Sound waves with a frequency higher than the upper limit of human hearing (about 20,000hz) are called ultrasound.\.\

Ultrasonic waves have very short wavelengths, only a few centimeters or even a few thousandths of a millimeter, so they have poor diffraction skills and can propagate in a uniform medium in a directional linear manner.

In addition, ultrasonic waves have another strange characteristic, which is "cavitation effect":

Because ultrasonic frequency is very high, ultrasonic waves have very high power compared to ordinary sound waves.

When ultrasonic waves spread in the liquid, due to the violent vibration of the liquid particles, small holes will be created inside the liquid. These small holes will quickly expand and close, causing violent impacts between the liquid particles, thereby generating pressures of thousands to tens of thousands of atmospheric pressures.

This violent interaction between particles will cause the temperature of the liquid to suddenly increase. In addition, it can also play a good role in stirring, thereby emulsifying two incompatible liquids, such as oil and water, and accelerating the dissolution of solutes and accelerating the chemical reaction...

At this time, in addition to the water component, the small puddle in front of Ding Bao also had a layer of oil from unknown animals floating on its surface. From the fluctuation and heating up to the final emulsification of water and oil, under the subtle representations that only his eyes can observe, there were changes that conform to the "cavitation effect", which made him immediately distinguish it.

The situation was urgent before. Although I found that sound waves that were suspected to be inaudible to someone's ears were commanding the heavenly soldiers remotely, I had no time to calm down and verify and analyze them carefully.

Because as a core backbone who has been immersed in the bioengineering industry for many years, he is very aware that sound waves that exceed the hearing range of the human ears are also infrasound waves.

These two kinds of sound waves have their own characteristics, and there are animals that can emit and listen to in the biological world, so it is not easy to judge in a short period of time.

For example, mosquitoes, bats, cats, dogs and domestic animals can hear ultrasound waves; elephants, whales, dolphins and other marine animals can feel infrasound waves. Therefore, he cannot draw a conclusion on what kind of sound waves are used to control the heavenly soldiers.

In fact, at that time, he was more inclined to infrasonic waves.

Because the wavelength of infrasonic waves is very long, they propagate far and are not easily absorbed. In some cases, they may even propagate hundreds of kilometers, thousands of kilometers, orbit the earth for three or two weeks!

The most important thing is that although they are sound waves that cannot be heard by the human ear, the vibration frequencies of certain frequencies are similar or even the same as those of human organs, and can resonate with human organs. In the physical therapy of the Earth in previous lives, "infrasound diagnostic instruments" were used to check whether the human organs work normally. So he speculated whether the synergistic resonance of infrasound waves was used to control the heavenly soldiers.

The only difficult thing to explain is that infrasonic waves are more common in earthquakes, tsunamis, auroras, meteors, etc., and are not easy to emit. Moreover, the control of heavenly weapons through organ resonance is exquisite, but it is actually very dangerous. Maybe the organ blood vessels will be broken, and it is too cumbersome and difficult to control.

However, the obvious "cavitation effect" in the puddle at this time proves that ultrasonic waves are used to control the heavenly soldiers.

This is easier to understand.

Because Ding Bao knew that in Europe, Scotland and Ireland, people like to call and command their beloved dogs with a whistle called the dog flute. The dog flute emits ultrasound, and the pedestrians around him know nothing, and the puppy has acted according to the commands sent from the dog flute.

In this way, the truth is not that complicated. Heavenly soldiers are equivalent to puppies, just simply accepting specific commands and slogans.

I just don’t know how these heavenly soldiers “hear” ultrasound.

The cave was pitch black, but fortunately there was snowy outside, which was not very obscure. After adapting to the eyes, I could barely see the scene within three or two steps around me.

Ding Bao stared at the puddle in front of him, raised his palm and signaled Lao Feng not to speak for now. He waited until the puddle gradually calmed down and the cavitation disappeared. He lay at the entrance of the cave and swept away with his eyes. He did not find any traces of heavenly soldiers. He seemed to have searched for it. Then he turned back, but he was shocked to find Lao Feng that he had already fallen into a coma.

"Old Feng, wake up, haven't told me yet, where is the box?"

The old wind, who had already been exhausted, suddenly heard the word "box" and immediately opened his eyes. The turbid eyes burst out with a kind of brilliance like the afterglow of the sunset, which made Ding Bao feel sad. He closed his lips and said, "...box is not on me. In order to avoid... letting you take unnecessary danger, go to Fuyao Peak... You only need to send me a message to the little fox fairy... She will take it."

Ding Bao nodded silently and promised in a solemn voice: "Don't worry, Lao Feng. I will definitely get this done."

Old Feng made him promise, and the brilliance in his eyes became brighter and dimmed again. He tried to raise his neck, put it in Ding Bao's ear, and explained: "That box... is placed..."

"What?!"

Presiding Ding buckled his ears with his hand, suspected that he had heard it wrong, and immediately said in surprise: "Are you sure you are wrong? How can the little fox fairy get it in that place?!"

Lao Feng wanted to laugh proudly, but only a few loud coughs were heard. Ding Bao quickly patted him on the back, but Lao Feng said violently: "Cough cough... you can't imagine, the enemy can't think of it... I have been three months before I... found an opportunity to hide the box there, which is a first-class place... But don't worry, even if there are only two people in the world who have the ability to touch it, one of them must be this little fox fairy..."

Ding Bao nodded and said wonderingly: "Where is the other person?"

"You." Lao Feng did not hesitate.

"..." Ding Bao opened his mouth but didn't say anything. Looking at Lao Feng's complicated but extremely trusting gaze, his mood was as heavy as lead, and his fists were clattering.

"Ningbao, hurry, hurry, time is up. Left chest... inner bag, small silver bottle."

When Ding Bao was stunned and feeling uncomfortable, Lao Feng suddenly thrust his body, grabbed his collar and said anxiously.

Ding Bao didn't know why, but he still found a small silver bottle the size of a little finger in a very delicate and secret inner bag inside his clothes. As soon as the silver bottle was touched, Ding Bao's nose moved and his face immediately changed: "Bone-eroding muscle fluid! Lao Feng, you want..."

"This is...the...the destination of every Feng family. There is no bone left or dust."

After the old Feng said in a misty way, he grabbed Ding Bao's arm and hung down weakly. When he closed his eyes, he passed away.

Bang! Ding Bao punched the rock wall next to him, and blood flowed down his fingers, but he was motionless. His face was so gloomy and solemn.

It took him a long time to recover from his stiff body. He took a deep breath, picked up the small silver bottle, opened the plug, and poured it all over the withered body of Lao Feng. He squeaked and squeaked, and the smoke suddenly started. However, Ding Bao did not take a look again, and suddenly stood up and headed towards the outsider of the cave.

After taking two steps, I suddenly felt like I was stepping on something soft.

He lowered his head and found that this was a dead animal.

The size of a mouse, the snout is like a fox, the outer ear protrudes forward and is very large. The neck is short, the chest and shoulders are wide, the breasts are well developed, and the hips and legs are slender. The whole body is covered with hair, the back is gray in different shades of gray, and the ventral color is light. A pair of wing membranes are grown on the back, which is light brown.

"bat?"

Ding Bao said in surprise, and his heart moved, and immediately turned around and walked into the cave.

If he remembers correctly, the bat is a master of ultrasound. Because it can not only accept it, it can also emit.

The reflection of sound is related to the length, thickness of the obstacle. The lower the frequency, the longer the wavelength, the greater the linearity of the obstacle that reflects. A large wall can reflect our shouts, but a telephone pole cannot reflect the sound we make.

Bats can emit waves of ultrasound waves with extremely short wavelengths. Even a wire or a mosquito can form reflections, which allows bats to locate, avoid wire, and catch mosquitoes.

Before he walked far, he saw the bats hanging upside down on the top of the cave.

Bats are animals that lie down on the day and come out at night. It is the night at this time and it is time to go out for food. But in fact, many people don’t know that bats also have the habit of hibernation.

It's just that it does not hibernate deeply, and sometimes excrete and eat during hibernation. It only reduces the ability of metabolism, breathing and heartbeat only a few times per minute, slows down blood flow, and reduces the body temperature to the same as the ambient temperature. Once awakened, it can immediately return to normal.

At this time, due to the sound brought by Ding Bao, some bats had already woken up and were about to fly.
Chapter completed!