Biomedical Engineering Reference
In-Depth Information
Fig. 32
Microchannels in the PIMMS for gas intake
actual pressure in the chamber, which requires being very accurate for adequate
function. Since rather long the capillaries have to be used, small tolerance may have
a strong impact.
Microsystem technology with its high precision can be used instead to fabricate
the required flow resistances as etched channels in silicon. The advantages of this
approach are multiple: the pressure stage length can be easily controlled and by
using different channel geometries (width, depth) connected in series, the area nec-
essary to fix the capillaries is avoided, the injection system can be manufactured
along with the chip, and gluing of the capillaries is avoided. As a result the injection
system is directly integrated into the PIMMS.
In first experiments for this integration very narrow channels with a well-defined
length were etched into silicon. Thus, the desired pressure drop was achieved in a
process-integrated solution. Figure 32 shows a PIMMS prototype with integrated
pressure stages. In this example, capillaries are still glued to the system for connect-
ing the gas supply. The robustness and batch manufacturing capability of this injec-
tion system makes it very attractive for mobile and harsh environment applications.
8.3
Microvaporizer
The variety of applications of the PIMMS can be significantly extended, if liquids
can be analyzed in an appropriately sized vaporizer.
Consequently such a microvaporizer uses a glass-silicon-glass stack with a
microstructured silicon evaporator. This evaporator is heated up by a pulsed NIR-
laser diode. Thus, the liquids which are in contact with the evaporator within a
very short period of time are heated beyond their evaporation temperature. This
arrangement not only requires a low energy to evaporate in comparison to the
commonly used resistive heating, but the very rapid heating of the silicon vaporizer
also allows for simultaneous evaporation of sample mixtures with components of
different evaporation temperatures and partial pressures, respectively. Furthermore,
Search WWH ::




Custom Search