Piezoelectric, Electromagnetic, and Electrostatic Devices: A Comparison

Today’s post is a guest post by SensComp, a manufacturer of ultrasonic sensors. They also provided this cool infographic:

Which Is Better? Comparing Piezoelectric, Electrostatic, And Electromagnetic Devices

For your electronic sensor application, selecting the right equipment matters. Do you need a rugged device capable of handling substantial stress over time? Is a small physical footprint your critical consideration, or is pinpoint accuracy the priority?

With a host of options now available, it’s worth breaking down the benefits, drawbacks and common characteristics of three popular sensor solutions — piezoelectric, electromagnetic and electrostatic — to discover which electrical approach is the best-fit for your operations.

Good Vibrations

Piezoelectric devices depend on vibration to both create electrical current and sense changes in the environment. Here’s how it works: When a crystal — or crystal-like structure — is placed between two metal plates and mechanical force is applied, electric charges within the crystal are disrupted. The resulting positive and negative charges are collected by the metal plates and used as voltage to create electric current.

This effect also works in reverse; when electrical energy is applied to the crystal directly, it expands and contracts, releasing mechanical energy as a sound wave. It is no surprise, then, that popular uses for piezoelectric devices include speakers, microphones and cellular phones. Piezoelectric systems are also ideal for detecting vibrations as seismic or ultrasonic sensors.

A piezoelectric device can be suitable for many applications, since the physical interaction between plate and crystal can produce high-output voltages. However, while its small size makes it easy to integrate, it is worth noting that this device can be expensive to produce, and the efficiency of the piezoelectric effect is directly related to the quality of materials used.

Opposites Attract

Electromagnetic equipment combines electric current and magnetism to produce controlled magnetic fields. The simplest form of an electromagnetic device uses a coil of wire — often copper — wrapped around a piece of ferromagnetic material, such as iron. When an electric current is applied to the coil, it causes the metal to magnetize and generate a magnetic field. When the current stops, so does the field. Altering the amount of electrical current applied also changes the strength of the field, allowing precise circuit control.

Electromagnetic devices come with the advantage of durability. Since no moving parts are required and magnetism doesn’t appreciably degrade over time, these sensors are long-lasting and can be used in almost any environment.

However, electromagnetic options also come with drawbacks. The apparatus is often inefficient at low frequencies and in small sizes. Plus, the material used to create one is usually expensive. This makes them ill-suited for precise sensor solutions such as MEMS devices, but ideal in systems that power washing machines, microwave ovens and power tools.

Shock Value

Electrostatic devices rely on the energy potential that exists between two oppositely charged materials. A simple example is the Van de Graff generator. This instrument leverages a positively charged metal sphere and a negatively charged grounding rod to facilitate the shift of potential — or static — energy from one point to another. The greater the differential between two points, the greater the discharge.

Devices such as photocopiers, printers, air cleaners and ultrasonic transducers all utilize the electrostatic effect to capture and convert controlled discharge into electric current. Consider, however, that uncontrolled discharge can cause physical harm or damage to equipment. Think of the small shock delivered after rubbing your feet on carpet and touching a metal object, but at much larger scale. Sturdy insulation of these devices critical.

Along with the danger of unpredictable discharges, electrostatic devices have low capacitances and their dimensions must be precisely controlled. They do, however, offer high-output voltages and are easily adjustable, making low-cost systems possible.

Current Considerations

Ultimately, it comes down to your application requirements. Need accurate sensing at a small size? Pick piezoelectric sensors. Want durability and high-output currents? Make the move to electromagnets. Looking for low-cost, easily adjustable systems? Select an electrostatic solution.

Author bio: 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.

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I have posted a number of articles over the years on sensors and sensing, and some of the terms we use in industrial automation may be a bit different than those used in this article; for electromagnetic sensing think hall effect sensors and inductive proximity switches. For electrostatic, think capacitive proximity sensors and liquid level sensors, and for piezoelectric, think accelerometers, ultrasonics, load cells and other inertial sensors. MEMS is an acronym for Micro Electro Mechanical Systems.

This article has some excellent technical information in it, and I’ll also be posting a link under the Sensors tab so people can find it easily. Thanks Margaret!

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Electrical Engineer and business owner from the Nashville, Tennessee area. I also play music, Chess and Go.

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