A “system-level” approach is galvanizing the technology of microelectromechanical-system (MEMS) devices into a boundless number of applications that are poised to emerge. It involves the integration of MEMS-based sensors, actuators, and structures with other functions like signal processing, packaging, testing, software development, and systems engineering.
MEMS devices have become such commodity components that they’re presenting the electronics industry with vast opportunities to be useful in a variety of fields, including medical, industrial, automotive, commercial, consumer electronics, communications, military/aerospace, geophysical, and energy exploration and management, as well as a host of unforeseen areas.
It’s interesting to note that the automotive field, which was one of the first industries to employ MEMS technology, is experiencing a rebirth in using MEMS technology for safety, driving control, fuel economy, pollution control, and a myriad of navigation and entertainment applications.
Key drivers include wireless connectivity and Internet access, allowing MEMS technology to revolutionize everything in our lives. This is enabling vast improvements in medical healthcare and well-being, creating environmental awareness around us, improving energy efficiency, and making our world safer and more secure.
We can see the amazing progress being made at the device level. MEMS accelerometers, gyroscopes, and inertial management units (IMUs) are becoming ever smaller and much more sophisticated while offering better performance. This is giving the electronics industry the foundation to build upon for intelligent MEMS-based system solutions.
Notable examples include the MXC6226XC digital accelerometer from MEMSIC. At just 1.2 by 1.2 by 1.0 mm, the company calls it the world’s smallest and most robust device. It even literally fits into the eye of a small sewing needle. Meanwhile, STMicroelectronics claims its L3G462A is the world’s smallest three-axis analog gyroscope, available in a 4- by 4- by 1-mm package.
Several companies are jumping into the MEMS magnetometer market, providing two-axis and three-axis units, some with two- or three-axis MEMS accelerometers. Such devices will have a dramatic impact on mobile products, improving acquisition time, providing dead reckoning in urban and hard to reach areas, and providing orientation for pedestrian navigation and location-based services.
In any MEMS applications, vital issues in packaging, testing, performance, and software algorithms must be carefully addressed to fit the user’s needs. This means working very closely with the intended user for a mutually agreeable solution that fits the user’s needs, hence the emphasis on a system-level solution.
Health monitoring for recovering patients and athletes as well as those who want to stay fit is a booming business for MEMS devices. Just one example is MEMS sensor technology being used for studying body kinematics in competitive rowing events.
Roessingh Research & Development, a Dutch scientific research center, is using the Xsens MVN system developed by Holland’s Xsens Technologies BV. Analog Devices’ iMEMS inertial sensor is combined with Xsens’ sensor fusion algorithms and biomechanical models to produce accurate 3D movement and kinematic outputs. Such advanced motion-tracking technology helps in competitive rowing applications, the resaerchers say.
IMEC, a Belgian microelectronics research organization, has unveiled an innovative three-lead electro-cardiogram (ECG) body patch with a 3D accelerometer. It uses ultra-low-power Bluetooth Low Energy (BLE) communications for long-term monitoring in heath, wellness, and medical applications. The patch consumes a mere 280 µA at 2.1 V running continuously for one month on a 200-mAh lithium-polymer battery.
A BLE link allows it to be used as a plug-and-play communications gateway to mobile devices such as smart phones and tablets. It was developed at IMEC’s Holst Centre in collaboration with Belgium’s DELTA, an independent technology service organization for private enterprises and public authorities.
A tiny passive MEMS LC resonator lies at the core of the FDA-approved (Food and Drug Administration) CardioMEMS Champion implantable device, which was designed for monitoring and treating aneurisms, a leading cause of heart failure (Fig. 1). Powered by external inductive coupling, the RF-addressed wireless pressure sensor needs no batteries. Pressure changes deflect the transducer’s diaphragm and change the LC circuit’s resonant frequency, which can be monitored externally.
CardioMEMS, an offshoot of the Georgia Institute of Technology, manufactures the electronics reader, signal-processing circuitry, and transmission circuitry. MEMSCAP supplies the device’s sensor, antenna, and packaging. Results thus far have been very encouraging.
R0R3 Engineered Solutions has developed a MEMS-based heart-rate monitor that can be worn as a wristwatch. The company says it provides advantages over conventional chest-strapped ECG monitors.
The monitor offers accurate heart-rate measurements for wearers engaging in periodic motion such as running, pushups, or jumping jacks. Also, it’s suited for medical applications. It offers an innovative wireless ANT+ communications protocol and conforms to the basic profile for heart-rate monitoring for GPS watches. Some models communicate directly with Droid and iPad devices for patient monitoring.
ANT ultra-low-power communications chips from Norway’s Nordic Semiconductor ASA are used in a wide range of health-monitoring applications. The most recent example, the nRF24AP2, is used in the LifeTouch HRV011 ECG monitor patch from the United Kingdom’s Isansys Lifecare Ltd. While the present patch does not use MEMS technology, the company plans on using MEMS for future upgrades.
More Than Sensors
There’s more to MEMS than sensing applications. A MEMS device also can act as an actuator and function as a structure as in microfluidics. Such properties are under constant investigation for medical implant applications.
The most notable is the implantable Jewel insulin pump jointly developed by Switzerland’s Debiotech and STMicroelectronics, which is providing its MEMS microfluidics expertise. The pump can be mounted on a disposable skin patch to provide continuous insulin diffusion for diabetics. FDA approval is pending.
The importance of MEMS microfluidics for medical applications is not lost on the researchers at the Charles Stark Draper Laboratory. In one project they’re working on, a silicon wafer micro- etched with tiny channels then can act as a master. In turn, the master can be used to make many copies. All of these copies are then stacked up as layers that can be used to replace organs like livers and kidneys as the blood flows through the micro-channels.
At the University of Houston’s College of Optometry, MEMS-based deformable mirrors from Boston Micromachines Corp. are being investigated for helping glaucoma patients. A mirror package with 140 actuators with low inter-actuator coupling is being used for wave-front adaptive optics to image living human eyes. Each mirror is capable of up to a 5.5-µm stroke at a 100-kHz frame rate.
The researchers have built an adaptive optics scanning laser ophthalmoscope that uses an iterative stochastic parallel-gradient descent algorithm to directly control the 140 digital mirrors, maximizing the mean intensity of the acquired retinal images. The goal is to determine earlier structural markers for glaucoma at the site of initial damage in the optic nerve head.
Researchers at North Carolina State University are investigating smart MEMS-based catheters that are both flexible and stiff, when needed, for stent delivery. MEMS technology is used to electronically modulate catheter stiffness. The catheter can be flexible enough to be maneuvered through winding blood vessels and positioned near the affected area, but it also can be stiffened to allow delivery of the stent to the lesion site.
Perfecting Drug Delivery
MEMS technology is playing a significant role in delivering and monitoring medical drugs. One of the most interesting and recent developments is the Raisin system from Proteus Biomedical for optimizing therapeutic benefits for those on frequent and timely medications.
As Mark Zdeblick, cofounder and chief technology officer at Proteus, points out, patients don’t take 30% to 50% of their prescribed medications, and the costs of hospitalization due to non-adherence is $100 billion a year according to a 2005 study. Zdeblick’s solution is the Raisin system, which marries medicine and mobile computing technologies.
This integrated pharmaceutical system identifies the pill, its authenticity, and its dosage when it is ingested. It then detects the pills and assigns time stamps. Also, it measures ECG signals, activity, and sleep and collects and presents data in real time. It then serves as a platform for data sharing, collaboration, and incentives.
The Raisin system consists of a handheld monitoring device, ingestible event markers (IEMs), and a receiver patch (Fig. 2). The tiny marker chips, measuring less than 1 mm, have been tested as accurate at more than 99% in drug detection in multiple human clinical trials. It produces an ECG-like signal conducted only in the body (not RFID).
Thin-film MEMS layers on each IEM are activated and powered using stomach electrolytes. The system modulates/pulses the current flow to encode information stored in it. It then communicates this data through the body tissue, where a receiver worn on the patient’s skin detects an electric field.
MEMS technology is also in use in a drug-delivery system devised at the University of British Columbia to treat diabetes-related vision loss. It is implantable behind the eye for controlled and on-demand release of drugs to treat retinal damage.
Key to the system is its ability to trigger drug delivery through an external magnetic field. This is accomplished by sealing the reservoir of the implantable device, which is no longer than the head of a pin, with an elastic magnetic polydiethylsiloxane (silicone) membrane. A magnetic field causes the membrane to deform and discharge a specific amount of the drug (Fig. 3).
IMEC researchers are looking beyond microelectronics technology like MEMS to nanotechnology for biomedical pharmaceutical applications. They’re proposing new measurement methods for drugs using nano-based biosensors. Molecular biosensors can detect biomarkers in the blood like enzymes, antibodies, DNA, diseased cells, and foreign substances like radioisotopes for pre-clinical and clinical tests and for therapy and post-therapy effectiveness (Fig. 4).
Infrastructure, Materials, Foods, And Drugs
No one needs to be told that the infrastructure supporting us like bridges, tunnels, pipelines, roadways, and buildings is badly in need of monitoring and repairs. MEMS technology is showing that it can do this job on a far less costly basis than present methods.
One demonstration comes from the University of Michigan’s Engineering Research Center for Wireless Integrated Microsystems (WIMS) in a bridge monitoring project. It tested the structural health of the new Carquinez Bridge in Northern California. The bridge spans the Carquinez Strait, forming part of U.S. Highway Interstate 80 between Crockett and Vallejo, California.
The project used 34 wireless acceleration and displacement MEMS sensors for accelerations in the 30 to 100 mg range along the bridge’s length. A parametric frequency increased generator was used for scavenging a broad range of low-frequency (wide bandwidth) and non-periodic vibrations, with vibrations being recorded for frequencies less than 10 Hz (Fig. 5). The system requires no tuning and operates from a 0.5- to 0.75-µW constant supply.
One exciting area MEMS technology is gaining entry into is portable, handheld, and low-cost analytical instrumentation that has been relegated to bulky and very expensive solutions (see “MEMS-Based Systems Solutions Emerge For Analytical Instruments,” p. 32). Such instruments are finding their way into the analysis of gases, foods, materials, drugs, and many other items.
Through its recent acquisition of Holland-based c2v, Thermo Fisher Scientific offers a portable (not yet handheld) mini gas chromatograph based on a microfluidics system for natural gas and hydrocarbon pipeline monitoring and analysis. The system determines the concentrations of the various constituents of gas components and calculates the caloric value of the sampled gas to determine its burning value as well as monitor the uniformity of the gas.
Each measurement channel, which measures 7.6 by 7.6 by 12.7 cm, of a two- to four-channel system uses a MEMS-based gas-chromatograph (GC) column, a gas concentrator, and a thermal conductivity detector. The system has an external gas line sample and reference gas connector, a power supply, and a USB port to connect the system to a computer where application algorithms and displays are located.
The micro GC system can provide full analysis of gas constituents in field conditions in approximately 30 s without compromising measurement accuracy. As such, it will enable an immediate, convenient, and low-cost way to monitor processes in-situ, saving the user time and money over having to transport samples from the line to the laboratory in gas bottles.