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After 24 US staff working at the Cuba embassy fell ill and complained of hearing strange noises last year, several US citizens have been evacuated over unexplained health issues from China. Authorities believe that they have fallen victim to the same sonic attack.

According to the reports, people who were affected by the sonic attack are hearing odd noises and experiencing subtle, but abnormal, sensations of sound and pressure.

Though the events remain shrouded in mystery, it is believed that a government or agency is targeting the US with a new type of sonic weapon. Also, the cases are happening amidst rising concerns about a possible trade war between the US and China.

What is a sonic attack?

Sonics attacks are inflicted by weapons, which can be categorized into two categories: Audible frequencies and those that are either ultrasonic or infrasonic.

While infrasound includes frequencies below 20Hz and are inaudible to human ears, Ultrasound is above 20,000Hz, or 20kHz, which is also inaudible to humans.

Infrasonic sounds, if too loud, can cause vertigo and even vomiting or uncontrollable defecation. Ultrasonic, on the other hand, can damage the parts of the ear, including hairs, that pick up the sound, according to BBC.

Probably, the US diplomats in Cuba became victims of Ultrasound sonic attack as the other one is more tedious to carry out.

Sound weapons have been used for crowd control and repelling pirates and some Ultrasonic (high frequency) bursts have been used as a teenager repellent in the United Kingdom.

Who is behind it?

The US till now is not clear who is carrying out these attacks. For the case in Cuba, the Caribbean island nation denied any involvement. The security analysts also said that probably the attacks were being carried out by a third country. "The US has been surprised at the extent to which others have caught up with them in all sorts of technologies... It's probably not so much a surprise that the technology exists, more than others are aware of it and using it," said Elizabeth Quintana, a senior research fellow at the UK-based military think tank the Royal United Services Institute (RUSI).

Quintana also specialises in emerging technologies in the defence world.

Currently, US state department has sent a team to Guangzhou – the city where people are falling sick - to examine the situation and establish possible links between their symptoms and those who suffered in Cuba.

Meanwhile, China's foreign ministry has said that the US has not been informed about the new cases. "If the United States communicates with us, we will adopt a responsible attitude to investigate this," a foreign ministry spokesperson said, according to The Guardian.