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Objective: Heart disease is the leading cause of death worldwide. Hypertension is an important precursor and the most common risk factor to heart failure. While some patients can control their high blood pressure with pharmaceuticals, many suffer from resistant hypertension, where antihypertensive medications do not achieve the desired outcome. Electrical stimulation is an emerging therapy to modulate blood pressure and integrating it with closed-loop feedback can improve blood pressure control. Methods: We design and fabricate two application-specific integrated circuits (ASICs) for stimulation and pressure sensing using TSMC's 180 nm MS RF G process. We create a closed-loop system by integrating the ASICs with a microscale pressure sensor and a custom-built Python script and test the full system in six Long Evans rats using vagus nerve stimulation. Results: After calibration and benchtop verification, we prove the functionality of the system in lowering, and maintaining a desired blood pressure in vivo. The system effectively monitors pressure and stimulates when that pressure exceeds the user-determined threshold. Conclusion: By combining this stimulation therapy with a pressure sensor, we present a novel closed-loop, electroceutical system that has the potential to monitor and modulate blood pressure. Significance: We present a drug-free, potentially side-effect-free electroceutical therapeutic for managing resistant hypertension. [ABSTRACT FROM AUTHOR]

Reliable chronic neural recording from focal deep brain structures is impeded by insertion injury and foreign body response, the magnitude of which is correlated with the mechanical mismatch between the electrode and tissue. Thin and flexible electrodes cause less glial scarring and record longer than stiff electrodes. However, the insertion of flexible microelectrodes in brain has been a challenge. Here, a novel insertion method is proposed, and demonstrated, for precise targeting deep brain structures using flexible micro-wire electrodes. The microelectrode is spun and slowly inserted in brain through an appropriate electrode guide. The electrode guide does not penetrate into cortex. Based on two new mechanisms, namely spinning and guided insertion, we have demonstrated successful insertion of 25-micron platinum flexible electrodes about 10-mm deep in rat brains without buckling. We present an electrode insertion device based on the proposed method and demonstrate its use to implant flexible microelectrodes in rat brains. The step-by-step insertion process is described. Microelectrodes were inserted in the Bötzinger complex and respiratory neural activity was recorded acutely in nine rats and chronically in two rats for 50 days. [ABSTRACT FROM AUTHOR]

The general coupling matrix representation of bandpass filter (BPF) circuits is a widely used technique that has simplified the analysis and optimization of complex microwave filters. In this paper, we demonstrate a novel application of the general coupling matrix for modeling wireless power-transfer (WPT) systems based on the BPF model of magnetically coupled resonators. Compared to other methods of WPT analysis, our model simplifies accommodation of complex loads and provides direct expressions for impedance matching (IM) in WPT systems. Using this tool, we achieve optimal IM for two resonator systems with a complex load, thus achieving the greatest possible power-transfer efficiency (PTE). Furthermore, our model reveals additional design constraints for optimizing PTE in coupled resonator systems exhibiting low quality factor and small interresonator coupling. Overall, this paper introduces a new, versatile framework for the analysis and optimization of coupled resonator WPT systems. Experimental results are presented, verifying the optimal IM design process. [ABSTRACT FROM PUBLISHER]

Objective:The goal of this paper is to create a large wireless powering arena for powering small devices implanted in freely behaving rodents. Methods: We design a cavity resonator based wireless power transfer (WPT) system and utilize our previously developed optimal impedance matching methodology to achieve effective WPT performance for operating sophisticated implantable devices, made with miniature receive coils (<8 mm in diameter), within a large volume (dimensions: 60.96 cm × 60.96 cm × 30 cm). We provide unique cavity design and construction methods which maintains electromagnetic performance of the cavity while promoting its utility as a large animal husbandry environment. In addition, we develop a biaxial receive resonator system to address device orientation insensitivity within the cavity environment. Functionality is demonstrated with chronic experiments involving rats implanted with our custom designed bioelectric recording device. Results: We demonstrate an average powering fidelity of 93.53% over nine recording sessions across nine weeks, indicating nearly continuous device operation for a freely behaving rat within the large cavity resonator space. Conclusion: We have developed and demonstrated a cavity resonator based WPT system for long term experiments involving freely behaving small animals. Significance: This cavity resonator based WPT system offers an effective and simple method for wirelessly powering miniaturized devices implanted in freely moving small animals within the largest space. [ABSTRACT FROM PUBLISHER]

In a multiple-receiver wireless power transfer (WPT) system, determining the condition for uniform power distribution at a high transfer efficiency is a challenging issue. In this paper, a selective WPT technique using magnetic resonance coupling (MRC) is introduced for smart power delivery in a multiple-receiver system. The proposed method selectively and exclusively delivers power to only one designated receiver among multiple receivers, eliminating the cross-coupling effect and unbalanced power division problem across the receivers. This is achieved by separating the resonant frequencies of the receivers to isolate the coupling effects between coils. The power division ratio of the receivers is controlled by changing the duration time ratio for power transfer. In this paper, a one-transmitter three-receiver selective MRC system is designed and fabricated. The power distribution is demonstrated under impedance matched condition, showing a power transfer efficiency of 24%–29% at a very small coupling coefficient of 0.01 with a 12-mm-diameter receiver coil. Distance compensation and a one-way communication of time division multiple access are demonstrated for a multiple-receiver system, using the proposed method. [ABSTRACT FROM PUBLISHER]

This letter describes the development and implementation of an impedance-matching (IM) method for achieving optimal power transfer efficiencies (PTE's) in cavity resonator wireless power transfer (WPT) systems. Specifically, we develop a bandpass filter (BPF) circuit model and utilize network analysis to predict and realize maximum achievable PTE to miniature systems enclosed within a hollow metallic cylindrical cavity excited in TM010 resonant mode. Measured PTE results are demonstrated matching closely with the developed theory and circuit simulations. We achieve a peak PTE of 33% to a 5-mm-diameter receive coil that occupies a volume that is 5.23 ×106 times smaller than the volume of the cylindrical cavity. Our achieved PTE is 4 times larger than the PTE achieved to a system with no optimal IM network but only a single resonant capacitor connected in series with the receive coil. The model and results presented illustrate our optimal design methodology for realizing maximum achievable PTE in cavity resonator WPT systems. [ABSTRACT FROM PUBLISHER]

We demonstrate an alternative method of designing electrical stimuli-termed burst modulation—for producing different patterns of nerve fiber recruitment. By delivering electrical charge in bursts of “pulsons”—miniature pulses-instead of as long continuous pulses, our method can optimize the waveform for stimulation efficiency and fiber selectivity. In our in vivo validation experiments, while maintaining C fibers of the rat vagus nerve at \sim 50\% activation with different waveforms, the burst-modulated waveform produced 11% less A fiber activation than the standard rectangular pulse waveform (rectangular: 50.8\pm1.5\% of maximal A response, mean \pm standard error of the mean; burst-modulated: 39.8 \pm 1.3\%), which equates to a 20% reduction in A fiber response magnitude. In addition, the burst-modulated waveform required 45% less stimulus charge per phase to maintain 50% C fiber activation (rectangular: 20.7 \pm 0.86~\muC; burst-modulated: 11.3 \pm 0.41~\muC). Burst-modulated waveforms produced consistent patterns of fiber recruitment within and across animals, which indicate that our methods of stimulus design and response analysis provide a reliable way to study neurostimulation and deliver therapy. [ABSTRACT FROM AUTHOR]

An ultra-low-power wirelessly powered radiofrequency (RF) transceiver for wireless sensor network is implemented using 180-nm CMOS technology. We propose a 98- \mu\mboxW 457.5-MHz transmitter with output radiation power of $-$22 dBm. This transmitter utilizes 915-MHz wirelessly powering RF signal by frequency division using a true-single-phase-clock divider to generate the carrier frequency with very low power consumption and small die area. The transmitter can support up to 5-Mb/s data rate. The telemetry system uses an eight-stage Cockcroft–Walton rectifier to convert RF to dc voltage for energy harvesting. The bandgap reference and linear regulators provide stable dc voltage throughout the system. The receiver recovers data from the modulated wireless powering RF signal to perform time-division multiple access (TMDA) for the multiple-node system. Power consumption of the TDMA receiver is less than 15 \mu\mboxW. Our proposed transmitter and receiver each occupies 0.0018 and 0.0135 mm 2 of active die area, respectively. [ABSTRACT FROM PUBLISHER]

Neural recording and stimulation have great clinical potential. Long-term neural recording remains a challenge, however, as implantable electrodes eventually fail due to the adverse effects of the host tissue response to the indwelling implant. Astrocytes and microglia attempt to engulf the electrode, increasing the electrical impedance between the electrode and neurons, and possibly pushing neurons away from the recording site. Faster insertion speed, finer tip geometry, smaller size, and lower material stiffness all seem to decrease damage caused by insertion and reduce the intensity of the tissue response. However, electrodes that are too small result in buckling, making insertion impossible. In this paper, we assess the viability of high-speed (27.8 m/s) deployment of 25 \mum, ferromagnetic microelectrodes into rat brain. To characterize functionality of magnetically inserted electrodes, 4 Long-Evans rats were implanted for 31 days with impedance measurements and neural recordings taken daily. Performance was compared to 150 \mum diameter PlasticsOne electrodes since 25 \mum electrodes buckled during “slow speed” insertion. Platinum-iron magnetically inserted electrodes resolved single unit activity throughout the duration of the study in one rat, and saw no significant change (p=0.970) in impedance (4.54% increase) from day 0 (Z0\approx 144\ k\Omega,Z31\approx 150\ k\Omega). These findings provide a proof-of-concept for magnetic insertion as a viable insertion method that enables nonbuckling implantation of small (25 \mum) microelectrodes, with potential for neural recording applications. [ABSTRACT FROM PUBLISHER]

Controlled, wireless neuromodulation using miniature implantable devices is a long-sought goal in neuroscience. It will allow many studies and treatments that are otherwise impractical. Recent studies demonstrate advances in neuromodulation through optogenetics, but test animals are typically tethered, severely limiting experimental possibilities. Existing nontethered optical stimulators either deliver light through a cranial window limiting applications to superficial layers of the brain, are not widely accessible due to highly specialized fabrication techniques, or do not demonstrate robust and flexible control of the optical power emitted. To overcome these limitations, we have developed a novel, miniature, wireless, deep-brain, modular optical stimulator with controllable stimulation parameters for use in optogenetic experiments. We demonstrate its use in a behavioral experiment targeting a deep brain structure in freely behaving mice. To allow its rapid and widespread adoption, we developed this stimulator using commercially available components. The modular and accessible optogenetic stimulator presented advances the wireless toolset available for freely behaving animal experiments. [ABSTRACT FROM PUBLISHER]

Electrical vagus nerve stimulation is a treatment alternative for many epileptic and depressed patients whose symptoms are not well managed with pharmaceutical therapy. However, the fixed stimulus, open loop dosing mechanism limits its efficacy and precludes major advances in the quality of therapy. A real-time, responsive form of vagus nerve stimulation is needed to control nerve activation according to therapeutic need. This personalized approach to therapy will improve efficacy and reduce the number and severity of side effects. We present autonomous neural control, a responsive, biofeedback-driven approach that uses the degree of measured nerve activation to control stimulus delivery. We demonstrate autonomous neural control in rats, showing that it rapidly learns how to most efficiently activate any desired proportion of vagal A, B, and/or C fibers over time. This system will maximize efficacy by minimizing patient response variability and by minimizing therapeutic failures resulting from longitudinal decreases in nerve activation with increasing durations of treatment. The value of autonomous neural control equally applies to other applications of electrical nerve stimulation. [ABSTRACT FROM AUTHOR]

In this brief, we have proposed a design strategy for an energy-efficient circuit/architecture to detect the onset of epileptic seizures with high efficacy. The architecture consists of two stages. The first stage is a low complexity Coastline parameter algorithm that consumes very low energy per computation. The second stage is a more efficacious wavelet-based algorithm (discrete wavelet transform-quasi-averaging) that consumes relatively higher energy and is powered ON only if determined by the low-complexity first stage. Using this proposed strategy, we achieve significant reduction in the energy consumption of the circuit by avoiding redundant computations, thereby increasing the longevity of the battery. We also observe that it leads to an improvement in efficacy. The two algorithms are user-programmable to compensate for the intersubject variations of neural signals. We use in vivo neural recordings from large animals (rats) to test the functionality of the system and calculate efficacy, subjected to minimum delay in detection. The system is simulated using 65-nm bulk-Si technology library. The simulated results show 32% energy savings (compared with a single-stage wavelet-based algorithm), consuming an average of 31.2 nJ/computation. The results also show a 12% increase in efficacy. [ABSTRACT FROM PUBLISHER]

Far-field RF powering is an attractive solution to the challenge of remotely powering devices implanted in living tissue. The purpose of this study is to characterize the peak obtainable power levels in a wireless myoelectric sensor implanted in a patient while maintaining safe local temperature and RF powering conditions. This can serve as a guide for the design of onboard electronics in related medical implants and provide motivation for more efficient power management strategies for implantable integrated circuits. Safe powering conditions and peak received power levels are established using a simplified theoretical analysis and Federal Communications Commission-established limits for radiating antennas. These conditions are subsequently affirmed and improved upon using the finite-element method and temperature modeling in bovine muscle. [ABSTRACT FROM PUBLISHER]

Glaucoma is a detrimental disease that causes blindness in millions of people worldwide. There are numerous treatments to slow the condition but none are totally effective and all have significant side effects. Currently, a continuous monitoring device is not available, but its development may open up new avenues for treatment. This work focuses on the design and fabrication of an active glaucoma intraocular pressure (IOP) monitor that is fully wireless and implantable. Major benefits of an active IOP monitoring device include the potential to operate independently from an external device for extended periods of time and the possibility of developing a closed-loop monitoring and treatment system. The fully wireless operation is based off using gigahertz-frequency electromagnetic wave propagation, which allows for an orientation independent transfer of power and data over reasonable distances. Our system is comprised of a micro-electromechanical systems (MEMS) pressure sensor, a capacitive power storage array, an application-specific integrated circuit designed on the Texas Instruments (TI) 130 nm process, and a monopole antenna all assembled into a biocompatible liquid-crystal polymer-based tadpole-shaped package. [ABSTRACT FROM PUBLISHER]

This paper presents a fully wireless cardiac pressure sensing system. Food and Drug Administration (FDA) approved medical stents are explored as radiating structures to support simultaneous transcutaneous wireless telemetry and powering. An application-specific integrated circuit (ASIC), designed and fabricated using the Texas Instruments 130-nm CMOS process, enables wireless telemetry, remote powering, voltage regulation, and processing of pressure measurements from a microelectromechanical systems (MEMS) capacitive sensor. This paper demonstrates fully wireless-pressure-sensing functionality with an external 35-dB⋅m RF powering source across a distance of 10 cm. Measurements in a regulated pressure chamber demonstrate the ability of the cardiac system to achieve pressure resolutions of 0.5 mmHg over a range of 0-50 mmHg using a channel data-rate of 42.2 kb/s. [ABSTRACT FROM AUTHOR]

We report live animal studies that verify and quantify successful transocular transmission of data from a miniature low-power implant. To minimize damage, implantation within layers of the eye requires an ultrasmall device on a scale of just a few millimeters on each side and less than 500 μm in thickness. A high-frequency transmitter integrated circuit (IC) was designed, fabricated, and bonded onto a board containing an antenna, matching network components, and interconnects. The transmitter must achieve sufficient efficiency to draw minimal power from the limited onboard storage array while outputting a sufficiently large signal to overcome tissue-induced attenuation. Two different versions of the system were developed, one using a low-temperature co-fired ceramic material for the substrate and the other using silicon. Animal studies performed using live rabbits followed by empirical measurements verified the feasibility of a wireless telemetry scheme for a low-power miniature ocular implant. [ABSTRACT FROM AUTHOR]

The article describes the theory involved in the design of an inductively powered system for use with miniature implantable neural recording devices. In addition, it provides the designer with a detailed guide to the design of such systems and discusses a specific real-world application of inductive powering.