Thursday 05 Jun 2014: Microwave-to-terahertz sensors: a challenge for graphene and beyond
Professor Norbert Klein, Chair in Electromagnetic Materials - Department of Materials, Imperial College London
HAR/170 (3D Visualisation Suite) 14:00-15:00
Electromagnetic radiation at microwave-to-terahertz frequencies can be used as probe to study the electronic and dielectric properties of a large variety of materials. Since this frequency range is relevant for wireless communication and sensor applications, devices being designed for material characterization often pave the way to the development of practical sensors.
The first part of my lecture is about our measurements of the dielectric properties of liquids at microwave and terahertz frequencies. Dielectric resonators have been used successfully for precise measurements of the complex dielectric permittivity in liquids on the nanolitre volume scale. As an application as label free biosensor, we have developed a microwave method for precise haemoglobin concentration measurements in blood. Novel device structure for the THz range, such spoof plasmon surface wave structures and photonic crystal defect cavities will be discussed with emphasis on sensor applications.
Similar resonator methods are very interesting in connection with our work on graphene. From the perspective of a microwave engineer, graphene has very unique properties, which are challenging to be utilized in wireless communication. Graphene represents an ideal resistive sheet with real-valued surface impedance, which is almost frequency independent up to several 100 GHz. Therefore, it enables to control the quality factor of a resonant device without changing its resonant frequency. Moreover, its surface impedance can be controlled by an external gate voltage, which makes it potentially attractive for fast switchable devices being used in high data rate wireless communication links at mm wave frequency bands. Our methods to assess the electrodynamic properties will be presented and measured results at microwave and terahertz frequencies will be discussed and compared with theoretical expectations.