Millimeter and submillimeter Waves in Nuclear Magnetic Resonance Signal Enhancement

Oleksandr Rybalko

Research focus
The main objective of this project is to improve the sensitivity of DNP by maximizing the efficiency of transmission of microwave energy from the microwave source (increasing the amount of power delivered) to the sample and to produce a concentrated homogeneous microwave field across the sample volume.

One method to increase the amount of power delivered to the sample is to use a low loss, oversized waveguide covering several frequency bands (94 GHz, 140 GHz, 188 GHz). The challenge lies in balancing the microwave and mechanical properties of the window.

An additional means of increasing power delivered to the sample is to minimize the losses of microwave energy in the waveguide as well as optimizing the sample irradiation. Several methods and techniques to efficiently transport microwave energy from the microwave source to the sample have been developed. For instance, corrugated waveguide allows transmission of mm-wave energy with minimal losses. The waveguide needs to be adapted to the DNP probe to achieve optimal performance. The conventional approach at high frequencies is to irradiate the sample directly from the waveguide, while at low frequencies the cavity of the probe is used as a microwave resonator. It is important to optimize the arrangement of microwave, RF and sample handling components. In this part of the project the construction of the microwave probe will be detailed.

Other research activities include experimental and theoretical investigations of the efficiency of GaAs frequency multipliers (188/282 GHz) from room to cryogenic temperatures. For instance, the multiplier can be placed inside the polarization system, where the temperature of the environment is in the range from 77 to 100 K. Usually the performance of commercially available multipliers is not specified at such temperatures. First results indicate that cooling to 77 K results in a 48% increase of output power. The application, however, calls for theoretical and practical evaluation of the multiplier behavior in a cryogenic environment.

Scientific output
Find Oleksandr's publications at DTU's online research database ORBIT.

Funding
Oleksandr has worked on projects funded by Lundbeck Foundation (R95-A10581) and Danish Council for Independent Research. The projects are part of the HYPERMAG Center of Excellence funded by Danish National Research Foundation (DNRF124).

Project Period
February 2014 - September 2015 (Lundbeck Foundation)
October 2015 - January 2017 (Danish Council for Independent Research)

http://www.cmr.healthtech.dtu.dk/Research/Postdocs/Oleksandr-Rybalko
26 JANUARY 2020