Courtyard House: Starting with a 28-inch motorcycle

The next day, when Xiao Yao stepped into the courtyard, the first thing he saw was Han Chunming standing under the jujube tree with three bruises on his head, looking like a gourd that had just been struck by lightning.

Xiao Yao stared intently, then frowned and asked:

"What's wrong with your head...?"

……

"Don't even mention it, it was pure bad luck, I got beaten up."

Han Chunming grinned and reached out to hook his arm around Xiao Yao's shoulder, acting as if they were old drinking buddies reunited.

"Long time no see! I heard you've been working really hard lately? Come on, let me treat you to a couple of drinks!"

Han's mother quickly cooked three or four hot dishes and brought them to the small table in the backyard where Xiao Yao lived. The two sat facing each other and drank slowly. Only then did Han Chunming explain the events of the previous night in detail—it was purely coincidental, without any falsehood.

"By the way, Xiao Yao, I'm thinking of taking over a small restaurant. You're quick-witted, could you give me some advice?"

Xiao Yao picked up some peanuts with his chopsticks and said with a smile, "Cook, please be well. The stove is half-finished now."

But as soon as he said that, his heart sank. Han Chunming had escaped by sheer luck this time, but how many "just in time" moments are there in this world? What if one day he had tens of thousands of yuan in cash in his pocket, and the other party got greedy and actually pulled out a knife?

The more he thought about it, the more uneasy he felt—Han Chunming had treated him with utmost sincerity, depositing every penny of his monthly dividends into Xiao Yao's savings account from the very beginning. Yesterday, he casually glanced at the ledger and nearly crushed his teacup: after more than a year, he had actually saved over 20,000!

After seeing Han Chunming off, Xiao Yao went straight to the Su family's house. She had come specifically to see him, but unexpectedly stumbled upon this incident.

The case of Han Chunming being beaten quickly alarmed higher authorities.

There was no other way; he was doing very well in the trade market, which in turn revitalized the flow of goods in the surrounding three counties.

The leader slammed his fist on the table: "This must be thoroughly investigated! They robbed us and even injured someone, almost smashing a young, key employee's skull open!"

"Severe, swift, and ruthless! These bad apples need to know that now is not the time to turn a blind eye!"

Previously, these kinds of street disturbances were mostly considered minor incidents—stealing a watermelon or a wallet—no one was seriously hurt, so people didn't bother to pursue them. But this time is different: the nature of the incident has changed, and things have taken a wrong turn. If this is left unchecked, it could really lead to a major disaster.

Thus, without Xiao Yao's knowledge, the city's security network quietly tightened.

Those petty thieves operating in the gray area were all nipped in the bud overnight; those who habitually committed pickpocketing and extortion were all brought to the police station.

As for the thugs who robbed Han Chunming? They were sentenced to at least three years in prison for stealing ten yuan.

Upon hearing the news, Han Chunming, who was squatting at the street corner eating a candied hawthorn, almost bit the bamboo skewer off: "The case is closed so quickly?"

He scratched the back of his head and clicked his tongue in genuine amazement: "This time we really have to give the police station a banner."

Xiao Yao was unaware of the dramatic changes happening outside. He was enjoying a lazy and cozy holiday with Su Man, basking in the sun by the lake.

Two days before returning to the research institute, he started thinking about self-defense: he needed to find something handy—something inconspicuous, bloodless, and capable of subduing an enemy with a single strike.

Guns? Don't even think about it. That's an ironclad prohibition, and he doesn't want to be the one getting scolded instead of visiting Han Chunming at the police station next time.

He turned to the system for advice: "Is there any small self-defense weapon? Preferably silent and effective."

The system scoffed twice: "Tsk, bored out of their mind."

He casually tossed me a copy of "Illustrated Guide to Civil Security Equipment".

Xiao Yao flipped through the pages. The slingshot was too wild, the stun gun might cause accidental injury, and the hidden sword was too conspicuous...

"This thing can easily knock you out, electrocuting you until you foam at the mouth, and then I have to give you CPR?" He shook his head and laughed.

"Here, flip through this one too." The system's tone was tinged with helplessness.

Xiao Yao's fingertips traced across the pages, finally stopping on a certain page—the sound wave jammer.

The palm-sized, disc-shaped device resembles an old-fashioned radar receiver.

The instructions state: Upon activation, it can cause the target to experience temporary hearing loss, dizziness, and loss of limb control, lasting approximately eight seconds.

"That's it!" Xiao Yao's eyes lit up.

"This thing is simply an 'invisible killer.' Compared to it, Tang Clan's hidden weapons are like child's play."

"This is not a concealed weapon; it's a compliant technology product," the system said in a serious tone.

"But all hidden weapons are products of science—launch angle, kinetic energy conversion, trajectory calculation, none of them can be separated from mechanics. If you break down the Chinese character for 'force,' it's just 'science that requires effort,' isn't it?" Xiao Yao blinked, teasing it.

The system remained silent and let him be.

Xiao Yao held his breath, watching the entire assembly process of the weapon inch by inch. After watching, he silently clenched his fist, a heavy tremor running through his heart.

Don't underestimate this palm-sized contraption; it's packed with intricate details. Take the sonic attack module, for example. To make it truly "bite" the target, simply piling on components isn't enough. You have to thoroughly understand frequency, phase, power, and impedance. Other components can be pieced together to form a prototype, but this thing allows no compromises: even a slight decrease in sound pressure level renders it ineffective; even a millisecond deviation in phase causes the energy to dissipate haphazardly.

You must understand the underlying logic and choose the right materials—if you're even slightly off, the whole chain will break in your hands.

Fortunately, the institute has just established a basic research project on sound waves. Although it is still in its early stages and only a few rough lines have been drawn on the drawings, it is better than starting from scratch.

For Han Chunming's sake, Xiao Yao dared not be careless. If he were ever summoned to a funeral banquet, it would be too late.

The next day, right after lunch break, he knocked on Professor Chen's office door and asked if he could work as an intern with Professor Xu's team for a while.

Professor Chen looked up in surprise: "Oh? How did you suddenly get into this obscure field? The project is just starting out, the data isn't even running smoothly yet. If you go there, you probably won't even be able to tighten a screwdriver properly."

"I recently flipped through 'Introduction to Wave Theory' and became particularly engrossed in the section on sound waves—like sunlight, it's invisible, yet it can move matter, tear apart structures, and even rewrite human rhythms." Xiao Yao spoke slowly, but every word was substantial. "I have enough energy, and I want to take on more challenging tasks while I'm still young."

Professor Chen was genuinely pleased with a student who was willing to delve into the principles on his own, rather than just focusing on the results. Looking at the bright-eyed, upright young man before him, he suddenly realized that the most valuable quality of youth is not recklessness, but the courage to take the initiative in the unknown.

"Okay, I'll ask Professor Xu for you. But you know his temper, whether he agrees or not depends on whether he likes it or not." Professor Chen smiled and winked.

The news came back at 3 p.m.

Professor Xu had heard of Xiao Yao before—the high school student who had published three core papers in the low-temperature superconductivity group. Upon hearing that it was him coming, he immediately decided, "Welcome! We've just been needing someone who can calm down and focus on this."

Even more coincidentally, the other party was worried about not having anyone to help verify the resonance model and was hoping for a new pair of eyes to see the blind spots in the old path.

As Xiao Yao followed Professor Chen into the laboratory, Professor Xu was bending over, adjusting a spectrum analyzer. He straightened up, his gaze sweeping over them, and smiled broadly: "Xiao Yao? You've come at the right time. We're both 'newbie' players, so let's not laugh at each other."

With just one sentence, the tension on Xiao Yao's shoulders was quietly eased.

"Thank you for taking me in, Teacher Xu. I will definitely keep up with the pace and not hold everyone back." His voice was steady, and his back was ramrod straight.

Professor Xu nodded: "I'll give you thirty days. The first fifteen days will be spent laying the foundation—waveguide principles, transducer characteristics, dielectric attenuation curves, nothing will be overlooked; the next fifteen days will be for hands-on practice, participating in the first round of directional sound beam testing."

Xiao Yao quickly calculated in his mind: there was enough time. The equipment was readily available, and the materials were all prepared. He had no intention of making any revolutionary breakthroughs; he only wanted to create a portable infrasound generator that could be stably controlled within a safe threshold.

……

The deeper you go into physics, the more it's like opening one hidden door after another—just the word "sound" alone can unravel a whole web of vibrations, media, interference, diffraction, and biological effects.

In order to get every parameter right, Xiao Yao forced the system to bring up all the acoustic modules in the space, repeatedly reenacting the standing wave formation process and deducing the penetration loss of different frequencies in soft tissue.

When he finally stood beside the robotic arm and personally calibrated the polarization direction of the piezoelectric ceramic sheet, his fingertips burned—this was no longer just a formula on paper, but a real force that could vibrate the air and shake flesh. If he could truly tame it, it would be a silent shield in crucial moments.

An environment with a noise level of 120 decibels or higher, which is inaudible to the human ear, is enough to cause nerve endings to scream and cochlear hair cells to die off collectively.

At 150 decibels or higher, the eardrum will rupture like paper, blood will seep out of the ear canal, and consciousness will be instantly overwhelmed by the torrent of noise.

Infrasound is even more troublesome: it glides lazily through air and water, attenuating very slowly; its wavelength is often tens of meters, able to bypass walls and turn corners, spreading throughout the field like a ghost—powerful but difficult to aim at.

High-power infrasound can cause the internal organs to vibrate violently in rhythm: nausea, suffocation, bulging eyes, and in severe cases, ruptured blood vessels and torn liver and spleen.

Ultrasound is like a narrow-bladed dagger, advancing in a straight line with precise aim and amazing penetrating power, but with a pitifully small killing radius.

Therefore, practical acoustic equipment will never use audible frequencies—it's too conspicuous. The truly formidable weapons are hidden at the two ends that are inaudible to the human ear: infrasound and ultrasound.

Infrasound weapons fall into two categories:

One type specializes in targeting the brain, with frequencies between 8 and 12 Hz, fluctuating in alpha brainwaves. Once they resonate, a person immediately falls into hallucinations, convulsions, and a breakdown of consciousness.

Another type directly targets the internal organs, locking onto the natural vibrational rhythms of the heart (4-6 Hz) and liver (5-7 Hz). When they resonate together, the five internal organs feel as if they are being hammered, causing severe pain, shock, and sudden death.

Xiao Yao didn't aim too high; he set his sights on a small, palm-sized, lightweight infrasonic self-defense device that could fire instantly and stop instantly.

On the seventh day of Professor Xu's team's experiment, Xiao Yao had thoroughly digested all the theories. He disassembled the original design with reference to the drawings, eliminated redundant modules, redesigned the circuit topology, and compressed the entire system into a fist-sized titanium alloy casing.

The research institute was fully equipped, and he would deliberately choose to enter during the lunch break—while everyone else was in the cafeteria, he would solder circuits, attach crystal oscillators, and calibrate resonant cavities alone in the cleanroom.