Impedance characterization of microarray recording electrodes in vitro

The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. Humoral and cellular components of the brain foreign body response were evaluated to determine whether their presence on the electrode surface results in increased electrical impedance. Iridium oxide microelectrode recording arrays were electrically characterized in saline, culture media with 10% fetal bovine serum, and coated with various CNS cell types isolated from rat brain. Electrochemical impedance spectroscopy and cyclic voltammetry were performed using a three-electrode system. Potential cycling caused an immediate decrease in electrical impedance, which increased with time toward precycling values, with the effect of cycling remaining significant for several days. The addition of serum caused a significant increase in impedance of up to 28% relative to the saline control. Microelectrodes coated with various cell types known to participate in the foreign body response caused a 20%-80% increase in impedance immediately after contact that remained constant or gradually increased for several weeks. Our findings suggest that the attachment of molecular and cellular species following microelectrode implantation into brain tissue likely contribute to increases in impedance, but do not appear sufficient to hinder recording performance.     

Interconnection of multichannel polyimide electrodes using anisotropic conductive films (ACFs) for biomedical applications

In this paper, we propose a method for interconnecting soft polyimide (PI) electrodes using anisotropic conductive films (ACFs). Reliable and automated bonding was achieved through development of a desktop thermocompressive bonding device that could simultaneously deliver appropriate temperatures and pressures to the interconnection area. The bonding conditions were optimized by changing the bonding temperature and bonding pressure. The electrical properties were characterized by measuring the contact resistance of the ACF bonding area, yielding a measure that was used to optimize the applied pressure and temperature. The optimal conditions consisted of applying a pressure of 4 kg f/cm(2) and a temperature of 180 °C for 20 s. Although ACF base bonding is widely used in industry (e.g., liquid crystal display manufacturing), this study constitutes the first trial of a biomedical application. We performed a preliminary in vivo biocompatibility investigation of ACF bonded area. Using the optimized temperature and pressure conditions, we interconnected a 40-channel PI multielectrode device for measuring electroencephalography (EEG) signals from the skulls of mice. The electrical properties of electrode were characterized by measuring the impedance. Finally, EEG signals were measured from the mice skulls using the fabricated devices to investigate suitability for application to biomedical devices.     

A novel surface registration algorithm with biomedical modeling applications.

In this paper, we propose a novel surface matching algorithm for arbitrarily shaped but simply connected 3-D objects. The spherical harmonic (SPHARM) method is used to describe these 3-D objects, and a novel surface registration approach is presented. The proposed technique is applied to various applications of medical image analysis. The results are compared with those using the traditional method, in which the first-order ellipsoid is used for establishing surface correspondence and aligning objects. In these applications, our surface alignment method is demonstrated to be more accurate and flexible than the traditional approach. This is due in large part to the fact that a new surface parameterization is generated by a shortcut that employs a useful rotational property of spherical harmonic basis functions for a fast implementation. In order to achieve a suitable computational speed for practical applications, we propose a fast alignment algorithm that improves computational complexity of the new surface registration method from O(n3) to O(n2).     

Design,characterization and control of SMA springs-based multi-modal tactile display device for biomedical applications

Tactile display is recently attracting much attention in the field of human–computer interaction. There is a strong need for such a device especially for applications in which the touch feeling is lost, such as surgeons who are willing to feel the tissue hardness during laparoscopic surgeries. In this paper, a novel multi-modal tactile display device which can display both surface shape and stiffness of an object is introduced. The conceptual design is built upon using two springs, made of Shape Memory Alloys (SMA), for displaying shape and stiffness. The design parameters of this device are selected based on the spatial resolution of human finger and the elasticity range of the soft tissue. The display device is simulated using Finite Element Method (FEM) to study the effect of design parameters on the resulting stiffness. Simulation results show that the device can display stiffness of an object independent of its shape display. The experimental setup is built and used for the characterization and control of the SMA springs. Experimental results show that the device can display a stiffness range of (35–110) N/m and elongation up to 5 mm.     

Multifrequency microwave thermograph for biomedical applications

This paper presents problems related to thermal radiation of human bodies in microwave range with respect to diagnosis of breast carcinoma. A mathematical model of thermal radiation transfer through tissues is introduced and methods of measurement of temperature, depth and size of a heat source, by means of multifrequency microwave thermograph are described. Theoretical considerations are supplemented by presentation of experimental results.     

DC modeling and characterization of AlGaAs/GaAs heterojunctionbipolar transistors for high-temperature applications

The large signal dc characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBT) at high temperatures (27°-300°C) are reported. A high-temperature SPICE model is developed which includes the recombination-generation current components and avalanche multiplication which become extremely important at high temperatures. The effect of avalanche breakdown is also included to model the current due to thermal generation of electron/hole pairs causing breakdown at high temperatures. A parameter extraction program is developed and used to extract the model parameters of HBT's at different temperatures. Fitting functions for the model parameters as a function of temperature are developed. These parameters are then used in the SPICE Ebers-Moll model for the dc characterization of the HBT at any temperature between (27°-300°C)     

Nanopatterned UV curable hydrogels for biomedical applications

With an increasing use of emerging patterning technologies such as UV-NIL in biotechnological applications there is at the same time a raising demand for new material for such applications. Here we present a PEG based precursor mixed with a photoinitiator to make it UV sensitive as a new material aimed at biotechnological applications. Using HSQ patterned quartz stamps we observed excellent pattern replication indicating good flow properties of the resist. We were able to obtain imprints with <20 nm residual layer. The PEG based resist has hydrogel properties and it swelling in water was observed by AFM.     

Low temperature nanointegration for emerging biomedical applications

In this paper, surface activated nanointegration of computational, electrical, optical, and mechanical structures for intelligent telemetry, communication, and sensing systems is described. The design approach and integration of top-down systems and bottom-up devices is considered with the need for biologically compatible bonding. For the simplified interface between bottom-up and top-down design a bus-bar unit architecture is presented. Emerging biomedical applications using intelligent sensors for remote patient monitoring and systems for rehabilitation comparing surface vs. implanted sensors are considered. Requirements for nanointegration of biomedical systems are suggested. Diverse combinations of rigid and flexible substrates of copper, gold, gallium arsenide, gallium phosphide and liquid crystal polymer were bonded by using two different nanobonding techniques. In these techniques, the surface cleaning with/without simultaneous deposition of nano-adhesion layers and contact in ultra-high vacuum/high vacuum were accomplished. These nanobonding technologies provide void-free, strong, and nanometer scale covalent bonding at room temperature or at low temperatures (～240 °C), and do not require chemicals, adhesives, or high external pressure. A considerable electrical current conduction and low loss of the nanobonded laminate was observed at high frequency. This investigation reveals that a biocompatible, high performance, and miniaturized systems may be realized for intelligent, implantable biomedical sensors because of the strong bond, low toxicity and favorable electrical properties in surface activated nanobonding.     

Numerical characterization and modeling of subject-specific ultrawideband body-centric radio channels and systems for healthcare applications

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.     

超级电容器的阻抗特性及其复空间建模

以阻抗平面图分析法研究超级电容器的阻抗特性,揭示了该特性的典型区域:45°斜率的Warburg阻抗线和接近于垂直斜率的低频阻抗线,以此建立了四参数(Rs,R,C,p)表示的超级电容器复空间模型。试验结果表明,该模型预测的充电过程端电压变化历程与试验数据有着良好的一致性和适应性。     

CNFET-based voltage rectifier circuit for biomedical implantable applications

Carbon nanotube field effect transistor(CNFET) shows lower threshold voltage and smaller leakage current in comparison to its CMOS counterpart. In this paper, two kinds of CNFET-based rectifiers, full-wave rectifiers and voltage doubler rectifiers are presented for biomedical implantable applications. Based on the standard 32 nm CNFET model, the electrical performance of CNFET rectifiers is analyzed and compared. Simulation results show the voltage conversion efficiency(VCE) and power conversion efficiency(PCE) achieve 70.82% and 72.49% for CNFET full-wave rectifiers and 56.60% and 61.17% for CNFET voltage double rectifiers at typical 1.0 V input voltage excitation, which are higher than that of CMOS design. Moreover, considering the controllable property of CNFET threshold voltage, the effect of various design parameters on the electrical performance is investigated. It is observed that the VCE and PCE of CNFET rectifier increase with increasing CNT diameter and number of tubes. The proposed results would provide some guidelines for design and optimization of CNFET-based rectifier circuits.     

Applications of SPICE for modeling miniaturized biomedical sensor systems

This paper proposes a model for a miniaturized signal conditioning system for biopotential and ion-selective electrode arrays. The system consists of three main components: sensors, interconnections, and signal conditioning chip. The model for this system is based on SPICE. Transmission-line based equivalent circuits are used to represent the sensors, lumped resistance-capacitance circuits describe the interconnections, and a model for the signal conditioning chip is extracted from its layout. A system for measurements of biopotentials and ionic activities can be miniaturized and optimized for cardiovascular applications based on the development of an integrated SPICE system model of its electrochemical, interconnection, and electronic components.     

Low power analog comb filter for biomedical applications

An analog topology is proposed to implement a comb filter for removal of power-line interference from various low-amplitude biomedical signals. In this proposed methodology, an n-number of all-pass filters (APFs) and an adder circuit are used to suppress n-number of frequencies. All the APFs as well as the adder circuit are designed using a current conveyor to utilize the various properties of the current-mode circuits. The active and passive components used to design the comb filter include second-generation current conveyor (CCII±), resistor, and capacitor. The circuit is designed for n?=?4 to remove the power-line frequency of 50 Hz, and its three odd harmonics such as 150 Hz, 250 Hz, and 350 Hz. A PSPICE simulation is done to verify the performance of the proposed circuit. In simulation, all CCII±?are designed using macro model of commercially-available current feedback operational amplifier integrated circuit (IC) AD844 as well as dynamic threshold voltage metal oxide semiconductor technology. The proposed circuit is also implemented also using commercially available IC AD844 on breadboard for n?=?3. The output result on digital storage oscilloscope confirm the effectiveness of the proposed comb filter circuit in removing the power line interference i.e. the power-line frequency and its odd harmonics.     

Towards VCSEL-based integrated optical traps for biomedical applications

A new concept to miniaturise optical trapping and manipulation systems is presented. Integrated optical traps based on top-emitting vertical-cavity surface-emitting lasers (VCSELs) with near-infrared emission in combination with photoresist microlenses were fabricated, characterised and demonstrated. Elevation and trapping of 10 /spl mu/m-sized polystyrene particles in water is achieved at optical output powers as small as 9 mW.     

A telemetric pressure sensor system for biomedical applications

A new implantable pressure sensor for long-term monitoring of intracranial pressure is presented. The sensor is powered by telemetry and can be interrogated wirelessly. A capacitive pressure transducer, whose capacitance is converted to a frequency-encoded signal by an application-specific integrated circuit (ASIC), senses the absolute pressure. The pressure-encoded signal, the ASIC input voltage, and onboard calibration parameters are transmitted to an external reading unit. The proposed novel packaging solution is designed for long-term stability and reliability of the sensor. The accuracy of sensor at body temperature is better than 2 mbar across a pressure range of 600-1200 mbar. The sensor is 13 mm in diameter and 4.5 mm in height.     

ANN-based design of hybrid fractal antenna for biomedical applications

In this research paper, the development of an artificial neural network (ANN) model for the designing of a compact dual-band hybrid fractal antenna (CDHFA) that covers Wireless Medical Telemetry Service and industrial, scientific and medical (ISM) bands are described. The projected CDHFA is designed by using 1.6mm thick, FR4 substrate whose permittivity is 4.4 and obtained by the combination of different fractal geometries. The dimensions of the projected CDHFA are interlinked with each other. A set of 80 CDHFAs with different dimensions is designed to obtain a data dictionary for the implementation of ANN. From the experimental results, it is depicted that the resonant frequencies are 1.4290 and 2.4380 GHz with S(1,1) values ?12.4 and ?15.72 dB, respectively. A comparison between feed forward back propagation network, generalised regression neural network and desired outputs in terms of average absolute error is also done. The simulation, experimental and ANN results are well matched that indicates the effectiveness and accuracy of the developed ANN model for biomedical applications.     

Development of a miniature pressure transducer for biomedical applications

Miniature absolute pressure transducers are needed for biomedical implant applications. The design parameters are: 1) sensitivity, 2) size, 3) hysteresis, 4) temperature coefficient, 5) long-term stability, and 6) biocompatibility. The present devices cannot meet all the requirements, particularly in size, long-term stability, and biocompatibility. The results of a development program on implantable and indwelling pressure transducers are reported with emphasis on the study of long-term stability and reproducibility associated with reduced size. The sensor is a resistive bridge diffused on a     

Piezo-actuators modeling for smart applications

This paper deals with piezoelectric actuators modeling. The objective is to contribute in piezo-models library construction. Compared to existing models in commercial packages, the proposal model integrate nonlinear effects, especially hysteresis, while not requiring high computing efforts. This will help in the generalization of piezo-actuator usage for smart applications. Our methodology and approaches are clearly justified in the paper.     

Compact supercontinuum sources and their biomedical applications

Recent developments of compact white-light supercontinuum laser sources are reviewed. Basically these sources make use of a sub-nanosecond microchip laser and a photonic crystal fiber, leading to spectral broadening in the ultraviolet, visible and infrared ranges. The applicability of such supercontinuum sources to the biomedical field is introduced, with the demonstration of promising results in flow cytometry, CARS microscopy and optical coherence tomography. Their attractive benefits in terms of size, robustness, stability and cost are highlighted.