Electric Field Sensing (ElFiS)

Reliable measurement of the strength of an electric field is rather complex and hardly possible without severe interferences by the measurement device. Avoiding these disturbances would be of great interest for a vast amount of research areas, including lightning research. Hence, we propose a unique and new transduction technique for static and low-frequency electric fields that will pave the way for novel measurement techniques. The goal comprises miniaturized sensing elements enabling a passive transduction, a resolution of better than 100 V/m, an insignificant temperature dependence, and, mainly, a negligible distortion of the electrical field. Consecutive electro-mechanic, mechano- optic, and opto-electronic domain conversion is envisioned to meet these objectives. Sophisticated design goals have to be addressed for the micro-machined electro-mechanic transducer that serves also as light flux modulator and enables an extremely sensitive mechano-optical conversion. Dielectric waveguides are used to supply this transducer with light from the remote source and to guide the modulated light to the remote photodetector in order to maintain minimal distortions of the electric field. Owing to the number of involved physical domains, all scientific questions require an interdisciplinary research approach on numerous topics. Sophisticated transduction engineering is foreseen to convert the generally weak electrostatic forces into a detectable displacement. For that purpose, extensive 3D numerical modeling is intended to optimize the interaction of the virtually two-dimensional micro- electro-mechanic transducer with the external electric field. The influence of unipolar charges gathered at the transducer can interfere with the primary field and related effects like long term drift have to be studied thoroughly. Improvements of state-of-the-art micromachining technologies and advanced modeling enable sophisticated design measures which are required to meet the demands of the sensitive electro-mechanic conversion. To confirm the overall concept, field tests will be carried out to characterize practical implementations of the transducer in free space at geophysical measurement sites, especially for determining the electrical field strength of the atmosphere under fair weather condition and thunderstorms. The successful completion of the project will lead to a new generation of very sensitive transducers for static and slowly changing electric fields. The proposed approach promises unsurpassed advantages for numerous practical applications, e.g., in lightning and geophysical research. The research team comprises experts in the field sensor design and modeling (Dr. W. Hortschitz), microtechnology (Prof. Dr. F. Keplinger), as well as lightning research (Dr. G. Diendorfer) from the Danube University Krems, the Vienna University of Technology, and the OVE, respectively.

Within the project, which was co-founded by the Government of Lower-Austria, a new way of passive electric field transduction was developed that hardly distorts the electric field to be measured. The successful approach is based on microsystem technology and exploits electric field induced mechanical deflections in conjunction with a very sensitive optical readout. Since the electrostatic forces responsible for the deflections are extremely weak (in the order of Piconewtons and even smaller), both the actual transducer and the optical readout needed to be built to a level of cutting-edge sophistication. The requirement for distortion-free measurement was met by the new transduction not depending an electrical power supply or any grounded connection. Dielectric optical waveguides were used as the only interconnection between sensing head and electronics. Due to the simplicity of the integrated optical readout with a micro-shutter which is capable of resolving tiny deflections in the sub-picometer regime, there is no need for expensive, complicated components such as coherent light sources, optical couplers or beam splitters. The resulting rod-like probe with the transducer on its far end allows for almost point-like measurement of the electrical field strength with almost negligible distortions of the electric field. As an example to showcase the capability of the probe, highly precise, point-like mappings of the field of an electrostatic quadrupole were carried out within the project. These measurements were performed on one of the ELENA ring's quadrupole focusing elements at CERN, where there exists an unsatisfied need for instrumentation for quality control and optimisation of their electrostatic components. The findings of the project resulted in a new method of measuring the electric field. The unique properties of this method enable new types of measurements which are not viable with state-of-the-art systems. This will induce progress in numerous scientific and technological fields as diverse as lightning and atmospheric research, environmental and physiological impacts of high-voltage AC and DC infrastructure and autonomous navigation. The corresponding results bear the possibility for paradigm shifts within the respective fields.