Event-based camera refractory period characterization and initial clock drift evaluation

Event-based camera (EBC) technology provides high-dynamic range operation and shows promise for efficient capture of spatio-temporal information, producing a sparse data stream and enabling consideration of nontraditional data processing solutions (e.g., new algorithms, neuromorphic processors, etc.). Given the fundamental difference in camera architecture, the EBC response and noise behavior differ considerably compared to standard CCD/CMOS framing sensors. These differences necessitate the development of new characterization techniques and sensor models to evaluate hardware performance and elucidate the trade-space between the two camera architectures. Laboratory characterization techniques reported previously include noise level as a function of static scene light level (background activity) and contrast responses referred to as S-curves. Here we present further progress on development of basic characterization methods and test capabilities for commercial-off-the-shelf (COTS) visible EBCs, with a focus on measurement of pixel deadtime (refractory period) including results for the 4th-generation sensor from Prophesee and Sony. Refractory period is empirically determined from analysis of the interspike intervals (ISIs), and results visualized using log-histograms of the minimum per-pixel ISI values for a subset of pixels activated by a controlled dynamic scene. Our tests of the Prophesee gen4 EVKv2 yield refractory period estimates ranging from 6.1 msec to 6.8 μsec going from the slowest (20) to fastest (100) settings of the relevant bias parameter, bias_refr. We also introduce and demonstrate the concept of pixel bandwidth measurement from data captured while viewing a static scene – based on recording data at a range of refractory period setting and then analyzing noise-event statistics. Finally, we present initial results for estimating and correcting EBC clock drift using a GPS PPS signal to generate special timing events in the event-list data streams generated by the DAVIS346 and DVXplorer EBCs from iniVation

Lateral Diffusion Length Changes in HgCdTe Detectors in a Proton Environment

This paper presents a study of the performance degradation in a proton environment of very long wavelength infrared (VLWIR) HgCdTe detectors. The energy dependence of the Non-Ionizing Energy Loss (NIEL) in HgCdTe provides a framework for estimating the responsivity degradation in VLWIR HgCdTe due to on orbit exposure from protons. Banded detector arrays that have different detector designs were irradiated at proton energies of 7, 12, and 63 MeV. These banded detector arrays allo~vedin sight into how the fundamental detector parameters degraded in a proton environment at the three different proton energies. Measured data demonstrated that the detector responsivity degradation at 7 MeV is 5 times larger than the degradation at 63 MeV. The comparison of the responsivity degradation at the different proton energies suggests that the atomic Columbic interaction of the protons with the HgCdTe detector is likely the primary mechanism responsible for the degradation in responsivity at proton energies below 30 MeV

Measurement of \u27one over f noise\u27 in infrared detection using a novel technique

It has been shown that, one over f noise\u27 (1/f noise) limits the sensitivity in Mercury Cadmium Telluride (HgCdTe) infrared devices. It is therefore imperative to be able to measure and account for its contribution to the total device noise. In this thesis, the 1/f noise of a HgCdTe device is measured and studied using two measurement techniques. The first technique is the commonly used conventional method of measuring 1/f noise that analyzes 1/f noise in the frequency domain and extracts the 1/f noise contribution from the power spectral densities. The second approach is a novel technique that extracts the 1/f noise contribution from the total measured noise data that is collected as a function of integration time at a very low photon irradiance. By analyzing the 1/f noise of this device using the conventional method, the results using this novel technique can be compared and its accuracy validated. The advantages of the novel technique over the conventional method result in a simpler method of measuring and analyzing 1/f noise in these devices. First the data can be collected in a fairly short amount of time, as compared to the conventional method where data must be collected for very long periods of time. As a result of collecting data for such long periods of time, the environment must be extremely controlled such that drifts in temperature or the patience of the person taking the measurements do not limit the accuracy of the results. In addition the data analysis is also simplified using the novel technique. This novel technique of measuring 1/f noise has been developed at the Infrared Radiation Effects Laboratory (IRREL), Air Force Research Laboratory, Kirtland Air Force Base and is studied and validated here in this thesis.\u2

Measurement of 'one over f noise' in infrared detection using a novel technique

It has been shown that, ‘one over f noise’ (1/f noise) limits the sensitivity in Mercury Cadmium Telluride (HgCdTe) infrared devices. It is therefore imperative to be able to measure and account for its contribution to the total device noise. In this thesis, the 1/f noise of a HgCdTe device is measured and studied using two measurement techniques. The first technique is the commonly used conventional method of measuring 1/f noise that analyzes 1/f noise in the frequency domain and extracts the 1/f noise contribution from the power spectral densities. The second approach is a novel technique that extracts the 1/f noise contribution from the total measured noise data that is collected as a function of integration time at a very low photon irradiance. By analyzing the 1/f noise of this device using the conventional method, the results using this novel technique can be compared and its accuracy validated. The advantages of the novel technique over the conventional method result in a simpler method of measuring and analyzing 1/f noise in these devices. First the data can be collected in a fairly short amount of time, as compared to the conventional method where data must be collected for very long periods of time. As a result of collecting data for such long periods of time, the environment must be extremely controlled such that drifts in temperature or the patience of the person taking the measurements do not limit the accuracy of the results. In addition the data analysis is also simplified using the novel technique. This novel technique of measuring 1/f noise has been developed at the Infrared Radiation Effects Laboratory (IRREL), Air Force Research Laboratory, Kirtland Air Force Base and is studied and validated here in this thesis.Ball Aerospace & Technologies Corp.Master of Electrical EngineeringMastersUniversity of New Mexico. Dept. of Electrical and Computer EngineeringKrishna, SanjayKrishna, SanjayMalloy, KevinHuang, Da

Surface Modification of Electrospun Scaffolds for Endothelialization of Tissue-Engineered Vascular Grafts Using Human Cord Blood-Derived Endothelial Cells

Tissue engineering has gained attention as an alternative approach for developing small diameter tissue-engineered vascular grafts intended for bypass surgery, as an option to treat coronary heart disease. To promote the formation of a healthy endothelial cell monolayer in the lumen of the graft, polycaprolactone/gelatin/fibrinogen scaffolds were developed, and the surface was modified using thermoforming and coating with collagen IV and fibronectin. Human cord blood-derived endothelial cells (hCB-ECs) were seeded onto the scaffolds and the important characteristics of a healthy endothelial cell layer were evaluated under static conditions using human umbilical vein endothelial cells as a control. We found that polycaprolactone/gelatin/fibrinogen scaffolds that were thermoformed and coated are the most suitable for endothelial cell growth. hCB-ECs can proliferate, produce endothelial nitric oxide synthase, respond to interleukin 1 beta, and reduce platelet deposition

Carrier concentration and in-plane mobility in both non-intentionally and Si-doped InAsSb and InAs/InAsSb type-II superlattice materials for space-based infrared detectors

The sensitivity of III-V-based infrared detectors is critically dependent upon the carrier concentration and mobility of the absorber layer, and thus, accurate knowledge of each is required to design structures for maximum detector performance. Here, measurements of the bulk in-plane resistivity, in-plane mobility, and carrier concentration as a function of temperature are reported for non-intentionally doped and Si-doped mid-wave infrared InAs₀.₉₁Sb₀.₀₉ alloy and InAs/InAs₀.₆₅Sb₀.₃₅ type-II superlattice materials grown on GaSb substrates. Standard temperature- and magnetic-field-dependent resistivity and the Hall measurements on mesa samples in the van der Pauw configuration are performed, and multicarrier fitting and modelling are used to isolate transport of each carrier species. The results show that up to 5 carrier species of the surface, interface and bulk variety contribute to conduction, with bulk electron and hole mobility up to 2·10⁵ cm²/V s and 8·10³ cm²/V s, respectively and background dopant concentration levels were between 10¹⁴ and 10¹⁵ cm¯³. The in-plane mobility temperatures dependence is determined and trends of each carrier species with temperature and dose are analysed