The ability to chronically monitor pressure at the prosthetic socket/residual limb interface could provide important data to the research and clinical communities. With this application in mind, we describe a novel type of sensor which consists of a MEMS pressure sensor and custom electronics packaged in a fluid-filled bubble. The sensor is characterized and compared to two commercially-available technologies. The bubble sensor has excellent drift performance and good sensing resolution. It exhibits hysteresis which may be due to the silicone that the sensor is molded in. To reduce hysteresis, it may be advisable to place the sensor between the liner and the socket rather molding directly into the liner.
This paper describes the development of “smart” channels that can be used simultaneously as a fluid channel and as an integrated chemical, temperature, and flow sensor. The uniqueness of this device lies in the fabrication and processing of low-temperature co-fired ceramic (LTCC) materials that act as the common substrate for both the sensors and the channel itself. Devices developed in this study have employed rolled LTCC tubes, but grooves or other channel shapes can be fabricated depending on the application requirements. The chemical transducer is fabricated by depositing a conductive polymer “ink” across a pair of electrodes that acts as a chemical resistor (chemiresistor) within the rolled LTCC tube. Volatile organic compounds passing through the tube are absorbed into the polymers, causing the polymers to reversibly swell and change in electrical resistance. The change in resistance is calibrated to the chemical concentration. Multiple chemiresistors have been integrated into a single smart channel to provide chemical discrimination through the use of different polymers. A heating element is embedded in the rolled tube to maintain a constant temperature in the vicinity of the chemical sensors. Thick-film thermistor lines are printed to monitor the temperature near the chemical sensor and at upstream locations to monitor the incoming ambient flow. The thermistors and heating element are used together as a thermal anemometer to measure the flow rate through the tube. Configurations using both surface-printed and suspended thermistors have been evaluated.
Low Temperature Cofired Ceramic (LTCC) has proven to be an enabling medium for microsystem technologies, because of its desirable electrical, physical, and chemical properties coupled with its capability for rapid prototyping and scalable manufacturing of components. LTCC is viewed as an extension of hybrid microcircuits, and in that function it enables development, testing, and deployment of silicon microsystems. However, its versatility has allowed it to succeed as a microsystem medium in its own right, with applications in non-microelectronic meso-scale devices and in a range of sensor devices. Applications include silicon microfluidic 'chip-and-wire' systems and fluid grid array (FGA)/microfluidic multichip modules using embedded channels in LTCC, and cofired electro-mechanical systems with moving parts. Both the microfluidic and mechanical system applications are enabled by sacrificial volume materials (SVM), which serve to create and maintain cavities and separation gaps during the lamination and cofiring process. SVMs consisting of thermally fugitive or partially inert materials are easily incorporated. Recognizing the premium on devices that are cofired rather than assembled, we report on functional-as-released and functional-as-fired moving parts. Additional applications for cofired transparent windows, some as small as an optical fiber, are also described. The applications described help pave the way for widespread application of LTCC to biomedical, control, analysis, characterization, and radio frequency (RF) functions for macro-meso-microsystems. Tables Executive SummaryUpon the recognition that LTCC technology can play an important part in integration of macro-, meso-, micro-, and nano-scale systems, several areas have been investigated. These include new sacrificial volume materials/methods (SVM), new structures, creative use of thermistors, and setter and jacketed setter materials to fabricate structures never before envisioned. These include moving parts that are self-assembling at the mesoscale. These parts have been actuated electrostatically, pneumatically, and directly mechanically. 6March 2007 In a sense, almost every use of solid SVM is crying out for a patterned definition. Many more ways to do this exist when the SVM is in the form of a fluid. SVMs have no real minimum thickness with respect to the scale of features envisioned for thick films. We have also investigated the upper end of features, successfully fabricating channels and volumes with mm scale dimensions. By using composite SVMs, there is essentially no limit.We have fabricated stacked parts in the form of washers of diameter approximately 1.2 cm. Evaluations have been performed on similar parts that are inches in diameter.The application of sensitive materials has made it possible to fabricate smart channels. The bulk of this work has been carried out with polymeric chemiresistors, but new promise is held for cofirable sensitive materials as well. The two that were examined in detail include thermoresistive and piezor...
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