Students who have chosen electronics as a career often ignore a field of Electrical Engineering that one can base an entire career of specialization. It is the world of “Transducers”. Wikipedia defines it as:
“A transducer is a device that converts a signal in one form of energy to another form of energy. Energy types include (but are not limited to) electrical, mechanical, electromagnetic (including light), chemical, acoustic and thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a transducer. Transducers are widely used in measuring instruments.
A sensor is used to detect a parameter in one form and report it in another form of energy, often an electrical signal. For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electricity for display at a remote gauge.
An actuator accepts energy and produces movement (action). The energy supplied to an actuator might be electrical or mechanical (pneumatic, hydraulic, etc.). An electric motor and a loudspeaker are both actuators, converting electrical energy into motion for different purposes.
Combination transducers have both functions; they both detect and create action. For example, a typical ultrasonic transducer switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves. Rotating a DC electric motor's rotor will produce electricity and voice-coil speakers can also act as microphones.”
Engineers who are experts in this field of electronics often find a niche in a company and act as on-site gurus when projects require this expertise.
Transducers exploit some physical phenomena such as motion (velocity, acceleration, force, momentum), light, electromagnetism, temperature, pressure, chemical reaction, fission (nuclear radiation), electro fluorescence (oscilloscope tube, TV, X-ray imaging), and magnetostriction.
Some examples of transducers include:
Accelerometers (Electro mechanical today implemented by hybrid ICs)
Buzzers (Electro mechanical)
Capacitive Touch Sensors (Electro magnetic)
Color Sensors (Photoelectric effect usually implemented with ICs)
Current Transducers (Electro magnetic)
Dust and Smoke Sensors (Hybrid IC based on radiation)
Encoders/Potentiometers (Electro mechanical)
Flex Sensors/Strain Gauges (Electro mechanical)
Float Level Sensors (Electro mechanical)
Flow Sensors (Electro mechanical)
Force Sensors (Electro mechanical)
Gas Sensors (Electro chemical)
Gyroscopes (Electro mechanical now implemented in hybrid ICs)
Image Sensors (Photo electric effect)
Inclinometers (Electro mechanical in hybrid ICs)
Magnetic Sensors (Electro magnetism)
Moisture Sensors (Electro chemical in hybrid ICs)
Motion Sensors (Electro mechanical)
Optical Sensors (Photo electric effect)
Position Sensors (Electro mechanical)
Pressure Sensors (Electro mechanical in hybrid ICs)
Proximity Sensors (Electro mechanical and capacitance effect)
Temperature Sensors (Resistance change in ICs)
Thermistors (Resistance change in materials)
Thermocouple (Dissimilar metals voltage effect)
Ultrasonic Transducer (Piezoelectric effect)
Vibration Sensors (Electro mechanical)
Don’t forget the lowly switch. What can you possibly learn about a switch? Well, there are toggle, push button, rotary, and sliding switches. They may be designed for logic circuits or handle large currents. Are they for AC or DC? Is a particular switch designed to be used in a commercial, industrial, or military environment? How many operations will it withstand before needing replacement? How do you trade off cost versus longevity? If used for logic, does it need to be debounced?
On the other scale of things, take a motor for instance. There are very small and light motors designed for driving drone propellers. There are medium sized motors for rolling up/down the windows in your car. There are very large motors for industrial uses. There are DC motors (separately excited, shunt, series, permanent magnet), AC motors (induction, synchronous), Other motors (stepper, brushless, hysteresis, reluctance), etc. All of these motor types require some sort of electronic control and monitoring. It’s a very large field of knowledge.
How about a lamp or “Indicator” as they are called in the profession. Do you use an incandescent type or LED or perhaps Neon? What power supply must be available to light it? How about ergonomics? Should it be round or square? What color should it be to prevent confusion?
When you hear people talking about electronic categories such as “digital”, “analog”, “radio or RF”, don’t forget the world of transducers. You can make a living from that knowledge.
This article doesn't fit well in any of the categories since it's more philosophical than practical.