Kulite (United States)

Accurate static and dynamic pressure measurements in liquids, such as fuel, oil, and hydraulic fluid, are critical to the control and health monitoring of turbomachinery and aerospace systems. This work presents a theoretical and experimental study of the frequency response of pressure transducers and pressure measurement systems in liquid media. First, we theoretically predict the frequency response of pressure transducers based upon a lumped-parameter model. We then present a liquid-based dynamic pressure calibration test apparatus that validates this model by performing several critical measurements. This system first uses a vibrating liquid column to dynamically calibrate and experimentally determine the frequency response of a test pressure transducer, measurement system or geometry. Second, this calibration system experimentally extracts the bulk modulus of the fluid and the percent of entrained and/or dissolved air by volume. Bulk modulus is determined by measuring the speed of sound within the liquid and through static pressure loading while measuring the deflection of the liquid column. Bulk modulus and the entrained/dissolved gas content within the liquid greatly impact the observed frequency response of a pressure transducer or geometry. Gases, such as air, mixed or dissolved into a fluid can add substantial damping to the dynamic response of the fluid measurement system, which makes measurement of the bulk modulus and entrained and/or dissolved air critical for accurate measurement of the frequency response of a system when operating with a liquid media. All experimental results are compared to theoretical predictions.

Abstract We present the results of an investigation of the dependence of the photoluminescence (PL) spectra on preparation conditions, the resulting microstructure, and post-anodization treatment of porous silicon carbide films which were formed from both p and n-type 6H-SiC substrates. Porous samples were prepared by anodic dissolution under different galvanostatic conditions, resulting in different porosities and crystallite sizes. Selected-area electron diffraction patterns taken on similarly prepared porous silicon carbide (PSC) samples confirmed that the films were monocrystalline. Transmission electron microscopy of as-anodized films revealed an isotropie porous network; a dependence of porosity and nanocrystallite size on porous layer formation current density was established. Some PSC samples were passivated using a short, thermal oxidation treatment. The effects of porosity and crystallite size, and of oxide passivation in these PSC films, on PL spectra and intensity were studied using a 365 nm Kr-ion laser as excitation. Under certain conditions, the spectrally integrated PL intensity of a passivated film is more than 450x that for the original bulk SiC substrate. PL spectra are presented, and possible mechanisms are discussed.

A novel fabrication process for monolithic, electrically isolated diamond resistors is discussed. Selective growth of p‐type diamond resistors on undoped diamond has been accomplished by using as a sacrificial, “lift‐off” layer. Diamond resistors with linewidths less than 10 μm exhibited resistivities of 10 to 20 Ω‐cm. No measurable leakage between the resistors or to the substrate was observed.

In this paper a nonthermal photoelectrochemical etching technique for is reported. The measured etch rates of 1–100 μm/min in this process are much faster than other etching methods currently available for this material. UV radiation is necessary for efficient photogeneration of holes near the surface. These holes are transported in the presence of an external bias to the semiconductor/liquid interface, where dissolution occurs through the anodic oxidation of the and the removal of the oxide by F− ions present in the electrolyte. The electrochemistry of and the etching process variables are discussed.

Recent advances in SiC technology have demonstrated that the material is a potentially useful semiconductor for high temperature and high frequency applications. However, unlike silicon and GaAs, SiC is chemically inert, thus limiting the amount of etchants that can be effectively used to pattern devices. In fact, no patterning technique has been reported to date for SiC which shows high selectivity between p- and n-type material. In this letter, we will show how an n-type SiC epilayer can be patterned using photoelectrochemical etching, while a p-type substrate underneath acts as an etch stop. This process is useful for the fabrication of electromechanical transducers, mesa structures, and bipolar and CMOS devices in SiC.

The development of semi-conductor sensors particularly aimed at gas turbine technology applications is outlined. Methods of manufacture and means of utilizing some of the inherent advantages of this type of sensor are discussed. A novel technique, where miniature sensors are attached directly to the surface where the measurement is required, is described. This technique combines a high surface density of measurement points with a high frequency response capability. Detailed tests of the sensor’s performance have been conducted and results obtained using this technology are presented. The performance tests include frequency response, base strain sensitivity, g sensitivity, and software temperature compensation schemes. Finally, possible future applications for these techniques in gas turbine technology are outlined.