Technology & Research News

TECHNOLOGY AND RESEARCH NEWS
Integrated Solutions for Industrial Inductive Positioning Sensors
There is tremendous demand for industrial sensors that can work in harsh environment such as high temperature and humidity [1]-[6]. They have to meet certain criteria such as reliability, wide temperature range, insensitivity to moisture, dust and mechanical offsets and long life. Contact-less inductive sensors [3] are prime candidates to meet these demanding requirements in particular in harsh environments. One type of inductive sensors is based on inductive resonance. It utilizes the physical phenomenon of mutual inductance between an antenna and a target as shown in Fig. 1. An antenna containing transmitter and receiver coils on a printed circuit board is supplied with an AC signal to drive the transmitter. The driving signal usually has a frequency range between 1 and 4 MHz. An alternating electromagnetic field is formed in the region of the antenna. When a target, which is made of a passive resonant circuit enters the antennas transmit field, currents are induced to flow in the target. Subsequently, these induced currents emit their own field which is picked up by the receiver coils. The frequency of the antenna transmitted signal is chosen to be the same frequency at which the target resonates. Further analysis of the signals picked up by the receiver coils in terms of phase and amplitude determine the position of the target. In addition, multiple targets can be detected by using different transmit frequencies. Most of the circuit realizations for this inductive type of sensor have been implemented using discrete solutions.
Integration of these electronic circuits in an ASIC offers significant advantages such as: • Reduced number of external components; • Reduced cost; • Increased reliability; • Enhanced sensitivity; • Programmability. Novel analog techniques are being introduced in this area that will significantly improve the front-end of the inductive sensor system and thus enable the commercialization of these in industrial applications.
Acknowledgment: This research is being funded by the UK Department of Trade and Industry (DTI) under grant TP/4/MHP/6/I/22071.
References [1] X. Li and G.M. Meijer, “A novel smart resistive-capacitive position sensor,” IEEE Trans. Instrum. Meas., vol. 44, no. 3, pp.768-770, Jun. 1995. [2] G. Zhang, Y. Chen, Z. Zhou and S. Li, “Design of an inductive long displacement measurement instrument,” Proc. 6th IEEE World Congress on Intelligent Control and Automation (WCICA’06), pp. 5098-5101, June, 2006. [3] M. Jagiella, S. Fericean, R. Droxler and A. Dorneich, “New magneto–inductive sensing principle and its implementation in sensors for industrial applications,” Proc. IEEE Sensors, pp. 1020-1023, Oct. 2004. [4] F.L. Yassa and S.L. Garverick, “A multichannel digital demodulator for LVDT/RVDT position sensors,” IEEE J. Solid-State Circuits, vol. 25, no. 2, pp. 441-450, Apr. 1990. [5] A. Drumea, A. Vasile, M. Comes and M. Blejan, “System on chip signal conditioner for LVDT sensors,” Proc. 1st IEEE Electro. System Integration Technology Conf., pp. 629-634, 2006. [6] R. Pallas-Areny, and G. Webster, Sensors and Signal Conditioning, 2nd Edition, New York: Wiley, 2001.
M. Rahal (Email: m.rahal@ee.ucl.ac.uk) and A. Demosthenous (Email: a.demosthenous@ee.ucl.ac.uk), Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, United Kingdom

Complex Systems Viewpoints in Nano-material Research
Bombardments of materials by energetic particles like neutrons and heavy-ions in irradiation facilities typically produce regions of displacement damage at a rate of ~1012 hits per second per cm3. When the damaged region cools down, crystal defects are “quenched in”. As irradiation proceeds, crystal defects accumulate and interact, and the microstructure evolves. Nano-scale ordered structures are often produced under such conditions. Shown in the figure is a classic example: a BCC void lattice in Nb irradiated with 7.5 MeV Ta+ ions at 800°C. [from: B.A. Loomis, S.B. Gerber and A. Taylor, J. Nucl. Matter. vol. 68 (1977) p. 19]. Despite the fascinating elegance and the obvious scientific and technological implications of this type of phase-transition-like behavior under non-equilibrium conditions, an understanding is only slowly coming into focus in the last few years. The evolution of the accumulating defects is conventionally described by coupled rate equations, analogous to the description of diffusion-controlled chemical processes, the dynamic complexity of which is now well known. However, to maintain the manageability of the calculation, a simplifying mean-field approximation is usually adopted, in which the spatial and size distributions of the microstructure and the mobile-defect concentrations are averaged out. The simplicity of the equations in such a form often leaves one with the impression that microstructure evolution proceeds in a continuous way. It has now been realized that in this treatment, important features of complex systems such as dynamic instabilities and bifurcations may have been overlooked and neglected, together with the accompanying phase-change-like behavior of the system. It is realized that the spatial and size distributions of the reaction partners have to be considered in detail, because they may be a prevailing factor in the dynamic behavior of the system. Thus, when the long-wave-length Fourier components of the concentration of the diffusing reactants become unstable and disappear, dominance of the shorter wave length leads to strong spatial ordering. A more subtle and yet equally strong effect is caused by the instability of the size distribution of the microstructure components, which occurs due to positive feed back effects such as stochastic shrinkage. The presence of a small bias at the instability point due to one-dimensionally migrating self-interstitials with mean-free path comparable to the scale of the structure, influences the post-bifurcation evolution of the system, which produces alignment of the microstructure along the crystallographic directions. This type of reasoning has been applied also to other order structure formation during irradiation yielding encouraging results.
C.H. Woo, The Hong Kong Polytechnic University, Hong Kong (Email: enchwoo@polyu.edu.hk)