 1 KHz)
Except for amplifying raw EMG signals to reject commonmode signals using differential amplifiers, a Bandpass filter
are required to increase the signal-to-noise ratio and reject
other physiological signals, such as the electrocardiogram
(ECG) signal and axon action potential (AAP).
A filter is a device designed to attenuate specific ranges of
frequencies, while allowing others to pass, and in so doing
limit in some fashion the frequency spectrum of a signal.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
The frequency range(s) which is attenuated is called the Stop
band, and the range which is transmitted is called the Pass
band. The EMG signal falls within the audio frequency
range 10 Hz to 5 KHz. The prominent frequency range from
40 Hz to 1 kHz has to be isolated to be then processed.
Hence, filters play a vital role in signal conditioning part of
this project. Fourth order Low pass filter with cut-off 1 kHz
is followed by Fourth order High pass filter with cut-off 40
Hz is designed with a low power ,wide Bandwidth dual
JFET input operational Amplifier op amp TL082(Texas
Instruments) in order to obtain the prominent part of the
signal which has already been extracted from the muscle.
Fig 5 Fourth Order Low Pass Butterworth Filter
Fig 7 50Hz Notch Filter
F. Non- Inverting Differential Amplifier
Raw EMG signal contains noise and its amplitude is in
microvolt range. At the pre amplifier stage we had set limited
gain as signal contains noise so we need further amplification
of filtered signal. So output of the notch filter is given to
differential amplifier. The gain of this differential amplifier is
set 50. At this stage total amplification becomes 7909 means
approximately
8000(25(instrumentation
amplifier
gain)*1.586(2nd order low pass filter gain)*1.586(2nd order
low pass filter gain)*1.586(2nd order high pass filter
gain)*1.586(2nd order high pass filter gain)*50(Differential
amplifier gain)).
Fig 6 Fourth Order High Pass Butterworth Filter
Fig 8 Non Inverting Differential Amplifier
E. Notch Filter
An EMG amplifier can “catch” ground noise from the power
line which results in increased baseline noise (50/60 Hz
noise).Notch filter is commonly used for the rejection of the
single frequency such as 50 Hz power line frequency hum.
The most commonly used notch filter is the twin-T network.
This is a passive filter composed of two T-shaped networks.
One T-Shape network is made up of two resistors and a
capacitor, while the other uses two capacitors and a resistor.
The notch out frequency is frequency at which maximum
attenuation occurs, it is given by
ISSN: 2231-5381
G. Full Wave Rectifier
In a rectification stage all negative amplitudes are
converted to positive amplitudes, the negative spikes are
“moved up” to plus or reflected by the baseline. It is useful for
taking the absolute value of the raw signal mainly used as an
intermediate step before another process (e.g., averaging,
linear envelope and integration) can be done electronically
and in real-time. Here bridge rectifier is use to rectify raw
EMG signal. Diode 1N4148 is used for this purpose.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
Fig 9 Full Wave Bridge Rectifier
IV. CONCLUSIONS
The determination of optimal characteristics of EMG
sensor for Transfemoral amputation is challenging and
important, but difficult due to various issues of noises. From
this study we can easily identify the placement of electrode on
Transfemoral amputee (above knee) and the most common
placement of electrode on the Transfemoral amputees patients
are rectus femoris’s which is responsible for flexors and Semimembraneous’s which is responsible for Extensors which give
maximum and best result.
At Final stage we got efficient result of EMG Signal which
is specially used in knee joint flexors and knee joint extensors.
This system is also used for the Neuro surgeons, doctors,
scientist and manufacturer who can work on the EMG signal
processing, rehabilitation research and who can work mainly
on the Transfemoral amputees.
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Fig. 10 Hardware of EMG Sensor
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Fig 11 EMG Signal Acquired from Biceps Femoris (Short Head)
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Fig 12 Rectified EMG
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