In this paper, we describe how magnetoresistive sensors can be integrated with microelectromechanical systems (MEMS) devices enabling the mechanical modulation of DC or low frequency external ...magnetic fields to high frequencies using MEMS structures incorporating magnetic flux guides. In such a hybrid architecture, lower detectivities are expected when compared with those obtained for individual sensors. This particularity results from the change of sensor's operating point to frequencies above the 1/
noise knee.
Neuronal activity generates ionic flows and thereby both magnetic fields and electric potential differences, i.e., voltages. Voltage measurements are widely used but suffer from isolating and ...smearing properties of tissue between source and sensor, are blind to ionic flow direction, and reflect the difference between two electrodes, complicating interpretation. Magnetic field measurements could overcome these limitations but have been essentially limited to magnetoencephalography (MEG), using centimeter-sized, helium-cooled extracranial sensors. Here, we report on in vivo magnetic recordings of neuronal activity from visual cortex of cats with magnetrodes, specially developed needle-shaped probes carrying micron-sized, non-cooled magnetic sensors based on spin electronics. Event-related magnetic fields inside the neuropil were on the order of several nanoteslas, informing MEG source models and efforts for magnetic field measurements through MRI. Though the signal-to-noise ratio is still inferior to electrophysiology, this proof of concept demonstrates the potential to exploit the fundamental advantages of magnetophysiology.
•Spin-electronics-based probes achieve local magnetic recordings inside the neuropil•Magnetic field recordings were performed in vivo, in anesthetized cat visual cortex•Event-related fields (ERFs) to visual stimuli were up to several nanoteslas in size•ERFs could be detected after averaging less than 20 trials
Caruso et al. report in vivo, intra-cortical recordings of magnetic fields that reflect neuronal activity, using magnetrodes, i.e., micron size magnetic sensors based on spin electronics.
This paper reports on the integration of magnetic tunnel junction (MTJ) sensing devices with magnetoresistance responses above 150% on flexible substrates. The sensors are integrated in a fabrication ...process based on polyimide materials, and demonstrate sensitivities up to 250 μV/Oe for bias currents in the 100-μA range. Assessment of the sensors performance is done under controlled mechanical load conditions, and the magnetoresistance is only slightly affected (1% variation) while sensitivity changes by 7.5% when the bending radii reduce down to 5 mm. The results demonstrate the high potential of the MTJ sensors to be used in applications requiring bending and conforming to non-planar geometries, bringing magnetoelectronic technologies to hard-to-reach regions of space.
The detection of low-intensity and low-frequency signals requires magnetic sensors with enhanced sensitivity, low noise levels, and improved field detection at low operating frequencies. Two ...strategies to improve the detectivity levels of devices based on tunnel magnetoresistive sensors are demonstrated: 1) a large number of sensors connected in series or 2) an individual sensor with a large sensing area and integrated magnetic flux guides. State-of-the-art MgO-based magnetic tunnel junctions with a soft pinned sensing layer were used in this paper. For 952 sensors in series a sensitivity of 29.3%/mT and a detection level of 455 pT/Hz 1/2 were obtained at 100 Hz, whereas the integration of magnetic flux guides in a single sensor yielded a sensitivity of 138.3%/mT and a detection level of 576 pT/Hz 1/2 at the same frequency. These two strategies imply a large device footprint, being suitable when a high spatial resolution is not an application requirement.
A Medicina Dentária Forense tem um papel preponderante na identificação humana, sendo esta um direito humano, estando nós vivos ou não, toda a gente tem direito a ter a sua ...identificação.Infelizmente, episódios de índole natural como terramotos e incêndios, e de índole criminosa, como assaltos e homicídios, são uma constante ao redor do globo. Cabe aos profissionais da área médico-legal investigar o sucedido, dando respostas tanto ao sistema jurídico como aos familiares das vítimas. Para o efeito, estes profissionais têm ao seu dispor um leque de procedimentos, tanto a nível corporal, como mais especificamente relatado nesta dissertação, a nível oro facial.Desde a Identificação Dentária Comparativa, passando pela Reconstrução Craniofacial, Palatoscopia, Queiloscopia e Marcas de Mordida, podemos observar que a cavidade oral fornece muitas formas que podem ser a chave para o sucesso de uma determinada investigação forense. Estes métodos descritos dependem bastante das histórias clínicas e outros dados antemortem, sendo os Médicos Dentistas de extrema importância neste assunto.Caso estes métodos descritos anteriormente falhem pela sua inutilização pelas mais variadas razões, técnicas de processamento de DNA passam a ser os métodos de eleição na identificação humana.Um local específico no ser humano onde é possível recolher DNA viável para estudo é a polpa dentária, visto ter uma enorme resistência a alterações de temperatura, de pressão e de força mecânica fornecida pela dureza do esmalte e dentina que a envolvem, protegendo-a destes estímulos. A extração de DNA contido na câmara pulpar é por si só um desafio, sendo necessários meticulosos procedimentos e protocolos de forma a manter o material utilizável.Após a extração, o DNA “capturado” pode ser de um dos dois principais tipos, DNA genómico ou nuclear e DNA mitocondrial e o seu processo de análise depende do tipo, das características e do comprimento do fragmento extraído.
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