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Cost effective power amplifiers for pulsed NMR sensors
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1  Nottingham Trent University


Sensors that measure magnetic resonance relaxation times are increasingly finding applications in areas such as food and drink authenticity and waste water treatment process control. Modern permanent magnets are used to provide the static magnetic field in many commercial instruments and advances in electronics, such as field programmable gate arrays, have provided  lower cost console electronics for generating the series of RF pulses and detecting the resultant magnetic resonance signals. One area that still remains prohibitively expensive for many sensor applications of pulsed magnetic resonance is the requirement for a high frequency power amplifier. With many permanent magnet sensors providing a magnetic field in the 0.25T to 0.5T range, a power amplifier that operates in the 10MHz to 20MHz rage is required.  This frequency range falls at the low end of the amateur “ham” radio frequency spectra designated for private recreation and non-commercial exchange of messages. In this work we demonstrate that low cost commercial amateur radio amplifiers can be simply modified, to operate as pulsed magnetic resonance power amplifiers. We demonstrate two amplifier systems, one medium power that can be constructed for less than Euro 100 and a second higher power system which produces comparable results to commercial pulse amplifiers that are an order of magnitude more expensive. Data is presented using both the commercial NMR MOUSE and a permanent magnet system used for monitoring the clog state of constructed wetlands.  

Keywords: magnetic resonance, amplifier, low cost
Comments on this paper
Alberto Vallan
toward a portable NMR system
Do you think that your system could be fully powered with batteries? The spectrometer can be operated with a 24 V battery but I am wondering what is the power consumption of the amplifiers.

Robert Morris
Thank you for your interest. We have tested the current needed using a typical CPMG sequence on the MR MOUSE (200mA for opamp/KL and 350mA for the henry/KL) which suggests that it would work equally well running from batteries. This may also come with a benefit in terms of noise reduction.