Frederick Seng

Optical sensing of electrical fields in harsh environments

This paper shows a method allowing electric field sensing in high vibration environments. The vibration sensitivity is reduced using a push-pull configuration and external phase modulation. This paper provides both theoretical description and experimental verification.

Split Hopkinson bar measurement using high-speed full-spectrum fiber Bragg grating interrogation.

The development and validation of a high-speed, full-spectrum measurement technique is described for fiber Bragg grating (FBG) sensors. A FBG is surface-mounted to a split-Hopkinson tensile bar specimen to induce high strain rates. The high strain gradients and large strains that indicate material failure are analyzed under high strain rates up to 500  s-1. The FBG is interrogated using a high-speed full-spectrum solid-state interrogator with a repetition rate of 100 kHz. The captured deformed spectra are analyzed for strain gradients using a default interior point algorithm in combination with the modified transfer matrix approach. This paper shows that by using high-speed full-spectrum interrogation of an FBG and the modified transfer matrix method, highly localized strain gradients and discontinuities can be measured without a direct line of sight.

Slab-coupled optical sensor fabrication using side-polished Panda fibers

A new device structure used for slab-coupled optical sensor (SCOS) technology was developed to fabricate electric field sensors. This new device structure replaces the D-fiber used in traditional SCOS technology with a side-polished Panda fiber. Unlike the D-fiber SCOS, the Panda fiber SCOS is made from commercially available materials and is simpler to fabricate. The Panda SCOS interfaces easier with lab equipment and exhibits ∼3  dB less loss at link points than the D-fiber SCOS. The optical system for the D-fiber is bandwidth limited by a transimpedance amplifier (TIA) used to amplify to the electric signal. The Panda SCOS exhibits less loss than the D-fiber and, as a result, does not require as high a gain setting on the TIA, which results in an overall higher bandwidth range. Results show that the Panda sensor also achieves comparable sensitivity results to the D-fiber SCOS. Although the Panda SCOS is not as sensitive as other side-polished fiber electric field sensors, it can be fabricated much easier because the fabrication process does not require special alignment techniques, and it is made from commercially available materials.

Push–pull slab coupled optical sensor for measuring electric fields in a vibrational environment

Vibration-insensitive fiber optic electric field sensor is created by fabricating two sensing elements in close proximity onto the same optical fiber and subtracting the two signals. The device is used to measure an electric field of 10  kV/m, while the sensor is being bent and impacted.

Optical Sensing of Electric Fields in Harsh Environments

Fiber optic electric field sensors are ideal for characterizing the electric field in many different systems. Unfortunately, many of these systems produce one or more noise types, like vibrational noise which contribute to a harsh sensing environment on the fiber optic sensor. When fiber optic sensors are placed in a harsh vibration environment, multiple noise types can overwhelm the measurements. This work shows how to simultaneously eliminate three different noise types in a fiber optic sensor induced by a harsh vibration environment. Specifically, nonlocalized vibration-induced interferometric noise is up converted to higher frequency bands by single-tone phase modulation. Then, localized vibrational noise, and radio frequency noise are all eliminated using a push–pull slab coupled optical sensor configuration to allow for an optical measurement of an electric field in a harsh environment.

Optical electric field sensor sensitivity direction rerouting and enhancement using a passive integrated dipole antenna

This work introduces a passive dipole antenna integrated into the packaging of a slab-coupled optical sensor to enhance the directional sensitivity of electro-optic electric field measurements parallel to the fiber axis. Using the passive integrated dipole antenna described in this work, a sensor that can typically only sense fields transverse to the fiber direction is able to sense a 1.25 kV/m field along the fiber direction with a gain of 17.5. This is verified through simulation and experiment.

Measuring arc dynamics using a slab coupled optical sensor (SCOS)

Electric arcs are a form of electric discharge through a non-conductive media caused by a high electric potential between two points. The timing of this discharge serves as an important parameter in high pulse power applications and a short discharge time is often desirable. We put together a circuit which operates on the principle of inducing a high voltage pulse on an ignition coil controlled by a MOSFET. Slab coupled optical sensor (SCOS) technology was used to characterize arc dynamics such as the discharge time, charge time, slope of the discharge, and effects of changing spark gap distance. In triggering the spark gap, we were able to characterize the discharge of pulses with times between 100 ms and 170 ns.

High electric field measurement with slab coupled optical sensors using nonlinear calibration

We describe the application of SCOS technology in non-intrusive, directional and spatially localized measurements of high electric fields. When measuring electric fields above a certain threshold, SCOS measurement sensitivity starts varying to a great extent and the linear approximation that assumes sensitivity to be constant breaks down. This means that a comprehensive nonlinear calibration method is required for accurate calibration of both low and high electric fields, while linear calibration can only be accurately applied for low fields. Nonlinear calibration method relies on the knowledge of the variability of sensitivity, while linear calibration relies on approximation of sensitivity with a constant value, which breaks down for high fields. We analyze and compare the two calibration methods by applying them to a same set of measurements. We measure electric field pulses with magnitudes from 1 MV/m to 8.2 MV/m, with sub-300 ns rise time and fall-off time constant of 60 μs. We show that the nonlinear calibration very accurately predicts all measured fields, both high and low, while the linear calibration becomes increasingly inaccurate for fields above 1 MV/m.