Power efficient ReLU design for neuromorphic computing using spin Hall effect

We demonstrate a magnetic tunnel junction injected with spin Hall current to exhibit linear rotation of magnetization of the free-ferromagnet using only the spin current. Using the linear resistance change of the MTJ, we devise a circuit for the rectified linear activation (ReLU) function of the artificial neuron. We explore the role of different spin Hall effect (SHE) heavy metal layers on the power consumption of the ReLU circuit. We benchmark the power consumption of the ReLU circuit with different SHE layers by defining a new parameter called the spin Hall power factor. It combines the spin Hall angle, resistivity, and thickness of the heavy metal layer, which translates to the power consumption of the different SHE layers during spin-orbit switching/rotation of the free FM. We employ a hybrid spintronics-CMOS simulation framework that couples Keldysh non-equilibrium Green's function formalism with Landau-Lifshitz-Gilbert-Slonzewski equations and the HSPICE circuit simulator to account for diverse physics of spin-transport and the CMOS elements in our proposed ReLU design. We also demonstrate the robustness of the proposed ReLU circuit against thermal noise and non-trivial power-error trade-off that enables the use of an unstable free-ferromagnet for energy-efficient design. Using the proposed circuit, we evaluate the performance of the convolutional neural network for MNIST datasets and demonstrate comparable classification accuracies to the ideal ReLU with an energy consumption of 75 $pJ$ per sample

Enhancement of Thermal Spin Transfer Torque via Bandpass Energy Filtering

We propose the use of energy bandpass filtering approach in the magnetic tunnel junction device as a route to enhance the thermal spin transfer torque. Using the spin-resolved non-equilibrium Green's function formalism, we harness the optical analog of anti-reflective coating in a heterostructure MTJ device, that reports a huge spin torque in the linear regime of temperature bias. In particular, we discuss the position of transmission function with respect to the Fermi energy that caters the maximum thermal effect. The boxcar transmission feature of anti-reflective configuration enhances the charge and spin transport through the structure in comparison to the normal superlattice configurations. The thermally excited spin transfer torque is enhanced by almost five times more with our device design. Although, the thermally driven spin torque is much smaller than the potential driven torque, this technique provides an energy-efficient way to switch the magnetization. This opens up a new viable area in the spintronics applications. With the existing advanced thin-film growth technology, the optimized superlattice configurations can be achieved

Decrement Evoked Potential Mapping to Guide Ventricular Tachycardia Ablation: Elucidating the Functional Substrate.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadEmpirical approaches to targeting the ventricular tachycardia (VT) substrate include mapping of late potentials, local abnormal electrogram, pace-mapping and homogenisation of the abnormal signals. These approaches do not try to differentiate between the passive or active role of local signals as the critical components of the VT circuit. By not considering the functional components, these approaches often view the substrate as a fixed anatomical barrier. Strategies to improve the success of VT ablation need to include the identification of critical functional substrate. Decrement-evoked potential (DeEP) mapping has been developed to elucidate this using an extra-stimulus added to a pacing drive train. With knowledge translation in mind, the authors detail the evolution of the DeEP concept by way of a study of simultaneous panoramic endocardial mapping in VT ablation; an in silico modelling study to demonstrate the factors influencing DeEPs; a multicentre VT ablation validation study; a practical approach to DeEP mapping; the potential utility of DeEPs to identify arrhythmogenic atrial substrate; and, finally, other functional mapping strategies

Comparison of new-generation renal artery denervation systems: assessing lesion size and thermodynamics using a thermochromic liquid crystal phantom model

Aims: The aim of this study was to evaluate and compare lesion dimensions and thermodynamics of the new-generation multi-electrode Symplicity Spyral and the new-generation multi-electrode EnligHTN renal artery denervation systems, using a thermochromic liquid crystal phantom model. Methods and results: A previously described renal artery phantom model was used as a platform for radiofrequency ablation. A total of 32 radiofrequency ablations were performed using the multi-electrode Symplicity Spyral (n=16) and the new-generation EnligHTN systems (n=16). Both systems were used as clinically recommended by their respective manufacturer. Lesion borders were defined by the 51°C isotherm. Lesion size (depth and width) was measured and compared between the two systems. Mean lesion depth was 2.15±0.02 mm for the Symplicity Spyral and 2.32±0.02 mm for the new-generation EnligHTN (p-value <0.001). Mean lesion width was 3.64±0.08 mm and 3.59±0.05 mm (p-value=0.61) for the Symplicity Spyral and the new-generation EnligHTN, respectively. Conclusions: The new-generation EnligHTN system produced lesions of greater depth compared to the Symplicity Spyral under the same experimental conditions. Lesion width was similar between both systems. Achieving greater lesion depth by use of the new-generation EnligHTN may result in better efficacy of renal artery denervation

Omnipolarity applied to equi-spaced electrode array for ventricular tachycardia substrate mapping

Aims : Bipolar electrogram (BiEGM)-based substrate maps are heavily influenced by direction of a wavefront to the mapping bipole. In this study, we evaluate high-resolution, orientation-independent peak-to-peak voltage (Vpp) maps obtained with an equi-spaced electrode array and omnipolar EGMs (OTEGMs), measure its beat-to-beat consistency, and assess its ability to delineate diseased areas within the myocardium compared against traditional BiEGMs on two orientations: along (AL) and across (AC) array splines. Methods and results: The endocardium of the left ventricle of 10 pigs (three healthy and seven infarcted) were each mapped using an Advisor™ HD grid with a research EnSite Precision™ system. Cardiac magnetic resonance images with late gadolinium enhancement were registered with electroanatomical maps and were used for gross scar delineation. Over healthy areas, OTEGM Vpp values are larger than AL bipoles by 27% and AC bipoles by 26%, and over infarcted areas OTEGM Vpp values are 23% larger than AL bipoles and 27% larger than AC bipoles (P < 0.05). Omnipolar EGM voltage maps were 37% denser than BiEGM maps. In addition, OTEGM Vpp values are more consistent than bipolar Vpps showing less beat-by-beat variation than BiEGM by 39% and 47% over both infarcted and healthy areas, respectively (P < 0.01). Omnipolar EGM better delineate infarcted areas than traditional BiEGMs from both orientations. Conclusion: An equi-spaced electrode grid when combined with omnipolar methodology yielded the largest detectable bipolar-like voltage and is void of directional influences, providing reliable voltage assessment within infarcted and non-infarcted regions of the heart.This work was funded by Abbott Laboratories, St. Paul, MN, USA.S

Transcatheter non-contact microwave ablation may enable circumferential renal artery denervation while sparing the vessel intima and media

Aims: Trials of transcatheter renal artery denervation (RDN) have failed to show consistent antihypertensive efficacy. Procedural factors and limitations of radiofrequency ablation can lead to incomplete denervation. The aim of the study was to show that non-contact microwave catheter ablation could produce deep circumferential perivascular heating while avoiding injury to the renal artery intima and media. Methods and results: A novel microwave catheter was designed and tested in a renal artery model consisting of layers of phantom materials embedded with a thermochromic liquid crystal sheet, colour range 50-78°C. Ablations were performed at 140 W for 180 sec and 120 W for 210 sec, delivering 25,200 J with renal arterial flow at 0.5 L/min and 0.1 L/min. Transcatheter microwave ablations 100-160 W for 180 sec were then performed in the renal arteries of five sheep. In vitro, ablations at 140 W and 0.5 L/min flow produced circumferential lesions 5.9±0.2 mm deep and 19.2±1.5 mm long with subendothelial sparing depth of 1.0±0.1 mm. In vivo, transcatheter microwave ablation was feasible with no collateral visceral thermal injury. There was histological evidence of preferential outer media and adventitial ablation. Conclusions: Transcatheter microwave ablation for RDN appears feasible and provides a heating pattern that may enable more complete denervation while sparing the renal arterial intima and media