The effects of excess loop delay in continuous-time sigma-delta modulators

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 79-80).Continuous-time sigma-delta (CT-Sigma Delta) modulators have recently received great attention in the academia as well as in the industry. Despite the improved understanding of the operation of CT-Sigma Delta modulators, the problem due to excess loop delay that arises from timing mismatch and parasitic delay still remains unsolved. Thus, the thesis investigates the effects of the excess loop delay. In specific, the sensitivity of various CT-Sigma Delta topologies to the excess loop delay is explored by converting the CT modulators to its DT equivalents and realizing loop filters in state-space representations in MATLAB ©.by Hyunjoo Jenny Lee.M.Eng

Neural Probes for Chronic Applications

Developed over approximately half a century, neural probe technology is now a mature technology in terms of its fabrication technology and serves as a practical alternative to the traditional microwires for extracellular recording. Through extensive exploration of fabrication methods, structural shapes, materials, and stimulation functionalities, neural probes are now denser, more functional and reliable. Thus, applications of neural probes are not limited to extracellular recording, brain-machine interface, and deep brain stimulation, but also include a wide range of new applications such as brain mapping, restoration of neuronal functions, and investigation of brain disorders. However, the biggest limitation of the current neural probe technology is chronic reliability; neural probes that record with high fidelity in acute settings often fail to function reliably in chronic settings. While chronic viability is imperative for both clinical uses and animal experiments, achieving one is a major technological challenge due to the chronic foreign body response to the implant. Thus, this review aims to outline the factors that potentially affect chronic recording in chronological order of implantation, summarize the methods proposed to minimize each factor, and provide a performance comparison of the neural probes developed for chronic applications

A flexible multimodal tactile display for delivering shape and material information

The growing complexity of telemanipulation tasks calls for increased realism and intuitiveness of the interaction between the user and the master control. Humans perceive multiple haptic features of an object such as its stiffness, temperature, and shape, and rely on this multimodal information to achieve dexterous manipulation. However, to date, remote manipulators rarely provide haptic information to the operator. Moreover, current multimodal displays are often too rigid and bulky to be integrated into the manipulator. Thus, to improve the quality of teleoperation, there is a high demand for flexible devices that are capable of matching the skin's curvature while delivering multimodal haptic information to the operator. In this paper, we present a flexible tactile display delivering tactile and thermal stimuli to the user's skin. We propose a hybrid electromagnetic-pneumatic actuation to operate a 2 x 2 array of tactile cells. Each cell provides a repetitive stimulation with a force and an indentation that are above the human perception threshold for the finger, palm, and forearm. In addition, the temperature of the display's surface is controlled using a Peltier element attached to an air-cooled heatsink. By providing a reproducible cooling gradient, our display simulates common materials encountered in the daily environment. User study results show that (1) the tactile stimulation is perceived well and (2) the identification rates of objects simulated with the display were comparable to those obtained with real objects. Unlike previous devices, the thermal stimulation is delivered while the display is in constant contact with the user's skin, a necessary requirement for teleoperation. These results demonstrate the potential of our device as a promising tactile display for providing haptic feedback in teleoperation. (C) 2015 Elsevier B.V. All rights reserved

The influence of the acoustic reflector design on the temperature coefficient of frequency for shear and longitudinal mode AlN resonators

Most of the applications of solidly mounted resonator need the compensation of temperature coefficient of resonant frequency. The presence of materials with different properties in the stack makes it complicated to explain the influence of each material individually on temperature coefficient. To reduce design and fabrication costs, an accurate and precise modeling of the resonators is required. In this paper, Mason model and finite-element analysis are used to design the resonators and results for both models, which are almost similar, are presented. Different kinds of configuration (symmetric and asymmetric, according to the thickness of the layers) are designed to achieve the temperature coefficient of frequency as near-zero as possible with an optimized response. Such designs are fabricated and characterized obtaining measurements of the temperature coefficient of frequency. The result shows that useful and reliable information on the performance of resonators can be achieved with accurate modeling

Transcranial focused ultrasound stimulation in the infralimbic cortex facilitates extinction of conditioned fear in rats

Transcranial focused ultrasound (tFUS) neuromodulation emerges as a promising non-invasive approach for improving neurological conditions. Extinction of conditioned fear has served as a prime model for exposure-based therapies for anxiety disorders. We investigated whether tFUS stimulation to a critical brain area, the infralimbic subdivision of the prefrontal cortex (IL), could facilitate fear extinction using rats. In a series of experiments, tFUS was delivered to the IL of a freely-moving rat and compared to sham stimulation (tFUS vs. SHAM). Initially, Fos expression in the IL was measured shortly after the stimulation. The results show that Fos expression was significantly increased in the IL but not in the neighboring regions compared to SHAM. Subsequently, two groups of rats were subjected to fear conditioning, extinction, and retention while receiving stimulation during the extinction. Rats in the tFUS group froze significantly less than SHAM during both extinction and retention tests. Importantly, the reduced freezing in the tFUS group was not attributable to non-specific effect such as auditory noise, as both groups demonstrated a similar level of locomotive activity in an open field regardless of the stimulation condition. Finally, we replicated the procedure with a shortened conditioning-to-extinction interval (15 min) to induce immediate extinction deficit. The tFUS group showed a facilitated reduction in freezing during the extinction, which persisted in the subsequent retention session compared to SHAM. In summary, the current findings suggest that tFUS stimulation in the IL facilitates fear extinction, offering a potential therapeutic regimen for fear-related psychiatric disorders

Blue Transparent OLEDs with High Stability and Transmittance for Modulating Sleep Disorders

Abstract Optoelectronics devices utilizing organic light‐emitting diodes (OLEDs) are emerging as new platforms for healthcare applications. In particular, wearable optoelectronics such as visual stimulus systems offer a distinctive advantage to intervene in and improve sleep disorders. In this study, two improvements are proposed for transparent OLEDs (TrOLEDs) that will be critical for visual applications. First, zinc sulfide with high surface energy and a high refractive index is explored as a seed and capping layer. An ultra‐thin silver cathode of 8 nm is demonstrated to be feasible in TrOLEDs, and luminous transmittance of 91% is achieved. Second, in general, achieving the operational stability of TrOLEDs with high transmittance is challenging due to the vulnerability of thin electrodes. By introducing a doping process to the electron transport layer, a lifetime comparable to that of control OLEDs with thick cathodes (>90%) is secured. Last, a preclinical model using blue light is proposed to modulate sleep patterns. Melanopsin is stimulated at the highest level of sleep desire, reducing non‐rapid eye movement sleep duration in mice by up to 14%. Based on these results, the proposed TrOLEDs are promising candidates for modulating sleep disorders such as insomnia and narcolepsy–cataplexy with the convenience of wearable form factors