Session G16: Experimental Techniques: Probes, Sensors, Microscopy and Surface Measurements

Fast-response hot-wire flow sensors for wind and gust estimation on UAVs

Unsteady airflow phenomena such as wind gusts present a control challenge for Unmanned Aerial Vehicle (UAV) operations. The prevailing control strategy is to apply corrective action after setpoint error is detected. A proactive approach, enabling faster and more precise control, requires measuring the wind directly with onboard flow sensors. Existing anemometry techniques are unsuitable due to form factor, resolution, or robustness requirements. To overcome this, a novel, fast-response sensor to measure a wind vector in two dimensions is introduced. This sensor, named 'MAST' (MEMS Anemometry Sensing Tower), leverages advances in microelectromechanical (MEMS) hot-wire devices to produce a solid-state, lightweight, and robust flow sensor suitable for real-time wind estimation onboard a UAV. The MAST is a modular system that supports multiple configurations, which were evaluated in the wind tunnel. A neural network sensor model was trained to predict the direction (0-360 degrees) and magnitude (0-5 m/s) of the wind. Additionally, the bandwidth of the MAST system is sufficiently high to capture the relevant atmospheric phenomena. The resulting system stands to greatly enhance UAV wind estimation capabilities.   

AC Plasma Anemometer in a High Speed Preionized Hydrogen Jet

Measurements in a high-speed, preionized, low pressure hydrogen jet using a novel AC-driven glow discharge flow sensor are

presented.  These results examine the sensitivity and voltage-current characteristics of a plasma sensor with and without the presence of a background RF plasma.  These results extend the utility of the plasma sensor to a regime of rarefied and reactive, high speed gases. Recent experiments examine the effects of electrode geometry, AC frequency, and background ionization on the plasma sensor response.     

A wearable sweat rate sensor enabling continuous exercise performance evaluation

Sweat rate sensing is essential for evaluating a physical load during the exercise. An individual analysis of the perspiration would provide a beneficial guide for personalized physical activities. As a wearable health monitoring platform, we have developed a flexible flow rate sensor that can measure sweat flow rate with the order of several μL/min. The developed sensor relies on the convective thermal transfer to quantify the flow rate around a microheater in a microchannel embedded in a polyimide film. With appropriate signal processing, we found that evaluation of a physical exercise of a human is possible using our developed sensor.   

Optimization of novel luminescent temperature and phase change sensor within ice.

A novel luminescent sensor for temperature and phase change within water ice was developed. The sensor behavior relies on the interaction between the two luminescent peaks of the luminophore pyranine and sucrose within liquid water and, upon freezing, ice. When excited by 365nm light, pyranine emits light with distinct peaks at 440nm and 511nm. These two peaks can be separated into blue and green signals by a color camera or other photosensitive device. The amplitude of these peaks are sensitive to temperature within ice and the ratio of the intensities of these peaks is linear with temperature. The absolute value of the slope of this line is the sensitivity of the sensor, which should be maximized for optimum sensor performance. As with most chemical sensors, the sensitivity of the measurement technique is a function of the concentrations of the its constituent components, and can vary between 1.6 and 9.2%\K. Spectrometer data was collected on numerous solutions with various concentrations of sucrose and pyranine within distilled water. The final presentation will include the spectral performance of the sensor, as well as models describing the optimum sensitivity of the sensor as a function of additive concentration.   

Surface Pressure Measurement on Free-flight Cylinder using Motion-capturing PSP method

Most traditional pressure measurement techniques rely on connecting wires or onboard systems to record pressure. These requirements limit the ability of traditional techniques to measure in-flight objects. This study proposes using two-color pressure-sensitive paint (PSP) to measure the pressure distribution of a model exposed to a shockwave. PSP was chosen over traditional techniques because a wired connection may affect flight dynamics, and an onboard pressure transducer may affect weight distribution. Additionally, the two-color PSP allowed for consistent pressure measurement despite the motion of the model. An unsecured 10 mm diameter cylinder was coated in PSP and placed into a blast tube. The model was then exposed to a shockwave, and the subsequent flow and the results were recorded using a high-speed color camera. A traditional diaphragm pressure transducer was located in the wall of the blast tube for comparison. The pressure increase due to shockwave compression measured by the PSP was within 5% of the increase measured by the in-wall transducer, which resulted in a 3% difference in estimated shockwave speed. The PSP measured a high-pressure region at the leading edge and a dynamic pressure distribution across the model when exposed to post-shockwave flow.