Page 10 - EngineerIt March 2021
P. 10


           A caesium clock operates          energy level, and they in turn release additional photons. In this manner, a self-sustaining
        by exposing caesium atoms to         microwave field builds up in the bulb. The tuned cavity around the bulb helps to redirect
        microwaves until they vibrate at one of   photons back into the system to keep the oscillation going. The result is a microwave
        their resonant frequencies, and then   signal that is locked to the resonance frequency of the hydrogen atom and that is
        counting the corresponding cycles    continually emitted as long as new atoms are fed into the system. This signal keeps a
        as a measure of time. The frequency   quartz crystal oscillator in step with the resonance frequency of hydrogen.
        involved is that of the energy absorbed   “We employ both clocks for their difference in performance,” Matthee explained. “The
        from the incident photons when they   caesium clock is the most accurate but generates high levels of RF noise, while the
        excite the outermost electron in a   hydrogen clock is RF-wise, quiet.
        caesium atom to jump (“transition”)    While we generate very accurate local time, we also need to compare our time with
        from a lower to a higher orbit.      other laboratories. We monitor errors with any GPS or GLONASS satellite that is above
           The hydrogen maser is the most    our horizon. The International Bureau of Weights and Measures (BIPM) collects data from
        elaborate and expensive commercially   approximately 80 different time centres in the world and examines scenarios where a
        available frequency standard. The    number of time laboratories have a common view of a number of satellites at the same
        word maser is an acronym that        time. The differences are then calculated, and averages computed. The BIPM distributes
        stands for microwave amplification   a bulletin once a month, allowing us to review our accuracy. We analyse the data and
        by stimulated emission of radiation.   compare it with our own data and if there is a variation, we update the model that then
        Masers operate at the resonance      drives the correction to the clocks. It is done continually as we receive this comparative
        frequency of the hydrogen atom, which   information. Our aim is to stay with a ten nanosecond accuracy and constantly achieve
        is 1 20 405 752 Hz.                  better,” Matthee said.
           A hydrogen maser works by
        sending hydrogen gas through a       Leap seconds
        magnetic gate that allows only atoms in   Leap seconds were added periodically to adjust to irregularities in the earth’s rotation
        certain energy states to pass through.   in relation to Coordinated Universal Time (UTC), in order to remain close to mean solar
        The atoms that make it through the   time (UT1). At the 2015 World Radiocommunication Conference (WRC-15), it was
        gate enter a storage bulb surrounded   proposed to suppress the leap second. The decision by WRC-15 calls for further studies
        by a tuned, resonant cavity. Once    regarding current and potential future reference time scales, including their impact and
        inside the bulb, some atoms drop to a   applications.
        lower energy level, releasing photons   A report will be considered by the World Radiocommunication Conference in 2023. Until
        of microwave frequency. These photons   then, UTC shall continue to be applied as described in Recommendation ITUR TF.4606 and
        stimulate other atoms to drop their   as maintained by the International Bureau of Weights and Measures (BIPM).   n

        South Africa unveils world class

        photonics prototyping facility

             outh Africa’s photonics industry   optical equipment ranging from electronic, mechanical and diagnostic equipment, for a
             is set to benefit from the state-  variety of wave lengths.
       Sof-the-art photonics prototyping       The PPF seeks to develop ideas and identify needs for the current South
        facility (PPF) that was unveiled at the   African market. The national facility aims to address the current innovation chasm
        CSIR on Friday 5 March 2021.         experienced in the South African photonics industry by providing the necessary skills
           The facility will enhance the     and facilities to support the industrialisation and commercialisation of photonics-based
        development of photonics-based       technologies. This will help develop South Africa’s expertise in the area of photonics
        products, specifically the prototype   product development and prototyping, thus stimulating the growth of the country’s
        development phase, to test the market   photonics industry by forming small, medium and micro-sized enterprises (SMMEs) and
        for acceptance of the planned product in   sustainable jobs.
        the country. The facility offers class   The PPF, which is funded by the Department of Science and Innovation (DSI), will
        1 1000 cleanrooms, technical and     fast-track product development of photonics technologies and devices, in line with

                                                   EngineerIT | March 2021 | 8
   5   6   7   8   9   10   11   12   13   14   15