A Silent Sonic-Sweeping Motor David Lin From an early age, I watched engineers and my parents tinker with motors, sparking my passion for engineering. Reading Steve Jobs by Walter Isaacson inspired me to pursue entrepreneurship, admiring Jobs’s pursuit of perfection and his insight into problems in life—values that have become my own engineering principles. WHY Although an electric toothbrush cleans better than a manual one, its loud noise hurts the experience and discourages usage. Even Oral-B’s “quiet” models remain noisy—though the sound drops once brushing starts. I want it to be quiet from the very fi rst moment. Philips models are softer but too costly for the general public. For those prone to anxiety or insomnia, this daily high-pitched, mosquito-like noise may disturb calm and relaxation. I wonder: What causes the noise—and can I fi x it? HOW First ， to fi nd out where the noise is from? 1.1 Mechanical Noise During motor operation, contact between rotating components produces frictional noise. The motor shaft is supported by bearings, and as it rotates, the steel balls inside the bearings rub against the inner and outer raceways, generating friction and vibration. This mechanical interaction results in continuous noise, particularly noticeable at startup and under high-speed conditions. 1.2 Electromagnetic Noise Electromagnetic noise arises from the interaction between the magnetic fi eld of the permanent magnet and the copper coil. This interaction induces electromagnetic vibration, which creates an audible high- frequency hum. Such noise becomes more pronounced in compact motors and can cause discomfort for sound-sensitive users. Problem Analysis 2.1 Reduction of Mechanical Noise A preload spring was added between the bearings to stabilize the motor shaft and reduce bearing displacement. This design minimizes internal friction between the bearing components, ensures smoother rotation, and e ff ectively decreases mechanical noise levels during both startup and steady operation. 2.2 Reduction of Electromagnetic Noise To mitigate electromagnetic vibration, high- magnetic-strength magnets were selected to improve magnetic fi eld stability and reduce magnetic fl ux fl uctuation. Furthermore, the copper wire diameter was optimized to balance current fl ow and torque output. This adjustment not only improves motor performance but also signi fi cantly suppresses the electromagnetic noise generated during operation. Technical Solutions White-Motor Shaft Blue-Purple Bearing Red-Spring Blue-Magnet Light Purple- Rotor Core Yellow-Coil Purple-Bearing Green- Wire Frame Sky Blue - Motor Housing Gray-Stator Core Physical Illustration of the Motor Interior Spring Testing – Physical Illustration Spring Parameters: Wire Diameter × Height × Number of Coils ①φ0.42*5.0*4 ； ②φ0.4*5.0*4 ； ③φ0.5*5.5*4 ； ④φ0.6*5.0*4 ； ⑤φ0.5*5.0*5 ； ⑥φ0.6*8.0*6 ； ⑦φ0.65*12.0*5 。 Copper Wire Testing – Physical Illustration Copper Wire Specification: Wire Diameter ① φ 0.11 ；② φ 0.15 ；③ φ 0.22 ；④ φ 0.26 ； ⑤ φ 0.30 ； ⑥ φ 0.35 ；⑦ φ 0.4 。 Conclusion After repeatedly testing various combinations of spring dimensions, copper wire diameters, and coil counts, we concluded that using a spring ( φ 0.4 × 5.0 × 4 turns) provides the required motor preload and e ff ectively reduces bearing noise. Meanwhile, using copper wire ( φ 0.22 × 85 turns) achieves optimal current and torque performance while signi fi cantly reducing the electromagnetic noise generated during motor operation. Adding magnets on shafts Pressing a ball bearing into a motor shell Learning how to wind copper wire on a motor from an engineer Assembling springs to motors WHAT Brand: Oral-B Noise Level: 66 dB or above Brand: Philips Noise Level: 46 – 65 dB Brand: OMOMO Noise Level: 40 – 45 dB Title of Utility Model: A Low-Noise Sonic Toothbrush Motor Patent Holder: Dongguan Xinchaowei Intelligent Technology Co., Ltd. Address: Room 202, Building 2, No. 18 Gongye 1st Road, Tangxia Town, Dongguan City, Guangdong Province, 523000, China Inventors: Lin Zhangmin, Lin Kequan （ David Lin) Patent Number: ZL 2024 2 2052887.0 Publication Number: CN 223039785 U Filing Date: August 22, 2024 Date of Authorization and Announcement: June 27, 2025 Applicant: Dongguan Xinchaowei Intelligent Technology Co., Ltd. Inventors (at time of fi ling): Lin Zhangmin, Lin Kequan Statement: The China National Intellectual Property Administration (CNIPA) has examined this utility model patent application according to the Patent Law of the People's Republic of China, decided to grant the patent right, and hereby issues this certi fi cate. The patent right takes e ff ect from the date of announcement of the authorization. The validity of the patent right and any subsequent changes shall be subject to registration by the CNIPA. Director General: Shen Changyu Date: June 27, 2025 Seal: China National Intellectual Property Administration Page: 1 of 1 Utility Model Patent Certi fi cate This is not a great or high-tech invention, but one that was born out of countless trials and persistence. I spent nearly two months testing di ff erent spring materials, sizes, and heights, and repeatedly adjusting the diameter and coil count of the copper wire. Each failure brought me one step closer to the answer. In the end, I discovered the most compatible combination of materials, which signi fi cantly reduced the motor’s operating noise. Throughout this process, I didn’t rely on expensive equipment or complex algorithms. What I relied on was simple, continuous experimentation and veri fi cation. While giants like Oral-B and Philips approach problems through massive R&D systems, I relied on something much smaller but more enduring — persistence. I’ve come to realize that in both engineering and in life, great achievements are often born from ordinary things — as long as you keep testing, again and again, without giving up. Why I Earned This Patent ？