title: Measuring and improving Time-of-Flight camera light source electrical-to-optical power conversion efficiency

authors: Corlett, Dale Owen

subjects: electrical to optical power efficiency

abstract: Time of Flight (ToF) cameras capture three-dimensional depth images of a scene. They do this by transmitting a modulated light signal from a light source, which scatters off objects in the scene and returns to the camera’s modulated image sensor. Distance values for each pixel of the image sensor are calculated from the measured difference in phase between the transmitted and received signal.
There are two circuit topologies typically used for ToF camera light sources, shunt switching and series switching. Chronoptics Limited (Hamilton, New Zealand) is a company that develops ToF cameras. The light source of their Kea ToF camera drives four laser diodes using the iC-HG (iC-Haus GmbH, Bodenheim, Germany) Integrated Circuit (IC).  The iC-HG IC, and therefore the Kea light source, has a series switching topology. Texas Instruments (Dallas, Texas) has designed a ToF camera with a light source that has the shunt switching topology. Texas Instruments claim that the shunt switching topology has a better electrical input power to optical output power than the series switching topology.
The aim of this project is to investigate the shunt topology, in particular the Texas Instruments implementation, and to determine if the shunt topology could provide a substantial increase in efficiency for the Kea light source and future Chronoptics’ light source designs.
In this thesis, we measure the electrical input to optical output power efficiency of the Texas Instruments TIDA 01173 light source and compare it to the Kea light source and find the TIDA1173 does indeed have a higher power efficiency than the Kea light source. However, it is not as efficient as we anticipated, so we also investigate options for improving the power efficiency of the TIDA 01173 light source to maximise the benefits of designing a new light source. 
To achieve the aim, an apparatus is designed and constructed to measure the electrical input power and optical output power of the TIDA 01173 and Kea light sources. The input and output power measurements are used to calculate the efficiency of the light sources over a range of modulation frequencies from 10 MHz to 100 MHz. The electrical to optical power efficiency results show that the shunt switching topology TIDA 01173 light source is more power efficient than the series switching topology Kea light source. The TIDA 01173 has a measured power efficiency of 22% at 10 MHz modulation frequency, and Kea has an efficiency of 11% at the same frequency. These hardware measurement results are corroborated by the results of SPICE simulations made for each of the ToF light sources. To make these simulations, the electrical and optical properties of the BOB850T1000 laser diode (Bob Laser Co, Guangdong, China) used in the ToF light sources are extracted to make a laser diode SPICE model.
An account of the power consumption of each component in both light sources is conducted using the light source SPICE simulations. This account shows that the linear current limiter in the TIDA 01173 consumes the most power, so it is swapped for a buck current regulator. This modification increases the power efficiency of the TIDA 01173 light source to 28% at 10 MHz modulation frequency. The power efficiency of the Kea light source is increased to 13% at 10 MHz modulation frequency by decreasing the input voltage from 5 V to 4 V. Improving the efficiency of the ToF camera light sources allows higher optical output power for a given input power. This enables ToF cameras to be powered from low power sources such as, Universal Serial Bus (USB) ports or battery packs, therefore improving the versatility of ToF cameras.

text: Measuring and improving Time-of-Flight camera light source electrical-to-optical power conversion efficiency Time of Flight (ToF) cameras capture three-dimensional depth images of a scene. They do this by transmitting a modulated light signal from a light source, which scatters off objects in the scene and returns to the camera’s modulated image sensor. Distance values for each pixel of the image sensor are calculated from the measured difference in phase between the transmitted and received signal.
There are two circuit topologies typically used for ToF camera light sources, shunt switching and series switching. Chronoptics Limited (Hamilton, New Zealand) is a company that develops ToF cameras. The light source of their Kea ToF camera drives four laser diodes using the iC-HG (iC-Haus GmbH, Bodenheim, Germany) Integrated Circuit (IC).  The iC-HG IC, and therefore the Kea light source, has a series switching topology. Texas Instruments (Dallas, Texas) has designed a ToF camera with a light source that has the shunt switching topology. Texas Instruments claim that the shunt switching topology has a better electrical input power to optical output power than the series switching topology.
The aim of this project is to investigate the shunt topology, in particular the Texas Instruments implementation, and to determine if the shunt topology could provide a substantial increase in efficiency for the Kea light source and future Chronoptics’ light source designs.
In this thesis, we measure the electrical input to optical output power efficiency of the Texas Instruments TIDA 01173 light source and compare it to the Kea light source and find the TIDA1173 does indeed have a higher power efficiency than the Kea light source. However, it is not as efficient as we anticipated, so we also investigate options for improving the power efficiency of the TIDA 01173 light source to maximise the benefits of designing a new light source. 
To achieve the aim, an apparatus is designed and constructed to measure the electrical input power and optical output power of the TIDA 01173 and Kea light sources. The input and output power measurements are used to calculate the efficiency of the light sources over a range of modulation frequencies from 10 MHz to 100 MHz. The electrical to optical power efficiency results show that the shunt switching topology TIDA 01173 light source is more power efficient than the series switching topology Kea light source. The TIDA 01173 has a measured power efficiency of 22% at 10 MHz modulation frequency, and Kea has an efficiency of 11% at the same frequency. These hardware measurement results are corroborated by the results of SPICE simulations made for each of the ToF light sources. To make these simulations, the electrical and optical properties of the BOB850T1000 laser diode (Bob Laser Co, Guangdong, China) used in the ToF light sources are extracted to make a laser diode SPICE model.
An account of the power consumption of each component in both light sources is conducted using the light source SPICE simulations. This account shows that the linear current limiter in the TIDA 01173 consumes the most power, so it is swapped for a buck current regulator. This modification increases the power efficiency of the TIDA 01173 light source to 28% at 10 MHz modulation frequency. The power efficiency of the Kea light source is increased to 13% at 10 MHz modulation frequency by decreasing the input voltage from 5 V to 4 V. Improving the efficiency of the ToF camera light sources allows higher optical output power for a given input power. This enables ToF cameras to be powered from low power sources such as, Universal Serial Bus (USB) ports or battery packs, therefore improving the versatility of ToF cameras.

year: 2020

title: Fabrication, microstructure, mechanical, and electrochemical properties of NiMnFeCu high entropy alloy from elemental powders

authors: Kumar, Ashok

subjects: high entropy alloys

abstract: Transition metal based high entropy alloys (HEAs) are often used in electrocatalytic (water electrolysis) applications due to the synergistic effect operating among its constituent elements and unpaired electrons in d orbitals of the concerned metal. In this study, a low cost NiMnFeCu high entropy alloy was successfully synthesised using the combined techniques of mechanical milling (MA) and vacuum sintering. X‐ray diffraction was used to analyse the phase composition, optical microscopy, and scanning electron microscopy were used to characterise the fabricated material’s microstructure and chemical homogeneity, thermal, and mechanical properties were tested using the differential scanning calorimetry method and a universal testing machine, respectively. Electrochemical workstation was used to carry out preliminary electrochemical studies such as linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry. The results showed that the as‐ sintered NiMnFeCu HEA possessed a single‐ phase FCC structure. The HEA NiMnFeCu sintered at 1050 °C (S4) and 1000 °C (S2) with a holding time of 2 h showed a yield strength of 516.3 MPa and 389.8 MPa, respectively, and the micro‐hardness values were measured to be 233.45 ± 9 HV and 198.7 ± 8 HV, respectively. Preliminary electrochemical studies proved that the alloy sintered at 1000 °C (S2) with a holding time of 2 h exhibited excellent electrocatalytic properties with a measured overpotential of 322 mV at 10 mA cm⁻² at 100 cycles of CV and good stability for 10 h when compared to state‐of‐the‐art electrocatalytic materials IrO₂ and RuO₂ This suggested that the HEA NiMnFeCu fabricated under the condition S2 could potentially be used for industrial‐scale water electrolysis as it possesses permissible mechanical and good electrochemical properties.

text: Fabrication, microstructure, mechanical, and electrochemical properties of NiMnFeCu high entropy alloy from elemental powders Transition metal based high entropy alloys (HEAs) are often used in electrocatalytic (water electrolysis) applications due to the synergistic effect operating among its constituent elements and unpaired electrons in d orbitals of the concerned metal. In this study, a low cost NiMnFeCu high entropy alloy was successfully synthesised using the combined techniques of mechanical milling (MA) and vacuum sintering. X‐ray diffraction was used to analyse the phase composition, optical microscopy, and scanning electron microscopy were used to characterise the fabricated material’s microstructure and chemical homogeneity, thermal, and mechanical properties were tested using the differential scanning calorimetry method and a universal testing machine, respectively. Electrochemical workstation was used to carry out preliminary electrochemical studies such as linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry. The results showed that the as‐ sintered NiMnFeCu HEA possessed a single‐ phase FCC structure. The HEA NiMnFeCu sintered at 1050 °C (S4) and 1000 °C (S2) with a holding time of 2 h showed a yield strength of 516.3 MPa and 389.8 MPa, respectively, and the micro‐hardness values were measured to be 233.45 ± 9 HV and 198.7 ± 8 HV, respectively. Preliminary electrochemical studies proved that the alloy sintered at 1000 °C (S2) with a holding time of 2 h exhibited excellent electrocatalytic properties with a measured overpotential of 322 mV at 10 mA cm⁻² at 100 cycles of CV and good stability for 10 h when compared to state‐of‐the‐art electrocatalytic materials IrO₂ and RuO₂ This suggested that the HEA NiMnFeCu fabricated under the condition S2 could potentially be used for industrial‐scale water electrolysis as it possesses permissible mechanical and good electrochemical properties.

year: 2022

title: “You’re not coming out – you’ve been there all along and just no one’s looked”: Māori LGBT+ youth and identity exploration

authors: Laurence, Rebekah

subjects: Māori

abstract: This research is a Masters-level project on Māori LGBT-plus (lesbian, gay, bisexual, transgender, and other) youths’ experience of exploring their gender and sexual identities, highlighting how whānau (loosely, ‘extended family’) can provide mana (authority, power) such that youth can exercise mana rangatiratanga (a Maniapoto description of ‘autonomy, self-determination’) regarding their identities. This is a novel, exploratory study.
Adapted elements from a Mana Wāhine (Māori feminist) perspective of Kaupapa Māori theory comprised the theoretical framework for this project. These elements were Mana rangatiratanga (adapted from Tino rangatiratanga), Te reo Māori me ōna tikanga (Māori language and its culture), and Whanaungatanga (relationships). The three elements were adapted to fit a Ngāti Maniapoto worldview. 
Qualitative research methods were used for this study. There were five participants aged between 17 and 24 years, who were Māori and had diverse gender or sexual identities. Semi-structured, face-to-face interviews were conducted with participants, which allowed them to share their experiences of exploring their gender and sexual identities and of whānau support. Interviews were analysed using a process of inductive thematic analysis, which identified and analysed patterns across the dataset.
Eight themes were derived from participants’ experiences. These themes were Ko Tūhura, which described the process of discovery that participants have experienced; Ko Matatapu, which described participants’ experience of authenticity and concealment of their gender and sexual identities; Ko Tautoko, which described how whānau have empowered participants to explore their identities, and how participants have been denied empowerment; Ko Mata-ngaro, which described participants’ early lack of exposure to diverse identities, and their having their identities unseen by others; Ko te Ahunga-ki-te-aunoa, which described how diverse identities have been accepted within participants’ whānau; Ko Tauawhi, which described how participants have been embraced for their diverse identities; Ko Mata-pū-take, which describes participants’ experience of finding somewhere to belong; and Ko Kiritau, which describes participants’ becoming settled in their expression of their gender and sexual identities.
The findings of the thesis describe roles that whānau play in participants’ exploration of their gender and sexual identities and some of the effects that colonisation has had within participants’ whānau regarding their gender and sexual identities. Nonetheless, participants actively resisted these aspects of colonisations and found ways to give voice to their gender and sexual identities.
Given that participants shared that there was a dearth of information regarding gender and sexual identities available to them within their whānau and school environments, organisations within psychology and related fields may work to proactively provide all young Māori people and their whānau with information regarding diverse gender and sexual identities. Moreover, to address the dearth of resources designed for Māori LGBT-plus youth, New Zealand-based researchers may collate information specifically regarding Māori LGBT-plus youth experience of identity exploration and Māori knowledges regarding gender and sexual identities. This information may be collated in community-based resources that are designed specifically for members of this group and their whānau, and professionals who work for them.

text: “You’re not coming out – you’ve been there all along and just no one’s looked”: Māori LGBT+ youth and identity exploration This research is a Masters-level project on Māori LGBT-plus (lesbian, gay, bisexual, transgender, and other) youths’ experience of exploring their gender and sexual identities, highlighting how whānau (loosely, ‘extended family’) can provide mana (authority, power) such that youth can exercise mana rangatiratanga (a Maniapoto description of ‘autonomy, self-determination’) regarding their identities. This is a novel, exploratory study.
Adapted elements from a Mana Wāhine (Māori feminist) perspective of Kaupapa Māori theory comprised the theoretical framework for this project. These elements were Mana rangatiratanga (adapted from Tino rangatiratanga), Te reo Māori me ōna tikanga (Māori language and its culture), and Whanaungatanga (relationships). The three elements were adapted to fit a Ngāti Maniapoto worldview. 
Qualitative research methods were used for this study. There were five participants aged between 17 and 24 years, who were Māori and had diverse gender or sexual identities. Semi-structured, face-to-face interviews were conducted with participants, which allowed them to share their experiences of exploring their gender and sexual identities and of whānau support. Interviews were analysed using a process of inductive thematic analysis, which identified and analysed patterns across the dataset.
Eight themes were derived from participants’ experiences. These themes were Ko Tūhura, which described the process of discovery that participants have experienced; Ko Matatapu, which described participants’ experience of authenticity and concealment of their gender and sexual identities; Ko Tautoko, which described how whānau have empowered participants to explore their identities, and how participants have been denied empowerment; Ko Mata-ngaro, which described participants’ early lack of exposure to diverse identities, and their having their identities unseen by others; Ko te Ahunga-ki-te-aunoa, which described how diverse identities have been accepted within participants’ whānau; Ko Tauawhi, which described how participants have been embraced for their diverse identities; Ko Mata-pū-take, which describes participants’ experience of finding somewhere to belong; and Ko Kiritau, which describes participants’ becoming settled in their expression of their gender and sexual identities.
The findings of the thesis describe roles that whānau play in participants’ exploration of their gender and sexual identities and some of the effects that colonisation has had within participants’ whānau regarding their gender and sexual identities. Nonetheless, participants actively resisted these aspects of colonisations and found ways to give voice to their gender and sexual identities.
Given that participants shared that there was a dearth of information regarding gender and sexual identities available to them within their whānau and school environments, organisations within psychology and related fields may work to proactively provide all young Māori people and their whānau with information regarding diverse gender and sexual identities. Moreover, to address the dearth of resources designed for Māori LGBT-plus youth, New Zealand-based researchers may collate information specifically regarding Māori LGBT-plus youth experience of identity exploration and Māori knowledges regarding gender and sexual identities. This information may be collated in community-based resources that are designed specifically for members of this group and their whānau, and professionals who work for them.

year: 2020