A highly phase-stable differential detector amplifier for magnetic induction tomography

Magnetic induction tomography (MIT) has been proposed for the detection of cerebral oedema and haemorrhagic stroke. Achieving the required phase measurement precision for these applications is however a major technical challenge. A critical component within an MIT system is the detector amplifier and for this role an ultra-phase-stable, low noise instrumentation amplifier has been developed. The design of the amplifier is described and (i) the results of simulations and measurements of the amplifiers phase stability versus temperature and (ii) measurements of the phase noise and drift performance of the amplifier within a single-channel magnetic induction spectroscopy system are provided and discussed. For a 10 MHz signal the amplifier, with a gain of 21, displayed an average change in the measured phase of its output of just -0.1 ± 0.6 m° °C(-1) as the ambient temperature was varied between 35 and 50 °C, demonstrating a level of phase stability approaching that required for potential biomedical applications such as the detection of cerebral haemorrhage.