We live in a world governed by electronic sensors and devices, but rarely consider the processes that underpin these familiar functions. From smartphones to household appliances, IoT connected instruments to large-scale industrial operations, devices and sensors are ever-present — and often taken for granted.
Let’s take a look under the hood with a comprehensive guide to three functional frameworks. Where are they commonly found? How do they work, and what are their potential performance pitfalls?
Electromagnetic devices and sensors are commonly found in high-use, high-stress industrial and home appliance applications. For example, washing machines and dishwashers often use electromagnetic devices to open and close solenoids that allow water to flow or force it to stop.
The principle behind this push-pull performance is simple: When electric current is applied to lengths of wire wrapped around a piece of ferrous metal, the resulting electric field creates a corresponding magnetic field. When the current stops, the magnetic field fades. This reliable on/off effect makes electromagnetic devices ideal for machines that include repetitive, long-term stress, since even moderate degradation to component parts won’t prohibit electromagnetic interaction.
Some of the biggest benefits of electromagnets include high-output currents and above-average durability — they can be integrated into almost any large appliance. Where these devices and sensors struggle, meanwhile, is in size and cost. Small-scale devices of this type are inefficient, and the material required to build reliable electromagnets is often expensive. In addition, these mechanisms produce low-output voltages, making them less-than-ideal for applications that require substantial output immediately after activation.
Under Pressure — The Piezoelectric Promise
Piezoelectric devices and sensors leverage the inherent ability of crystalline structures to produce charge disparity under physical pressure, which can in turn be captured and harvested to create high-output voltages with high capacitances.
If you’re looking for piezoelectric sensors, you’ll often find them inside gadgets that deal with sound — such as cell phones, microphones and vibration sensors. Their high-output voltages also make them useful for applications such as grill ignition and diesel fuel injection.
Here’s how it works: When mechanical stress is applied to crystalline structures, the resulting physical deformation forces oppositely charged particles to opposite sides of the crystal. This charge imbalance can then be harvested to produce electricity. The effect also works in reverse; applying substantive charge to one side of a crystal will cause it to deform slightly. The greater the charge, the greater the physical change.
Because crystalline structures can be created at extremely small sizes, piezoelectric devices are ideal for applications where physical space is at a premium. In addition, there’s no need to control gaps or spacing within these mechanisms since the effect depends on mechanical stress rather than distance. The drawbacks? Piezoelectric devices are often expensive to produce, and the type of crystal used significantly impacts the output — cheaper crystals typically result in significantly reduced coupling coefficients.
So Much Potential — The Electrostatic Effect
While electrostatic devices and sensors are becoming more common, many end-users aren’t sure exactly how they work — or how they’re best used in practical applications.
Some popular electrostatic examples include photocopiers, laser and inkjet printers, air filters and ultrasonic transducers. Why? Because these mechanisms combine the benefits of high-output voltages with easily adjustable coupling coefficients and increased capacitances — even as size is reduced. In addition, it’s possible to build highly sensitive electrostatic systems that are also low in cost.
There are some potential pitfalls to using these static-driven devices, however, including a lack of direct mechanical-to-electrical conversion and the need to strictly control sensor dimensions for optimal performance.
Wondering how an electrostatic device works? It’s simple: Take two oppositely charged metal plates and place them near each other. Keeping them slightly apart creates stored potential energy that remains within the system — unless they’re moved. Pulling the plates further apart releases this potential energy, which can then be captured and converted into electricity.
While the action of each device framework is similar — all create electric current under the right circumstances — their functions vary significantly. As a result, common usage informs best use case. For rugged, long-term applications, electromagnets stick the landing; piezoelectric performance is ideal for many audio applications; and electrostatic solutions excel in systems that require highly sensitive, high-voltage outputs.
Margaret Bezerko is President of SensComp, a world leader in ultrasonic sensors. She has 18 years of experience in the industry and currently focuses on leading the company in second stage growth.