System design of a low-power wireless link for neural recording in a visual prosthesis

Restoring visual function in blind people through technology can be challenging but very beneficial in improving the quality of life. For most cases of blindness, the only option is to stimulate the visual cortex directly. Such a system requires external cameras, image processing and implanted electrodes. Powering, stimulating the brain, and recording neural activity is preferably done wirelessly to avoid infections. The wireless link for sending the neural activity (uplink) out of the brain is vital as the neural recording is for calibration and monitoring. Uplink requirements on (low-power) consumption at the implanted transmitter and a high data rate lead us to compare two promising wireless link options. A system-level analysis is carried out on the feasibility of impulse radio ultrawideband (IR-UWB) by a worst-case link budget. A low power CMOS IR-UWB transmitter consisting of an on-off keying (OOK) modulator and an impulse generator is proposed closely, fulfilling low-power and high data rate requirements

Low-power BPSK inductive data link for an implanted intracortical visual prosthesis

In making visually impaired people see again, for most cases the only option is to stimulate the visual cortex. In building such a system, it is desired that the communication to/from the implant and powering be done wirelessly to avoid infections. For the downlink, which is sending stimulation data to the implanted electrode, bandpass-sampled binary phase shift keying (BPSK) is chosen due to its potential for low-power consumption at its digital receiver. However, since an inductive link is most suited, designing practical inductive links with a flat band region to avoid poor phase transition and also refining the reset timing for imperfect transition times as well as designing low-power custom 1- bit Analog-to-digital converter is crucial. The bandpass-sampled BPSK system is designed and simulated at circuit level in Cadence using 180 nm CMOS technology at data rates of 0.5-4 Mbps and carrier frequency of 5-12 MHz. The improved bandpass-sampled BPSK system meets the requirements on data-rate, low-power consumption and robustness and is an integral part of the overall wireless communication and powering of the implanted intracortical visual prosthesis

Low-power communication for an implanted intracortical visual prosthesis

Assisting visually impaired people to see again using technology is quite challenging, especially for cases where most of the visual pathway is damaged. The only viable option is to stimulate the visual cortex directly. Sending the stimulation data to electrodes on the visual cortex is preferably done wirelessly to avoid infections and to ease mobility. The receiver on the implant poses a challenge in design, as the power supply is limited. In this paper, vital system requirements for this communication link are discussed. A low power system-level approach is presented which seeks to avoid power hungry components. This leads to the consideration of a bandpass sampled phase shift keying scheme via an inductive link. We propose a non-coherent digital demodulator, which relaxes the need for low phase noise oscillators which consume more power and, also avoids the use of phase locks loops. The overall communication system has a potential to deliver stimulation data to the implant side in the presence of simultaneous power transfer and reception of recorded data from the brain. Index Terms—Low-power, Inductive link, Non-coherent digital demodulator, Phase shift keying, Intracortical Visual Prosthesi

An MRI-compatible hyperthermia applicator for small animals

Introduction to design novel treatment combinations involving mild hyperthermia, pre-clinical trials are essential. These studies into treatment effectiveness require close monitoring of the temperature during testing . Invasive thermometry restricts testing of the link between hyperthermia and immune responses, so MRI-compatibility is a necessity. Next to that, the applicator must heat locally, and secondary hot spots especially in vulnerable regions like the spinal cord must be prevented. Lastly, the system must be non-invasive, for disturbances in the tissues studied interfere with the accuracy of the research.With these goals in mind, we designed and built an applicator based on a novel water-embedded antenna design. In this study, we report the mode of operation for the head&neck region, but it can also be used for other tissues up to about 2 cm deep.MethodsA simulation-based approach was used to design the antenna element, and the surrounding system including the load. Simulation programs SEMCAD and CST were used, both of which use a Finite Difference Time Difference (FDTD) calculation methods. SEMCAD was also used for Penne’s Bioheat equation temperature predictions. The single antenna and array performance were assessed by simulating the power absorption distributions, i.e. the Specific Absorption Rate (SAR), and the temperature distribution. The antenna was designed to achieve at least a -15 dB match to 50 Ω at 2.45 GHz. Furthermore, it was stabilized for various water temperatures and for disturbances in the air-water bolus boundary. The metal plates were designed to be thin enough to ensure MRI compatibility. The latter property was tested by inspecting MRI images for disturbances when the antenna plus related cables were scanned.ResultsAccording to our simulations, a single antenna operating at 5W power is able to heat tongue tissue to 42º C without creating hot spots in other areas. Next to that, experiments showed that the antenna stability required was achieved and a match of -19 dB was reached in all cases. Lastly, the MRI scan showed excellent compatibility in the area of interest.ConclusionsOur novel setup provides operation within the specifications defined. Based on these promising results, we will now elucidate on the experimental validation of the heating performance of the single antenna setup and develop a phased array for deep heating

An MRI-compatible hyperthermia applicator for small animals

Introduction to design novel treatment combinations involving mild hyperthermia, pre-clinical trials are essential. These studies into treatment effectiveness require close monitoring of the temperature during testing . Invasive thermometry restricts testing of the link between hyperthermia and immune responses, so MRI-compatibility is a necessity. Next to that, the applicator must heat locally, and secondary hot spots especially in vulnerable regions like the spinal cord must be prevented. Lastly, the system must be non-invasive, for disturbances in the tissues studied interfere with the accuracy of the research.With these goals in mind, we designed and built an applicator based on a novel water-embedded antenna design. In this study, we report the mode of operation for the head&neck region, but it can also be used for other tissues up to about 2 cm deep.MethodsA simulation-based approach was used to design the antenna element, and the surrounding system including the load. Simulation programs SEMCAD and CST were used, both of which use a Finite Difference Time Difference (FDTD) calculation methods. SEMCAD was also used for Penne’s Bioheat equation temperature predictions. The single antenna and array performance were assessed by simulating the power absorption distributions, i.e. the Specific Absorption Rate (SAR), and the temperature distribution. The antenna was designed to achieve at least a -15 dB match to 50 Ω at 2.45 GHz. Furthermore, it was stabilized for various water temperatures and for disturbances in the air-water bolus boundary. The metal plates were designed to be thin enough to ensure MRI compatibility. The latter property was tested by inspecting MRI images for disturbances when the antenna plus related cables were scanned.ResultsAccording to our simulations, a single antenna operating at 5W power is able to heat tongue tissue to 42º C without creating hot spots in other areas. Next to that, experiments showed that the antenna stability required was achieved and a match of -19 dB was reached in all cases. Lastly, the MRI scan showed excellent compatibility in the area of interest.ConclusionsOur novel setup provides operation within the specifications defined. Based on these promising results, we will now elucidate on the experimental validation of the heating performance of the single antenna setup and develop a phased array for deep heating

Murine head & neck applicator:hyperthermia prototype development

IntroductionCancer treatments remain a heavy load for the patient due to the many side effects. Mild hyperthermia, locally heating tissue to 42⁰ C, has proven to be a powerful treatment enhancer with no severe side effects. Recently, new potential applications of mild hyperthermia in cancer therapy were discovered. Converting these cell-culture based findings into clinical protocols requires pre-clinical investigation of the various strategies by clinical trials with small animals. For this goal, a site-specific head & neck hyperthermia applicator for murine models was developed. Hereto, we studied a design with an antenna array operating at 2.45 GHz embedded in a water bolus.Methodology A simulation-based approach was used to design the separate antennas operating at 2.45 GHz, and later on the antenna array. Simulation programs SEMCAD and CST are used, both of which use a Finite Difference Time Difference (FDTD) calculation methods. The design yields an air-water boundary between the antenna feed and antenna arms. To reduce detuning due to varying water levels, the connections between those elements (feed lines) were embedded within the PCB. A capacitive patch, also used for attachment of the connector, matched the antenna to 50 Ohm. Next, the antenna return loss (S11) was experimentally validated for various circumstances. Lastly, the single antenna and array performance was assessed by simulating first the power absorption distributions, and second the temperature distribution using Penne’s bioheat equation [1]. ResultsThe Simulation results as well as measurements show that the antenna is stable for variations in water levels. Simulation results of a grid of nine antennas show that controlled and focused application of heat can be delivered at target regions under the tongue, and that 14-25W suffices.ConclusionsBased on these promising results, we will now embark on experimental validation of the heating performance of a single antenna setup: firstly in tissue-equivalent gels and secondly in vivo

Theoretical and experimental nonlinear dynamics of a clamped-clamped beam MEMS resonator

Microelectromechanical resonators feature nonlineardynamic responses. A first-principles based modeling approach is proposed for a clamped-clamped beam resonator. Starting from the partial differential equation for the beam including geometric and electrostatic nonlinear effects, a reduced-order model is derived. The model captures the experimentally observed nonlinear dynamic behaviour of the resonator and allows for fast simulation and prediction of its response

Effect of finite precision on em simulations for high-contrast biological media at low frequencies

\u3cp\u3eAt low frequencies, biological media are characterized by extremely high permittivities. As a result, the most commonly used simulation methods, i.e. finite-difference time domain (FDTD), finite element method (FEM), and domain integral equations (DIE), suffer from severe limitations in accuracy. These limitations are caused by the round-off errors in finite-precision floating point operations. Finite precision causes error accumulation in FDTD due to the large number of time steps required to simulate one period and to maintain stability. In FEM, finite precision causes the numerical derivative to collapse due to the dependence on the mesh size. While the DIE is hardly influenced by the mesh size, the extreme permittivities cause a large difference in the order of magnitude of the various terms in the DIE.\u3c/p\u3

Design and numerical analysis of an electrostatic energy harvester with impact for frequency up-conversion

Integration of vibration energy harvesters (VEHs) with small-scale electronic devices may form an attractive alternative for relatively large batteries and can, potentially, increase their lifespan. However, the inherent mismatch between a harvester’s high-frequency resonance, typically in the range 100 - 1000 Hz, relative to the available low-frequency ambient vibrations, typically in the range 10–100 Hz, means that low-frequency power generation in microscale VEHs remains a persistent challenge. In this work, we model a novel electret-based, electrostatic energy harvester (EEH) design. In this design, we combine an out-of-plane gap-closing comb (OPGC) configuration for the low-frequency oscillator with an in-plane overlap comb configuration for the high-frequency oscillator and employ impact for frequency up-conversion. An important design feature is the tunability of the resonance frequency through the electrostatic nonlinearity of the low-frequency oscillator. Impulsive normal forces due to impact are included in numerical simulation of the EEH through Moreau’s time-stepping scheme which has, to the best of our knowledge, not been used before in VEH design and analysis. The original scheme is extended with time-step adjustments around impact events to reduce computational time. Using frequency sweeps, we numerically investigate power generation under harmonic, ambient vibrations. Results show improved low-frequency power generation in this EEH compared to a reference EEH. The EEH design shows peak power generation improvement of up to a relative factor 3.2 at low frequencies due to the occurrence of superharmonic resonances