Jonathan L. Geisheimer

A continuous-wave (CW) radar for gait analysis

A fully coherent, continuous-wave (CW) radar operating near 10.5 GHz has been developed to record the radar signature corresponding to the walking human gait. The received signal is the sum of Doppler shifted signals reflected from the various parts of the moving body. Since the legs, arms, and torso all move at different relative velocities throughout the gait cycle, the human gait signature contains a wealth of information. Using signal processing techniques such as the short-time Fourier transform (STFT) and the chirplet transform, various parameters of the human gait can be extracted from the signal.

High-resolution Doppler model of the human gait

A high resolution Doppler model of the walking human was developed for analyzing the continuous wave (CW) radar gait signature. Data for twenty subjects were collected simultaneously using an infrared motion capture system along with a two channel 10.525 GHz CW radar. The motion capture system recorded three-dimensional coordinates of infrared markers placed on the body. These body marker coordinates were used as inputs to create the theoretical Doppler output using a model constructed in MATLAB. The outputs of the model are the simulated Doppler signals due to each of the major limbs and the thorax. An estimated radar cross section for each part of the body was assigned using the Lund & Browder chart of estimated body surface area. The resultant Doppler model was then compared with the actual recorded Doppler gait signature in the frequency domain using the spectrogram. Comparison of the two sets of data has revealed several identifiable biomechanical features in the radar gait signature due to leg and body motion. The result of the research shows that a wealth of information can be unlocked from the radar gait signature, which may be useful in security and biometric applications.

A non-contact lie detector using radar vital signs monitor (RVSM) technology

Traditional lie detector testing requires the subject to be physically attached to a variety of sensors. This is impractical for scenarios such as checkpoints where a large number of individuals are entering at a high rate, necessitating the employment of other methods. Currently, checkpoint officers must make a quick decision to determine if an individual is being deceptive, and if, in turn, they should be searched. The remote detection of deception (RDD) concept uses a non-contact sensor to obtain physiological information that can be used to aid the checkpoint officers decision. Such a device must be able to sense physiological signals from the body that may indicate deception in an unobtrusive and non-contact manner.

Extraction of micro-Doppler data from vehicle targets at x-band frequencies

The authors are utilizing an X-band radar to recover the natural resonance frequencies of a tractor trailer truck (18 wheeler) moving at highway speed. The aspect at which the truck is observed will be from the front and the radar will be raised above the roadway. The natural resonant frequency of the tractor and trailer can be as low as 1 Hz, and as high as 5 Hz depending on the gross weight of the cargo and how the cargo is arranged within the trailer. The condition of the trucks shock absorbers and other suspension stiffening members may also determine the natural resonance frequency of the tractor and trailer. The technical challenge is recovering the 1 to 3 Hz resonance induced signal that is imposed on the normal Doppler shifted signal of the truck when it is moving at 70 Miles Per Hour (MPH) using an X-band homodyne radar. This paper discusses: 1) the research goals; 2) the instrumentation being used for a test target; 3) tests that have been conducted using controlled test targets; and 4) signal processing methods that are being used to extract the micro-Doppler signal components.

A Microwave Blade Tip Clearance Sensor for Active Clearance Control Applications

Active clearance control has been used to improve efficiency and performance in commercial aircraft engines. Technologies implemented to date rely on compressor bleed air to control clearances based on open loop control and the flight regime (takeoff, cruise, etc.). Open loop systems necessitate a wide safety margin to accommodate the uncertainty in system models that are used to drive such systems. Implementing a feedback control system to optimize clearance has been difficult due to the lack of survivability of clearance measurement technology. Current technologies such as eddy current, capacitive, and laser sensors have been effectively used in laboratory environments but lack the robustness and reliability necessary for long-term use at high engine temperatures. This paper describes a microwave-based sensor designed to operate in temperatures up to 2500°F with a resolution of 0.2 mils and bandwidth up to 25 MHz. The sensor can effectively operate in dirty environments and has the ability to see through oil, combustion products, and other common contaminants. Performance data on the sensor from spin pit testing at 1100°F will be presented to show the viability of the sensor for use in active clearance control.

Performance Testing of a Microwave Tip Clearance Sensor

*The largest barrier to effective operation of tip clearance sensors in aero engines has been survivability and sensor accuracy within difficult thermal environments, especially in the turbine area. Thermal cycling, high thermal gradients and total time at temperature often contribute to premature sensor degradation and failure. This paper describes the results of testing a microwave tip clearance sensor designed to operate within either the compressor or turbine. The testing included resolution and linearity measurements along with thermal cycling of the cable in a high temperature furnace. I. Introduction HE measurement of tip clearance within gas turbine engines is normally performed within the context of providing information back to engine designers. It is desired that tip clearances be designed as close as possible, yet still not rub the case as the engine goes through its operating envelope. It has been documented that tip clearance pinch points occur on takeoff and landing as differences in thermal expansions between the case and rotor occur during the full output power condition at takeoff as well as the thermal soak back that occurs immediately after landing. 1 It is difficult to obtain actual tip clearance data in the field, due to the difficulty in getting tip clearances sensors to provide accurate and reliable data for an extended period of time. Therefore, design tip clearances can often be conservative, since it normally desirable to operate at a larger clearance then risk significant mechanical contact between the blades and case. Large tip clearances can have a substantial impact on efficiencies. It has been reported in the literature that a 0.001” the tip clearance can be closed can contribute as much as an additional 0.1% in efficiency improvement. 2 Normal operation of the engine typically causes clearances to increase over time as the blades and case coatings gradually erode due to the gas path or mechanical contact between the blades and case. If an active clearance control system could be designed able to adjust the tip clearances dynamically for the current engine condition, then the clearances could be optimized for the current location within the operating envelope as well as assist in maintaining constant engine performance in-between overhauls. A variety of active tip clearance control methods have been proposed including thermal techniques that control the clearance using compressor bleed air as well as active mechanical techniques that shift the rotor axially or use some type of segmented case to squeeze the case around the blades. New large commercial engine designs use compressor bleed air to actively control the tip clearance. Due to the inability to directly measure clearances in the engine, the tip clearance is scheduled using available data off of the engine combined with various models and algorithms. This technique also has some conservatism within it, which would benefit from actual clearance data to close the loop and thus optimize the control system. To date, the main types of sensors that are used for measuring tip clearance include capacitive, eddy current, optical, and microwave. Each of these different sensing principals has positives and negatives associated with them. The largest barrier to date in implementing a tip clearance sensor on a production engine has been sensor reliability, especially in the hottest areas of the engine. Sensor reliability in the turbine will typically be tens to hundreds of hours without some type of external active cooling, such as nitrogen or circulated water. Therefore, the ability to implement a sensor with long term reliability remains the most significant barrier to improved active clearance control performance. The microwave sensor described in this paper contains some unique characteristics, which make it highly suitable for use in the turbine environment. This paper will describe those characteristics as well as provide the results of performance testing showing the applicability of the sensor for use within an active clearance control system.

The use of passive radar for mapping lightning channels in a thunderstorm

The state of Georgia has experienced a number of tornadoes that occur without warning and in several cases have caused fatalities. Researchers at the Severe Storms Research Center (SSRC) of the Georgia Tech Research Institute (GTRI), Georgia Institute of Technology are attempting to detect tornado formation within severe thunderstorms occurring in the vicinity of Atlanta, Georgia using non-radar sensors that may provide early tornado warning and provide cueing to existing national weather service (NWS) radars. The goal of these studies is to increase the warning time of tornado formation within the parent thunderstorm. GTRI researchers use real time S-band Doppler weather radar data from three national weather service (NWS) WSR-88D NEXRAD radars to complement the development of the non-radar tornado sensors. Three NWS Doppler radars provide severe weather surveillance coverage of the north Georgia area to determine if a thunderstorm contains the Doppler signature that indicates tornado formation. The radar data, displayed on a work station developed and optimized for tornado detection by the National Severe Storms Laboratory (NSSL), serves as ground truth data for the non-radar sensor development. GTRI can display cloud to ground (CG) lightning strikes, a capability provided by overlaying data from a national monitoring network onto the radar reflectivity map. GTRI also uses a local lightning direction finder (DF) system that supplies azimuth and range to the lightning strike. This paper discusses the early lightning channel research and the passive parasitic radar system being operated by the SSRC.

Applications of neural networks to the radarcardiogram (RCG)

Displacement cardiography techniques such as the ballistocardiogram and seismocardiogram use accelerometers to measure body motion caused by the beating heart. The radarcardiogram (RCG) measures this motion using highly sensitive radar developed at the Georgia Tech Research Institute. Combining the portability and non-invasiveness of radar along with neural network processing techniques opens a host of potential new applications including unknown person identification, stress measurement, and medical diagnosis. Correlation between displacement cardiography and the RCG will be discussed along with preliminary research using RCG data and a neural network to identify unknown persons. It was found that a neural network could accurately identify the RCG of an unknown individual out of a small pool of training data. In addition, the system was able to correctly reject individuals not within the training set.

Novel sensors to enable closed-loop active clearance control in gas turbine engines

Active clearance control within the turbine section of gas turbine engines presents and opportunity within aerospace and industrial applications to improve operating efficiencies and the life of downstream components. Open loop clearance control is currently employed during the development of all new large core aerospace engines; however, the ability to measure the gap between the blades and the case and close down the clearance further presents as opportunity to gain even greater efficiencies. The turbine area is one of the harshest environments for long term placement of a sensor in addition to the extreme accuracy requirements required to enable closed loop clearance control. This paper gives an overview of the challenges of clearance measurements within the turbine as well as discusses the latest developments of a microwave sensor designed for this application.

FARM EQUIPMENT COLLISION AVOIDANCE USING ONLY HOMODYNE RADAR

GTRI is conducting research on the Safety Warning System (SWS), an off-the-shelf highway safety system that contains a 24 GHz motorist communications system and 24 GHz homodyne radar. This system is being evaluated to determine if it can reduce these types of farm equipment accidents. These research being conducted by GTRI on farm equipment accidents is part of a more comprehensive Federal Highway Administration research project being conducted on vehicular safety technology. The goal of this research, as it relates to farm equipment safety, is to determine if the SWS system can be used to warn both the approaching driver and farm equipment operator. Specifically, can the homodyne radar be used to warn the farm equipment driver of a motorists approach and can the approaching driver equipped with an SWS receiver be warned of the farm equipments presence in time to avoid a collision.