Comparison of Radio Frequency Current and Microwave Energy for Transcatheter Renal Denervation
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We present the feasibility of using microwave energy as a different energy source for RDN ablation treatment, by comparing to RF current energy source. In this paper, we designed a coaxial-slot antenna for microwave (2.45 GHz) and an electrode for RF current (500 kHz), with phantoms that match human muscle dielectric properties at each respective working frequency. Both phantoms thermal properties and material density were measured, and then used in simulation. A total of 10 ablation experiments were conducted to validate the numerical simulation results. Each temperature points of the experiments were measured at 1 mm interval between thermometer probes. The results of the experiment temperature distributions agree well with the simulation results, RF achieved 5-6 mm while microwave achieved 7-8 mm. Additionally, numerical calculations with different input power were conducted to understand the temperature characteristics of both energy source. Microwave energy offers higher input power for a more profound and broader ablation area as opposed to RF current.
Modelling of the temperature changes induced by transcutaneous spinal direct current stimulation (tsDCS)
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In this study, the temperature increase induced by a 3 mA stimulation in the tissue target (i.e. the spinal cord), in its surrounding tissues and in other tissues possibly more vulnerable to temperature increase were assessed through a computational approach. That solves Laplace equation and BioHeat equation for electric field and temperature distribution, respectively, on six whole body high resolution anatomical models, including three models of pregnant women at different gestational ages. Results show that temperature increase distribution in those targets is guided by a complex interaction between different mechanism in which electric stimulation plays a secondary role, in particular when blood perfusion is active. The very low heating assessed (below 1.5 m°C) is not consistent with the hypothesis that the induced temperature increase would critically activate metabolic changes in the target tissues here considered or would contribute to the few side effect that the applications of spinal direct current stimulation protocols have shown.
Field Focusing for Implanted Medical Devices
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The small gap between the tips of the lines provides constructive coupling and augments the focused field. Compared to the case where no lines are used, the focused power is 8 times and 16 times larger if one line and two lines are utilized, respectively. The proposed design can be modified to focus fields with arbitrary polarizations at different depths inside the body. We propose a method to create this focusing structure by extrusion inside the body using heat-activated polymer-based conductors.
Electromagnetic Inversion for Noninvasive Specific Absorption Rate Characterization
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The unique aspect of this inverse source algorithm is that it casts the problem as the simultaneous inversion (SI) of two sets of equivalent currents: one for the device under test (DUT), and the other for the phantom. The dependency of these two sets of currents is then incorporated as an explicit regularization term in the resulting algorithm. The method is proposed to be relatively robust in terms of measurement noise. A simplified two-dimensional problem is presented to support this proposition.
A 0.09 mm2On-Chip Coil Designed in 0.5 μm CMOS process for Brain Neuromodulation Applications
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To stimulate multiple neurons simultaneously, distributed miniaturized implants are needed to cover a wide range of areas. In this paper, an on-chip design of an inductively coupled wireless power transfer (WPT) system for an optogenetic implant is presented. A $0.3 text{mm} times 0.3 text{mm}$ on-chip spiral coil is designed using a standard $0.5 mu m$ CMOS process and characterized as the receiver of the WPT system. The EM field distribution through different tissue layers is investigated which helps to further evaluate the maximum Specific Absorption Rate (SAR) and temperature through the brain tissue. The system achieves a power transfer efficiency (PTE) of 0.65% and 0.96% with matching networks through 10 mm tissue layer and air links respectively. At 10 dBm transmitted power, the maximum SAR value is simulated to be 1.51 W/kg with the maximum temperature increase of 0.73 °C through the skin layer due to the EM field exposure. A case study of the proposed on-chip coil based WPT system shows the different light intensity level that can be achieved for optognetic neuromodulation application. Thus, the proposed miniaturized system proves to be a good candidate for the future distributive neural interfacing application.
Design and Optimization of a Slotted Monopole Antenna for Ultra-wide Band Body Centric Imaging Applications
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To ensure that the proposed designs are meeting the required specifications with reduced design time, the parallel surrogate model-assisted hybrid differential evolution for antenna optimization (PSADEA) is proposed to optimize the design. Based on the best set of geometry parameter for the optimum antenna performance, the antenna prototype is realized on an FR-4 substrate and analyzed in terms of bandwidth, gain, efficiency, and radiation pattern with and without the tissue models. All measured results are found to be in good agreement with the simulated results. The antenna provides a good reflection coefficient (S11 <-10 dB) in the UWB frequency band from 3.1 GHz to 10.6 GHz and maintains its bandwidth UWB operation without detuning when placed in closed contact with the human body or breast mimicking tissues (phantoms).
