In this paper, we presented the fabrication process of miniature pH sensor arrays on flexible polymer
substrates. The repeatability of the sensors based on sol-gel fabrication processes was investigated. The
sensor repeatability was characterized with linearity, decay time, environmental parameter control and
potential stability. Similar linear responses were found in different batches of sensor arrays. Near super-
Nernstian responses were measured on each sensor with slope ranges from
-71.6 to -110 mV/pH within a
pH range between 2 and 12. The response times were compared in different batches. Six to twenty five
seconds of average decay time were shown in each sample repeatedly. Three sensors showed the close
potential response in different volumes of pH buffer solution. The sensor showed good stability in each
step of the titration process between pH values of 1.8 and 11.9. The peak and saturated potential values
presented high correlation with pH values with minor noises. The results showed good sensitivity,
stability and repeatability using the sol-gel processes for iridium-oxide pH sensors on flexible substrates.
A passive strain sensor was investigated using patch antennas. For early damage detection in structures
due to external loads, reliable strain information is necessary. A noninvasive method of measuring strain
using a patch antenna was investigated to overcome the limitations of existing strain sensing technologies.
The metal patch antenna was made on a thin sheet of low-loss polymer with a ground plane on the
opposite side. When fed with RF signals, the patch antenna radiates at its resonant frequency. The
resonant frequency of the patch antenna varies with its dimensions. Strain-induced change in the
dimensions results in a shift in the resonant frequency. A single-frequency antenna, designed and
simulated using the Sonnet simulation tool, has a resonant frequency corresponding to its length, so the
antenna is sensitive only to the length-direction strain yet insensitive to the width-direction strain. Effect
of strain on frequency shift and its sensitivity to strain were calculated. The antenna was fabricated using
conventional micromachining techniques. Effects of strain on resonant frequency were verified
experimentally and in good agreement with simulated results.
pH sensor is an essential component used in many chemical, food, and bio-material industries. Conventional
glass electrodes have been used to construct pH sensors, however, have some disadvantages in specific applications.
It is difficult to use glass electrodes for in vivo biomedical or food monitoring applications due to size limitation and
no deformability. In this paper, we present design and fabrication processes of a miniature iridium oxide thin film
pH sensor array on flexible polymer substrates. The amorphous iridium oxide thin film was used as the sensing
material. A sol-gel dip-coating process of iridium oxide film was demonstrated in this paper. A super-Nernstian
response has been measured on individual sensors of the array with a slope of -71.6±3 mV/pH at 25°C within the
pH range between 2.83 and 11.04.
Phase shifter is one of the core components for phased-array antennas which find wide applications in satellite systems,
telecommunications, wireless systems, radar systems and tracking systems. The current high-frequency phase shifters
are mainly built upon active semiconductor technologies which suffer from high fabrication and assembly costs. In this
work, we propose a cost-effective approach to fabricate distributed MEMS transmission line phase shifters on a
polymer-glass substrate. The fabrication procedure is compatible with CMOS and post-CMOS processes. The polymerglass
phase shifter was characterized from DC to 26 GHz. The measurements show a phase shift of 120° and a 2.5-dB
insertion loss at 26 GHz.
RF phase shifters find wide applications in telecommunications, satellite systems, personal wireless
communication systems, radar systems, tracking systems, and sensors. They have been conventionally
manufactured by semiconductor technologies which suffer from high insertion losses due to high RF series
resistances. They are expensive due to fabrication and assembly costs.
The RF MEMS phase shifters provide low insertion losses, low fabrication costs and high linearity compared
with the semiconductor ones. Furthermore, polymer materials have demonstrated low material costs and low
RF attenuations. In this work, we proposed to build RF MEMS phase shifters on polymer substrates. The
proposed devices were successfully manufactured and tested from DC to 26 GHz. Our experimental results
indicated more than 35 degrees phase shifts and low insertion losses.
In this paper, we propose a new method to detect gastroesophageal reflux wirelessly. Based on passive telemetry using
inductive links, impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated
with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the
esophagus using currently available clinical techniques. In vitro experiments were conducted by passing different acidic
or non-acidic solutions onto the implanted electrodes and measuring the signal amplitudes with an external receiver. Air,
drinking water and different concentrations of artificial stomach fluids were used to test the impedance sensor. System
configuration, device designs, fabrication processes and measurement results will be presented in this paper.
In this paper, reconfigurable antenna design consideration is discussed. The antenna design constrains are base on the use of radio frequency microelectromechanical system (RF MEMS) switches. The design consideration includes practical issues in using the switches to either change the antenna feeding networks or change the antenna topologies. In the first design, a coplanar waveguide (CPW)-to-microstripline transition technique is used to integrate the small switches onto the antenna feeding networks to achieve beam steering. In the second design, the switches are used to change the antenna ground plane topology to achieve frequency switching. Both antennas are modeled using our Finite-Difference Time-Domain (FDTD) simulator. The beam steering antenna will be capable of more than 60° scanning angles and the frequency switching antenna can operate at 2.4GHz and 5.8 GHz for WLAN applications.
The advantages of polymers have made them popular choices in many micro device applications. The benefits of low material and fabrication costs have been demonstrated in many micro-fluidic devices. The low conductivities and low dielectric constants of polymers provide potentials for high quality-factor RF MEMS applications. Nevertheless, the extension of using polymers for electronic components has not been well explored. In this work, we investigated the fabrication processes and RF performances of coplanar waveguide (CPW) transmission lines, with which many RF MEMS phase shifters, tuners, switches and interconnects are built, on polymer dielectric layers. In order to achieve optimum results, the CPW transmission lines were fabricated on benzocyclobutene (BCB), kapton and polyimide polymers. Our experimental results indicated very low insertion losses of CPW transmission lines with BCB as a dielectric layer and with kapton as substrate, and a moderate insertion loss with polyimide as a dielectric layer.