A High-Frequency Sound based PGC Demodulation Scheme for Fiber Optics Hydrophone

In the research field of fiber-optic hydrophone, the performance of demodulation scheme is crucial. In this work, a phase-generated-carrier (PGC) demodulation scheme based on high-frequency sound source is proposed. Highfrequency acoustic signal from the external sound source is applied to the fiber-optic hydrophone to achieve phase modulation of the interference signal instead of the piezo-electrical transducer (PZT) or frequency-modulated laser. It possesses the merits of low system complexity and low cost. Through the acoustic detection experiment, we achieve demodulation of acoustic signal at frequency varying from 300 Hz to 800 Hz, and the signal-to-noise ratio (SNR) is higher than 45 dB. Furthermore, the proposed scheme is successfully applied to time division multiplexing (TDM) experiment.

Exposure to High-Frequency Sound and Ultrasound in Public Places: Examples from Zurich, Switzerland

The public is unknowingly exposed to very high-frequency sound (VHFS; 11.2–17.8 kHz) and ultrasound (US; >17.8 kHz) signals in air in public places, as evidenced by previously published reports. The present report provides evidence for the presence of VHFS/US signals in the air at public places in Zurich, Switzerland. The analysis of the signals measured revealed that they: (i) contain one, two or multiple frequencies; (ii) comprise frequencies ranged from 15.5 kHz to 36.0 kHz; (iii) were either quasi constant in their amplitude or exhibit a clear amplitude modulation; and (iv) were in their characteristics (frequencies, modulation, intensity) specific for each place. Based on the signal characteristic it is likely that the signals are generated by public-address voice-alarm (PAVA) systems. The work presented: (i) documents the presence of VHFS/US signals at public places in Zurich, possibly caused by PAVA systems; and should (ii) show that is easily possibly to measure the signals with an affordable measurement equipment as a “citizen scientist”, and stimulate others also to measure and analyse VHFS/US signals with this citizen scientist approach in other cities worldwide. Due to the possible negative health-related effects of a human exposure to VHFS/US signals, further research is needed to document VHFS/US signals at public places and to evaluate biological effects of this exposure with laboratory studies.