Robert C. Roberts

An Interstitial Fluid Transdermal Extraction System for Continuous Glucose Monitoring

A novel microfluidic system which is fabricated with five polydimethylsiloxane layers for interstitial fluid (ISF) extraction, collection, and measurement toward the application of continuous and real-time glucose monitoring is presented in this paper. The system consists of a micro vacuum generator for ISF transdermal extraction and fluid manipulation, micro chambers for the collection of ISF, micro pneumatic valves for fluid management, and a micro flow sensor for ISF volume measurement. Sequentially controlled by the pneumatic valves, the ISF extraction, collection, and volumetric measurement functions of the system were demonstrated using the stable vacuum generated by the integrated vacuum generator. Through low-frequency ultrasound pretreated full-thickness pig skin, the normal saline solution with different glucose concentrations was transdermally extracted, collected, and measured. The absolute error in the volume measurement of the transdermally extracted “ISF analog” was less than 0.05 μL. The microfluidic system makes it possible to realize the clinical application of continuous glucose monitoring based on ISF transdermal extraction technology.

Design, fabrication and testing of a micro-Venturi tube for fluid manipulation in a microfluidic system

In this paper, a micro-Venturi tube fabricated with polydimethylsiloxane (PDMS) is studied for interstitial fluid (ISF) transdermal extraction and fluid manipulation in a microfluidic system toward the application of continuous glucose monitoring. The fabrication structure parameters of the PDMS Venturi tube were theoretically analyzed and experimentally validated against the output vacuum efficiency of the Venturi structure. The optimization methods of the Venturi structure were also discussed. In addition, an optimized micro-Venturi structure was proposed and fabricated. A vacuum pressure of less than 86 kPa had been achieved when an external pressure of 240 kPa was applied to this optimized Venturi tube. Both experimental and mathematical results demonstrate the potential applicability of the micro-Venturi tube in ISF transdermal extraction and fluid manipulation.

Silicon carbide (SiC) membrane nanomechanical resonators with multiple vibrational modes

We report on experimental demonstration of a new type of nanomechanical resonators based on very thin silicon carbide (SiC) square membranes. An optical interferometry with a radio-frequency two-port measurement scheme enables sensitive and efficient detection of many vibrational modes of the membranes. Membranes with sizes up to 1mm × 1mm and thicknesses down to t ≤ 500nm, offer very high aspect ratios and compelling resonance spectra of multiple-mode operations from kHz range to the HF (3–30MHz) band. Typical resonances have Qs ∼ 800–30000 at room temperature and in vacuum of ∼20mTorr. Some high-Q modes exhibit fairly strong nonlinear effects.

Additive Processes for Semiconductors and Dielectric Materials

This chapter presents an overview of the key methods and process recipes commonly employed in the deposition of semiconductor and dielectric thin films used in the fabrication of microelectromechanical systems (MEMS). These methods include chemical vapor deposition, epitaxy, physical vapor deposition, atomic layer deposition, and spin-on techniques. The materials featured in this chapter include silicon and its oxide, nitride, and carbide derivatives, silicon–germanium, diamond and diamondlike carbon, III-V semiconductors, aluminum oxide, and other notable semiconductor and dielectric materials used as structural, sacrificial, and passivation layers. The process recipes presented in this chapter largely come from publications that report not only processing details, but also key material properties of importance to MEMS that result from the reported processes. Whenever possible, the references included in this chapter are papers that are readily available via commonly used electronic databases such as IEEE Xplore™ and ScienceDirect™ so as to aid the reader in gathering more detailed information than can be practically presented herein. Furthermore, the processes selected for inclusion in this chapter were, for the most part, successfully used in the fabrication of MEMS structures or components, thus verifying their utility in MEMS technology. For select materials, case studies are included to provide process-related details that cannot easily be tabulated but are nonetheless of critical importance to successful usage of the process.

Electrostatically Driven Touch-Mode Poly-SiC Microspeaker

This paper presents an electrostatically driven microspeaker utilizing a SiC membrane operating in the touch-mode configuration. The device is formed using conventional wafer bonding to hermetically seal a low-stress, heavily-doped polycrystalline 3C-SiC (poly-SiC) membrane to a bulk micromachined silicon back-plate containing a thin oxide insulating layer. The bonding process is done in high vacuum, causing the poly-SiC membrane to flex down into contact with the back-plate when exposed to atmospheric pressure. Sound Pressure Level (SPL) measurements were recorded for a device with a poly-SiC membrane thickness of 1 mum, a diameter of 800 mum, and a diaphragm/back-plate spacing of 8 mum. At a distance of 10 mm, a maximum SPL of 73 dB was found at a frequency of 16.59 kHz.

Thermoresistive characteristics of sintered inkjet printed gold nanoparticle microstructures

This paper presents the thermoresistive characteristics of hexanethiol encapsulated gold nanoparticles (NPs), inkjet printed onto Corning 0215 glass and sintered in air. The use of organic encapsulated metal NP precursors enables the growing field inkjet printed microsystems to build low-cost sensors and actuators on non-traditional substrates. However, this technology requires post-deposition thermal steps to sublimate organics and induce NP sintering. The resulting microstructures can have unique characteristics, giving rise to new sensing capabilities. Gold NP microstructures were patterned using inkjet printing and sintered under varied conditions. Four-point resistance measurements were performed on a hotplate to characterize the thermoresistive response of the resulting microstructures between 25°C and 150°C. Temperature coefficients of resistance (TCR) of 2000 and 2300 ppm/°C±10% have been measured for Au-NP films sintered at 175 and 225°C, respectively.

A micro flow sensor for volumetric measurement of conductive fluids

We present a microfluidic volumetric measurement system for applications involving conductive fluids. The low cost polydimethylsiloxane (PDMS) device consists of an interconnected Venturi Tube to generate vacuum for fluid manipulation, and a resistance based sensor for fluid volume quantification. The Venturi Tube achieves less than 88 kPa (absolute pressure) vacuum when a 256 kPa external pressure is applied. Measurements using the volumetric sensor have been demonstrated with deionized water, and the results correlate well (R2=0.9996) with the micro syringe references. The demonstrated system provides excellent functionality for conductive fluids, such as those used in biomedical applications.

Modeling and measurement of microfabricated corona discharge structures

This paper reports on corona discharge needle-to- plane configurations to act as ionizers for airborne particulate analysis applications. Three electrode configurations are explored with the objective of obtaining a high electric field strength to maximize the probability that all incoming particles are ionized. The hybrid FE-Trefftz method, which has been developed to combine the best of both finite elements (FE) and boundary elements (BE), is used to calculate the electric fields of our ionizers. According to the simulations using the electrostatic analysis of ANSYStrade, the rounded needle-to-one-plane and needle-to-two-plane are found to produce higher electric fields, when compared to the needle-to-three-plane. Our modeling results are verified and validated by the maximum electric fields, which are governed by the Paschens law, and the experimental results, which are based on our measurements and the previously published report respectively. The Townsend current-voltage approximations of corona currents are also formulated based on our measurements to find the closed forms of the objective functions for optimization and design in future.

A time-of-flight flow sensor for the volume measurement of trace amount of interstitial fluid

Transdermal extraction of interstitial fluid (ISF) offers an attractive method for noninvasive blood glucose monitoring. The existing macroscale systems are not suitable for ISF collection, mainly because of the minute volume of the transdermally extracted ISF which scatters on the skin surface. Human skins low permeability to glucose and its varying permeability exemplify the crucial need to make precise ISF volume measurements in order to calculate blood glucose concentrations accurately. In this paper, we present a novel time-of-flight flow sensor consisting of four electrode pairs fabricated directly into the channel of a polydimethylsiloxane (PDMS) microfluidic device designed to accurately measure the volume of transdermally extracted ISF. As fluid traverses the channel, it bridges each electrode pair and changes its resistance. By measuring the time difference in resistance change between each electrode pair, a precise fluid volume can be measured. In order to verify the suitability of the sensor for biological applications, experiments were conducted using a normal saline solution which is similar to ISF. The stability of the sensor was tested using a fixed volume, and the coefficient of variation for 20 tests was determined to be 0.0041. The consistency of the sensor for varied volume measurements was shown by the high correlation coefficient (R2?= 0.9992) between the tested volume and the volume measured by a commercial micro syringe. The excellent functionality of the flow sensor can be extended toward the measurement of conductive chemical and biochemical buffers and reagents.

An integrated microfluidic system for interstitial fluid transdermal extraction

We present a new microfluidic system for transdermal interstitial fluid (ISF) extraction, collection, and volumetric measurement towards the application of continuous glucose monitoring. This device consists of a venturi tube, a volume sensor, pneumatic valves, and microchannels. Under the management of pneumatic valves, demonstration of the defined volume normal saline injection, ISF extraction, collection and volumetric measurement functions of the system is presented using the stable vacuum generated by the integrated venturi structure. The stability of defined volume normal saline injection is tested, and the coefficient of variation for 20 tests is 0.0041. A simulating test of ISF collection and volumetric measurement is done with the system, and the measurement results correlate well (R2=0.9992) with the values measured by micro syringe.