The use of frequency convert to regulate the speed of rotation according to the character of mine fan can reach the goal of the modulation of air flow and have a very good effect of saving energy.

根据矿井通风机的特性，使用变频器进行转速调整以达到调节风量的目的，且有很好的节能效果。

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Transducers are made from arrays of tiny piezoelectric structures that convert electrical signals into ultrasound waves by vibrating at an appropriate frequency.

换能器由阵列微压电结构组成，这种压电材料在合适频率下的振动能够将电信号转换成超声波。

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This system has adopted the algorithm of digital down convert FFT, so the frequency resolution is improved greatly.

使用先进的数字信号处理器，缩减了分立元件的数量，提高了系统的稳定性和扫频的速度；

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"Usually, bat sounds are inaudible to humans as they are too high for us to hear but special 'time expansion' ultrasonic detectors convert these sounds to a lower frequency, " Prof Jones, who is also chairwoman of the UK Bat Conservation Trust, explained.

BBC: Website calls on people to become 'bat detectives'