There is an increasing demand for highly sensitive, low-G, microscale acceleration sensors in the expanding universe of electronics. Accelerometers are mechanical sensors that measure an object’s acceleration in a single- or multi-axis direction for gravity, tilt, and vibrational inputs.
The “direction of the detectable accelerations” via an STMicroelectronics MEMS 3-axis accelerometer. Image used courtesy of LIS2DH datasheet.
Before the 1970s, designers were relegated to bulky, expensive conventional accelerometers. Meanwhile, the market was becoming saturated with smaller consumer devices that required small-footprint ICs. This led to the research and development of MEMs (micro-electro-mechanical systems) technology. Researchers found a way to miniaturize sensors while still maintaining robust packaging for operation in severe conditions.
Now, designers are able to seamlessly integrate MEMs accelerometers into sensitive commercial devices such as smartphones, shock monitoring equipment, and vibration measurement devices used in civil engineering practices. Utilizing MEMS technology in accelerometers has helped reduce device size and costs.
However, like any electronic device, there are still challenges designers face, particularly regarding accelerometer bandwidth and sensitivity.
A Brief Recap of AC and DC Accelerometers
There are two classes of accelerometers, AC and DC response. AC accelerometers devices have an AC-coupled output and DC accelerometers have a DC-coupled output. The main difference is that, with a DC response, the output is able to drive down to zero Hz making it easier to sense small changes in motion.
DC-based accelerometers are the most commonly used over AC accelerometers since they are not equipped with the same level of sensitivity to measure smaller changes of motion.
AC-response accelerometers (top) vs. DC-response accelerometers (bottom). Image used courtesy of TE Connectivity
Of this class of accelerometers, the prominent is a capacitive type which can be found in large commercial applications such as automotive air-bag systems and mobile devices. In physics, the principle of acceleration sensing revolves around the inertia of a moving body that is converted into a force.
Applying this rule to capacitive sensors, allows designers see an object’s acceleration convert into current, charge, or voltage.
MEMS Accelerometers: Challenges and Improvements
By employing MEMs technology, developers are able to achieve low manufacturing costs. The attraction of MEMs accelerometers also lies in their ability to operate in low temperatures, reduce noise levels, and offer low power dissipation.
They do, however, suffer from poor signal-to-noise ratio and limited dynamic range. As hinted at above, many design challenges for MEMs devices stem from their sensitivity due to their low bandwidth and low noise tolerance, along with keeping a small physical geometry.
Single-axis MEMs accelerometers are limited in the type of information they can gather (i.e., only from one direction). A common solution is to couple these accelerometers with external multiple-degrees-of-freedom ICs. The downside of this addition is increased footprint and costs, as well as calibration errors when simulations and testing occurs. Obviously, industry focus on flexibility, low costs, and small footprints are at odds with such a design.
To combat calibration errors, designers utilize various simulation software programs such as CoventorWare, which targets design issues that are faced when integrating external components.
TDK Corporation and Tronics Microsystems’ AXO315 Sensor
TDK plans to roll out a new MEMs-base sensor through its Tronics Microsystems division of temperature and pressure sensors mid next year.
The sensor, the Tronics AXO®315, is a single axis, closed-loop MEMs accelerometer, equipped with a 24-bit digital interface, and is claimed to outperform commercial MEMs sensors by handling severe temperature and intense vibration. The 4 g (1 g = acceleration caused by the Earth’s gravity) vibrations with an outstanding vibration rejection, for precise industrial motion and tilt control.
TDK’s AXO315 Sensor has an operating temperature range of -55 °C to +105 °C and runs on a 5V power supply. Image used courtesy of TDK Corporation.
Notably, TDK has chosen to make an Arduino-based evaluation kit available for this sensor, which is intended to help engineers attain better testing functionalities. Being able to use a portable device along with an electronic prototyping platform such as an Arduino enables users to design and test anywhere. This makes for a promising solution to the new work-from-home lifestyle that most manufacturers have had to adapt.
MEMs Accelerometers Level Up for Data Center Bandwidths
MEMs accelerometers such as this one are arguably a step in the right direction as it shows a bandwidth of slightly over 300Hz, but with a data rate of 2500Hz, giving it a slight advantage against the current market.
In order to meet the growing rate of data transfer in electronics, an increase in bandwidth would allow for more MEMS accelerometers to be utilized in data centers and highly-sensitive information applications.
As a designer, do you prefer having design flexibility over bandwidth? Share your MEMs experience in the comments below.