832 research outputs found
A model of transport nonuniversality in thick-film resistors
We propose a model of transport in thick-film resistors which naturally
explains the observed nonuniversal values of the conductance exponent t
extracted in the vicinity of the percolation transition. Essential ingredients
of the model are the segregated microstructure typical of thick-film resistors
and tunneling between the conducting grains. Nonuniversality sets in as
consequence of wide distribution of interparticle tunneling distances.Comment: 3 pages, 1 figur
Quasiuniversal connectedness percolation of polydisperse rod systems
The connectedness percolation threshold (eta_c) and critical coordination
number (Z_c) of systems of penetrable spherocylinders characterized by a length
polydispersity are studied by way of Monte Carlo simulations for several aspect
ratio distributions. We find that (i) \eta_c is a nearly universal function of
the weight-averaged aspect ratio, with an approximate inverse dependence that
extends to aspect ratios that are well below the slender rod limit and (ii)
that percolation of impenetrable spherocylinders displays a similar
quasiuniversal behavior. For systems with a sufficiently high degree of
polydispersity, we find that Z_c can become smaller than unity, in analogy with
observations reported for generalized and complex networks.Comment: 5 pages with 3 figures + 2 pages and 4 figures of supplemental
materia
Load sensing surgical instruments
Force and pressure sensing technology applied to smart surgical instruments as well as implants allow to give a direct feedback of loads to the surgeon lead to better reliability and success of surgical operations. A common technology used for sensors is low-cost piezoresistive thick-film technology. However, the standard thick-film firing conditions degrade the properties of medical alloys. In order to avoid this problem, the solution is to decrease the firing temperature of thick films. This work presents the development and characterisation of low-firing thick-film systems (dielectrics, resistors and conductors), formulated to achieve chemical and thermal expansion compatibility with an austenitic stainless steel medical alloy. Adherence tests and results on electrical properties of these systems: resistance, temperature coefficient of resistance (TCR) are presented. It was found that the main issue in these systems lies in mastering the materials interactions during firing, especially at the silver-based resistor terminations. The interaction of silver, resistor and dielectric tends to give rise to highly resistive zones at the terminations, affecting reliability. This can be circumvented by post-firing the resistor terminations at a moderate temperatur
Sensors and packages based on LTCC and thick-film technology for severe conditions
Reliable operation in harsh environments such as high temperatures, high pressures, aggressive media and space, poses special requirements for sensors and packages, which usually cannot be met using polymer-based technologies. Ceramic technologies, especially LTCC (Low-Temperature Cofired Ceramic), offer a reliable platform to build hermetic, highly stable and reliable sensors and packages. This is illustrated in the present work through several such devices. The examples are discussed in terms of performance, reliability, manufacturability and cost issue
Microsystems - from technologies to products
In this paper, we outline the process leading from technologies to successful products in the MEMS (Microelectromechanical Systems) and MST (Microsystems Technology) field. The development of new products involves a lot of factors, such as mature technologies, interdisciplinary team, identifying the right business potential and long term oriented investors. The paper summarizes a survey of different technologies and point out that packaging, test and calibration are still major shortcomings for the concerned industries
Anisotropic random resistor networks: a model for piezoresistive response of thick-film resistors
A number of evidences suggests that thick-film resistors are close to a
metal-insulator transition and that tunneling processes between metallic grains
are the main source of resistance. We consider as a minimal model for
description of transport properties in thick-film resistors a percolative
resistor network, with conducting elements governed by tunneling. For both
oriented and randomly oriented networks, we show that the piezoresistive
response to an applied strain is model dependent when the system is far away
from the percolation thresold, while in the critical region it acquires
universal properties. In particular close to the metal-insulator transition,
the piezoresistive anisotropy show a power law behavior. Within this region,
there exists a simple and universal relation between the conductance and the
piezoresistive anisotropy, which could be experimentally tested by common
cantilever bar measurements of thick-film resistors.Comment: 7 pages, 2 eps figure
Ultra-low pressure sensor for neonatal resuscitator
AbstractA Venturi-type flow sensor has been designed and fabricated for neonatal respiratory assistance to control airway pressure and tidal volume. As the low flow range and sensing principle require the measurement of correspondingly very low pressures, a very responsive sensor, based on a polymer membrane acting onto a piezoresistive cantilever force sensor based on low-temperature co-fired ceramic (LTCC), was developed. This paper details the 3D modelling, manufacture, assembly and characterisation of the sensor. Compared to expensive and fragile MEMS-based devices, this sensor, based on LTCC, thick-film technology and polymer parts, provides an accurate and robust, yet low-cost alternative
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