Due to the actual interest for bioengineering in the osteoarthritis (OA) healing context, researchers need accurate qualitative and quantitative methodologies to evaluate in vivo the integration and functionality of their cartilage-like biomaterials. As in clinical diagnostic strategies, advances in Magnetic Resonance Imaging (MRI) seem promising for non-vulnerant assessments of articular cartilage bio-architecture and morphology in small animal models. These experimental models are commonly used to monitor the physiopathology of OA and to evaluate therapeutic responses mediated by chondroprotective drugs or tissue engineering. Nowadays, the application of MR protocols to in vivo small animal cartilage imaging is achievable with the development of high magnetic fields and the adaptation of methodologies to reach the required spatial resolution and contrast. The purpose of this article is to summarize these current MRI strategies used for in vivo small animal articular cartilage assessments.

A novel ultra compact microwave tuneable impedance transformer topology is proposed. It consists of a classical p CLC network where an equivalent tuneable inductance is realised with a high impedance transmission line in series with fixed inductance and a diode's varactors. The realised hybrid prototype at 900 MHz operating frequency is only 0.06l-long. Impedance loads from 16.5 to 280 O can be matched with a return loss better than À20 dB, and the relative bandwidth equals AE 36% for a fixed 50 O load.Introduction: Impedance transformers are widely used for microwave applications such as matching networks, filters, power dividers, etc. Tunable impedance transformers could offer interesting possibilities and constitute a great challenge in the field of modern telecommunication systems. For example, they could be used in microwave amplifiers matching networks to modify, after realisation, their behaviour, so that the optimal characteristics of the amplifier could be reached, even if its model is not perfectly known a priori. Also, they could be used to tune amplifier matching networks for wideband applications without sacrificing the amplifier characteristics, power gain or noise factor. We could also design tunable power dividers.Some realisations have been published on microwave tuneable impedance transformers, but not many. Sinsky and Westgate have presented a topology based on a p CLC (capacitor -inductorcapacitor) network [1]. The three elements have to be tunable to achieve a tunable impedance transformer. Tunable capacitors are realised with reverse biased Schottky diodes acting as varactors. The tunable inductor, in series between the two shunt capacitors, is realised with a shunt varactor connected between two quarter wave transmission lines.The use of quarter wave transmission lines is a problem. They reduce the device bandwidth, lead to a relatively long device (half wavelength), increasing losses, and induce a cost due to the used surface for MMIC devices. In [2], we have published an original topology, not based on a p CLC network. Its length is about a third of a wavelength, and complex loads can be matched, with a wide coverage of the Smith chart.In this Letter, we propose a topology based on a p CLC network, like [1], but the tunable inductor is not realised with a varactor inserted between two quarter wavelength transformers, leading to very small devices with a length of a few percent of wavelength. The tunable inductor is achieved by inserting a varactor (C 0 ) in series with an inductor (L), leading to a resonant circuit. Working above the resonant frequency leads to the realisation of an equivalent tunable inductor. To minimise insertion losses, the inductor value L is realised in practice with a short high impedance transmission line in series with a fixed inductance. Our first concepts, at frequencies from 1 to 10 GHz, have shown that this approach leads to impedance transformers of very small length, always lower than 10% of the guided wavelength. Moreover, the bandwidth is only limited by...

In this paper, we demonstrate the use of a LiTaO 3 crystal associated with a typical nuclear magnetic resonant loop coil to perform an optically remote radio frequency magnetic-field characterization. The whole transduction scheme is theoretically and experimentally studied. The measurement dynamics reaches 60 dB. The minimum detectable magnetic field is lower than 1 nT, which corresponds to an induced inner crystal electric field as low as 30 mV/m. To evaluate the spatial potentialities of the sensor, a 1-D mapping of the field along an asymmetric butterfly-shaped loop coil is performed. The result is in good agreement with finite-difference time-domain simulations and demonstrates the vectorial behavior of the sensor device.