For this purpose they generate a high frequency ultrasonic pulse the echo of which is detected and evaluated by the sensor.

为此，他们产生高频率的超声波脉冲回波是由传感器检测和评估。

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High frequency ultrasonic power supply controlled by AT89C51, can adjust its power, frequency and phase in high performance.

以单片机at89c 51控制的高频超声电源，其功率、频率及相位可进行有效的调节。

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The mechanism and kinetics of parathion degradation was investigated under high frequency ultrasonic irradiation in aqueous solution.

研究了高频超声降解水溶液中对硫磷的反应动力学以及机理。

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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'