Comparative analysis of energy transfer mechanisms for neural implants

As neural implant technologies advance rapidly, a nuanced understanding of their powering mechanisms becomes indispensable, especially given the long-term biocompatibility risks like oxidative stress and inflammation, which can be aggravated by recurrent surgeries, including battery replacements. This review delves into a comprehensive analysis, starting with biocompatibility considerations for both energy storage units and transfer methods. The review focuses on four main mechanisms for powering neural implants: Electromagnetic, Acoustic, Optical, and Direct Connection to the Body. Among these, Electromagnetic Methods include techniques such as Near-Field Communication (RF). Acoustic methods using high-frequency ultrasound offer advantages in power transmission efficiency and multi-node interrogation capabilities. Optical methods, although still in early development, show promising energy transmission efficiencies using Near-Infrared (NIR) light while avoiding electromagnetic interference. Direct connections, while efficient, pose substantial safety risks, including infection and micromotion disturbances within neural tissue. The review employs key metrics such as specific absorption rate (SAR) and energy transfer efficiency for a nuanced evaluation of these methods. It also discusses recent innovations like the Sectored-Multi Ring Ultrasonic Transducer (S-MRUT), Stentrode, and Neural Dust. Ultimately, this review aims to help researchers, clinicians, and engineers better understand the challenges of and potentially create new solutions for powering neural implants.

Pushing the Limits of Biosensing: Selective Calcium Ion Detection with High Sensitivity via High-k Gate Dielectric Engineered Si Nanowire Random Network Channel Dual-Gate Field-Effect Transistors

Calcium ions (Ca2+) are abundantly present in the human body; they perform essential roles in various biological functions. In this study, we propose a highly sensitive and selective biosensor platform for Ca2+ detection, which comprises a dual-gate (DG) field-effect transistor (FET) with a high-k engineered gate dielectric, silicon nanowire (SiNW) random network channel, and Ca2+-selective extended gate. The SiNW channel device, which was fabricated via the template transfer method, exhibits superior Ca2+ sensing characteristics compared to conventional film channel devices. An exceptionally high Ca2+ sensitivity of 208.25 mV/dec was achieved through the self-amplification of capacitively coupled DG operation and an enhanced amplification ratio resulting from the high surface-to-volume ratio of the SiNW channel. The SiNW channel device demonstrated stable and reliable sensing characteristics, as evidenced by minimal hysteresis and drift effects, with the hysteresis voltage and drift rate measuring less than 6.53% of the Ca2+ sensitivity. Furthermore, the Ca2+-selective characteristics of the biosensor platform were elucidated through experiments with pH buffer, NaCl, and KCl solutions, wherein the sensitivities of the interfering ions were below 7.82% compared to the Ca2+ sensitivity. The proposed Ca2+-selective biosensor platform exhibits exceptional performance and holds great potential in various biosensing fields.

Electrical Interference Simulation and Prediction Model for Acoustoelectric Logging Detector

Acoustic logging instruments generate high voltages in the order of thousands of volts. Electrical interferences are thus induced by high-voltage pulses that affect the logging tool and make it inoperable owing to damaged components in severe cases. High-voltage pulses from the acoustoelectric logging detector interfere with the electrode measurement loop through capacitive coupling, which has seriously affected the acoustoelectric signal measurements. In this paper, we simulate high voltage pulses, capacitive coupling and electrode measurement loops based on qualitative analysis of the causes of electrical interference. Based on the structure of the acoustoelectric logging detector and the logging environment, an electrical interference simulation and prediction model was developed to quantify the characteristics of the electrical interference signal.

Noninvasive electrical stimulation as an adjunct to fusion procedures: a systematic review and meta-analysis

OBJECTIVE

Noninvasive electrical stimulation represents a distinct group of devices used to augment fusion rates. However, data regarding outcomes of noninvasive electrical stimulation have come from a small number of studies. The goal of this systematic review and meta-analysis was to determine outcomes of noninvasive electrical stimulation used as an adjunct to fusion procedures to improve rates of successful fusion.

METHODS

PubMed, Embase, and the Cochrane Clinical Trials database were searched according to search strategy and PRISMA guidelines. Random-effects meta-analyses of fusion rates with the three main modalities of noninvasive electrical stimulation, capacitively coupled stimulation (CCS), pulsed electromagnetic fields (PEMFs), and combined magnetic fields (CMFs), were conducted using R version 4.1.0 (The R Foundation for Statistical Computing). Both retrospective studies and clinical trials were included. Animal studies were excluded. Risk-of-bias analysis was performed with the Risk of Bias 2 (RoB 2) and Risk of Bias in Nonrandomized Studies of Interventions (ROBINS-I) tools.

RESULTS

Searches of PubMed, Embase, and the Cochrane Clinical Trials database identified 8 articles with 1216 participants meeting criteria from 213 initial results. There was a high overall risk of bias identified for the majority of randomized studies. No meta-analysis could be performed for CCS as only 1 study was identified. Meta-analysis of 6 studies of fusion rates in PEMF did not find any difference between treatment and control groups (OR 1.89, 95% CI 0.36-9.80, p = 0.449). Meta-analysis of 2 studies of CMF found no difference in fusion rates between control and treatment groups (OR 0.90, 95% CI 0.07-11.93, p = 0.939). Subgroup analysis of PEMF was limited given the small number of studies and patients, although significantly increased fusion rates were seen in some subgroups.

CONCLUSIONS

This meta-analysis of clinical outcomes and fusion rates in noninvasive electrical stimulation compared to no stimulation did not identify any increases in fusion rates for any modality. A high degree of heterogeneity between studies was noted. Although subgroup analysis identified significant differences in fusion rates in certain groups, these findings were based on a small number of studies and further research is needed. This analysis does not support routine use of these devices to augment fusion rates, although the data are limited by a high risk of bias and a small number of available studies.

A Novel Coupling Mechanism for CSRRs as Near-Field Dielectric Sensors

This work proposes a novel coupling mechanism for a complementary split-ring resonator as a planar near-field microwave sensor for dielectric materials. The resonator is etched into the ground plane of a microstrip line. This mechanism is based on the inductive coupling synthesized by utilizing a via that connects the power plane of the microstrip line to the central island of the resonator. The proposed coupling makes the coupling capacitance between the transmission line and the resonator relatively small and insignificant compared to the capacitance of the resonator, making it more sensitive to changes in the dielectric constant of the materials under test. In addition, the coupling is no longer dependent solely on the capacitive coupling, which significantly reduces the coupling degradation caused by loading the resonator with dielectric materials, so the inductive coupling plays an important role in the proposed design. Therefore, the proposed coupling mechanism improves the sensitivity and enhances the coupling between the transmission line and the resonator. The sensor is evaluated for sensitivity, normalized resonance shift, and coupling factor using a full-wave numerical simulation. The sensitivity of the proposed sensor is 12% and 5.6% when detecting dielectric constants of 2 and 10, respectively. Compared to recent studies, the sensitivity improvement when detecting similar permittivity is 20% (1.32 times) and 9.8% (1.1 times). For verification, the proposed sensor is manufactured using PCB technology and is used to detect the presence of two dielectric laminates.

Electronic Bone Growth Stimulators for Augmentation of Osteogenesis in In Vitro and In Vivo Models: A Narrative Review of Electrical Stimulation Mechanisms and Device Specifications

Since the piezoelectric quality of bone was discovered in 1957, scientists have applied exogenous electrical stimulation for the purpose of healing. Despite the efforts made over the past 60 years, electronic bone growth stimulators are not in common clinical use. Reasons for this include high cost and lack of faith in the efficacy of bone growth stimulators on behalf of clinicians. The purpose of this narrative review is to examine the preclinical body of literature supporting electrical stimulation and its effect on bone properties and elucidate gaps in clinical translation with an emphasis on device specifications and mechanisms of action. When examining these studies, trends become apparent. In vitro and small animal studies are successful in inducing osteogenesis with all electrical stimulation modalities: direct current, pulsed electromagnetic field, and capacitive coupling. However, large animal studies are largely unsuccessful with the non-invasive modalities. This may be due to issues of scale and thickness of tissue planes with varying levels of resistivity, not present in small animal models. Additionally, it is difficult to draw conclusions from studies due to the varying units of stimulation strength and stimulation protocols and incomplete device specification reporting. To better understand the disconnect between the large and small animal model, the authors recommend increasing scientific rigor for these studies and reporting a novel minimum set of parameters depending on the stimulation modality.

Optimal Solutions for Underwater Capacitive Power Transfer

Capacitive power transfer (CPT) has attracted attention for on-road electric vehicles, autonomous underwater vehicles, and electric ships charging applications. High power transfer capability and high efficiency are the main requirements of a CPT system. This paper proposes three possible solutions to achieve maximum efficiency, maximum power, or conjugate-matching. Each solution expresses the available load power and the efficiency of the CPT system as functions of capacitive coupling parameters and derives the required admittance of the load and the source. The experimental results demonstrated that the available power and the efficiency decrease by the increasing of the frequency from 300 kHz to 1 MHz and the separation distance change from 100 to 300 mm. The maximum efficiency solution gives 83% at 300 kHz and a distance of 100 mm, while the maximum power solution gives the maximum normalized power of 0.994 at the same frequency and distance. The CPT system can provide a good solution to charge electric ships and underwater vehicles over a wide separation distance and low-frequency ranges.

Short-Time Impedance Spectroscopy Using a Mode-Switching Nonsinusoidal Oscillator: Applicability to Biological Tissues and Continuous Measurement

Herein, we propose an impedance spectroscopy method using a mode-switching nonsinusoidal oscillator and apply this method for measuring the impedance of biological tissues and continuous impedance measurement. To obtain impedance spectra over a wide frequency range, we fabricated a novel nonsinusoidal oscillator incorporating binary counters and analog switches. This oscillator could periodically switch oscillation frequency through the mode switching of the feedback resistor. From the oscillation waveform at each oscillation frequency of this circuit (oscillator), we determined the impedance spectrum of a measured object using the discrete-time Fourier transform. Subsequently, we obtained the broad impedance spectrum of the measured object by merging odd-order harmonic spectral components up to the 19th order for each oscillation frequency. From the measured spectrum, the resistive and capacitive components of the circuit simulating bioimpedance were estimated with high accuracy. Moreover, the proposed method was used to measure the impedance of porcine myocardium; changes in the impedance spectrum of the myocardial tissue due to coagulation could be measured. Furthermore, rapid variations in the resistance value of a CdS photocell could be continuously measured using the proposed method.

High-Q Silicon Nitride Drum Resonators Strongly Coupled to Gates

Silicon nitride (SiN) mechanical resonators with high quality mechanical properties are attractive for fundamental research and applications. However, it is challenging to maintain these mechanical properties while achieving strong coupling to an electrical circuit for efficient on-chip integration. Here, we present a SiN drum resonator covered with an aluminum thin film, enabling large capacitive coupling to a suspended top-gate. Implementing the full electrical measurement scheme, we demonstrate a high quality factor ∼10⁴ (comparable to that of bare drums at room temperature) and present our ability to detect ∼10 mechanical modes at low temperature. The drum resonator is also coupled to a microwave cavity, so that we can perform optomechanical sideband pumping with a fairly good coupling strength G and demonstrate mechanical parametric amplification. This SiN drum resonator design provides efficient electrical integration and exhibits promising features for exploring mode coupling and signal processing.

Highly Sensitive and Transparent Urea-EnFET Based Point-of-Care Diagnostic Test Sensor with a Triple-Gate a-IGZO TFT

In this study, we propose a highly sensitive transparent urea enzymatic field-effect transistor (EnFET) point-of-care (POC) diagnostic test sensor using a triple-gate amorphous indium gallium zinc oxide (a-IGZO) thin-film pH ion-sensitive field-effect transistor (ISFET). The EnFET sensor consists of a urease-immobilized tin-dioxide (SnO₂) sensing membrane extended gate (EG) and an a-IGZO thin film transistor (TFT), which acts as the detector and transducer, respectively. To enhance the urea sensitivity, we designed a triple-gate a-IGZO TFT transducer with a top gate (TG) at the top of the channel, a bottom gate (BG) at the bottom of the channel, and a side gate (SG) on the side of the channel. By using capacitive coupling between these gates, an extremely high urea sensitivity of 3632.1 mV/pUrea was accomplished in the range of pUrea 2 to 3.5; this is 50 times greater than the sensitivities observed in prior works. High urea sensitivity and reliability were even obtained in the low pUrea (0.5 to 2) and high pUrea (3.5 to 5) ranges. The proposed urea-EnFET sensor with a triple-gate a-IGZO TFT is therefore expected to be useful for POC diagnostic tests that require high sensitivity and high reliability.

Exploiting Colloidal Metamaterials for Achieving Unnatural Optical Refractions

The scaling down of meta-atoms or metamolecules (collectively denoted as metaunits) is a long-lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta-units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near-infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self-assembly as a strategy for the realization of optical metamaterials. Colloidal self-assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost-effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self-assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self-assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed.

Capacitive-Coupling Impedance Spectroscopy Using a Non-Sinusoidal Oscillator and Discrete-Time Fourier Transform: An Introductory Study

In this study, we propose a new short-time impedance spectroscopy method with the following three features: (1) A frequency spectrum of complex impedance for the measured object can be obtained even when the measuring electrodes are capacitively coupled with the object and the precise capacitance of the coupling is unknown; (2) the spectrum can be obtained from only one cycle of the non-sinusoidal oscillation waveform without sweeping the oscillation frequency; and (3) a front-end measuring circuit can be built, simply and cheaply, without the need for a digital-to-analog (D-A) converter to synthesize elaborate waveforms comprising multiple frequencies. We built the measurement circuit using the proposed method and then measured the complex impedance spectra of 18 resistive elements connected in series with one of three respective capacitive couplings. With this method, each element's resistance and each coupling's capacitance were estimated independently and compared with their nominal values. When the coupling capacitance was set to 10 nF or 1.0 nF, estimated errors for the resistive elements in the range of 2.0-10.0 kΩ were less than 5%.

Numerical Simulations as Means for Tailoring Electrically Conductive Hydrogels Towards Cartilage Tissue Engineering by Electrical Stimulation

Cartilage regeneration is a clinical challenge. In recent years, hydrogels have emerged as implantable scaffolds in cartilage tissue engineering. Similarly, electrical stimulation has been employed to improve matrix synthesis of cartilage cells, and thus to foster engineering and regeneration of cartilage tissue. The combination of hydrogels and electrical stimulation may pave the way for new clinical treatment of cartilage lesions. To find the optimal electric properties of hydrogels, theoretical considerations and corresponding numerical simulations are needed to identify well-suited initial parameters for experimental studies. We present the theoretical analysis of a hydrogel in a frequently used electrical stimulation device for cartilage regeneration and tissue engineering. By means of equivalent circuits, finite element analysis, and uncertainty quantification, we elucidate the influence of the geometric and dielectric properties of cell-seeded hydrogels on the capacitive-coupling electrical field stimulation. Moreover, we discuss the possibility of cellular organisation inside the hydrogel due to forces generated by the external electric field. The introduced methodology is easily reusable by other researchers and allows to directly develop novel electrical stimulation study designs. Thus, this study paves the way for the design of future experimental studies using electrically conductive hydrogels and electrical stimulation for tissue engineering.

High-performance extended-gate ion-sensitive field-effect transistors with multi-gate structure for transparent, flexible, and wearable biosensors

In this study, we developed a high-performance extended-gate ion-sensitive field-effect transistor (EG-ISFET) sensor on a flexible polyethylene naphthalate (PEN) substrate. The EG-ISFET sensor comprises a tin dioxide (SnO₂) extended gate, which acts as a detector, and an amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) for a transducer. In order to self-amplify the sensitivity of the pH sensors, we designed a uniquely-structured a-IGZO TFT transducer with a high-k engineered top gate insulator consisting of a silicon dioxide/tantalum pentoxide (SiO₂/Ta₂O₅) stack, a floating layer under the channel, and a control gate coplanar with the channel. The SiO₂/Ta₂O₅ stacked top gate insulator and in-plane control gate significantly contribute to capacitive coupling, enabling the amplification of sensitivity to be enlarged compared to conventional dual-gate transducers. For a pH sensing method suitable for EG-ISFET sensors, we propose an in-plane control gate (IG) sensing mode, instead of conventional single-gate (SG) or dual-gate (DG) sensing modes. As a result, a pH sensitivity of 2364 mV/pH was achieved at room temperature - this is significantly superior to the Nernstian limit (59.15 mV/pH at room temperature). In addition, we found that non-ideal behavior was improved in hysteresis and drift measurements. Therefore, the proposed transparent EGISFFET sensor with an IG sensing mode is expected to become a promising platform for flexible and wearable biosensing applications.

Wireless Power Transfer Techniques for Implantable Medical Devices: A Review

Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants. The design and implementation of high power transfer efficiency WPT systems are, however, challenging. The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems. This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance. The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods. The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems. Necessary improvements and trends of each WPT techniques are also indicated per specific IMD.

Ion Gel Capacitively Coupled Tribotronic Gating for Multiparameter Distance Sensing

Developing sophisticated device architectures is of great significance to go beyond Moore's law with versatility toward human-machine interaction and artificial intelligence. Tribotronics/tribo-iontronics offer a direct way to controlling the transport properties of semiconductor devices by mechanical actions, which fundamentally relies on how to enhance the tribotronic gating effect through device engineering. Here, we propose a universal method to enhance the tribotronic properties through electric double layer (EDL) capacitive coupling. By preparing an ion gel layer on top of tribotronic graphene transistor, we demonstrate a dual-mode field effect transistor (i.e., a tribotronic transistor with capacitively coupled ion gel and an ion-gel-gated graphene transistor with a second tribotronic gate). The resulted tribotronic gating performances are greatly improved by twice for the on-state current and four times for the on/off ratio (the first mode). It can also be utilized as a multiparameter distance sensor with drain current increased by ∼600 μA and threshold voltage shifted by ∼0.8 V under a mechanical displacement of 0.25 mm (the second mode). The proposed methodology of EDL capacitive coupling offers a facile and efficient way to designing more sophisticated tribotronic devices with superior performance and multifunctional sensations.

Influence of dielectric layer thickness and roughness on topographic effects in magnetic force microscopy

Magnetic force microscopy (MFM) has become a widely used tool for the characterization of magnetic properties. However, the magnetic signal can be overlapped by additional forces acting on the tip such as electrostatic forces. In this work the possibility to reduce capacitive coupling effects between tip and substrate is discussed in relation to the thickness of a dielectric layer introduced in the system. Single superparamagnetic iron oxide nanoparticles (SPIONs) are used as a model system, because their magnetic signal is contrariwise to the signal due to capacitive coupling so that it is possible to distinguish between magnetic and electric force contributions. Introducing a dielectric layer between substrate and nanoparticle the capacitive coupling can be tuned and minimized for thick layers. Using the theory of capacitive coupling and the magnetic point dipole-dipole model we could theoretically explain and experimentally prove the phase signal for single superparamagnetic nanoparticles as a function of the layer thickness of the dielectric layer. Tuning the capacitive coupling by variation of the dielectric layer thickness between nanoparticle and substrate allows the distinction between the electric and the magnetic contributions to the MFM signal. The theory also predicts decreasing topographic effects in MFM signals due to surface roughness of dielectric films with increasing film thickness.

Spatiotemporal Information Processing Emulated by Multiterminal Neuro-Transistor Networks

All external sensory stimuli produce a spatiotemporal pattern of action potentials, which is transmitted to the biological neural system to be processed. The relative timing of synaptic spikes from different presynaptic neurons represents the features of the stimuli. A fundamental prerequisite in cortical information processing is the discrimination of different spatiotemporal input sequences. Here, capacitively coupled multiterminal oxide-based neuro-transistors are proposed for spatiotemporal information processing, mimicking the dendritic discriminability of different spatiotemporal input sequences. The experimental results demonstrate that such multiterminal neuromorphic devices can act as spatiotemporal information processing compartments for fundamental cortical computation. Also, as an example of spatiotemporal information processing, sound location functionality of the human brain is also emulated by constructing a simple artificial neural network based on such oxide-based multiterminal neuro-transistors.

A Novel CNN-Based Framework for Classification of Signal Quality and Sleep Position from a Capacitive ECG Measurement

The further exploration of the capacitive ECG (cECG) is hindered by frequent fluctuations in signal quality from body movement and changes in sleep position. The processing framework must be fundamentally adapted to make full use of this signal. Therefore, we propose a new signal-processing framework that determines the signal quality for short signal segments (2 and 4 seconds) using a multi-class classification model (qua_model) based on a convolutional neural network (CNN). We built another independent deep CNN classifier (pos_model) to classify the sleep position. In the validation, 12 subjects were recruited for a 30-minute experiment, which required the subjects to lie on a bed in different sleeping positions. The short segments, classified as clear (C1 class) by the qua_model, were used to determine sleep positions with the pos_model. In 10-fold cross-validation, the qua_model for signals of 4-second length could recognize the signal of the C1 class at a 0.99 precision and a 0.99 recall; the pos_model could recognize the supine sleep position, the left, and right lateral sleep positions at a 0.99 averaged precision and a 0.99 averaged recall. Given the amount of data accumulated per night and the instability in the signal quality, this fully automatic processing framework is indispensable for a personal healthcare system. Therefore, this study could serve as an important step for cECG technique trying to explore the cECG for unconstrained heart monitoring.

Exploiting Self-Capacitances for Wireless Power Transfer

Conventional approaches for wireless power transfer rely on the mutual coupling (near-field or far-field) between the transmitter and receiver transducers. As a result, the power-transfer efficiency of these approaches scales non-linearly with the cross-sectional area of the transducers and with the relative distance and respective alignment between the transducers. In this paper, we show that when the operational power-budget requirements are in the order of microwatts, a self-capacitance (SC)-based power delivery has significant advantages in terms of the power transfer-efficiency, receiver form-factor, and system scalability when compared to other modes of wireless power transfer (WPT) methods. We present a simple and a tractable equivalent circuit model that can be used to study the effect of different parameters on the SC-based WPT. In this paper, we have experimentally verified the validity of the circuit using a cadaver mouse model. We also demonstrate the feasibility of a hybrid telemetry system where the microwatts of power, which can be harvested from SC-based WPT approach, is used for back-scattering a radio-frequency (RF) signal and is used for remote sensing of in vivo physiological parameters such as temperature. The functionality of the hybrid system has also been verified using a cadaver mouse model housed in a cage that was retrofitted with 915 MHz RF back-scattering antennas. We believe that the proposed remote power-delivery and hybrid telemetry approach would be useful in remote activation of wearable devices and in the design of energy-efficient animal cages used for long-term monitoring applications.

Low-Cost and Lightweight 3D-Printed Split-Ring Resonator for Chemical Sensing Applications

In this paper, a microwave cavity resonator is presented for chemical sensing applications. The proposed resonator is comprised of a three dimensional (3D) split-ring resonator (SRR) residing in an external cavity and capacitively coupled by a pair of coaxial probes. 3D-printing technology with polylactic acid (PLA) filament is used to build the 3D SRR and cavity. Then, the surfaces of the SRR and the inside walls of cavity are silver-coated. The novelty of our proposed structure is its light weight and inexpensive design, owing to the utilization of low density and low-cost PLA. A Teflon tube is passed through the split-gap of the SRR so that it is parallel to the applied electric field. With an empty tube, the resonance frequency of the structure is measured at 2.56 GHz with an insertion loss of 13.6 dB and quality factor (Q) of 75. A frequency shift of 205 MHz with respect to the empty channel was measured when deionized water (DIW) was injected into the tube. Using volume occupied by the structure, the weight of the proposed microwave resonator is estimated as 22.8 g which is significantly lighter than any metallic structure of comparable size.

[Design and implementation of hand-held electrocardiogram monitor]

A hand-held electrocardiogram (ECG) monitor with capacitive coupling is designed in this study that can rapidly detect ECG signals through clothing. This new device improves many deficiencies of the traditional ECG monitor, such as infection due to direct skin contacting, inconvenience, and time-consuming. In specificity, the hand-held ECG monitor consists of two parts, a sensor and an embedded terminal. ECG signals are initially detected by a sensing electrode placed on the chest through clothing, then treated by single ended differential amplification, filtering and master amplification, and later processed through A/D conversion and ECG signal transmission by CC2540 module. The waveform and heart rate are finally displayed on the screen based on digital filtering and data processing for the received ECG signal on the embedded terminal. Results confirm that the newly developed hand-held ECG monitor is capable of detecting real-time ECG signals through clothing with advantages of simple operation, portability and rapid detection.

An Energy Efficient Technique Using Electric Active Shielding for Capacitive Coupling Intra-Body Communication

Capacitive coupling intra-body communication (CC-IBC) has become one of the candidates for healthcare sensor networks due to its positive prevailing features of energy efficiency, transmission rate and security. Under the CC-IBC scheme, some of the electric field emitted from signal (SIG) electrode of the transmitter will couple directly to the ground (GND) electrode, acting equivalently as an internal impedance of the signal source and inducing considerable energy losses. However, none of the previous works have fully studied the problem. In this paper, the underlying theory of such energy loss is investigated and quantitatively evaluated using conventional parameters. Accordingly, a method of electric active shielding is proposed to reduce the displacement current across the SIG-GND electrodes, leading to less power loss. In addition, the variation of such loss in regard to frequency range and positions on human body was also considered. The theory was validated by finite element method simulation and experimental measurement. The prototype result shows that the receiving power has been improved by approximate 5.5 dBm while the total power consumption is maximally 9 mW less using the proposed technique, providing an energy efficient option in physical layer for wearable and implantable healthcare sensor networks.

Improved sensing characteristics of dual-gate transistor sensor using silicon nanowire arrays defined by nanoimprint lithography

This work describes the construction of a sensitive, stable, and label-free sensor based on a dual-gate field-effect transistor (DG FET), in which uniformly distributed and size-controlled silicon nanowire (SiNW) arrays by nanoimprint lithography act as conductor channels. Compared to previous DG FETs with a planar-type silicon channel layer, the constructed SiNW DG FETs exhibited superior electrical properties including a higher capacitive-coupling ratio of 18.0 and a lower off-state leakage current under high-temperature stress. In addition, while the conventional planar single-gate (SG) FET- and planar DG FET-based pH sensors showed the sensitivities of 56.7 mV/pH and 439.3 mV/pH, respectively, the SiNW DG FET-based pH sensors showed not only a higher sensitivity of 984.1 mV/pH, but also a lower drift rate of 0.8% for pH-sensitivity. This demonstrates that the SiNW DG FETs simultaneously achieve high sensitivity and stability, with significant potential for future biosensing applications.

The Substrate is a pH-Controlled Second Gate of Electrolyte-Gated Organic Field-Effect Transistor

Electrolyte-gated organic field-effect transistors (EGOFETs), based on ultrathin pentacene films on quartz, were operated with electrolyte solutions whose pH was systematically changed. Transistor parameters exhibit nonmonotonic variation versus pH, which cannot be accounted for by capacitive coupling through the Debye-Helmholtz layer. The data were fitted with an analytical model of the accumulated charge in the EGOFET, where Langmuir adsorption was introduced to describe the pH-dependent charge buildup at the quartz surface. The model provides an excellent fit to the threshold voltage and transfer characteristics as a function of the pH, which demonstrates that quartz acts as a second gate controlled by pH and is mostly effective from neutral to alkaline pH. The effective capacitance of the device is always greater than the capacitance of the electrolyte, thus highlighting the role of the substrate as an important active element for amplification of the transistor response.

Graphene FETs with Low-Resistance Hybrid Contacts for Improved High Frequency Performance

This work proposes a novel geometry field effect transistor with graphene as a channel-graphene field-effect transistor (GFET), having a hybrid contact that consists of an ohmic source/drain and its extended part towards the gate, which is capacitively coupled to the channel. The ohmic contacts are used for direct current (DC) biasing, whereas their capacitive extension reduces access region length and provides the radio frequency (RF) signal a low impedance path. Minimization of the access region length, along with the paralleling of ohmic contact's resistance and resistive part of capacitively coupled contact's impedance, lower the overall source/drain resistance, which results in an increase in current gain cut-off frequency, f_T. The DC and high-frequency characteristics of the two chosen conventional baseline GFETs, and their modified versions with proposed hybrid contacts, have been extensively studied, compared, and analyzed using numerical and analytical techniques.

Electrical stimulation to enhance spinal fusion: a systematic review

Study Design Systematic review. Clinical Questions Compared with no stimulation, does electrical stimulation promote bone fusion after lumbar spinal fusion procedures? Does the effect differ based on the type of electrical stimulation used? Methods Electronic databases and reference lists of key articles were searched up to October 15, 2013, to identify randomized controlled trials (RCTs) comparing the effect of electrical stimulation to no electrical stimulation on fusion rates after lumbar spinal fusion for the treatment of degenerative disease. Two independent reviewers assessed the strength of evidence using the Grades of Recommendation Assessment, Development and Evaluation (GRADE) criteria. Results Six RCTs met the inclusion criteria. The following types of electrical stimulation were investigated: direct current (three studies), pulsed electromagnetic field (three studies), and capacitive coupling (one study). The control groups consisted of no stimulation (two studies) or placebo (four studies). Marked heterogeneity in study populations, characteristics, and design prevented a meta-analysis. Regardless of the type of electrical stimulation used, cumulative incidences of fusion varied widely across the RCTs, ranging from 35.4 to 90.6% in the intervention groups and from 33.3 to 81.9% in the control groups across 9 to 24 months of follow-up. Similarly, when stratified by the type of electrical stimulation used, fusion outcomes from individual studies varied, leading to inconsistent and conflicting results. Conclusion Given the inconsistency in study results, possibly due to heterogeneity in study populations/characteristics and quality, we are unable to conclude that electrical stimulation results in better fusion outcomes compared with no stimulation. The overall strength of evidence for the conclusions is low.

Up-regulation of expression of selected genes in human bone cells with specific capacitively coupled electric fields

The objective of the described experiments was to determine the electrical parameters that lead to optimal expression of a number of bone-related genes in cultured human bone cells exposed to a capacitively coupled electric field. Human calvarial osteoblasts were grown in modified plastic Cooper dishes in which the cells could be exposed to various capacitively coupled electric fields. The optimal duration of stimulation and optimal duration of response to the electrical field, and the optimal amplitude, frequency and duty cycle were all determined for each of the genes analyzed. Results indicated that a capacitively coupled electric field of 60 kHz, 20 mV/cm, 50% duty cycle for 2 h duration per day significantly up-regulated mRNA expression of a number of transforming growth factor (TGF)-β family genes (bone morphogenetic proteins (BMP)-2 and -4, TGF-β1, - β2 and -β3) as well as fibroblast growth factor (FGF)-2, osteocalcin (BGP) and alkaline phosphatase (ALP). Protein levels of BMP-2 and -4, and TGF-β1 and - β2 were also elevated. The clinical relevance of these findings in the context of a noninvasive treatment modality for delayed union and nonunion fracture healing is discussed.

A comb-drive actuator driven by capacitively-coupled-power

This paper presents a new actuation mechanism to drive comb-drive actuators. An asymmetric configuration of the finger overlap was used to generate capacitive coupling for the actuation mechanism. When the driving voltages were applied on the stators, a voltage would be induced at the rotor due to the capacitive coupling. Then, an electrostatic force would be exerted onto the rotor due to the voltage differences between the stators and the rotor. The actuator's static displacement and resonant frequency were theoretically analyzed. To verify the design, a comb-drive actuator with different initial finger overlaps, i.e., 159.3 μm and 48.9 μm on each side, was fabricated and tested. The results show that the actuator worked well using the proposed actuation mechanism. A static displacement of 41.7 μm and a resonant frequency of 577 Hz were achieved. Using the actuation mechanism, no electrical connection is required between the rotor and the outside power supply. This makes some comb-drive actuators containing heterogeneous structures easy to design and actuate.

The science of electrical stimulation therapy for fracture healing

This article is a brief review of the basic science research conducted in the field of electrical stimulation for fracture healing. Direct electrical current, capacitive coupling, and inductive coupling have been studied as potential techniques to enhance fracture healing through the proliferation and differentiation of osteogenic cells. These techniques are particularly appealing as they offer a potential minimally invasive solution to the difficult clinical problem of delayed fracture healing and nonunion. Basic science studies have shown conclusively that electrical stimulation techniques lead to bone cell proliferation and have attempted to elucidate the intracellular processes by which this bone cell proliferation occurs. Further basic science and clinical research is required to enhance the effectiveness of this therapy for the treatment of fracture nonunions.