Richard H. Selfridge

Microbatteries for self-sustained hybrid micropower supplies

This paper describes the characteristics of microbatteries suitable for use in a hybrid micropower supply for powering autonomous MEMS and other microsystems. The hybrid power supply includes an energy conversion device, microscopic batteries for energy storage, and control/interface circuitry. Comparison of the hybrid approach with single power sources (either a battery or energy conversion device alone) shows that it offers several potential advantages including reduced size, increased flexibility, long lifetime and increased reliability. Such an approach is well suited to the expected duty cycles of remote microsensors. Realization of the advantages of a hybrid system depends on the availability of a battery with the required characteristics. Initial experimental results demonstrate the feasibility of fabricating microbatteries with the proper characteristics and the use of these batteries as part of a hybrid micropower supply. It is anticipated that hybrid micropower supplies with suitable microbatteries will play a critical role in the successful implementation of a wide variety of autonomous microsystems.

In-plane linear displacement bistable microrelay

In this paper we investigate the linear displacement bistable mechanism (LDBM) for use in microrelays. The LDBM, thermal actuators and contacts are integrated to demonstrate a relay design. The performance of the relay is characterized using relay performance metrics, including size (1.92 mm2), contact force (23.4 μN), switching time (340 μs), breakdown voltage (>475 V) and isolation (>235 V). The actuation voltage and current are 11 V and 85 mA, respectively. The ac characteristics, including contact-to-contact crosstalk and ac isolation are also measured. The testing results demonstrate that it is feasible to use the LDBM as a microrelay and that it has potential for use in future applications.

High-temperature sensing using surface relief fiber Bragg gratings

We present a new type of fiber Bragg grating (FBG) that can be used in high-temperature sensing applications. We use the flat side of a D-shaped optical fiber as a platform to etch the grating into the surface of the fiber. Because the grating becomes a physical feature of the fiber, it is not erased at high temperatures as are standard FBGs. These surface relief fiber Bragg gratings will operate up to high temperatures. We provide a brief explanation of the fabrication process and present our results for operation up to 1100/spl deg/C.

Teaching electromagnetic field theory using differential forms

The calculus of differential forms has significant advantages over traditional methods as a tool for teaching electromagnetic (EM) field theory. First, films clarify the relationship between field intensity and flux density, by providing distinct mathematical and graphical representations for the two types of fields. Second, Amperes and Faradays laws obtain graphical representations that are as intuitive as the representation of Gausss law. Third, the vector Stokes theorem and the divergence theorem become special cases of a single relationship that is easier for the student to remember, apply, and visualize than their vector formulations. Fourth, computational simplifications result from the use of forms: derivatives are easier to employ in curvilinear coordinates, integration becomes more straightforward, and families of vector identities are replaced by algebraic rules. In this paper, EM theory and the calculus of differential forms are developed in parallel, from an elementary, conceptually oriented point of view using simple examples and intuitive motivations. We conclude that because of the power of the calculus of differential forms in conveying the fundamental concepts of EM theory, it provides an attractive and viable alternative to the use of vector analysis in teaching electromagnetic field theory.

Volatile organic compound sensing using a surface-relief D-shaped fiber Bragg grating and a polydimethylsiloxane layer

The authors use a surface-relief fiber Bragg grating with a polydimethylsiloxane (PDMS) layer as a volatile organic compound chemical sensor. A PDMS layer is used because it is compatible with the optical properties of the grating and exhibits good chemical selectivity. As the analyte is absorbed the refractive index of the PDMS changes, causing the Bragg wavelength to shift, and this shift is correlated to chemical type and concentration. The direction and amount of the Bragg wavelength shift is dependent on the absorbed chemical. The authors demonstrate chemical differentiation between dichloromethane and acetone in gaseous states.

Full-spectrum interrogation of fiber Bragg gratings at 100 kHz for detection of impact loading

This paper explains key innovations that allow monitoring of detailed spectral features of an FBG in response to impact loading. The new system demonstrates capture of FBG spectral data at rates of 100 kHz. Rapid capture of the entire reflection spectrum at such high reading rates shows important features that are missed when using systems that merely track changes in the peak location of the spectrum. The update rate of 100 kHz allows resolution of features that occur on transient time scales as short as 10 µs. This paper gives a detailed description of the unique features of the apparatus and processes used to capture the data at such a rapid rate. Furthermore, we demonstrate this interrogation scheme on a composite laminate system during impact.

Electro-optic sensor from high Q resonance between optical D-fiber and slab waveguide.

An electric-field sensor is specially fabricated with an optical D-fiber that utilizes weak evanescent coupling with a lithium niobate slab waveguide. Resonant modes with a Q-factor of ~13,000 yield high sensitivity for detecting electric fields.

Controlled core removal from a D-shaped optical fiber

The partial removal of a section of the core from a continuous D-shaped optical fiber is presented. In the core removal process, selective chemical etching is used with hydrofluoric (HF) acid. A 25% HF acid solution removes the cladding material above the core, and a 5% HF acid solution removes the core. A red laser with a wavelength of 670 nm is transmitted through the optical fiber during the etching. The power transmitted through the optical fiber is correlated to the etch depth by scanning electron microscope imaging. The developed process provides a repeatable method to produce an optical fiber with a specific etch depth.

Analysis of etching-induced birefringence changes in elliptic core fibers

A mathematical model is presented that predicts birefringence changes in an optical fiber as the cladding is removed. This model approximates a highly elliptical fiber core with a rectangular dielectric waveguide. The birefringence calculations obtained with the model compare well with experimental evidenceobtained with real-time birefringence monitoring during cladding removal by chemical etching. The information is used to control the amount of cladding removed from a D fiber to within approximately 0.05 microm for use in the production of passive optical fiber components.

Electric-field sensors utilizing coupling between a D-fiber and an electro-optic polymer slab.

This paper provides a detailed analysis of electric field sensing using a slab-coupled optical fiber sensor (SCOS). This analysis explains that the best material for the slab waveguide is an inorganic material because of the low RF permittivity combined with the high electro-optic coefficient. The paper also describes the fabrication and testing of a SCOS using an AJL chromophore in amorphous polycarbonate. The high uniform polymer slab waveguide is fabricated using a hot embossing process to create a slab with a thickness of 50 μm. The fabricated polymer SCOS was characterized to have a resonance slope of ΔP/Δλ=6.83E5 W/m and a resonance shift of Δλ/E=1.47E-16 m(2)/V.