Though thermoluminescent dosimeters (TLDs) are one of the most commonly used and well-known radiation detectors in the industry today, they do not typically provide real-time feedback. A radiation detector that could alert users in real-time and that is small enough to fit in a pocket would be very useful for those who work near sources of radiation or to counter radiation weapons. In this project, a compact, low-power, portable detector is being developed to provide real-time radiation detection and discrimination that allows the user to vary the threshold and sensitivity of detection based on the radiation intensity.
The prompt and accurate detection of laser strikes is increasingly important to the survivability of military assets in modern warfare as offensive and defensive laser weapon systems have become more widely implemented. Current laser detection systems on military assets can compromise an asset’s low observability features. This paper presents an addressed detection system based on an array of thermoelectric generators (TEGs) that can be integrated into the skin of an asset. An irradiated TEG harvests the incident energy of a high energy laser (HEL) strike to power a sensor node that transmits an address, via a wireless medium, to a reader in order to indicate which TEG within the array is being irradiated. The wireless sensor node consists of an ultralow voltage step-up converter and microcontroller and a low power RF link.
Detection of high-energy laser strikes is key to the survivability of military assets in future warfare. The introduction of laser weapon systems demands the capability to quickly detect these strikes without disrupting the stealth capability of military craft with active sensing technologies. We explored the use of thermoelectric generators (TEGs) as self-powered passive sensors to detect such strikes. Experiments were conducted using lasers of various power ratings, wavelengths, and beam sizes to strike 2 × 2 cm2 commercially available TEGs arranged in different configurations. Open-circuit voltage and short-circuit current responses of TEGs struck with 808-, 1070-, and 1980-nm lasers at irradiance levels between 8.5 and 509.3 W / cm2 and spot sizes between 2 and 8 mm are compared. TEG surface temperatures indicate that the sensor can survive temperatures nearing 400°C. TEG open-circuit voltage magnitudes correlate more strongly with net incident laser power than with specific irradiance levels, and linearity is limited by Seebeck coefficient variation with temperature. Open-circuit voltage responses are characterized by 10% to 90% rise times of ∼2 to 10 s despite surface temperatures not reaching equilibrium. With open-circuit voltage as the sensing parameter, detection thresholds three times above the standard deviation noise level can be exceeded within 300 ms of the start of a laser strike with irradiance levels of ∼200 W / cm2. Potential harvested power levels as high as 16 mW are estimated based on measured electrical responses. A multiphysics finite-element model corresponding to the experiments was developed to further optimization of a lightweight, low-profile TEG sensor for detection of high-energy laser strikes.
Detection of high energy laser strikes is key to the survivability of military assets in future warfare. The introduction of laser weapon systems demands the capability to quickly detect these strikes without disrupting the stealth capability of military craft with active sensing technologies. This paper explores the use of thermoelectric generators (TEGs) as selfpowered passive sensors to detect such strikes. Experiments were conducted using lasers of various power ratings, wavelengths, and beam sizes to strike 2cm x 2cm commercially available TEGs arranged in different configurations. Open circuit voltage and short circuit current responses of TEGs struck with 808nm, 1070nm, and 1980nm lasers at irradiance levels between 8.5-509.3W/cm2 and spot sizes between 2-8mm are compared. TEG surface temperatures indicate that the sensor can survive temperatures nearing 400°C. TEG open circuit voltage magnitudes correlate more strongly with net incident laser power than with specific irradiance levels, and linearity is limited by Seebeck coefficient variation with temperature. Open circuit voltage responses are characterized by 10%-90% rise times of ~2-10s, despite surface temperatures not reaching equilibrium. With open circuit voltage as the sensing parameter, detection thresholds three times the above the standard deviation noise level can be exceeded within 300ms of the start of a laser strike with irradiance levels of ~200W/cm2. Potential harvested power levels as high as 16mW are estimated based on measured electrical responses. A multi-physics finite element model corresponding to the experiments was developed to further optimization of a lightweight, low-profile TEG sensor for detection of high energy laser strikes.
An embedded distributed optical fiber sensor (DOFS) based on Rayleigh scattering is used to measure the localized thermal response of a carbon fiber/epoxy composite to directed energy. The thermal impulse from a laser strike is detected while the composite is subjected to cyclic mechanical strain. The ultimate goal is rapid detection of directed energy on the surface of the composite. Prior research demonstrated the use of distributed optical fiber sensors embedded in carbon fiber/epoxy composite structures to rapidly detect temperature changes approaching 1000℃ during a high energy laser strike. However, swept wavelength interferometry used to interrogate a DOFS uses shifts in frequency which can be caused by both changes in temperature and strain. Hence, strain in the composite resulting from mechanical loading is also detected by the embedded sensor and can interfere with rapid detection and measurement of a localized thermal response. Initial tests have demonstrated the simultaneous response of the DOFS to both temperature and strain. A sensing network has been designed to mitigate the response of the sensor to mechanically applied strains, and a simple signal processing technique has been used to cancel the response of the sensor to bending strain while enhancing the thermal response when directed energy is incident on the composite surface. Additional testing indicates that the network and processing technique can also be used to isolate localized impacts on the composite surface from bending strain.
In this research, distributed sensing based on Rayleigh scattering is used to measure temperature and strain in a composite panel during a high energy laser strike. The ultimate goal is to rapidly detect a laser strike by sensing the localized, rapid temperature rise caused when directed energy is incident on the surface of a composite structure. A secondary goal is to determine if the thermal response can be detected even in the presence of applied strain. Initial results will be discussed for composite structures comprised of carbon fiber/epoxy of various thicknesses using embedded distributed optical fiber sensors (DOFS) to rapidly detect temperature changes greater than 1000° on the surface or between plies of the composite. Measurements of the temporal and spatial response are taken at rates greater than 20Hz with sub-millimeter resolution. An infrared camera is used to validate the temperature measurements obtained using DOFS. In addition, since DOFS respond to strain as well as to temperature, any strain in the composite as a result of mechanical loading is coupled into the embedded fiber and is also detected by the sensor. Initial measurements are taken to demonstrate the simultaneous response to both temperature and strain and to characterize the typical strain that results. A DOFS-based sensing architecture can then be designed to mitigate the mechanical response of the sensor, allowing for isolation and rapid detection of the thermal response when high energy radiation is incident on the composite surface.
This paper describes a unique technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real-time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two-layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous-doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from lower layer transmission lines to upper layer lines, thereby pinpointing the location and strength of incident radiation. Simulations based on a high frequency three-dimensional planar electromagnetics model are presented and compared to the experimental results. The experimental results are described for GHz range RF signal control for 300- and 180-mW incident energy from 975- to 1060-nm wavelength lasers, respectively, where upon illumination, RF transmission line signal output power doubled when compared to nonilluminated results. The experimental results are also reported for 100-W incident energy from a 1060-nm laser. Test results illustrate real-time signal processing would permit a structure to be controlled in response to incident radiation.
Rapid sensing of near infrared (IR) energy on a composite structure would provide information that could mitigate
damage to composite structures. This paper describes a novel technique that implements photoconductive sensors in a
radio frequency (RF) switching network designed to locate in real time the position and intensity of IR radiation incident
on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches
in a two layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous doped silicon
photoconductive sensors are inserted in GHz range RF transmission lines. Photoconductive sensors use semiconductor
materials that are optically sensitive at material dependent wavelengths. Incident radiation at the appropriate wavelength
produces hole-electron pairs, so that the semiconductor becomes a conductor. By permitting signal propagation only
when a sensor is illuminated, the RF signals are selectively routed from the lower layer transmission lines to the upper
layer lines, thereby pinpointing the location and strength of incident radiation on a structure. Simulations based on a high
frequency 3D planar electromagnetics model are presented and compared to experimental results. Experimental results
are described for GHz range RF signal control for 300 mW and 180 mW incident energy from 975 nm and 1060 nm
wavelength lasers respectively, where upon illumination, RF transmission line signal output power doubled when
compared to non-illuminated results. Experimental results are reported for 100 W incident energy from a 1060 nm laser.
Test results illustrate that real-time signal processing would permit a structure or vehicle to be controlled in response to
incident radiation
In this research, fiber Bragg grating (FBG) temperature sensors are embedded in composites in order to detect highly localized temperature gradients in the composite structures. The primary goal is to perform structural health monitoring on a composite structure. A secondary goal is to use the sensors as a diagnostic tool to determine the optimal composite materials, architectures, or structures that are the least susceptible to thermal damage. Initial results will be discussed for two composite materials using a single sensor to measure temperature variations. The tests include measurements of the temporal and spatial thermal response of the composite resulting either from an applied heat source or to high energy radiation incident on the surface. Additional tests demonstrate the response using a 3x2 array of sensors to simultaneously measure the temperature at three varying depths in the composite, using three FBGs aligned with the heat source, and three FBGs located a short lateral distance (3cm) away from the heat source. In addition, since FBGs respond to strain as well as to temperature, any strain in the composite is coupled into the embedded fiber and is also detected by the FBG sensors. Initial measurements demonstrate the simultaneous response of FBG sensors to both temperature and strain. The various components of strain that are observed in the composite will be discussed, and possible methods to isolate these components and mitigate their response will be considered.
Long distance data transmission using solitons multiplexed on different wavelengths makes more efficient use of fiber bandwidth than transmission on a single wavelength channel. However, perturbations and nonlinear distortions limit the number of wavelengths which can be multiplexed and detected at the end of the fiber. Perturbations, such as loss, cause permanent frequency shifts if a collision occurs between solitons widely separated in frequency. Densely packing the solitons spectrally, though, results in distortions in spectral intensity which limit the use of standard wavelength demultiplexing techniques. We examine methods by which solitons, densely multiplexed in wavelength, may still be detected even during collisions. The theoretical feasibility of encoding the data on the eigenvalues of the linear evolution equations associated with soliton propagation by the inverse scattering transform is discussed, as are more practical techniques using only the spectral intensity of the waveform.
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