The invention
of transistor enabled the first use of radiometry capsules, which
used simple circuits for the internal study of the gastro-intestinal
(GI) [1] tract. They couldn't be used as they could transmit only
from a single channel and also due to the size of the components.
They also suffered from poor reliability, low sensitivity and
short lifetimes of the devices. This led to the application of
single-channel telemetry capsules for the detection of disease
and abnormalities in the GI tract where restricted area prevented
the use of traditional endoscopy.
They were
later modified as they had the disadvantage of using laboratory
type sensors such as the glass pH electrodes, resistance thermometers,
etc. They were also of very large size. The later modification
is similar to the above instrument but is smaller in size due
to the application of existing semiconductor fabrication technologies.
These technologies led to the formation of "MICROELECTRONIC
PILL".
Microelectronic
pill is basically a multichannel sensor used for remote biomedical
measurements using micro technology. This is used for the real-time
measurement parameters such as temperature, pH, conductivity and
dissolved oxygen. The sensors are fabricated using electron beam
and photolithographic pattern integration and were controlled
by an application specific integrated circuit (ASIC).
There are
basically 4 sensors mounted on two chips- Chip 1 & chip 2.
On chip 1(shown in fig 2 a), c), e)), temperature sensor silicon
diode (4), pH ISFET sensor (1) and dual electrode conductivity
sensor (3) are fabricated. Chip 2 comprises of three electrode
electrochemical cell oxygen sensor (2) and optional NiCr resistance
thermometer.
1) Sensor
chip 1:
An array consisting of both temperature sensor & pH sensor
platforms were cut from the wafer & attached onto 100-µm-
thick glass cover slip cured on a hot plate. The plate acts as
a temporary carrier to assist handling of the device during level
1 of lithography when the electric connections tracks, electrodes
bonding pads are defined. Bonding pads provide electrical contact
to the external electronic circuit.
Lithography
[2] was the first fundamentally new printing technology since
the invention of relief printing in the fifteenth century. It
is a mechanical Plano graphic process in which the printing and
non-printing areas of the plate are all at the same level, as
opposed to intaglio and relief processes in which the design is
cut into the printing block. Lithography is based on the chemical
repellence of oil and water. Designs are drawn or painted with
greasy ink or crayons on specially prepared limestone. The stone
is moistened with water, which the stone accepts in areas not
covered by the crayon. Oily ink, applied with a roller, adheres
only to the drawing and is repelled by the wet parts of the stone.
Pressing paper against the inked drawing then makes the print.
Lithography
was invented by Alois Senefelder in Germany in 1798 and, within
twenty years, appeared in England and the United States. Almost
immediately, attempts were made to print pictures in color. Multiple
stones were used; one for each color, and the print went through
the press as many times as there were stones. The problem for
the printers was keeping the image in register, making sure that
the print would be lined up exactly each time it went through
the press so that each color would be in the correct position
and the overlaying colors would merge correctly.
Early colored lithographs used one or two colors to tint the entire
plate and create a watercolor-like tone to the image. This atmospheric
effect was primarily used for landscape or topographical illustrations.
For more detailed coloration, artists continued to rely on hand
coloring over the lithograph. Once tinted lithographs were well
established, it was only a small step to extend the range of color
by the use of multiple tint blocks printed in succession. Generally,
these early chromolithographs were simple prints with flat areas
of color, printed side-by-side.
Increasingly
ornate designs and dozens of bright, often gaudy, colors characterized
chromolithography in the second half of the nineteenth century.
Overprinting and the use of silver and gold inks widened the range
of color and design. Still a relatively expensive process, chromolithography
was used for large-scale folio works and illuminated gift books
that often attempted to reproduce the handwork of manuscripts
of the Middle Ages. The steam-driven printing press and the wider
availability of inexpensive paper stock lowered production costs
and made chromolithography more affordable. By the 1880s, the
process was widely used for magazines and advertising. At the
same time, however, photographic processes were being developed
that would replace lithography by the beginning of the twentieth
century.
