Steve Kannengieszer has more than 20 years of experience with process control instruments and currently serves as the director of marketing for the Mass Flow Products unit of Brooks Instrument, which manufactures a MEMS-based thermal flow sensor. Mr. Kannengieszer earned a bachelor’s degree in Mechanical Engineering from Drexel University and an MBA from Temple University. Mr. Kannengieszer can be reached at 215 362-3608 or Steve.Kannengieszer@EmersonProcess.com.
Q: What is MEMS?
A: Micro-Electro-Mechanical Systems (MEMS) are also referred to as Micro-Machines or Mico-Robots (in Japan), or Micro Systems Technology – MST (in Europe).
MEMS are the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro-fabrication technology. While the electronics are fabricated using integrated circuit (IC) processes, the micro-mechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
Microelectronic integrated circuits can be thought of as the “brains” of a system, and MEMS augments this decision-making capability with “eyes” and “arms.” This blending of attributes allows a micro-system to sense and control its environment. Sensors gather information from the environment by measuring mechanical, thermal, biological, chemical, optical, and magnetic properties. The electronics then process the information derived from the sensors and direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose.
Q: What advantages does MEMS offer in flow measurement and control applications specifically?
A: Because MEMS devices are manufactured using IC processes, higher levels of functionality, reliability, and sophistication can be placed on a small silicon chip.
1. Increased sensitivity: MEMS sensors can be more sensitive and have faster speed of response compared to conventional sensors. Their structures are finer and more easily influenced by environmental change, which can provide some advantage over conventional sensors.
2. Small size: MEMS technology allows a designer to populate more components in a small area and to shrink conventional “machines” by a factor of 10 or 100. This opens up previously unexploited applications and markets.
3. Low power consumption: Because MEMS devices are smaller and more sensitive, they typically require less power than their conventional sensor counterparts.
4. Cost: With sufficient volume, MEMS technology has the potential to bring costs down because it can be batch fabricated using streamlined techniques, requiring less labor compared to conventional manufacturing of sensors.
For industrial flow measurement and control applications, Brooks Instrument has introduced the 4800 Series mass flow products. These products incorporate a MEMS flow sensor, which measures the gas flow directly across the sensor. The new sensor provides extremely fast response and enables a dramatic reduction in package size compared to traditional products. The broad flow range, fast response time, and compact size make the Brooks Instrument 4800 Series a good fit for many applications.
Q: For what sort of flow applications are MEMS devices a particularly good fit?
A: In today’s automotive applications, MEMS devices are intimately involved in measurement and control of engine parameters, an essential element in increasing fuel economy. MEMS flow sensors can also be found in a wide variety of industrial applications such as, automotive component testing, hydraulic and pneumatic monitoring/control, HVAC fan control, leak detection systems, spray coating systems, fuel cell test stands, bioreactor systems, environmental test systems, analyzer flow control, and many other industrial process control applications. MEMS flow sensors have also found applications in the medical field.
MEMS flow measurement devices are an excellent choice for measurement and control of many common fluids including air, N2, O2, Ar, He, H2, CO2, CO, N2O, CH4, CH3H6, and C3H8.
Q: Do you see MEMS devices evolving to support higher flow applications? If so, how do you anticipate the technology evolving to support higher flows?
|Gas flow across a MEMS sensor|
A: MEMS devices will continue to evolve to support higher flow applications. In traditional thermal mass flow devices, a flow restrictor is often used to cause only a small portion of the flow to go through the sensor. The balance of the flow bypasses the sensor at a constant ratio to the sensor flow. This same technique is employed in MEMS-based mass flow sensors for applications with high flowrates. Using this bypass technique, flowrates in lines sizes up to two inches can be achieved.
In combination with thermal dispersion (a.k.a. insertion thermal) or differential pressure, the ability for MEMS devices to measure flowrates in very large lines is quite possible.
Q: Where are we in terms of the evolutionary cycle of MEMS technology? What technological obstacles remain to be overcome?
A: Although MEMS technology has been around for decades, we are now just passing through the early adopter stage as it relates to flow measurement and control devices. As with any technology, the majority of users want it to be proven before they adopt it into their equipment or processes.
The primary technical obstacles are material compatibility and high line
pressures. The material compatibility of MEMS structures and bonding materials limit MEMS device applications in corrosive environments. The fine structures in MEMS devices and the attachment methods can limit their application in high pressure environments.
Q: What is the ultimate potential MEMS holds for flow measurement and control applications? How do you see MEMS playing in the flow measurement and control space going forward?
A: MEMS is an intriguing option for many flow customers, especially those who value the small size and speed of response provided by this technology. In time, MEMS sensors will find a place in the flow control industry, and nearly every product category for that matter, by bringing together silicon-based micro-electronics with micro-machining technology, making possible the realization of complete systems-on-a-chip. MEMS will allow the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of micro-sensors and micro-actuators.
We will continue to see more and more functionality integrated into smaller and smaller devices. MEMS-based flow measurement and control devices integrated with MEMS pressure, temperature, and other sensors will provide true multivariable process measurement and control.