Lecture 9
Dimitar Stefanov
Recapping
DC and AC instrumentation amplifiers:
•Errors due to the capacitance of the shielded wires that connect electrodes with the
amplifier
•The capacitors between the electrodes and the input stage of the amplifier cause
charging effects from the input bias current.
•Solution of the problem: Input guarding
Differential Shield Driver
Common-Mode Shield Driver
5mm X 4mm X 1.75 mm !
Techniques which eliminate` the influence of the
capacitance of the connective electrode wires
Best elimination of the capacitance – if no wires are used.
Bipolar Concentric ring sensor for surface Laplacian ECG
(University of Miami)
Double-sided 13x13
mm PC board
The contact area of the outer ring and the inner dot are equal.
More information: M.Talero, C.C.Lu, Active Bipolar Concentric Ring Sensor for surface Laplacian ECG, in the
Proc. First BMES/EMBS conference on Serving Humanity, Advancing Technology, Oct. 13-16, 1999, Atlanta,
GA, USA
Tripolar electrode sensor for Laplacian cardiograms
(University of Miami, Department of Biomedical Engineering)
The sensor contains three closely spaced rings.
The width of each ring is 1.0 mm.
The diameters of the outer ring and the middle
ring are 36 mm and 18 mm respectively.
The ring/dot in the center is 2.0 mm in diameter.
An instrumentation amplifier with an input
impedance of 10 Gohms is used.
Further information: http://sbec.abe.msstate.edu/abstracts/lu.htm
Wireless electrodes for surface electromyography
(Keio University – Japan)
Electrode part (Ag/AgCl electrodes)
+ amplifier + high-pass filter + built-in
transmitter + battery
Instrumentation amplifier AD620BR
FM transmitter
five button battery cells
20 m distance between the electrodes
and the receiver
15 hours operation with one set
batteries.
Before
transmission
After transmission
More information: M. Ohyama, Y. Tomita, S. Honda, H. Uchida, and N. Matsuo, Active
wireless electrodes for surface electromyography, Proc. Of the 18th Annual International
Conference of the IEEE EMBS, Amsterdam, 1996, pp. 295 – 296.
Micro system for sensing of biological parameters
(Waseda University – Japan)
•There are no wire lines between the sensors and the transmitter.
One transmitter, located on the wrist, is used for transmission of the
data from all sensors.
•Between the detector part and the transmitter, the signals are sent
as a AC micro current flow through the tissue of the body.
ECG monitoring system
The dipole map for the heart from
Waller (1889)
(All electrodes are mounted on a common frame.
The distance between the electrodes is 5 cm.)
A./ Block diagram of the ECG detector transmitter
Sampling frequency – 900Hz
Carrier frequency – 70 kHz
(sinusoidal signal)
B./ Block diagram of the relay transmitter
C./ Transmission of the signals between the ECG transmitter and the
relay transmitter (transmission of the signal in the human body):
Tissue equivalent circuit
Equivalent circuit of the tissue-electrodes
contour
D./ Frequency characteristic
The distance between the
electrodes RF and T (electrodes
where the signals are applied) is
7 cm.
The distance between the
electrodes B, S and T
(electrodes for detection of the
signals) is 3 cm.
In case of two channels, two carrier frequencies are chosen: 50 kHz and 70 kHz.
More information: T. Handa, S. Shoji, S. Ike, S. Takeda, and T. Sekiguchi, A Very low-power consumption
wireless ECG monitoring system using body as a signal transmission medium, Proc. Transducer’97- Int. Conf.
On solid-state sensors and actuators, Chicago, June 16-19, 1997
Eiji Takeda, Takashi Handa, Shuichi Shoji, Akihiko Uchiyama, STUDIES ON BIO-SENSING
MICROSYSTEMS FOR HEALTH CARE, XIV International Symposium on Biotelemetry, Marburg,
Germany April 6 - 11, 1997, http://baby.indstate.edu/isb/publications/abstracts/session3-6.htm
Prosthetics and Orthotics
Amputations
Result of:
•Decrease in blood supply to the muscles and periphery (diseases of the
arteries to the limbs or diabetes).
•Automobile and motorcycle accidents
•Bone cancers and tumors
•Direct trauma (train wheels, power saw)
•Osteomyelitus and other infections
•War and natural disasters.
Prosthesis – device which replaces a part of the functions of a missing limb.
Prosthetics and Orthotics
Orthosis – device which is applied to the exterior of the body to
stabilize or enhance motion of a limb or joint.
Functions of the orthoses :
•to reduce the stress on body parts;
•to protect of diseased or injured limbs
•to prevent or correct skeletal deformities;
• to stabilize joints.
- Post-operative treatment for amputations
Temporary prostheses – applied after the surgical operation and minimize loss of
sensory motor coordination.
Prosthesis - example
socket
(individually fitted component)
residual limb (soft tissue and bones)
Orthosis - example
Classification of the prostheses:
1.
2.
3.
4.
Upper-limb and lower-limb prostheses
Functional and cosmetic prostheses
Body-driven and external-power-driven prostheses (body-operated, cablecontrolled, electrically operated)
External power: electrical power (batteries), pneumatic and hydraulic driven
(some old models)
Classification based on the level of
amputation :
1. Upper-limb prostheses can be classified as
shoulder disarticulation prostheses, above-elbow
(AE) prostheses, below-elbow (BE) prostheses
2. Lower-limb prostheses can be classified as
above-the-knee (AK) prostheses and below-theknee (BK) prostheses
Functional classification of orthoses:
1.
2.
3.
4.
Immobilization or stabilization of joints and limbs (A)
Prevention of skeletal and joint deformations (B)
Chance of the position of a body part (traction) in case of weak muscle
performance (C).
tremor-suppression orthosis (D).
B
A
C
Tremor-suppression orthosis
Jack Kotovsky and Michael J. Rosen, A wearable tremor-suppression orthosis, in the Journal of Rehabilitation
Research and Development, Vol. 35 No. 4, October 1998, pp. 373-387
The orthosis damps wrist
flexion and extension
tremor.
constrained layer damping
(CLD)
Fluid damping
Pneumatic damping
•Active damping orthoses - permits electrically tunable damping.
• Piezoelectric or electro-rheological (ER) damping elements - their damping
properties may be controlled with an applied voltage.
Prosthesis = functionality + good cosmetic appearance
Energy sources:
•External power – electric, pneumatic and mechanical
•Body power.
Actuators: electromotor, piston, “McKibben” artificial muscle
Prosthesis fitting
Design of customized components to match to body shape.
Socket:
•most critical element of the prosthesis:
•individually fitted component of the prosthesis
•in contract with the residual limb.
Fitting:
•casting the residual limb – a cast of the residual limb is used to
make a socket for the prosthesis.
•CAD-CAM methods
Illustration of CAD-CAM above-knee (AK) socket design
Ultrasonic and computer tomography – future aspects of the CAD-CAM socket
design
•Instead of casting, a non-invasive imaging process is applied.
•The external shape and the external tissue structure of the residual limb are
recorded.
•Prosthesis often can be made lighter than the limb it replaces.
•Prosthesis length – near the length of the natural limb.
Upper-extremity prostheses
Terminal devices
allow grasping functions
Internally or externally powered
Mechanical hook
Voluntary opening and closing
Cosmetic glove to a hook