When washing the black fungus, put a little flour to wash it more clean. Use aluminum foil paper to stack two or three sheets together and cut with scissors to make the scissors restore sharply.
At the Apple Spring New Product Conference on April 21, Apple officially released the AIRTAG tracker, which is a Tile -like Bluetooth tracking device. Find them directly in my “application.
However, compared with publicity, this product, which is known as the anti -lost artifact, is not ideal.
In Apple’s propaganda, Airtag can be used as a small tracking device to put it on the key string or package. Once these items are lost, it can use the iPhone of many strangers around it to help long -distance positioning. When nearby, use the mobile phone for a short distance positioning navigation, and finally find the lost items. The technology and ideas of this product are very advanced, but many consumers have found that they have just lost a bag in the past, but now they have lost a bag to add an AIRTAG.
In real scenes, such as densely crowded shopping malls, theoretically more people use Apple phones. It is an indoor place again. It is where this kind of anti -lost artifact shows his body, but the result is exactly the opposite, because AIRTAG cannot identify the floor in a multi -story building, and it is not good to encounter the cover effect. difficulty.
Why this short -range positioning navigation system often fails, and why indoor navigation with smaller space is more than our commonly used outdoor satellite navigation. It’s difficult. For example, putting the bag in the mall and wanting to find the bag back by AIRTAG are basically not realistic. For example, in the underground garage of the mall, you often cannot find your own car. I want to use iPad to help find a car and find it difficult to find a car. I often see your car, but there is no response on the phone.
What is the working principle of AIRTAG? Yuan Hong, a researcher at the Institute of Empty Sky Information Innovation of the Chinese Academy of Sciences, said,
AIRTAG uses two technologies, and the first technology is to use Bluetooth as a communication connection. The second technology UWB is a technique of communication with superbody. These two connections form the basis of AIRTAG communication connection.
The basic principle of AIRTAG is that if my mobile phone can be tracked to the label of AIRTAG, my AIRTAG and my phone can be directly connected with Bluetooth. If the Bluetooth signal is not far away, the signal of the Bluetooth can be transmitted to each other. The mobile phone judges the distance between the Bluetooth signal and the distance from me based on the size of the scene.
UWB is also called ultra -broadband, which is another kind of communication technology similar to Bluetooth. UWB (UWB) works through pulse radio. It uses a series of pulses on the broadband band, so it is sometimes called IR-UWB or pulse radio UWB. In contrast: satellites, Wi-Fi, and Bluetooth use the modulation sine waves on the narrow-frequency band to transmit information.
UWB pulse has multiple important features. First of all, they are steep and narrow, and they look like peaks. Even in the noisy channel environment, it is easy to recognize. In addition, compared with other technologies such as WIFI or BLE, UWB pulses are more suitable for dense multi -diameter environments for TOF ranging. Because the object next to the main signal path will cause reflection or interruption, the radio signal that reaches the receiver through multiple paths is easily distinguished from the main signal in the IR-UWB system. But this matter is very time -consuming and difficult in the narrowband system.
UWB’s other parts of the radio spectrum are far away from the busy ISM frequency band away from the 2.4 GHz. The UWB pulse for positioning and ranging is within the frequency range between 6.5 and 8 GHz, which will not interfere with wireless transmission that occurs in other frequency bands. This means that UWB can coexist with the most popular wireless forms, including satellite navigation, Wi-Fi and Bluetooth.
When working at a typical power level, the longest distance can be about 10 meters. But if you use higher power pulses, the distance of UWB can even reach 200 meters. UWB communication can also transmit data. Among them, the effective load of the UWB packet sends data at a rate of about 7 MBPS, and can continue to accelerate, up to 32 Mbps.
Now, UWB uses the pulse sequence, the duration is 2NS, which is very short. The pulse spacing can be the same or different. Pulse repetition frequency (PRF) ranges from hundreds of thousands per second to hundreds of millions of pulses per second. The generally supported PRF is 62.4 MHz and/or 124.8 MHz, which are called PRF64 and PRF128. UWB’s modulation technology includes pulse position modulation and binary phase shift key control.
Specific to Apple AirTag, my mobile phone issued a UWB signal. When you arrive on the AIRTAG tag, rebound a signal and return to my mobile phone. There is a time difference between the transceiver signal. I only need to measure the time difference of this time, and then 8 times per second of 10 meters per second at three multiplication speeds according to the transmission speed of radio waves. My mobile phone can measure its distance at the speed of the detected time by wireless radio waves.
In theory, the accuracy of ultra -broadband measurement can be centimeter. And you can also measure the direction of the signal. With both direction and distance, I can accurately know the specific location of Airtag.
But anti -lost artifacts such as Apple AIRTAG are not ideal in actual experience. First of all, whether it is Bluetooth or UW B, the frequency band of his work is a microwave frequency band. The operating frequency band of Bluetooth is 2.4g Hertz, and the frequency band of U W B work is about 3G to 10G. Its operating frequency bands are very high, and the penetration is very weak after the frequency band is very high. As long as there is a little obstacle, it will block its signal, and he will also be attenuated in space.
We often have this experience. We even have a Bluetooth headset. When your phone is a little farther away from your headset, your Bluetooth headset cannot be heard.
We all know that AIRTAG is like a small button. Its power supply is also a button battery that can be controlled for one year. Because the voltage of the button battery is very low, the power it is launched is also small, and it further limits his communication distance, so you can get a little further. I’m looking for something.
In addition, there are usually obstructions around us. For example, I put AIRTAG in the car and want to use it to find the car. However, most of the cars are made of metal, and the metal itself has a very strong blocking effect on electromagnetic waves. Window glass also has a shielding effect on electromagnetic waves. And the more expensive the car, the greater the attenuation of its glass.
The above reasons have caused the Apple AIRTAG wireless tracker to use poorly. A new product, no matter how fascinating he blows, we should have more hearts when we buy. Even if it is a large company like Apple, his new product is not determined to be credible