Zero-Power Inertial Switches: Moving Beyond the Limits of Power and Size

Miniaturized sensor technology allows engineers to build more functionality into less space than ever before; but increasingly complex features require more battery power, which takes up more space. How do design engineers decide which comes first, performance or portability? The world’s smallest inertial switch may offer the best of both worlds.

Selecting the right microelectromechanical system (MEMS) for an application depends on the role of the sensor. If the purpose of a device is to detect shock or impact, an inertial sensor is an ideal option. In this application, the sensor acts as a motion switch activated by a specific g-force. When the g-force threshold is detected, the switch wakes up and initiates a new process. In a medical alert system, for example, the impact of a patient’s fall is the signal, and alerting a caretaker is the new process.

Allocating the Power Budget

To accommodate smaller devices, engineers are thinking about battery power earlier in the design process. Essential components like sensors, processors, and displays all add to digital overhead, consuming much of the power budget even when operated at the lowest possible current. Dimming a screen or slowing processing speed also helps conserve power, but the most effective method is simply turning off components that don’t need to run continuously.

A zero-power motion switch is a builtin power saver. By remaining effectively off, or passive, until a defined signal is received, the switch has no impact on the power budget. Battery life is conserved for components that must remain awake to monitor for a signal, such as the presence (or absence) of human speech. Accelerometers are an example of an always-on component (see the sidebar, “Selecting the Right Motion Sensor: Accelerometer vs. Zero-Power Motion Switch”). They consume battery power quickly by continuously processing data. For devices like pacemakers, this function is critical, but for many applications nonstop data collection isn’t required or helpful. In these cases, accelerometers consume more of the power budget than their value warrants.

Passive motion switches respond only to relevant signals. If lower force or shorter duration impacts are not important, the switch doesn’t waste power logging them. For example, consider a wireless x-ray machine jostling on a cart between locations. Such low-level shocks are part of normal use and usually not a cause for concern. A drop to the floor, on the other hand, requires the unit to be recalibrated immediately. In this case, the shock sensor is activated and triggers an alert such as a flashing LED light.

Richard Halstead, CEO of Empire Magnetics, sees tremendous potential for this technology in manufacturing devices of all kinds, medical and otherwise. “An obvious application for this product is monitoring electric motors. As bearings in a motor begin to fail, the inertial sensor detects the change in acceleration and alerts the operator. This would be of particular value in remote locations,” he says.

Selecting the Right Motion Sensor: Accelerometer vs. Zero-Power Motion Switch

Accelerometers and motion switches perform some of the same functions, but there are important differences. The best choice for an application depends on the hardware interface, power budget, data processing needs, and battery accessibility for recharging or replacement.

“Based on the application, we typically evaluate a sensor technology on several criteria — battery shelf life, the ability to meet our motion requirements, and ease of integration into production at a reasonable price,” says Matt Bertram, director of manufacturing operations at SportsMEDIA Technology Corp (SMT). “Accelerometers have come a long way in terms of battery life, but only HT Micro’s inertial switch checks all the boxes for us.”

Inspiring the Next Next-Generation Medical Devices

The merging of sensing, motion, and analytics — in applications like medical wearables and implantable devices — was unimaginable to most people even just a few years ago. Growth in the medical device market shows no sign of abating. In 2021 alone, the FDA’s Center for Devices and Radiological Health received nearly 18,000 conventional premarket submissions and 2,200 Emergency Use Authorization (EUA) requests. As devices incorporate more customization, advanced analytics, and artificial intelligence, design engineers will continue to be challenged to accommodate more complex features without increasing the power budget or product size. The zero-power motion switch is a valuable tool for meeting these competing priorities.

This article was written by Danny Czaja, CEO, HT Micro, Albuquerque, NM. For more information, visit here . Contact: This email address is being protected from spambots. You need JavaScript enabled to view it. .

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