An Introduction to mems (Micro-electromechanical Systems)
tải về 1.48 Mb. Chế độ xem pdf
|
|
Figure 5. Modern day MEMS accelerometer (left), and the fully packaged device (right) [12].
An Introduction to MEMS
Prime Faraday Technology Watch – January 2002 8
and navigation control systems, vibration monitoring, fuel sensors, noise reduction, rollover detection, seatbelt restraint and tensioning etc. As a result, the automotive industry has become one of the main drivers for the development of MEMS for other equally demanding environments. Some of the leading airbag accelerometer manufacturers include Analog Devices, Motorola, SensorNor and Nippondenso.
Accelerometers are not just limited to automotive applications. Earthquake detection, virtual reality video games and joysticks, pacemakers, high performance disk drives and weapon systems arming are some of the many potential uses for accelerometers.
ii) Medical pressure sensor Another example of an extremely successful MEMS application is the miniature disposable pressure sensor used to monitor blood pressure in hospitals. These sensors connect to a patients intravenous (IV) line and monitor the blood pressure through the IV solution. For a fraction of their cost ($10), they replace the early external blood pressure sensors that cost over $600 and had to be sterilized and recalibrated for reuse. These expensive devices measure blood pressure with a saline-filled tube and diaphragm arrangement that has to be connected to an artery with a needle.
Figure 6. Schematic illustration of a piezoresistive pressure sensor.
The disposable sensor consists of a silicon substrate which is etched to produce a membrane and is bonded to a substrate (Figure 6). A piezoresistive layer is applied on the membrane surface near the edges to convert the mechanical stress into an electrical voltage. Pressure corresponds to deflection of the membrane. The sensing element is mounted on a plastic or ceramic base with a plastic cap over it, designed to fit into a manufacturer’s housing (Figure 7). A gel is used to separate the saline solution from the sensing element.
As in the case of the MEMS airbag sensor, the disposable blood pressure sensor has been one of the strongest MEMS success stories to date. The principal manufacturers being Lucas Novasensor, EG & G IC Sensors and Motorola with over 17 millions units per year. More recently, the technology from the blood pressure sensor has been taken a step further in the development of the catheter-tip pressure sensor. This considerably smaller MEMS device is designed to fit on the tip of a catheter and measure intravascular pressure (its size being only 0.15 mm x 0.40 mm x 0.90 mm).
Pressure sensors are the biggest medical MEMS application to date with the accelerometer MEMS a distant second. Although the majority of these accelerometer applications remain under development, advanced pacemaker designs include a MEMS accelerometer device that measures the patient’s activity. The technology, similar to that found in the airbag sensor, enables the patient’s motion and activity to be monitored and signals the pacemaker to adjust its rate accordingly.
|