The principle of a virtual multi-channel lock-in amplifier and its application to magnetoelectric measurement system

This letter presents principles and applications of a virtual multi-channel lock-in amplifier that is a simple but effective method to recover small ac signal from noise with high presison. The fundamentals of this method are based on calculation of cross-correlation function. Via this method, we successfully built up a magnetoelectric measurement system which can perform precise and versatile measurements without any analog lock-in amplifier. Using the virtual multi-channel lock-in amplifier, the output of the magnetoelectric measurement system is extensively rich in magnetoelectric coupling behaviors, including coupling strength and phase lag, under various dc bias magnetic field and ac magnetic field.Comment: 11 pages, 6 figures. To be submitted to Rev. Sci. Instr

Measurement of material loss

The 2011 edition of the England and Wales National Joint Registry shows an increased failure rate for resurfacing and Large Head Metal-on-Metal (LHMoM) hips compared to other designs. The recent recall of the DePuy ASR has only increased the worldwide interest in the assessment of wear of explanted hip joints. The failure of these components has been linked to increased wear rates. Worldwide there have been a number of reports of adverse soft- tissue reactions in patients who have undergone metal-on-metal hip replacement. The NJR in the UK has shown that LHMoM bearings have been seen to exhibit a higher revision rate when compared to conventional bearing surfaces. Furthermore these bearings have been seen to exhibit a markedly higher failure rate than the equivalent resurfacing replacements of the same design. This leads to the conclusion that some factor relating to the modular nature of the LHMoM bearings must be contributing towards this increase in revision rate. Measuring the wear of explanted components allows a direct insight into the in-vivo behaviour of the implants. Wear analysis is a vital tool in determining failure mechanisms and ultimately improving the longevity of joint replacements through improved design and manufacturing control. To achieve this methods have been developed to quantify in vivo total joint replacement wear from retrieved total hip replacement components. This study aims to improve the understanding of the interaction at the modular taper junction by developing a protocol for the measurement of material loss and resultant surface topography at this interface in clinically retrieved components. A pilot study exploring the issues surrounding measurement of stem taper surfaces is presented