Cleumar S. Moreira

Figures of merit and optimization of a VO 2 microbolometer with strong electrothermal feedback

The influence of electrothermal feedback and hysteresis on the operation conditions, noise, and performance of a VO2 transition-edge microbolometer has been evaluated. The material undergoes a first-order semiconductor-to-metal phase transition (SMT) within the temperature range 40<T<70 °C. Due to electrothermal feedback, all device parameters, including the required heat-sink temperature, output voltage and current response, response time, linear dynamic range, responsivity, noise, and detectivity, display complex and nonlinear variations with temperature, electrical biasing conditions, input radiation levels, and hysteresis width. In the constant-current mode, the device responsivity extends over a broad temperature range, but under constant-voltage operation it is sharply localized and restricted to the SMT center. Film quality, as represented by the transition and the hysteresis width and the flicker noise magnitude, crucially affects device performance. In the weak hysteretic case and at low 1/f noise levels, the device detectivity improves substantially in both operation modes. The spectral range of the device is largely determined by the optical absorptivity of the VO2 film. For operation within the SMT, it extends well into the far IR wavelength region of the atmospheric window, but is substantially smaller for operation in the semiconducting region.

A Surface Plasmon Resonance Biochip That Operates Both in the Angular and Wavelength Interrogation Modes

This paper presents a surface plasmon resonance system based on a polymer prism chip. The device allows operation in both the angular and wavelength interrogation modes. The biochip design is discussed emphasizing the effect of the ambient temperature over the optical behavior. Birefringence effect, biochip polishing, and responsivity are also reported. The basic mathematical formulation for both operating modes is discussed, and morphological parameters are considered in the data analysis. Experimental sensorgrams obtained at both interrogation modes with the same polymer prism chip are presented and compared. The experimental sensorgrams obtained with assays providing reversible (phosphate buffered saline and hypochlorite solutions) and irreversible (neutravindin solution) bindings demonstrate the feasibility of the proposed design.

An electro-thermal approach to dielectric breakdown in solids: application to crystalline polymer insulators

A dielectric breakdown model, linked to appearance of a singularity, has been developed and applied to a high purity alkane type (n-C36H74) insulator. The polymer material, which exhibits low defect / trap density, represents the single-crystalline iso-electronic analog to polyethylene. At high fields, and based on experimental findings, carrier transport is mediated by delocalized states in the conduction and valence band, respectively. Field induced impact ionization and carrier multiplication are triggered by hot carrier photoinjection above a critical field magnitude of 0.8 MV for holes and 1.26 MV for electrons, in accord with the band model. Associated critical sample thickness values have been estimated. The related electrical properties have been explored on the basis of the electrothermal heat balance equation. The non-linear differential equation has been solved numerically, with appropriate thermo-physical materials and carrier transport parameters, considering the dielectric breakdown phenomenon as a singularity. It leads to thermal run-away as a consequence of strong positive electro-thermal feedback, under conditions of initial transient behavior. Required thermo-physical parameters are attributed to and explain filamentary charge transport. The temporal evolution of temperature and current in the conducting filament during the breakdown event exhibits a time scale up to the microsecond range. The dynamic properties of the phenomenon are strongly affected by heat transfer from the conducting section into the surrounding nonconducting material, as well as the temporal characteristics of the initial trigger conditions.

A surface plasmon resonance biosensor for angular and wavelength operation

This paper presents a surface plasmon resonance (SPR) sensor system based on a polymer prism chip. The device allows operation in both, the angular (AIM) and wavelength (WIM) interrogation modes. The basic mathematical formulation for both operating modes is discussed. Experimental sensogrammes obtained for both modes with the same polymer prism chip, are presented and compared. The results illustrate the feasibility of the proposed solution.

Linear peristaltic pump driven by three magnetic actuators: Simulation and experimental results

A bi-directional linear peristaltic pump is presented that avoids use of a rotating step motor and rollers. Fluid displacement, flow and pump function, respectively, are achieved by means of three electro-magnetic actuators. They are electronically controlled and designed to periodically squeeze an elastic tube that contains the liquid. The device reveals a very simple construction, is maintenance free, has very low power consumption, thus accounting for very low manufacture and operation costs. Upon reducing the size of the actuators, it can be easily integrated with micro fluidic arrangements. Flow and pressure pulsation can be reduced by increasing the number of actuators. A finite element-based numerical model has been developed, using the fluid structure interaction (FSI) model. The flow dynamics inside the tube has been treated, using the coupling between the Navier-Stokes and the elastic displacement equations of the elastic tube. The appropriate and optimum timely driving sequence of the actuators, as well as the response characteristics of the physical system, were also numerically evaluated. Experimental results fully agree with the numerical simulation results. The dynamic range of the flow rate was determined as ranging from 7 00μ/min to 79ml/min, while the back pressure varies between 400 mmHg to 14 mmHg.

Polymer-based surface plasmon resonance biochip: construction and experimental aspects

Abstract Introduction: Surface plasmon resonance biosensors are high sensitive analytical instruments that normally employ glass materials at the optical substrate layer. However, the use of polymer-based substrates is increasing in the last years due to favorable features, like: disposability, ease to construction and low-cost design. Review Recently, a polymer-based SPR biochip was proposed by using monochromatic and polychromatic input sources. Its construction and experimental considerations are detailed here. Experimental considerations and results, aspects from performance characteristics (resonance parameters, sensitivity and full width at half maximum – FWHM – calculations) are presented for hydrophilic and hydrophobic solutions. It is included also a brief description of the state of the art of polymer-based SPR biosensors.

Design and theoretical analysis of a bidirectional calorimetric flow sensor

A calorimetric flow meter have been proposed here, where a finite element-based software is used to model and design it. Some parameters have been investigated and the results are also shown. Finally, an experimental setup has been presented to check the theoretical design.

Leishmania spp. Detection Using a Surface Plasmon Resonance Biosensor

The detection of Leishmania spp. through a disposable surface plasmon resonance (SPR) biochip, using mono- and polychromatic sources, is presented here. A highly specific and sensitive-constrained synthetic peptide (LC2) derived from a mimotope of Leishmania chagasi antigen was immobilized on the sensing region using a simple protocol. ELISA- and PCR-confirmed negative and positive sera of Leishmania chagasi infected patients were used. Detection of positive IgG showed a fast response with good sensitivity and specificity for the proposed method.

Surface Plasmon Resonance Sensing Characteristics of Thin Aluminum Films in Aqueous Solution

Surface plasmon resonance (SPR) sensors, utilizing thin aluminum (Al) films, are reported. The sensor designs are based in the novel optical trapezoidal prism chip, made from either polymer or BK7 glass. Optimum Al-film thickness was determined to 20 ± 5 nm, and deposited by thermal e-beam evaporation and rf-magnetron sputtering. Upon contact to air, and in de-ionized aqueous solution, a self-limited surface oxide layer forms. Determined by ellipsometric recordings, its thickness grows from 4.6 ± 0.6 nm in air to 12.3 ± 2 nm in the wet interface. A single SP-resonance applies to the dry interface. Unusual spectral broadening, due to the presence of multiple resonances, is predicted and experimentally verified at the wet interface. The Al-oxide adlayer is beneficial in the angular interrogation, where the instrumental response approaches the one exhibited by the noble metals. Under wavelength interrogation conditions, the presence of the Al-oxide adlayer causes severe degradation of the sensor response. Both, angular and wavelength interrogation at the metal-aqueous solution interface were exploited experimentally and compared with theoretical predictions regarding the sensing features of gold (Au), copper (Cu), and silver (Ag) metal films as well. Limitations, cost aspects and alternative routes to overcome degradation and the loss of SPR-activity in the presence of ionic phosphate buffered saline aqueous solutions are outlined for Al-films.

Design methodology of a self-priming PMMA valveless piezoelectric micro-pump

A design methodology for a self-priming PMMA valveless piezoelectric micro-pump has been proposed. A finite element-based software has been used to investigate the feasible device configurations. Both actuator and diffuser parameters have been studied. The experimental tests have shown that the proposed design approach yielded a low-cost and highly efficiency micro-pump.