Lecture 9Lecture 9Dimitar Stefanov

Recapping

•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

DC and AC instrumentation amplifiers:

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

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

Best elimination of the capacitance – if no wires are used.

Tripolar electrode sensor for Laplacian cardiogramsTripolar electrode sensor for Laplacian cardiograms(University of Miami, Department of Biomedical Engineering)(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 Wireless electrodes for surface electromyographyelectromyography

(Keio University – Japan)(Keio University – Japan)

Electrode part (Ag/AgCl electrodes) + amplifier + high-pass filter + built-in transmitter + batteryInstrumentation amplifier AD620BRFM transmitterfive button battery cells20 m distance between the electrodes and the receiver15 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 systemECG monitoring system

(All electrodes are mounted on a common frame.(All electrodes are mounted on a common frame.The distance between the electrodes is 5 cm.)The distance between the electrodes is 5 cm.)

The dipole map for the heart from Waller (1889)

A./ Block diagram of the ECG detector - A./ Block diagram of the ECG detector - transmittertransmitter

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 Equivalent circuit of the tissue-electrodes contour 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

ProstheticsProsthetics and Orthotics and OrthoticsAmputations

Prosthesis – device which replaces a part of the functions of a missing limb.

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.

ProstheticsProsthetics and Orthotics 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

residual limb (soft tissue and bones)

(individually fitted component)

Orthosis - example

Classification of the prostheses:1. Upper-limb and lower-limb prostheses2. Functional and cosmetic prostheses3. Body-driven and external-power-driven prostheses (body-operated, cable-

controlled, electrically operated)4. External power: electrical power (batteries), pneumatic and hydraulic driven

(some old models)

Classification based on the level of Classification based on the level of amputation :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-the-knee (BK) prostheses

Functional classification of orthoses:1. Immobilization or stabilization of joints and limbs (A)2. Prevention of skeletal and joint deformations (B)3. Chance of the position of a body part (traction) in case of weak muscle

performance (C).4. tremor-suppression orthosis (D).

A

B

C

Tremor-suppression orthosisTremor-suppression orthosisJack 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.

Energy sources:•External power – electric, pneumatic and mechanical•Body power.

Actuators: electromotor, piston, “McKibben” artificial muscle

Prosthesis fitting

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

Prosthesis = functionality + good cosmetic appearance

Design of customized components to match to body shape.

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 devicesallow grasping functions

Internally or externally powered

Mechanical hook

Voluntary opening and closingCosmetic glove to a hook