The Square Kilometre Array (SKA) is a next-generation radio astronomy facility that will revolutionize our understanding of the Universe and the laws of fundamental physics. To achieve the intended objectives, it needs a stable reference frequency and accurate timing signals at each digitizer. These references are used for digitizing astronomical signals received from the receptors. The stability and accuracy of these references are highly important for coherently sampling the astronomical data. They are distributed using long-distance fibers that are susceptible to environmental perturbations, which makes meeting the requirements a challenge. The system overcomes these perturbations by actively stabilizing the noise during fiber transmission to achieve the required reference signal stability and sub-nanosecond level of timing accuracy. We collect together summary descriptions of the sub-systems designed for distributing the reference frequency and timing signals for each telescope, to provide an overview of the whole timing and frequency system for the SKA. (C) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)

This paper proposed a simple-structured, low cost, high-efficiency piezoelectric energy conditioning system, replacing the active electronic controllers with electrostatic MEMS switch, to decrease the intrinsic energy consumption and the complexity of the energy management circuit. With the extremely small leakage current, the average power consumption of the MEMS switch was approximately equal to as low as $1.85\times 10^{-12}\mathrm{W}$ within one charging cycle, and the highest energy conversion efficiency of 76% was obtained during testing.

A new approach is developed for environment energy harvesting based on an electrostatic MEMS switch due to its hysteresis property. A hysteresis model of the electrostatic MEMS switch is established, and theoretical and experimental results show that the hysteresis window is designable. A demo for piezoelectric energy harvesting based on the MEMS switch is designed and finished. The approach is compacted, passive and efficient, which facilitates the development of energy harvesting.

The rapid development of high-precision time and frequency transfer techniques allow the real-time comparison of remote hydrogen masers (H-masers). Since the year of 2013, we have been working on building a fiber-based frequency synchronization network in Beijing, using our homemade frequency transfer devices and buried city fiber links. So far, frequency signals of 3 Hmasers from 2 different institutes are transferred to our laboratory in Tsinghua University and are compared with the local Hmaser in real time, forming up a clock ensemble of 4 clocks from 3 places. Using this frequency network, we studied the correlation of the pair of co-located H-masers. With our measurement we found that the correlation is at the magnitude of 10?30 and only shows up after the averaging time is larger than 103s.

Fiber-based frequency synchronization system is sensitive to temperature change because of the limited isolation and nonlinear effect of RF components in the system. In order to make it suitable for the use of large-scale scientific and engineering projects in which the ambient temperature of the fiber link changes dramatically, we designed a non-harmonic frequency dissemination system immune to temperature fluctuation. After the lab tests in which the ambient temperature of fiber fluctuates 40 degrees centigrade per day and 20 degrees centigrade per hour respectively, the relative frequency stabilities of this system reached 4.0 E-14/s and 3.0 E-16/1E4 s. It is demonstrated that the proposed non-harmonic scheme shows a strong robustness to the complicated working environment with dramatic temperature fluctuation.

This paper introduces the formation of a physical real-time time scale using data of remote clocks from different time laboratories in Beijing region linked via fiber-based high-precision frequency transfer network.