Abstract-An analytical model which predicts the attenuation of ultrawide-band (UWB) signals as they traverse various inhomogeneous tissues is presented. The model provides a computationally efficient method of determining the frequency-dependent losses encountered by electromagnetic radio frequency (RF) signals used to communicate with biomedical implants.Classic transmission line theory is employed to generate an analytical representation which models the inhomogeneous tissue using layers of homogeneous material. The proposed model was verified experimentally with tests of both single and multilayer samples. A realistic abdominal implant scenario was also modeled and the predictions were verified using a commercially available 3D electromagnetic (EM) simulator. The results of this study indicate that for deep implants the higher frequency portion of the UWB spectrum is attenuated much more strongly than the lower end of the band. This implies that for robust communication UWB signals targeting biomedical implants should be limited to the lower portion of the spectrum.

A new method of sensing the vibrational motions of a exible structure by measuring the dierence in GPS (global positioning system) carrier phase at separate antennas on the structure is presented. Differential carrier phase measurements have been recently used to determine the attitude of rigid bodies such as aircraft and spacecraft, and for aircraft landing with ground based GPS pseudolites. This technology is still rapidly developing and has often proven to be a powerful, low cost alternative to traditional sensing methods. This paper presents the main issues that must be considered to extend GPS to exible systems. Sensor bandwidth, measurement accuracy, and receiver architecture issues are discussed as well as the techniques for real-time state estimation. This paper emphasizes the following: 1. Why is GPS valuable as a structural deformation sensor? 2. What are the challenges to realizing this sensor? 3. How are these challenges being addressed?

This paper demonstrates active control of the attitude and vibration of a exible structure using the Global Positioning System GPS. Measurements of the carrier phase of the GPS signal at several antennas are used to estimate the deformation and orientation of the structure. This distributed measurement capability, combined with excellent zero-frequency performance, makes the GPS sensor an excellent choice for a wide range of applications, including space structures, suspension bridges, and skyscrapers. This paper presents the control system developed around the GPS sensor for a particular structure modeled after the Space Station. The results from several new experiments demonstrate that the GPS sensor provides rotational accuracies better than 0.1 for static tests. Measured spectra also demonstrate that the carrier phase GPS techniques are su ciently accurate to resolve many of the modes of vibration. Several feedback control experiments are used to show that the sensor provides an accurate and robust measure of the structural deformations. These experiments culminate in a fast slew maneuver under feedback control which provides a clear demonstration of the application of carrier phase GPS for both alignment and vibration control. This work represents an exciting advancement in the eld of GPS sensing because it shows the potential for GPS as a high precision, real-time structural sensor.

Executive SummaryProblem Definition The Army Aviation and Missile Research. Development, and Engineering Center (AM-RDEC) Unmanned Systems Office looks beyond next generation systems to determine what capabilities and systems may become a viable part of strategy and tactics in the future. Specific to Unmanned Aircraft Systems (UAS). they see a strong and central role for them in the future, post Future Combat Systems (FCS). Based on assumptions about advancement of data transmission, stealth capability, and computational power. AMRDEC wants to maximize the UAV : s effectiveness.One method is to establish a more direct link between operational users and the system itself. They do not want to limit direct access to only Military Occupational Specialty (MOS) trained UAS operators. Rather, they feel that opportunities will exist that will allow any soldier in the battle space to employ one or more Unmanned Aerial Vehicles (UAVs) for a specific task during a specific time and still effectively execute the duties of their primary MOS. This can be done by embedding Semi-Autonomous and Self-Collaborating (SASC) characteristics within swarms of UAS that support operations. Technical ApproachThe approach taken to model this system begins with an examination of the state of the art. Since the inception of the Global War on Terror (GWOT). UAS use has climbed dramatically each year, over 300.000 hours in fiscal year 2007 alone. US Army UAV operators have the ability to generate routes and Areas of Interest (AOI) for the UAS to fly to. Soon they will be able to control up to 4 different UAV from the same location. However, the UAVs still require specific mission planning and dedicated payload operators in order to acquire and identify targets. AMRDEC is looking to SASC UAS that can support multiple craft in a bounded area in order to. for instance, conduct reconnaissance.The approach is comprised of three parts; stakeholder analysis, designing the system, and simulating the UAS behavior.1) Stakeholder Analysis. Speak to UAS operators and determine what capabilities they think the system would need to become SASC. Have them provide their proposed improvements.2) System Design. Assume that an infantry Soldier needs the service of UAS to improve their intelligence picture. They could draw from a bank of UAS standing by. The few that are chosen to help him are given the coordinates of the AOI, a doctrinal task, and a list of "interesting" items to search for. His new recon team forms a loose network in order to collaborate. When one or more UAVs spot an "interesting" item, they contact the Soldier and track the object until told to continue with the search. Meanwhile the other UAVs take up the slack in the AOI left by UAVs holding over targets. Though this system seems complex, it can be managed with a few simple rules.With simplicity in mind, I examined systems of collaborating entities, specifically insects and animals. Individual UAVs will not have a global operating picture yet they must work in concert with other UAVs to exe...

Current laboratory tests demonstrate vibration and orientation control of a highly flexible vehicle using only the GPS carrier to measure motion. A 30 ft long test structure has been constructed that is suspended from above, and moves in a manner analogous to that of a flexible orbiting platform. Experiments show simultaneous rigid-body orientation and elastic vibration control by closing a feedback loop from the GPS differential carrier phase (DCP) measurements to onboard thrusters. Use of the subcentimeter-level differential position information in DCP measurements is challenging because of inherent, and arbitrarily large, measurement biases (cycle ambiguities). This paper presents a new bias ambiguity resolution algorithm that combines measurements taken during motion of the structure with a model of the platform dynamics to initialize the unknown biases. The techniques presented are applicable to systems that exhibit relative motions with frequencies (< 10 Hz) and deflections (> 1 cm) that are detectable by current receivers.