A polymer pellet-based sensor device comprised of polypyrrole (PPy), polymethyl methacrylate (PMMA) and
polyethylene glycol (PEG), its fabrication methods, and the experimental results for low-concentration acetone detection
are presented. The design consists of a double layer pellet, where the top layer consists of PPy/PMMA and the bottom
layer is composed of PPy/PMMA/PEG. Both sets of material compositions are synthesized by readily realizable
chemical polymerization techniques. The mechanism of the sensor operation is based on the change in resistance of PPy
and the swelling of PMMA when exposed to acetone, thereby changing the resistance of the layers. The resistances
measured on the two layers, and across the pellet, are taken as the three output signals of the sensor. Because the
PPy/PMMA and PPy/PMMA/PEG layers respond differently to acetone, as well as to other volatile organic compounds,
it is demonstrated that the three output signals can allow the presented sensor to have a better sensitivity and selectivity
than previously reported devices. Materials characterizations show formation of new composite with PPy/PMMA/PEG.
Material response at various concentrations of acetone was conducted using quartz crystal microbalance (QCM). It was
observed that the frequency decreased by 98 Hz for 290 ppm of acetone and by 411 Hz for 1160 ppm. Experimental
results with a double layer pellet of PPy/PMMA and PPy/PMMA/PEG show an improved selectivity of acetone over
ethanol. The reported acetone sensor is applicable for biomedical and other applications.
A temperature-stable, low-power ring oscillator design with a wide tuning frequency range, for implementation in an
ASIC is presented. The design uses a new arrangement of chain delay elements consisting of a current-starved inverter
and a CMOS capacitor. The delay is controlled by changing the current through the delay elements. The simulation
results show that the frequency of the presented oscillator is stable against ambient temperature variations, with less than
0.5% deviation in frequency when the temperature was changed from 0 to 50°C. The oscillation frequency is highly
sensitive to the control voltage (sensitivity ~10 mV) with a tuning range of 203 MHz for 0.9 V increase in the input
voltage, and simulated power consumption of 1.2 nW. The design and simulation results of the ring oscillator with 180
nm technology are presented and discussed. The presented design is applicable in advanced sensing systems, including
biomedical, chemical, and other sensors.