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.
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.
An enzyme based biosensor was fabricated by employing a simple, inexpensive and rapid xurography fabrication
process. The electrodes and channel were made from the conducting polymer poly(3,4-ethyelenedioxythiphene)
poly(styrene sulfonate) (PEDOT:PSS). PEDOT:PSS was selectively deposited using a polyimide tape mask. The tape
mask was peeled off from the substrate after annealing the polymer in vacuum. Polymer wells of defined dimensions
were made and were attached to the device to accommodate the solutions. This sensor utilizes the change in current as a
parameter to measure different analyte concentrations. Initial experiments were done by using the sensor for glucose
detection. The sensor is able to detect the glucose concentrations approximately from 1 μM to 10 mM range covering
glucose in human saliva (8-210 μM). The glucose oxidase activity was independently measured using colorimetric
method and the results indicate that the sensor retains the enzyme activity and can be used as a biosensor to detect
various analytes. The analyte of interest can be measured by preloading the corresponding enzyme into the wells.
A chipless sensor tag-based radio frequency identification (RFID) technology that allows wireless collection of
information from the environment, and the monitoring and accessing of the given information through cyberspace is
presented. The developed system consists of a cyber enabled RFID reader and passive chipless RFID sensor tags. The
reader is comprised of an analog part that wirelessly communicates with the sensor tags, and a single board computer
(SBC) part. Each passive chipless sensor tag consists of a microstrip antenna and a sensor. The sensor information is
amplitude modulated in the backscattered signal of the tag. The analog reader part receives the backscattered signal and
feeds it to the SBC, which computes the sensor information into a 96 bit serialized global trade item number (SGTIN-96)
electronic product code (EPC). Moreover, the SBC makes the information available on a cyberspace-accessible secure
user interface. The reported system has been applied for temperature sensing, where the change in temperature at the tag
ranging from 27°C to 140°C resulted in a 28% amplitude change at the analog part of the reader. The temperature at the
tag has been monitored by accessing the reader through cyberspace using a web-based user interfaces developed for the
SBC.
A polymer-based dynamic microlens system that can provide variable focal length and field-of-view (FOV) is fabricated and tested for its optical imaging characteristics. A flexible polydimethylsiloxane (PDMS) polymer membrane is used to form the lens surface. Two such membranes are combined with a spacer in between to form the fluidic lens chamber. The entire assembly is actuated by fluidic pressure using an external syringe pump to form either a double convex (DCX) or double concave (DCV) lens. The relationship between the focal length (f) and FOV of this dynamic lens as a function of the volume of the fluid pumped into or out of the lens chamber is investigated. The focal length of the single dynamic lens system can be tuned over the range of 75.9 to 3.1 mm and -75.9 to -3.3 mm, respectively, for the DCX and DCV lens configurations. The FOV that could be achieved using this dynamic lens system as DCX and DCV lenses is in the range of 0.12 to 61 degrees and 7 to 69 degrees, respectively. The smallest f-number (f/#) of 0.61, which corresponds to a numerical aperture of 0.64, could be achieved for a single dynamic lens system. An integrated two or three variable focal length DCV microlens system to provide wide FOV has also been fabricated and tested. The effective focal length of the integrated dynamic microlens system with two and three DCV lenses can be tuned in the range of -37.9 to -2.1 mm and -25.3 to -1.8 mm, respectively. The FOV achieved using the integrated two and three variable focal length DCV microlens systems were in the range of 8 to 76.7 degrees and 11.5 to 90.4 degrees, respectively.
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