In another article, we reviewed some of the main types of MEMS devices and discussed some typical applications in the Industrial Internet of Things (IIoT). In this article, we’ll look at how MEMS products are used in some other fields.
An automobile can include many MEMS devices – over thirty in current-generation luxury vehicles.
MEMS accelerometers have long replaced electromechanical technologies as crash detection sensors in airbag systems; accelerometers and gyroscopes also appear in headlight leveling, navigation, active suspension, traction control, infotainment and rollover-detection systems.
MEMS pressure sensors are key components in engine controllers; they also appear in tire-pressure monitoring systems.
The appearance of autonomous vehicles on public roads is making headlines worldwide. Lacking a human driver’s eyes and ears, an autonomous vehicle employs a wide variety of sensors to construct a virtual image of its surroundings. Light distance and ranging (LiDAR) technology is a key part of this process, but current systems are bulky and prone to failure because they use rotating mirrors to reflect the laser light around the vehicle. Optical MEMS technology promises a great increase in performance coupled with a reduction in both cost and size; it uses an electronically-controlled MEMS micromirror to execute a scan of the vehicle surroundings in a fraction of a second.
To date, most optical MEMS devices are designed for the relatively benign consumer environment, but several suppliers are developing LiDAR MEMS devices to meet the tough automotive quality and reliability standards.
MEMS appears in the broader transportation market, too: ships and submersibles, for example, both use MEMS gyroscopes to aid in position control and navigation.
Medical Electronics
Figure 1: A few of the many biomedical functions of MEMS (Image Source: Solid-State Technology)
Medicine is fertile ground for MEMS devices. MEMS pressure sensors have been used in clinical applications for decades. A selection of non-invasive applications includes:
- Measuring intravenous (IV) blood pressure in IV lines
- Providing barometric pressure correction in blood gas analysis
- Controlling drug-release activity in inhalers
- Monitoring intrauterine pressure and baby blood pressure during birth
- Monitoring respiratory activity in ventilators
- Monitoring vacuum pressure during eye surgery
MEMS devices are moving into invasive applications, too: pressure sensors can be implanted directly into arteries to measure blood pressure and heart rate in cardiac patients.
MEMS accelerometers are used in cardiac pacemakers and senior-care residential slip-and-fall and activity-monitoring systems, among others. MEMS electrodes find applications in neuro-stimulation; MEMS sensors detect biological and chemical agents in analytical instruments; and MEMS microphones are found in hearing aids.
New medical applications are on the horizon. Researchers at UCSF and elsewhere are using MEMS technology to develop nanopore membranes for use in implantable bioartificial kidneys.
Glucose monitoring for management of diabetes is another active research area. Although home testing kits have been available for years, they require pricking a finger and depositing a blood sample on a test strip. There is considerable effort devoted to developing a non-invasive glucose test based on a MEMS sensor and an alternative physiological fluid: sweat, ocular fluid (tears), saliva, breath, urine or cellular interstitial fluid.
Consumer Products
In consumer products, MEMS accelerometer applications include screen rotation, image stabilization, and dead-reckoning tracking in smartphones and tablets; protection for hard drives in laptops, and activity tracking in wearables such as fitness bands. Video game controllers, virtual-reality headsets, and smartphones use MEMS motion sensors and microphones; football helmets use MEMS accelerometers to monitor for possible concussions. MEMS magnetometers are used in numerous consumer products as electronic compasses.
The list goes on: home environmental monitoring systems use MEMS for gas detection and humidity monitoring; many HDTVs use MEMS mirrors; the rapidly-expanding drone market includes accelerometers, pressure sensors, and other MEMS devices; E-cigarettes can use MEMS flow sensors and even MEMS pumps for aerosol generation. And let’s not forget wheeled applications: the well-known Segway® human transporter uses a MEMS gyroscope as part of its self-balancing system.
Telecommunications
As 5G networks begin their rollout and countries around the world add new frequency bands, smartphone manufacturers must design their RF front ends to handle both new and legacy standards. At the same time manufacturers must fit their designs into smaller, slimmer form factors.
Compared to a discrete design, the MEMS device can provide a wider bandwidth, higher reliability and more design flexibility in a smaller package. Telecommunication applications use RF MEMS devices such as resonators, tunable inductors, switched capacitors, varactors and multiport switches. Such blocks are found in software-defined radios, electronically-scanned phase arrays and other RF circuits. Figure 3 shows a tunable MEMS inductor, consisting of two inductors, two fixed capacitors and a shunt-variable capacitor.
Figure 2: A MEMS tunable inductor (Image source: Dr Wajiha Shah/Slideplayer.com)
Smartphones use RF MEMS technology in antenna tuners to maximize efficiency by impedance-matching between the antenna and transmitter or receiver. By digitally switching between multiple capacitive states, a MEMS antenna tuner can lower insertion loss and produce increased linearity compared to conventional approaches.
Military and Aerospace
Figure 3: The extreme mil/aero environment requires robust MEMS packaging (Image Source: Memsense)
Commercial aircraft and all branches of the military are currently using MEMS accelerometers, pressure sensors and gyroscopes for navigation, engine control and monitoring. These applications mirror those in other industries, but the military/aerospace (mil /aero) market has stringent qualification, reliability and traceability requirements that exceed the capability of commercial products and require product modifications. The Memsense MP00062-008 inertial measurement unit (IMU) in figure 4, for example, is encapsulated in a compact aluminum housing to allow for operation in extreme environments. A family of IMUs are available at various performance levels.
In many cases, mil/aero applications also have unique application requirements. MEMS gas sensors, for example, must be designed to detect trace quantities of chemical warfare (CW) agents, or the combustion products caused by a fire in an aircraft cargo compartment; researchers are developing MEMS-based hydrophones for submarine detection; and forward-looking infrared (FLIR) systems use MEMS technology to generate high-energy IR signals for identification-friend-or-foe (IFF) applications.
Conclusion: The MEMS story is just beginning
In the next few years, expect to see an explosion of MEMS applications in numerous fields. In transportation, “smart roads” will incorporate millions of MEMS sensors to gather data about road conditions and transmit them to local hubs and then to the cloud for further analysis. Medical researchers are working on several MEMS-based treatments for blindness such as artificial retinas, or MEMS robots that can deliver drugs or perform surgical operations inside the eye.
Future MEMS devices promise to bring change on a grand scale: the emerging field of “Smart Dust” technology, which will employ billions of almost-invisible MEMS devices to gather information, promises to both revolutionize entire industries and give privacy advocates nightmares.
More than fifty years after the appearance of the first MEMS device, it looks as though the MEMS story is just getting started.
