A plasmonic 'ac Wheatstone bridge' circuit for high-sensitivity phase measurement and single-molecule detection

In this paper, a plasmonic “ac Wheatstone bridge” circuit is proposed and theoretically modeled for the first time. The bridge circuit consists of three metallic nanoparticles, shaped as rectangular prisms, with two nanoparticles acting as parallel arms of a resonant circuit and the third bridging nanoparticle acting as an optical antenna providing an output signal. Polarized light excites localized surface plasmon resonances in the two arms of the circuit, which generate an optical signal dependent on the phase-sensitive excitations of surface plasmons in the antenna. The circuit is analyzed using a plasmonic coupling theory and numerical simulations. The analyses show that the plasmonic circuit is sensitive to phase shifts between the arms of the bridge and has the potential to detect the presence of single molecules.

Modelo de ashkin-teller de três cores na rede ponte de wheatstone

In this work we study the phase transitions of the ferromagnetic three-color Ashkin-Teller Model in the hierarquical lattice generated by the Wheatstone bridge using real space renormalization group approach. With such technique we obtain the phase diagram and its critical points with respective critical exponents v. This model presents four phases: ferromagnetic, paramagnetic and two intermediates. Nine critical points were found, three of which are of Ising model type, three are of four states Potts model type, one is of eight states Potts model type and the last two which do not correspond to any Potts model with integer number of states. iv

Field measurement of wheel-rail impact force at insulated rail joint

When wheels pass over insulated rail joints (IRJs) a vertical impact force is generated. The ability to measure the impact force is valuable as the force signature helps understand the behaviour of the IRJs, in particular their potential for failure. The impact forces are thought to be one of the main factors that cause damage to the IRJ and track components. Study of the deterioration mechanism helps finding new methods to improve the service life of IRJs in track. In this research, the strain-gage-based wheel load detector, for the first time, is employed to measure the wheel–rail contact-impact force at an IRJ in a heavy haul rail line. In this technique, the strain gages are installed within the IRJ assembly without disturbing the structural integrity of IRJ and arranged in a full wheatstone bridge to form a wheel load detector. The instrumented IRJ is first tested and calibrated in the lab and then installed in the field. For comparison purposes, a reference rail section is also instrumented with the same strain gage pattern as the IRJ. In this paper the measurement technique, the process of instrumentation, and tests as well as some typical data obtained from the field and the inferences are presented.

SOI membrane-based pressure sensor in stress sensitive differential amplifier configuration

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar). © 2012 IEEE.

A thermally stable tension meter for atmospheric soundings using kites

Kites offer considerable potential as wind speed sensors—a role distinct from their traditional use as instrument-carrying platforms. In the sensor role, wind speed is measured by kite-line tension. A kite tether line tension meter is described here, using strain gauges mounted on an aluminum ring in a Wheatstone bridge electronic circuit. It exhibits a linear response to tension 19.5 mV N−1 with good thermal stability mean drift of −0.18 N °C−1 over 5–45 °C temperature range and a rapid time response 0.2 s or better. Field comparisons of tether line tension for a Rokkaku kite with a fixed tower sonic anemometer show an approximately linear tension-wind speed relationship over the range 1–6 ms−1. © 2010 American Institute of Physics. doi:10.1063/1.3465560

Fases e criticalidade no modelo ashkin - teller de três cores

The usual Ashkin-Teller (AT) model is obtained as a superposition of two Ising models coupled through a four-spin interaction term. In two dimension the AT model displays a line of fixed points along which the exponents vary continuously. On this line the model becomes soluble via a mapping onto the Baxter model. Such richness of multicritical behavior led Grest and Widom to introduce the N-color Ashkin-Teller model (N-AT). Those authors made an extensive analysis of the model thus introduced both in the isotropic as well as in the anisotropic cases by several analytical and computational methods. In the present work we define a more general version of the 3-color Ashkin-Teller model by introducing a 6-spin interaction term. We investigate the corresponding symmetry structure presented by our model in conjunction with an analysis of possible phase diagrams obtained by real space renormalization group techniques. The phase diagram are obtained at finite temperature in the region where the ferromagnetic behavior is predominant. Through the use of the transmissivities concepts we obtain the recursion relations in some periodical as well as aperiodic hierarchical lattices. In a first analysis we initially consider the two-color Ashkin-Teller model in order to obtain some results with could be used as a guide to our main purpose. In the anisotropic case the model was previously studied on the Wheatstone bridge by Claudionor Bezerra in his Master Degree dissertation. By using more appropriated computational resources we obtained isomorphic critical surfaces described in Bezerra's work but not properly identified. Besides, we also analyzed the isotropic version in an aperiodic hierarchical lattice, and we showed how the geometric fluctuations are affected by such aperiodicity and its consequences in the corresponding critical behavior. Those analysis were carried out by the use of appropriated definitions of transmissivities. Finally, we considered the modified 3-AT model with a 6-spin couplings. With the inclusion of such term the model becomes more attractive from the symmetry point of view. For some hierarchical lattices we derived general recursion relations in the anisotropic version of the model (3-AAT), from which case we can obtain the corresponding equations for the isotropic version (3-IAT). The 3-IAT was studied extensively in the whole region where the ferromagnetic couplings are dominant. The fixed points and the respective critical exponents were determined. By analyzing the attraction basins of such fixed points we were able to find the three-parameter phase diagram (temperature £ 4-spin coupling £ 6-spin coupling). We could identify fixed points corresponding to the universality class of Ising and 4- and 8-state Potts model. We also obtained a fixed point which seems to be a sort of reminiscence of a 6-state Potts fixed point as well as a possible indication of the existence of a Baxter line. Some unstable fixed points which do not belong to any aforementioned q-state Potts universality class was also found

A load cell for grain-propelled ballistic rocket thrust measurement

A 1000-kgf resistive strain-gauge load cell has been developed for quality testing of rocket propellant grain. A 7075-T6 aluminum alloy has been used for the elastic column, in which 8 uniaxial, 120-Ω strain gauges have been bonded and connected to form a full Wheatstone bridge to detect the strain. The chosen geometry makes the transducer insensitive to moments and, also, to the temperature. Experimental tests using a universal testing machine to imposed compression force to the load cell have demonstrated that its behavior is linear, with sensitivity of 2.90 μV/kgf ± 0.34%, and negligible hysteresis. The designed force transducer response to a dynamic test has been comparable to that of a commercial load cell. © 2005 IEEE.

Development of a prototype for measuring plantar forces

Studies on the distribution of plantar pressure between the sole of the foot and the ground were developed before the 19th century. Currently, the most often employed plantar pressure measurement systems are Pedar® and FScan®, which have restrictions such as operational difficulty and high cost. In the present study, a device was constructed from two pressure plates capable of measuring plantar forces in discreet areas of the feet at a low cost, using strain-gages attached to sixteen strategic points of the mechanical elements. Sixteen prismatic beams were soldered to each frame, for which the free extremity of each beam represented a specific point of the foot. Two strain gauges were attached to each beam - one near the upper fixed extremity and the other near the lower fixed extremity. Using a Wheatstone bridge electric circuit, the gauges were used to measure the force acting on the extremity of the beam. Precision and accuracy of the prototype was about 10%. In some measurements, accuracy was 2%. The low precision and accuracy were mainly due to the restrictions of the available equipment, which only permitted four measurements at a time. Thus, it was necessary for participants to stand on the plates four separate times, which signified possible changes in the position of the feet on the pressure plates. Despite some limitations, the aim was achieved. The prototype has been used in some studies and represents a contribution to biomechanics, demonstrating the viability of using strain gauges.

Mechanical behavior of isolated intervertebral disc

The study on several components of intervertebral joints is essential to understand the spine's degenerative mechanisms and to assess the best method for their treatment. For such study it is necessary to know the mechanical properties of the isolated intervertebral disc (ID) mechanical properties and, it is necessary to evaluate its stresses and strains. In order to assess the ID displacements, a fine, U-shaped blade was developed, over which two extensometers connected in a Wheatstone bridge were placed. The device was then tested on porcine spine ID, where compression loads were applied and the extremities displacements of the blade coupled to the intervertebral disc were measured. Stress/strain diagram, both on the compression and on the decompression phases, evidencing the non-linear nature of such relationship. With the experiment, it was possible to obtain approximate values of the longitudinal elasticity module (E) of the disc material and of the Poisson coefficient (n ). After several tests, E results are compatible with those obtained by others studies, with very simple and low-cost device. This experiments can be used for obtained others mechanical properties of isolated ID with precision and accuracy.

Desenvolvimento de um circuito eletrônico experimental de anemômetro de fio quente

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Projeto e implementação de um nodo sensor para aquisição de sinais de extensômetros em redes de sensores sem fio aplicado ao monitoramento de deformações em estruturas

Esta dissertação tem como objetivo principal propor um nodo (ou nó) sensor sem fio para ser utilizado em redes de sensores sem fio, em sistemas de aquisição de dados de extensômetros. O sistema de aquisição para os extensômetros é baseado na ponte de Wheatstone e de modo a permitir várias configurações de extensômetros. O processamento e a comunicação sem fio é realizada pelo ATmega128RFA1, composto por um microcontrolador e um transceiver Rádio-Frequência com o padrão Zigbee. O nodo foi projetado para garantir confiabilidade na aquisição de dados e ser totalmente controlado remotamente. Entre os parâmetros controláveis estão: o ganho do sinal e a taxa de amostragem. Além disso, o nodo possui recursos para efetuar o equilíbrio da ponte de Wheatstone automaticamente. A escolha de seus componentes, baseou-se em critérios relacionados ao consumo de energia do mesmo e ao custo. Foi concebida uma placa de circuito impresso (PCI) para o nodo, e sobre ela foram realizadas estimativas sobre o consumo de energia e valor agregado do protótipo, com o objetivo de analisar a sua viabilidade. Além do projeto do nodo sensor, o trabalho apresenta a proposta de integração do mesmo em uma rede de sensores sem fio (RSSF), incluindo a sugestão do hardware complementar e desenvolvimentos dos softwares. Para os testes do nodo sensor, foi construido experimentalmente um transdutor de força.

Estudo, desenvolvimento e concepção de uma célula de carga

In engineering projects, it’s fundamental to determine the active loads in components in order to guarantee acceptable values of safety and reliability according to project specifications. On the other hand, force measurement methods might be very complex and impracticable in some cases and, so that, load cells with eletric resistance strain gages can be applied as a simple and accurate option to measure the required load. The main purpose of this paper is to present the development of a load cell that measures uniaxial forces using electric resistance strain gages without being influenced by the location of the loading in a cantilever beam. For that, it was taken as basis a secondary purpose which is to present a general study of basic and wide concepts about transducers, load cells and extensometers primarily. Information such as: loading and measurements types, characteristics of the presented devices as well as factors that influence its functioning, the most common kinds of Wheatstone bridge links, the main points of a load cell project, cements used to fix extensometers and, finally, the project itself with the tests of the built transducer are presented. By the end of this paper, all the results are shown and analyzed, concluding about the designed load cell and the work itself

The Electrical Resistance of Metals and Alloys in Their Hard and Soft States

It is known that the electrical resistance of annealed metals is usually smaller than that of metals in their cold worked state. The curve showing the relation between electrical resistance and annealing temperature reaches a minimum; continued annealing at higher temperature produces an increase in the electrical resistance. In the case of alloys it has been noted that a second decrease occurs at higher annealing temperature. The following work corroborates the observance of previous investigations. The electrical resistance of cold worked copper, gold, nickel, and iron decreased with annealing and then increased, the minimum being around 300° C. or 400° C. Monel metal showed a minimum resistance followed by an increase which in turn was followed by a second decrease.

An Investigation of Age-Hardening in a Commercial Copper-Beryllium Alloy

This investigation is concerned with the age-hardening process as exemplified by the aging of a commercial Cu-Be alloy and, in particular, with this pro­cess as determined by X-ray methods. The amount of infor­mation available on age-hardening of commercial alloys is scanty and what information there is, is inaccurate.

Test sets I-49, I-49A, and I-49B and resistance bridges ZM-4A/U and ZM-4B/U.

"October 1957."