📚 Magnetism & Electromagnetism | 磁学与电磁学
Magnetism and electromagnetism form the backbone of many technologies we take for granted in modern computing, from the hard disk drives that store vast amounts of data to the tiny sensors that detect when a laptop lid is closed. Understanding how magnetic fields behave and how electric currents can create and manipulate them is a foundational topic that bridges physics and computer hardware. This article explores the core principles of magnetism and electromagnetism, then examines their crucial roles in data storage, power supplies, input devices, and emerging memory technologies.
磁学与电磁学是现代计算机中许多司空见惯技术的基石，从存储海量数据的硬盘驱动器，到检测笔记本电脑盖是否闭合的微型传感器，处处都离不开它们。理解磁场的特性以及电流如何产生和控制磁场，是连接物理学与计算机硬件的一个基础课题。本文将探讨磁学与电磁学的核心原理，并审视它们在数据存储、电源供电、输入设备以及新兴存储技术中的关键作用。
1. Magnetic Fundamentals | 磁的基本概念
Every magnet possesses two poles, north and south. Like poles repel each other while unlike poles attract. The region around a magnet where magnetic forces can be detected is called a magnetic field, which is represented by field lines running from north to south outside the magnet. The strength of the field is greatest at the poles. Magnetic materials, such as iron, nickel, and cobalt, experience a force when placed in a magnetic field.
每个磁体都有两个磁极，即北极和南极。同名磁极相互排斥，异名磁极相互吸引。磁体周围能够感受到磁力作用的区域称为磁场，通常用从北极指向南极的磁感线来表示。磁极附近的磁场最强。铁、镍、钴等磁性材料在磁场中会受到力的作用。
In computing, permanent magnets are used in speakers, microphones, and even to hold smartphone covers shut. The Earth itself acts like a giant magnet, which is why a compass needle aligns north–south. This concept of magnetic poles helps us understand how data is written on magnetic media, as tiny regions on a disk can be magnetised to represent 0s and 1s.
在计算设备中，永久磁铁用于扬声器、麦克风，甚至用来吸附智能手机的保护套。地球本身就像一个巨大的磁体，指南针的指向正是基于这一原理。磁极的概念有助于我们理解数据是如何写入磁性介质的，磁盘上的微小区域可以被磁化来表示0和1。
2. Magnetic Materials and Domains | 磁性材料与磁畴
Ferromagnetic materials like iron contain tiny regions called magnetic domains. In an unmagnetised state, these domains point in random directions, cancelling out the overall magnetic effect. When the material is placed in a strong magnetic field, the domains align in the direction of the field, and the material itself becomes a magnet. This process is called magnetisation. Soft magnetic materials, such as iron, lose their magnetism quickly once the external field is removed, while hard magnetic materials, like steel, retain it, making them suitable for permanent magnets.
铁等铁磁材料内部含有称为磁畴的微小区域。在未被磁化的状态下，这些磁畴指向混乱，整体磁性相互抵消。当材料被放置在一个强磁场中时，磁畴顺着磁场方向排列，材料本身就成了磁体。这一过程称为磁化。软磁材料（如铁）在外部磁场撤除后会很快失去磁性；而硬磁材料（如钢）能保持磁性，因此适合制作永久磁铁。
Hard disk platters are coated with a thin film of a hard magnetic material. The write head, an electromagnet, switches the direction of tiny domains to store binary information. The ability to keep these domain orientations stable for years is essential for reliable data retention.
硬盘盘片上涂覆着一层硬磁材料薄膜。写磁头（一个电磁铁）通过切换微小磁畴的方向来存储二进制信息。这些磁畴方向能多年保持稳定，对可靠的数据保存至关重要。
3. Electromagnetism: Current Creates Magnetism | 电磁学基础：电流产生磁性
When an electric current flows through a straight wire, a circular magnetic field is generated around it. The direction of the field can be found using the right-hand grip rule: if you grip the wire with your right hand so that your thumb points in the direction of conventional current (positive to negative), your curled fingers show the direction of the magnetic field. Wrapping the wire into a coil, or solenoid, strengthens the magnetic field inside; each turn of the coil contributes to the total field, creating a uniform and concentrated magnetic field similar to that of a bar magnet.
当电流通过一根直导线时，会在其周围产生一个环形磁场。磁场的方向可用右手握线定则来判断：用右手握住导线，使拇指指向传统电流方向（正极到负极），弯曲的四指即指向磁场方向。将导线绕成线圈（即螺线管）可以增强内部的磁场；每一匝线圈都对总磁场有贡献，从而产生一个类似于条形磁铁、均匀且集中的磁场。
Electromagnetism is the heart of the read/write heads in hard disk drives. A current pulse through the head's coil creates a strong magnetic field that can magnetise a tiny spot on the platter. Later, the same head can sense changes in magnetisation to read data back.
电磁学正是硬盘驱动器中读写头的核心。一个通过读头线圈的电流脉冲产生强磁场，能使盘片上极小的区域磁化。随后，同一磁头可以感知磁化状态的变化，从而读取数据。
4. Electromagnets and Their Applications | 电磁铁及其应用
An electromagnet is formed by inserting a soft iron core inside a solenoid. When current flows, the iron core becomes strongly magnetised, greatly enhancing the magnetic field. The key advantage of an electromagnet is that its magnetism can be switched on and off by controlling the current, and its strength can be adjusted by varying the current or the number of coil turns. Electromagnets are used in relays, electric bells, and lifting heavy scrap metal.
将软铁心插入螺线管内部就构成了电磁铁。当电流通过时，铁心被强烈磁化，显著增强了磁场。电磁铁的主要优点是可通过控制电流来开启和关闭磁性，并且可以通过改变电流或线圈匝数来调节磁场强度。电磁铁广泛应用于继电器、电铃以及起吊废钢的场合。
Inside a computer, small electromechanical relays (though mostly replaced by transistors) historically performed switching in early machines. More importantly, the voice coil motor that positions the hard disk's read/write arm is essentially an electromagnet interacting with a permanent magnet, allowing precise, high-speed movements.
在计算机内部，小型机电继电器（尽管已大多被晶体管取代）曾在早期机器中实现开关功能。更重要的是，定位硬盘读/写臂的音圈电机本质上是一个与永久磁铁相互作用的电磁铁，可实现精确、高速的移动。
5. Magnetic Storage: Hard Disk Drives | 磁存储：硬盘驱动器
Hard disk drives (HDDs) store data as tiny magnetised regions on spinning platters. Each platter is divided into concentric tracks and sectors. A read/write head floats on a thin cushion of air just nanometres above the surface. To write data, the head generates a magnetic field that aligns the magnetic domains in one of two possible directions, representing a binary 1 or 0. Reading is achieved by detecting the tiny voltage induced when the magnetised region passes under the head, a process based on electromagnetic induction.
硬盘驱动器（HDD）将数据以微小磁化区域的形式存储在旋转的盘片上。每个盘片被划分成同心磁道和扇区。读/写磁头悬浮在离盘片表面仅几纳米的空气薄垫上。写数据时，磁头产生磁场，使磁畴按两个可能方向之一排列，表示二进制的1或0。读取则是依靠磁化区域经过磁头下方时感应产生的微小电压来实现的，这一过程基于电磁感应原理。
Modern HDDs use giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) sensors, which are highly sensitive to small magnetic field changes. This allows for extremely high data densities, storing terabytes of data in a compact form factor.
现代硬盘采用巨磁阻或隧穿磁阻传感器，它们对微小的磁场变化高度敏感。这使得数据密度极高，能以紧凑的形态存储数TB的数据。
6. Magnetic Tape and Floppy Disks | 磁带与软盘
Before solid-state drives became ubiquitous, magnetic tape and floppy disks were common for backup and portable storage. Magnetic tape stores data in a linear fashion on a plastic strip coated with magnetic material. A read/write head scans along the tape, similar to an audio cassette. Floppy disks use a flexible plastic disk coated with magnetic oxide and housed in a protective sleeve. Both technologies rely on the same principle of domain alignment controlled by electromagnets.
在固态硬盘普及之前，磁带和软盘常用于备份和便携存储。磁带以线性方式在涂有磁性材料的塑料带上存储数据，读写头沿磁带扫描，类似于录音带。软盘则使用一张涂有磁性氧化物的软塑料盘片，装在保护套内。这两种技术都依赖于电磁铁控制磁畴排列这一相同原理。
Though largely obsolete in everyday computing, magnetic tape remains widely used in enterprise backup systems due to its low cost per gigabyte and long shelf life. Understanding these legacy technologies helps students appreciate the evolution of data storage.
尽管在日常计算中已基本过时，但磁带由于每GB成本低、保存期限长，仍广泛应用于企业备份系统。了解这些传统技术有助于学生领会数据存储的演进历程。
7. Magnetic Core Memory and Early Computing | 磁芯存储与早期计算
In the 1950s and 1960s, magnetic core memory served as the main working memory (RAM) for computers. It consisted of a grid of tiny ferrite rings (cores) through which wires passed. Each core could be magnetised in one of two directions, storing a single bit. Writing was accomplished by sending current pulses through the wires to set the core's magnetic state. Reading was destructive – a sense wire detected whether a core flipped, which would induce a voltage pulse.
在二十世纪五六十年代，磁芯存储器曾是计算机的主工作存储器（RAM）。它由一个由细小铁氧体环（磁芯）组成的网格构成，导线穿过这些磁芯。每个磁芯可以按两个方向的某一方向磁化，从而存储一个比特位。写入是通过导线发送电流脉冲来设定磁芯的磁态。读取具有破坏性——感应线检测磁芯是否翻转，如果翻转就会感应出一个电压脉冲。
Magnetic core memory was non-volatile, meaning it retained data without power, a property that modern RAM lacks. This pioneering use of electromagnetism laid the groundwork for later solid-state memory devices.
磁芯存储器是非易失性的，即断电后仍能保留数据，这是现代RAM所不具备的特性。这一先驱性的电磁学应用为后来的固态存储器件奠定了基础。
8. Principles of Electromagnetic Induction | 电磁感应原理
Electromagnetic induction is the process by which a changing magnetic field induces an electromotive force (EMF) and thus a current in a conductor. Michael Faraday discovered that moving a magnet in or out of a coil causes a deflection on a galvanometer. The magnitude of the induced EMF depends on the rate of change of the magnetic flux through the circuit. This principle is exploited in generators, transformers, and the read heads of magnetic storage devices.
电磁感应是指变化的磁场在导体中感应出电动势进而产生电流的过程。迈克尔·法拉第发现，将磁铁移入或移出线圈会使电流计发生偏转。感应电动势的大小取决于穿过电路的磁通量变化率。这一原理被应用于发电机、变压器以及磁存储设备的读磁头中。
In an HDD read head, the magnetised regions on the spinning platter act as the moving magnets. As they pass the read sensor, the changing flux induces voltage pulses that are decoded into binary data. Thus, the very act of reading data is a direct application of Faraday’s law of induction.
在硬盘读磁头中，旋转盘片上的磁化区域充当移动的磁铁。当它们通过读传感器时，变化的磁通量感应出电压脉冲，进而被解码为二进制数据。因此，读取数据这一行为本身就是法拉第感应定律的直接应用。
9. Transformers and Inductors in Computer Power Supplies | 计算机电源中的变压器和电感器
A transformer consists of two coils (primary and secondary) wound on a common iron core. An alternating current in the primary coil creates a changing magnetic flux in the core, which induces an EMF in the secondary coil. The ratio of the voltages is proportional to the ratio of the number of turns in the coils. In computer power supply units (PSUs), transformers step down the high-voltage AC mains to lower AC voltages, which are then rectified and regulated to provide stable DC outputs like +12V, +5V, and +3.3V.
变压器由绕在同一铁心上的两个线圈（初级和次级）组成。当初级线圈通过交流电时，铁心中产生变化的磁通量，从而在次级线圈中感应出电动势。电压比与线圈匝数比成正比。在计算机电源单元（PSU）中，变压器将高压交流市电降压至较低的交流电压，然后经整流和稳压，提供+12V、+5V和+3.3V等稳定的直流输出。
Inductors, also based on electromagnetism, are used in voltage regulator modules (VRMs) on motherboards to smooth out current ripples. They store energy in a magnetic field when current flows and release it when the current decreases, ensuring a steady supply to the CPU and other components.
电感器同样基于电磁学原理，用于主板上的电压调节模块，以平滑电流纹波。当电流流过时，它们在磁场中储存能量；当电流减小时释放能量，从而确保为CPU和其他组件提供稳定的供电。
10. Hall Effect Sensors in Computer Peripherals | 计算机外设中的霍尔效应传感器
The Hall effect occurs when a current-carrying conductor is placed in a magnetic field perpendicular to the current, generating a small voltage across the conductor. Hall effect sensors can detect the presence, strength, and polarity of a magnetic field. They are widely used in laptops to detect whether the lid is closed – a small magnet in the display triggers the sensor in the base, sending a signal to put the computer to sleep or turn off the screen.
霍尔效应是指当载流导体被置于与电流垂直的磁场中时，导体两侧会产生一个微小的电压。霍尔效应传感器能探测到磁场的存在、强度和极性。它们被广泛用于笔记本电脑检测盖子是否闭合——显示屏中的小磁铁触发基座内的传感器，发送信号使电脑进入休眠或关闭屏幕。
Hall sensors also appear in keyboards with magnetic switches (for gaming), cooling fan speed control (detecting rotation), and even in some tablet styluses to sense tilt and pressure. Their solid-state nature makes them reliable and durable.
霍尔传感器还出现在采用磁开关的键盘（游戏用）、散热风扇转速控制（检测旋转）中，甚至一些平板触控笔也利用它们来感知倾斜和压力。其固态特性使其可靠耐用。
11. Wireless Charging and Electromagnetic Fields | 无线充电与电磁场
Wireless charging, or inductive charging, uses two coils: a transmitter coil in the charging pad and a receiver coil in the device. An alternating current in the transmitter creates a time-varying magnetic field, which induces an alternating EMF in the receiver coil by electromagnetic induction. This EMF is then rectified to charge the battery. The principles are exactly those of a transformer, but with an air core and loose coupling.
无线充电（感应充电）使用两个线圈：充电板中的发射线圈和设备中的接收线圈。发射线圈中的交流电产生一个时变磁场，通过电磁感应在接收线圈中感应出交流电动势。此电动势经整流后为电池充电。其原理与变压器完全相同，只不过是用空气芯且耦合较松。
Many smartphones, smartwatches, and even some laptops now support Qi wireless charging. The efficiency depends on alignment and distance, prompting engineers to design magnetic alignment aids – again using permanent magnets to hold devices in the optimal position.
如今许多智能手机、智能手表乃至部分笔记本电脑都支持Qi无线充电。充电效率取决于对准和距离，促使工程师设计磁吸对准辅助装置——再次用到了永久磁铁来将设备固定在最佳位置。
12. Future Magnetic Technologies: MRAM | 未来磁技术：磁阻式随机存取存储器
Magnetoresistive Random Access Memory (MRAM) is an emerging non-volatile memory technology that stores bits using magnetic states rather than electric charges. In spin-transfer torque MRAM (STT-MRAM), a current of spin-polarised electrons flips the magnetisation of a free magnetic layer, altering the resistance of a magnetic tunnel junction. This resistance change is read as a 0 or 1.
磁阻式随机存取存储器（MRAM）是一种新兴的非易失性存储技术，它利用磁态而非电荷来存储比特。在自旋转移力矩MRAM（STT-MRAM）中，一股自旋极化电子流翻转自由磁性层的磁化方向，改变磁隧道结的电阻。这一电阻变化即被读取为0或1。
MRAM promises high speed, low power consumption, and unlimited endurance, combining the best traits of DRAM and flash memory. It is already used in niche applications, and as fabrication techniques improve, it may become a mainstream memory in future computing architectures, once again placing magnetism at the heart of computer storage.
MRAM有望实现高速度、低功耗和无限次的擦写次数，集DRAM和闪存的优点于一身。它已在某些小众领域得到应用，随着制造工艺的进步，可能成为未来计算体系中的主流存储器，让磁学再次站上计算机存储的核心位置。
Published by TutorHao | Computer Science Revision Series | aleveler.com
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