Angular Readout Research Articles

Modeling of the SPR resolution enhancement for conventional and nanoparticle inclusive sensors by using statistical hypothesis testing

This paper describes a statistical approach that improves the detection accuracy in simulated experimental surface plasmon resonance (SPR) systems operated in a conventional angular readout scheme. Two SPR system have been investigated: a conventional one and a second one, containing absorbing metallic nanoparticles within the sensing layer. The modified Maxwell-Garnett model that optimally describes the experimental literature results was applied to modeling of the nanoparticle-inclusive sensor. Statistical hypothesis testing was then used to determine the limit of detection of the analyte and nanoparticles. Analyte concentrations as low as 1 pM, corresponding to the refractive index change of 4x10(-8) have been detected with optimized metal layers operated close to the nanoparticle absorption maximum. This is about one order of magnitude smaller than the values obtained in conventional SPR systems with nanoparticles and comparable to the phase-sensitive surface plasmon resonance detection.

Is an angular standard necessary for rotary encoders?

A rotary encoder is an angular readout that reads an optical pattern written on the circumference of a shaft similar to a 360 degrees protractor and outputs angle position information. Since the output of a rotary encoder deviates from the true angle position due to optical pattern errors or eccentricity of the shaft about the rotation axis, users have encountered difficulty in ensuring the reliability of the angle information derived from an encoder. In order to solve this problem, SelfA: A Self-calibratable Angle device was developed. The SelfA can detect a variety of angle deviation sources by itself, and has the ability to output an angular calibration value. This SelfA can detect the angle deviation value from an optical encoder which has been a black box until now and enables visualization of these factors quantitatively.

Experimental Test of a New Precision Model for Microwave Rotary Vane Attenuators

Detailed measurements of scattering parameters have been made on a precision rotary vane attenuator (RVA) with high-resolution, direct angular readout. The aim of the measurements has been to test if the RVA can be used as a primary standard of attenuation by taking advantage of a precision model described recently by one of the authors (T. Guldbrandsen). Precision attenuation measurements have been made versus angle of rotation by means of a modulated subcarrier system. Within the uncertainty, the attenuation measurements agree with the functional dependence predicted by the model. Reflection coefficients have been measured versus angle of rotation by means of a computer-corrected automatic network analyzer and, within the uncertainty, they agree with the model. From the reflection measurements, corrections to the attenuation were calculated using relations derived from the model. The corrections were compared with the measured attenuation values. So far the agreement is not quite satisfactory and additional diagnostic measurements are planned.

A capacitance-based micropositioning system for x-ray rocking curve measurements

Certain types of x-ray experiments require very precise angular positioning of crystals in the vicinity of the Bragg reflection condition. A system applicable to some measurement of this type is described which achieves a long-term angular stability of approximately 10(-7) radians, coupled with a linear angular readout. This is achieved through a novel capacitance sensing system which provides angle measurement, together with the use of an auxilliary servo loop based on the Bragg condition to ensure long-term overall angular stability.

Thermal-Noise Errors in Simultaneous-Lobing and Conical-Scan Angle-Tracking Systems

Relationships for rms angular errors are developed for certain common active space probe and satellite angle-tracking systems. The only source of error considered is the thermal and shot noise of the receiver, bandlimited by the tracking servo noise bandwidth. If additional smoothing after angular readout is performed, only the special case of many samples averaged over a time long compared to the reciprocal servo noise bandwidth is considered. These thermal-noise errors are by no means the usual practical accuracy limitations of an angle-tracking system. They do, however, set bounds on minimal signal strength allowable for the desired tracking accuracy. The received signals were assumed to be sinusoidal of constant peak amplitude with the information, if any, contained in phase or frequency modulation. This is the most common signal in space probe or satellite tracking.