Question: How are the books in the library magnetized and degaussed? What are their principles?
Paper is a poor conductor of magnetism, so magnetism exists in books for a long time. When the degaussed book passes through the sensor, the magnetism in the book will have an electromagnetic effect on the wires in the sensor and will give an alarm. When degaussing, you can see the clerk put the book on a plastic box and degaussing: there is a magnetic pole opposite to the book in the plastic box. Because the magnetism in the book is caused by the friction between the book and the magnetic pole, there is only one magnetic pole. The magnet in the plastic box is opposite to the magnetic pole on the book, and the two cancel each other out. Hehe O(∩_∩)O~