title: Improved linearity using harmonic error rejection in a full-field range imaging system

authors: Payne, Andrew D.

subjects: phase detection

abstract: Full field range imaging cameras are used to simultaneously measure the distance for every pixel in a given scene using an intensity modulated illumination source and a gain modulated receiver array. The light is reflected from an object in the scene, and the modulation envelope experiences a phase shift proportional to the target distance. Ideally the waveforms are sinusoidal, allowing the phase, and hence object range, to be determined from four measurements using an arctangent function. In practice these waveforms are often not perfectly sinusoidal, and in some cases square waveforms are instead used to simplify the electronic drive requirements. The waveforms therefore commonly contain odd harmonics which contribute a nonlinear error to the phase determination, and therefore an error in the range measurement. We have developed a unique sampling method to cancel the effect of these harmonics, with the results showing an order of magnitude improvement in the measurement linearity without the need for calibration or lookup tables, while the acquisition time remains unchanged. The technique can be applied to existing range imaging systems without having to change or modify the complex illumination or sensor systems, instead only requiring a change to the signal generation and timing electronics.

text: Improved linearity using harmonic error rejection in a full-field range imaging system Full field range imaging cameras are used to simultaneously measure the distance for every pixel in a given scene using an intensity modulated illumination source and a gain modulated receiver array. The light is reflected from an object in the scene, and the modulation envelope experiences a phase shift proportional to the target distance. Ideally the waveforms are sinusoidal, allowing the phase, and hence object range, to be determined from four measurements using an arctangent function. In practice these waveforms are often not perfectly sinusoidal, and in some cases square waveforms are instead used to simplify the electronic drive requirements. The waveforms therefore commonly contain odd harmonics which contribute a nonlinear error to the phase determination, and therefore an error in the range measurement. We have developed a unique sampling method to cancel the effect of these harmonics, with the results showing an order of magnitude improvement in the measurement linearity without the need for calibration or lookup tables, while the acquisition time remains unchanged. The technique can be applied to existing range imaging systems without having to change or modify the complex illumination or sensor systems, instead only requiring a change to the signal generation and timing electronics.

year: 2008

title: Efficiency of cycled batteries analyzed through voltage-current phase differences

authors: Wilson, Marcus T.

abstract: Ageing of rechargeable batteries is routinely characterized in the frequency domain by electrochemical impedance spectroscopy, but the technique requires laboratory measurements to be made on a time scale of days. However, the normal cycling of a battery as it is used in situ provides equivalent information in the time domain, though extracting robust frequency information from a time series is challenging. In this work, we explore, in the time domain, the relationship between instantaneous voltage-current phase difference and cycle efficiency. Moreover, we demonstrate that phase measures can be used to identify battery ageing. We have cycled a 250 mA h Nickel-Cobalt cell several hundred times and used Hilbert Transforms to identify phase difference between voltage and current. This phase difference becomes closer to zero as the battery ages, commensurate with a drop in energy cycle efficiency. In another experiment, we applied a synthetic current profile mimicking behaviour of an electric car cell, to a 3.2 A h LiNiMnCoO2 cell, for 100 days. For this more complicated profile with a wide range of frequency content, we used wavelet analysis to identify changes in phase difference and impedance as the battery aged. For this cell, drop in cycle efficiency was associated with a rise in internal resistance. The results imply that time-series analysis of in situ measurements of voltage and current, when applied with equivalent circuit models and underlying theory, can identify markers of battery ageing.

text: Efficiency of cycled batteries analyzed through voltage-current phase differences Ageing of rechargeable batteries is routinely characterized in the frequency domain by electrochemical impedance spectroscopy, but the technique requires laboratory measurements to be made on a time scale of days. However, the normal cycling of a battery as it is used in situ provides equivalent information in the time domain, though extracting robust frequency information from a time series is challenging. In this work, we explore, in the time domain, the relationship between instantaneous voltage-current phase difference and cycle efficiency. Moreover, we demonstrate that phase measures can be used to identify battery ageing. We have cycled a 250 mA h Nickel-Cobalt cell several hundred times and used Hilbert Transforms to identify phase difference between voltage and current. This phase difference becomes closer to zero as the battery ages, commensurate with a drop in energy cycle efficiency. In another experiment, we applied a synthetic current profile mimicking behaviour of an electric car cell, to a 3.2 A h LiNiMnCoO2 cell, for 100 days. For this more complicated profile with a wide range of frequency content, we used wavelet analysis to identify changes in phase difference and impedance as the battery aged. For this cell, drop in cycle efficiency was associated with a rise in internal resistance. The results imply that time-series analysis of in situ measurements of voltage and current, when applied with equivalent circuit models and underlying theory, can identify markers of battery ageing.

year: 2024-03-07

title: Mai ngā pouwhirinaki - The experiences of whānau caring for Māori tangata whaiora with traumatic brain injury in the Waikato

authors: Silveira, Maia

subjects: Traumatic brain injury

abstract: In Aotearoa today, Māori have a disproportionate experience of Traumatic Brain Injury (TBI) in the community and in prisons compared to non-Māori. Furthermore, Māori have higher mortality rates following TBI, and are more likely to have a prolonged stay in hospital then be discharged without community support services compared with non-Māori. Currently, many of the post-acute rehabilitation services are located in the Auckland region which causes undue pressure of whānau needs, finances, and work commitments for many whānau and individuals with TBI from the Waikato region. My research focuses on the experiences of whānau navigators experience of caring for Māori tangata whaiora with TBI in the Waikato region. Whānau navigators for this thesis refers to members of the whānau who have familial obligations of care. Within this thesis I consult and engage with whānau about post-acute rehabilitation services. This is a qualitative based research project, which draws upon narrative inquiry, and a Kaupapa Māori research paradigm. Documenting these experiences will provide empirical evidence to highlight the invaluable role whānau have within recovery and the value of whānau support. This research can be used to identify the dynamic needs of whānau and encourage the healthcare system to provide a service that is consistent with Kaupapa Māori health frameworks and practices which at present is non- existent. As a result, the project will help inform the development of a service model within TBI that can better reflect and support the needs of whānau and Māori communities, that is a locally derived practice and more applicable and appropriate for Māori. Mauri ora!

text: Mai ngā pouwhirinaki - The experiences of whānau caring for Māori tangata whaiora with traumatic brain injury in the Waikato In Aotearoa today, Māori have a disproportionate experience of Traumatic Brain Injury (TBI) in the community and in prisons compared to non-Māori. Furthermore, Māori have higher mortality rates following TBI, and are more likely to have a prolonged stay in hospital then be discharged without community support services compared with non-Māori. Currently, many of the post-acute rehabilitation services are located in the Auckland region which causes undue pressure of whānau needs, finances, and work commitments for many whānau and individuals with TBI from the Waikato region. My research focuses on the experiences of whānau navigators experience of caring for Māori tangata whaiora with TBI in the Waikato region. Whānau navigators for this thesis refers to members of the whānau who have familial obligations of care. Within this thesis I consult and engage with whānau about post-acute rehabilitation services. This is a qualitative based research project, which draws upon narrative inquiry, and a Kaupapa Māori research paradigm. Documenting these experiences will provide empirical evidence to highlight the invaluable role whānau have within recovery and the value of whānau support. This research can be used to identify the dynamic needs of whānau and encourage the healthcare system to provide a service that is consistent with Kaupapa Māori health frameworks and practices which at present is non- existent. As a result, the project will help inform the development of a service model within TBI that can better reflect and support the needs of whānau and Māori communities, that is a locally derived practice and more applicable and appropriate for Māori. Mauri ora!

year: 2022