Trapped ions in a Paul trap can experience micromotion on top of the wanted secular motion.Micromotion can for example cause Doppler shifts in spectroscopy measurements, making it important to know the amplitude of the motion. In this master thesis we use the correlation between RF driving the trap and photons emitted by a single Beryllium ion during the fluorescence detection to determine the micromotion. This method also allows us to investigate the effect on micromotion from a phase mismatch between RF electrodes. The photon correlation method is compared to measuring the micromotion by taking the ratio between the micromotion sideband and the carrier transition, and also to a simulation of the residual RF fields in the trap by a finite element method. Finally, we vary the path length of RF lines, to tune the phase on individual RF electrodes. The result is that the phase mismatch effect is more than an order of magnitude less than expected from theory. / Fångade joner i en Paul-fälla upplever mikrorörelse utöver den önskade sekulära rörelsen. Mikrorörelse kan till exempel orsaka Dopplerförskjutning i spektroskopimätningar, vilket gör det viktigt att veta amplituden av rörelsen. I det här examensarbetet använder vi korrelationen mellan RF som driver jonfällan och fotoner utsända från en enskild berylliumjon under fluorescens-detektion, för att mäta mikrorörelsen. Den här metoden tillåter oss också att undersöka effekten på mikrorörelse från en fasförskjutning mellan RF-elektroder. Fotonkorrelationsmetoden jämförs med en mätning av mikrorörelse genom att ta förhållandet mellan mikrorörelse-sidobandet och bärar-övergången, och också med en simulering av RF-fälten i jonfällan med en finit element-metod. Slutligen varierar vi längden på RF-kopplingen, för att justera fasen mellan individuella RF-elektroder. Resultatet är att effekten från fasförskjutningen är mer än en storleksordning mindre än vad teorin förutsagt.

L'imagerie Radar à Synthèse d'Ouverture (RSO) est une technique bien connue dans les domaines de télédétection, de surveillance aérienne, de géologie et de cartographie. Obtenir des images de haute résolution malgré la présence de bruit, tout en prenant en compte les caractéristiques des cibles dans la scène observée, les différents incertitudes de mesure et les erreurs resultantes de la modélisation, devient un axe de recherche très important.Les méthodes classiques, souvent fondées sur i) la modélisation simplifiée de la scène ; ii) la linéarisation de la modélisation directe (relations mathématiques liant les signaux reçus, les signaux transmis et les cibles) simplifiée ; et iii) l'utilisation de méthodes d'inversion simplifiées comme la Transformée de Fourier Inverse (TFI) rapide, produisent des images avec une résolution spatiale faible, peu robustes au bruit et peu quantifiables (effets des lobes secondaires et bruit du speckle).Dans cette thèse, nous proposons d'utiliser une approche bayésienne pour l'inversion. Elle permettrais de surmonter les inconvénients mentionnés des méthodes classiques, afin d'obtenir des images stables de haute résolution ainsi qu'une estimation plus précise des paramètres liés à la reconnaissance de cibles se trouvant dans la scène observée.L'approche proposée est destinée aux problèmes inverses de l'imagerie RSO mono-, bi-, et multi- statique ainsi que l'imagerie des cibles à micromouvement. Les a priori appropriés de modélisation permettant d'améliorer les caractéristiques des cibles pour des scènes de diverses natures seront présentées. Des méthodes d'estimation rapides et efficaces utilistant des a priori simples ou hiérarchiques seront développées. Le problème de l'estimation des hyperparameters sera galement traité dans le cadre bayésin. Les résultats relatifs aux données synthétiques, expérimentales et réelles démontrent l'efficacité de l'approche proposée. / Synthetic Aperture Radar (SAR) imaging is a well-known technique in the domain of remote sensing, aerospace surveillance, geography and mapping. To obtain images of high resolution under noise, taking into account of the characteristics of targets in the observed scene, the different uncertainties of measure and the modeling errors becomes very important.Conventional imaging methods are based on i) over-simplified scene models, ii) a simplified linear forward modeling (mathematical relations between the transmitted signals, the received signals and the targets) and iii) using a very simplified Inverse Fast Fourier Transform (IFFT) to do the inversion, resulting in low resolution and noisy images with unsuppressed speckles and high side lobe artifacts.In this thesis, we propose to use a Bayesian approach to SAR imaging, which overcomes many drawbacks of classical methods and brings high resolution, more stable images and more accurate parameter estimation for target recognition.The proposed unifying approach is used for inverse problems in Mono-, Bi- and Multi-static SAR imaging, as well as for micromotion target imaging. Appropriate priors for modeling different target scenes in terms of target features enhancement during imaging are proposed. Fast and effective estimation methods with simple and hierarchical priors are developed. The problem of hyperparameter estimation is also handled in this Bayesian approach framework. Results on synthetic, experimental and real data demonstrate the effectiveness of the proposed approach.

Mechanical trauma to the brain, both big and small, and the method to protect the brain in its presence is a crucial field of research given the large population exposed to neuronal trauma daily and the benefit available through better understanding and injury prevention. A population of particular interest and risk are youth athletes in contact sports due to large accelerations they expose themselves to and their developing brains. To better monitor the risk these athletes are exposed to, their accumulation of head acceleration events (HAEs), a measure correlated with harmful neurological changes, was tracked over sport seasons. It was observed that few significant differences in HAEs accumulated existed between players of ages from middle school to high school, but there did exist a difference between sports with girls' soccer players accumulating fewer HAEs than football players. This highlights to risk youth athletes are exposed to and the importance of improved technique and individual player size. To better monitor HAEs for each individual, a novel head segmentation program was developed that extracts player specific geometries from a single T1 MRI scan that can improve the accuracy of HAE monitoring. Acceleration measures processed with individualized head model versus those using a standardized head model typically displayed higher accelerations, highlighting the need for individualized measure for accurate monitoring of HAEs and risk of neurological changes. In addition to the large accelerations present in contact sports, the small but constant strains produced by neural implants embedded in the brain is also an important field of neuro-mechanical research as the physical properties of neural implants have been found to contribute to the chronic immune response, a major factor preventing the widespread implementation of neural implants. To reduce the severity of the immune response and provide improved chronic functionality, researchers have varied neural implant design and materials, finding general trends but not precise relationships between the design factors and how they contribute the mechanical strain in the brain. Performing a large series of mechanical simulations and Cotter's sensitivity analyses, the relationships between neural design factors and the stain they produce in the brain was examined. It was found that the direction which neural implants are loaded contributes the most to the strain produced in the brain followed by the degree of bonding between the brain and the electrode. Directly related to the design of electrodes themselves, it was found that in most cases reducing the cross-sectional area of the probe resulted in a larger decrease of mechanical strain compared to softening the implant. Finally, a study was performed quantifying the resting micromotion of the brain utilizing a novel method of soft tissue micromotion measurement via microCT, applicable within the skull and the throughout the rest of the body.

Abstract The goal of this thesis was to investigate and build new circuit solutions for electrophysiological measurements that would be used in biophysical research of nervous system and brain activity. The first aim was to build a micromotion compensation system that could compensate for the relative movement of measurement microelectrodes and neurons that can cause signal attenuation or even loss. The purpose of this work was to stabilize the microelectrode with respect to the preparation in order to achieve more stable measurements with small test animals, such as insects, rodents or reptiles. The movement is measured with a touch probe sensor and a feedback loop containing a piezoelectric actuator that adjusts the position of the electrode. A prototype micromotion compensation system was built and its performance was measured in a realistic measurement condition. The compensation system was used to reduce the motion of the probe to below 1 µm, resulting in up to 98% compensation below 10 Hz. The design of the micromotion compensation system took advantage of a preceding study on a piezoelectric bimorph actuator/sensor structure. This study is also presented in the thesis. Another aim of the research was to design and build an integrated multichannel neural signal recording system with stimulation capabilities. The circuit was designed to amplify, digitize and stream out data from extracellular neuronal signal measurements. The main target of the measurement system are action potential signals, which are a type of “digital communication” between nerve cells that evolution has produced. The waveform of these action potential signals is the focus of interest. To accomplish this measurement, the developed circuit contains preamplification, multiplexing, post-amplification, A/D conversion and control logic for the A/D converter and data transmission. The circuit is also externally programmable, and it contains DACs for tuning high-pass filter corner frequency, amplifier bias current and stimulation current. The implemented electronics have low noise, low power and small circuit area. The gain of the circuit is adjustable from 100 to 5000 and the high-pass filter corner frequency from 0.5 Hz to 900 Hz. The sample rate is 20.833 kSps and the data rate is 3.5 Mbps. The measured noise level of the circuit is 7.5μV (rms) (300 Hz - 10 kHz) and the whole chip consumes less than 2 mW of power. A 16-channel prototype chip with 0.35μm CMOS technology was manufactured and its performance was measured. Backend electronics containing a microcontroller supporting high-speed USB data transfer was also programmed for the system. The device was tested in real measurements of neuronal signals in a cockroach (Periplaneta americana) preparation, and reliable streaming of the recorded data to the PC verified its proper function. / Tiivistelmä Tämän väitöskirjatyön tavoitteena oli kehittää mittaus- ja säätöjärjestelmiä aivotutkimuksen ja biofysiikan sovelluksiin. Ensimmäisenä tutkimuskokonaisuutena oli mittaus- ja säätöjärjestelmän kehittäminen, minkä tavoitteena oli mahdollistaa aivojen sähköisen signaloinnin mittaaminen mahdollisimman luonnollisessa tilassa olevilla koe-eläimillä (esim. hyönteiset, matelijat tai pienet nisäkkäät). Tätä varten kehitettiin aktiivinen liikekompensointimekanismi, jossa kosketusanturilla mitattiin aivokudoksen mikrometriluokan mekaanista liikettä ja kompensoitiin sähköistä mittausta suorittavan anturin ja aivon välinen suhteellinen liike liikuttamalla takaisinkytkentälenkissä olevaa pietsosähköistä aktuaattoria. Kompensointimekanismin toiminta testattiin realistisissa mittausolosuhteissa. Liikekompensoinnilla saatiin vähennettyä mittausanturin liikettä suhteessa kudokseen alle mikrometriin, maksimikompensoinnin ollessa noin 98 % alle 10 Hz:n taajuudella. Väitöskirjaan liitettiin pietsosähköisiin komponentteihin liittyen taustatiedoksi artikkeli aiemmin suunnitellusta pietsosähköisestä bimorph aktuaattori/sensori -komponentista. Toisen tutkimuskokonaisuuden muodosti suurten hermosolupopulaatioiden toiminnan mittaamiseen sekä stimulointiin kehitetty monikanavainen järjestelmä. Tärkeimpänä mittauskohteena työssä ovat ekstrasellulaariset aktiopotentiaalisignaalit, jotka ovat eräänlainen evoluution tuottama “digitaalinen” hermosolujen välinen kommunikaatiomenetelmä. Kiinnostuksen kohteena ovat näiden aktiopotentiaalisignaalien aaltomuodot. Mittauksia varten työssä kehitettiin hermosolujen solun ulkopuoliseen nesteeseen asetettaviin elektrodeihin kytkettävä elektroniikka, jolla pystytään sekä stimuloimaan että mittaamaan jokaista elektrodia. Suunniteltu vahvistinelektroniikka on matalakohinainen, matalatehoinen ja pienikokoinen. Mittausjärjestelmään on suunniteltu myös multipleksointi, A/D-muunninelektroniikka sekä ohjauslogiikka, joka sisältää muunnostulosten puskuroinnin integroidun piirin rekisteripankkeihin, SPI-liitynnän high-speed USB protokollaa tukevalle mikrokontrollerille sekä konfiguraatiorekistereitä, joihin SPI-väylän kautta kirjoittamalla voidaan säätää piirin vahvistusta, operaatiovahvistimien biasvirtoja, kaistanleveyttä sekä stimulaatiovirtojen voimakkuuksia. Piirin vahvistus on säädettävissä 100:n ja 5000:n välillä ja ylipäästösuodatuksen kulmataajuus välillä 0,5 Hz - 900 Hz. Piirin näytteistystaajuus on 20,833 kSps ja tiedonsiirtonopeus 3,5 Mbps. Piirin kohinatasoksi mitattiin 7,5 µV (rms) (300 Hz - 10 kHz) ja koko piirin tehonkulutukseksi alle 2 mW. Integroidusta piiristä valmistettiin 16-kanavainen prototyyppi 0,35 µm:n CMOS-teknologialla. Kehitetyn laitteen toiminta varmistettiin mittaamalla hermosignaaleja torakkapreparaatista (Periplaneta americana). Mittausdata siirrettiin onnistuneesti ja luotettavasti PC:lle.

In recent years, improved control of the motional and internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Many-body effects have been explored with hundreds of thousands of quantum-degenerate neutral atoms and coherent light-matter interfaces have been built. Systems of single or a few trapped ions have been used to demonstrate universal quantum computing algorithms and to detect variations of fundamental constants in precision atomic clocks. Now in our experiment we investigate how the two systems can be advantageously combined. We immerse a single trapped Yb+ ion in a Bose-Einstein condensate of Rb atoms. Our hybrid setup consists of a linear RF-Paul trap which is overlapped with a magnetic trap and an optical dipole trap for the neutral atoms. A first synergetic effect is the sympathetic cooling of the trapped ions to very low temperatures through collisions with the ultracold neutral gas and thus without applying laser light to the ions. We observe the dynamics of this effect by measuring the mean ion energy after having an initially hot ion immersed into the condensate for various interaction times, while at the same time monitoring the effects of the collisions on the condensate. The observed ion cooling effect calls for further research into the possibility of using such hybrid systems for the continuous cooling of quantum computers. To this end a good understanding of the fundamental interaction processes between the ion and the neutrals is essential. We investigate the energy dependent elastic scattering properties by measuring neutral atom losses and temperature increase from an ultracold thermal cloud of Rb. By comparison with a Monte-Carlo simulation we gain a deeper understanding of how the different parameters affect the collisional effects. Additionally, we observe charge exchange reactions at the single particle level and measure the energy-independent reaction rate constants. The reaction products are identified by in-trap mass spectrometry, revealing the branching ratio between radiative and non-radiative charge exchange processes.

No description available.