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Telemetry System

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Measuring set-up

Telemetry System

During the measurements, a power induction coil and a receiver antenna are fixed near the patient's implant. The implanted telemetry transmitter is powered inductively by the external magnetic field. The signals measured were transmitted to the external device TELEPORT for on-line force display on a notebook screen. The activities of the patient are videotaped, and the data from the implants are recorded simultaneously on the audio tracks of the same cassette.

Internal telemetry transmitters

Implantable 4-channel telemetry transmitter

4-channel telemetry transmitter
4-channel telemetry transmitter

The 4-channel telemetry transmitter was manufactured in double-sided thick film hybrid technology with 14 off-the-shelf integrated circuits and 17 passive components. It was used for three-dimensional force measurements with hip endoprostheses (hip I, 1984).

Dimensions: 15 x 7 mm. 8 connection pads for 3 strain sensors, energy coil and antenna.

Download data sheet: 4-channel-transmitter.pdf (330 KB)

Implantable 8-channel telemetry transmitter

8-channel telemetry transmitter
8-channel telemetry transmitter

The 8-channel telemetry transmitter was manufactured in double-sided thick film hybrid technology with a bipolar transistor array (4.2 x 5.0 mm) and 17 passive components. It was used for load measurements with internal spinal fixators and hip joint force and temperature measurements (hip II, 1991).

Dimensions: 14 x 7 mm. 12 connection pads for 6 external sensors, energy coil and antenna.

Download data sheet: 8-channel-transmitter.pdf (444 KB)

Implantable 9-channel telemetry transmitter

9-channel telemetry transmitter
9-channel telemetry transmitter
9-channel telemetry programed
9-channel telemetry programed

The 9-channel telemetry transmitter is made in double sided thick-film hybrid technology and has the dimensions of 12.5 x 6 mm. Analogous and digital parts are combined on a single custom-made chip in BICMOS technology with a structure of 0.8 µm. The total die size is only 2 x 2.6 mm. This low-power circuit includes a 9-channel multiplexer, a programmable memory, a pulse interval modulator and a radio-frequency transmitter. Channels 1 to 6 are used for semiconductor strain gauges or as temperature sensors. Channel 7 transmits the temperature of the hybrid circuit. Depending on the power information transmitted, the magnetic field is regulated by channel 8. Synchronisation of the pulse train is carried out by the aid of channel 9. A Zener diode PROM module stores all information of the calibration process and thus adapts each channel to its corresponding sensor resistance. After successful programming, this part of the hybrid circuit is cut off and total size is now reduced to 9.5 x 6 mm.

The 9-channel telemetry transmitter has been used since 2004 for the instrumentation of shoulder-, knee- , hip III implants  and vertebral body replacements.

Download data Sheet: 9-channel-transmitter.pdf (324 KB)

External equipment

External unit TELEPORT

Teleport
Teleport

TELEPORT is built up in a 19-inch case and has all of the external components needed for the telemetric measurements with one multi-channel telemetry transmitter.

The power oscillator generates a low-frequency sinusoidal output voltage for the energy coil. Amplitude and frequency are controlled automatically. The radio-frequency receiver has an input range from about 50 MHz up to 220 MHz and input facility for active and passive antennas. The signal generator (marker) creates a rectangular mark signal with a frequency of 1 kHz to synchronise time segments with other systems like gait-analysis systems. The microcontroller system (data link) controls the inductive power supply to a constant value, checks and synchronises the pulse-interval-modulated (PIM) data received, creates a time base and transmits all data by an USB cable to a personal computer. Special software shows all data in real-time on the screen. The PIM data - and, when necessary, the mark signal as well - were recorded synchronously with the patient's activity on the two audio tracks of the digital video camcorder.

TELEPORT is used mainly for load measurements involving our instrumented hip-, knee-, shoulder implants and vertebral body replacements.