How Theory Informs Practical Application: Medical Devices and Maglev Trains
What do MRI Machines and Maglev Trains Have in Common?
Surprisingly: Maxwell’s Four Equations.
Thanks to Dr. Kathir Krishnamurthi, who posed the timeless question:
அதை எப்படி வேலை செய்கிறது என்று அவர்கள் கேட்பார்களா? ஆர்வம் ஏற்படுமா?
(How does it work? Do you get curious?)
To answer, let’s explore applications using examples of medical devices that allow us to peek inside the human body without a scratch—MRI, X-Ray, CT Scan, ECG—and propulsion systems such as the Maglev Train that carry people without touching the ground.
Part 1: Theory Informing Practice
At the heart of medical devices like MRI and maglev trains are four elegant equations that unify electricity and magnetism:
\[ \begin{aligned} \text{a.} \quad & \nabla \cdot \mathbf{E} = \frac{\rho}{\epsilon_0} \quad \text{[Gauss's law for electricity]} \\ \text{b.} \quad & \nabla \cdot \mathbf{B} = 0 \quad \text{[Gauss's law for magnetism]} \\ \text{c.} \quad & \nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t} \quad \text{[Faraday's law of induction]} \\ \text{d.} \quad & \nabla \times \mathbf{B} = \mu_0 \mathbf{J} + \mu_0 \epsilon_0 \frac{\partial \mathbf{E}}{\partial t} \quad \text{[Ampere-Maxwell Law]} \end{aligned} \]
- Gauss’s law for electricity: How spread out the electric flux is from a point.
- Gauss’s law for magnetism: Magnetic field lines are closed.
- Faraday’s law of induction: Changing magnetic fields induce electric currents.
- Ampere-Maxwell Law: Electric currents & changing electric fields both create magnetic fields.
Part 2: Medical Devices
A. MRI (Magnetic Resonance Imaging)
Objective: Create non-invasive images of the body using radio-waves and magnetic fields.
How does MRI work? - Medical devices take advantage of our body’s natural bio-electric signals. - Both magnetic and radio waves are passed through the body, exploiting hydrogen atoms, and the returning signals are used to create images.
B. X-Ray
Objective: Create non-invasive images of the body using electromagnetic radiation.
How does X-Ray work? - Electromagnetic waves are accelerated through a metal target and decelerate abruptly, producing x-ray photons. - These x-rays pass through the body to form images on a detector.
C. CT-Scan
Objective: Create non-invasive images of the body to detect internal injuries using x-rays.
How does CT-Scan work? - The CT scan machine uses an x-ray tube and detectors, rotates the patient, takes multiple x-ray projections at various angles, and reconstructs them to create computerized images.
D. ECG
Objective: Non-invasive measurement of heart activity.
How does ECG work? - Uses 10 electrodes (sensors) to create 12 leads. - Generates different views of electrical activity. - Electrodes pick up nuanced signals from the heart. - Signals are amplified and displayed as waveforms or printed.
Part 3: Propulsion System – Maglev Train
Objective: Engineer a magnetic propulsion system to transport loads from point A to point B.
How does a Maglev train work?
Maglev = Electromagnetism + Levitation + Propulsion + Guidance + Control & Sensing + Diagnosis and Integration
- Core technology: Principles of electromagnetism.
- Two types: Electromagnetic attraction (EMS) & electrodynamic repulsion (EDS).
Levitation
- Faraday’s Law of Induction: Changing magnetic fields induce currents, generating magnetic fields that allow the train to levitate.
- Two main methods: EMS and EDS.
Propulsion
- Linear Induction Motors: Create linear motion from electricity using a primary and secondary track of coils and a moving plate with a three-phase motor.
Guidance
- PID Control: Keeps the train centered and stable.
- PID = Proportional (Kp), Integral (Ki), Derivative (Kd) gains.
- Used for precise levitation, stability, and smooth ride.
- Example: PID is also used in coffee makers for precise temperature control.
Sensing and Diagnosis
- Sensor Redundancy: Critical for safety.
- Central Onboard Controller: Handles real-time control tasks.
- Real-time Operating System (RTOS): For precise, high-speed, critical software operations.
- Fiber-Optic Communication: For data transmission across the maglev system.
From Theory to Practice
The journey from Maxwell’s electromagnetic papers to real-world applications in medical devices and maglev trains is a testament to scientific progress—theory underpins application.