​Semiconductor refrigerators and sound shields, the black technology of smart ca

In the past, when we bought cars, we emphasized the "engine, transmission, and chassis" as the three major components. In the era of electric vehicles, we discuss the "three electrics," namely "battery, motor, and electric control." However, now more and more cars are highlighting "refrigerators, color TVs, and large sofas" as promotional focuses. So, what high-tech is being used to make the in-car environment more comfortable?

01

Acoustic Shield for Rear Privacy

The AITO M9 features an innovative "privacy acoustic shield" function. When activated, it ensures that conversations in the rear are not overheard by the driver. This creates a private space for rear passengers. In user experience videos, when the rear passengers activate this feature and speak, the front driver can tell that there is a sound coming from the rear, but the voice seems to have passed through a thick body of water, becoming low and indistinct, making it impossible to discern the specific content of the conversation.

Even if the rear passengers speak loudly, the driver can only distinguish a few words and sense the speaker's emotions by moving their head casually. This is consistent with the official claim that it can shield 90% of the conversational information from the rear. This feature is likely a new application of active noise cancellation technology.

Active Noise Cancellation Technology

Active noise cancellation technology was initially applied in Bluetooth earphones. Since sound is produced by the vibration of objects, and these vibrations are transmitted through a medium as sound waves, when the peaks and troughs of sound waves overlap, the vibrations are canceled out, and the sound disappears. Therefore, as long as low-frequency noise (100-3000Hz) in the environment can be detected by a microphone before the noise waves reach the ears, the noise signal is transmitted to the control circuit, processed in real-time by a chip to produce an inverse phase sound wave with the same frequency and amplitude, and emitted through the speaker, interference and phase cancellation with the noise can be achieved. This way, a person wearing active noise-canceling headphones cannot hear external noise.

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Traditional automotive noise reduction methods mainly rely on passive means such as structural design, adding sound-absorbing/insulating materials, or silencers. This results in limited room for modification after the vehicle design is finalized, and due to weight and cost constraints, these traditional methods are more effective at controlling mid to high-frequency noise and less effective for mid to low-frequency noise.

After active noise cancellation technology was applied to automobiles, it first detected noise from the engine compartment and actively reduced it. Later, it further detected road noise and then used the car's speakers to play inverse phase audio to cancel out external noise, creating a quieter in-car atmosphere. The technical challenge to be solved here is that noise takes only 0.009 seconds to reach the passenger from its generation, requiring rapid calculation, transmission, and emission of inverse phase sound within this time, which poses high demands on sensors, processors, and transmission latency.Privacy Sound Shield Technology

The Privacy Sound Shield also employs active noise cancellation technology, which listens to the sounds from the back seats, performs inverse calculations, and then, using the working principle of audio zoning, tracks the specific location of the driver's head. It plays inverse audio through the headrest speakers and overhead accessory speakers to cancel out the voices from the back seats.

The key to this technology is speed; the one-way communication delay of the entire process must not exceed 20 microseconds, the multi-point sensor sampling synchronization accuracy must be within 1 micron, and it supports parallel transmission of dozens of signals. From the current test results, due to both parties being in the same space, this technology can only achieve disruption of language information and cannot completely eliminate the sounds emitted from the back seats.

02

Cooling Technology of Car Refrigerators

Car refrigerators (heating and cooling boxes) are also gradually becoming standard equipment in various "large vehicles" such as the Ideal L9, Xiaopeng X9, and Tengshi D9. The common technological routes for car refrigerators currently are semiconductor cooling and compressor cooling. Generally, the compressor cooling can reach 0°C, while the semiconductor cooling can only reach 5°C, which leads to user feedback that the cooling is not strong enough.

Semiconductor cooling utilizes the Peltier effect. As early as 1834, J.C.A. Peltier discovered that when an electric current passes through a circuit composed of different material conductors, in addition to generating a certain amount of Joule heat, there will also be heat absorption and heat release phenomena at the junctions of different conductors along the direction of the current.

This is because, under the action of an external electric field, electrons move directionally to form an electric current. The energy levels of charges in different materials are different. When passing through a junction, the charge moves from a high energy level to a low energy level, releasing energy. When it moves from a low energy level to a high energy level, it needs to absorb energy from the outside. This release and absorption of energy, when observed macroscopically, appear as a warming or cooling phenomenon at the interface of the two materials. Moreover, this phenomenon is reversible; when the current is reversed, the heat absorption point becomes the heat release point. This effect is relatively weak in metals, and metal thermometers measure the microcurrent generated due to the temperature difference between two different metals.In semiconductors, this thermoelectric effect is even more pronounced, allowing for the generation of electricity from temperature differences as well as the use of electricity for cooling/heating. A semiconductor thermocouple consists of N-type and P-type semiconductors. N-type materials have an excess of electrons, resulting in a negative thermoelectric potential. P-type materials have a deficiency of electrons, resulting in a positive thermoelectric potential; when electrons move from P-type to N-type across the junction, the temperature at the junction decreases, and their energy must increase, with the increased energy equivalent to the energy consumed at the junction. Conversely, when electrons flow from N-type to P-type material, the temperature at the junction will rise. Of course, simply connecting PN directly does not form a circuit; a third material, copper, must be introduced into the thermoelectric circuit. Connecting PN with copper does not alter the characteristics of the circuit.

By connecting a P-type semiconductor element with an N-type semiconductor element into a thermocouple and applying a direct current power source, a temperature difference and heat transfer will occur at the junction. At the upper junction, the current direction is from N to P, the temperature drops, and heat is absorbed, which is the cold end; at the lower junction, the current direction is from P to N, the temperature rises, and heat is released, thus it is the hot end. By arranging multiple PN particles in an array and sandwiching them between two insulating and thermally conductive ceramic plates, a sandwich-like structure can be formed to create a semiconductor cooling plate. Typically, the temperature difference between the top and bottom of a single layer of a semiconductor cooling plate can reach 50~60°C, and if three layers are connected in series, the temperature difference can reach 100°C.

Due to the advantages of semiconductor cooling, such as being noise-free, compact, having no moving parts, and relatively low energy consumption, it has long been used in car refrigerators. Moreover, by simply reversing the current, the cooling refrigerator can be turned into a heating box. Compared to car refrigerators using compressor solutions, the drawbacks of semiconductor cooling are that the cooling temperature is not low enough, and there may be heat leakage issues. On the other hand, the issue with compressors is that they operate with significant noise and higher energy consumption.