Medical Applications of Micro-Electro-Mechanical Systems (MEMS) Technology - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 67

• Special hospital beds for burn victims that employ inlatable mat-
tresses use MEMS pressure sensors to regulate the pressure inside
a series of individual inflatable chambers in the mattress. Sections
of the mattress can be inflated as needed to reduce pain as well as
improve patient healing.
• Physician's ofice and hospital blood analyzers employ MEMS pres-
sure sensors as barometric pressure correction for the analysis of
concentrations of O 2 , CO 2 , calcium, potassium, and glucose in a
pat ie nt 's blo o d.
• MEMS pressure sensors are used in inhalers to monitor the patient's
breathing cycle and release the medication at the proper time in the
breathing cycle for optimal effect.
• MEMS pressure sensors are used in kidney dialysis to monitor the
inlet and outlet pressures of blood and the dialysis solution and to
regulate the flow rates during the procedure.
• MEMS pressure sensors are used in drug infusion pumps of many
types to monitor the flow rate and detect for obstructions and block-
ages that indicate that the drug is not being properly delivered to the
patient.
• Many types of medical drilling equipment also use MEMS pressure
sensors to monitor blood and/or other internal fluids during the
drilling process.
The physically smallest MEMS pressure sensor is the GE NovaSensor
intracardial catheter-tip blood pressure sensor, which is used for diagnos-
tics during cardiac catheterization. The size of this device measures only
150 microns by 400 microns by 900 microns [52]. The implementation of this
device as well as a few other types of pressure sensors for medical applica-
tions is described in more detail below.
Integrated MEMS Pressure Sensor for disposable Medical Applications
The integrated pressure sensor (IPS) process technology was originally
developed and put into production by Motorola (now Freescale Semi-
conductor) in 1991 and represents one of the most successful and long-
standing high-volume MEMS products in the medical market. This sensor
employs the piezoresistive effect to measure the deflection of a thin silicon
membrane and combines bipolar microelectronics for signal conditioning
and calibration on the same silicon substrate as the sensor device, thereby
making it a fully integrated MEMS product (actually the first fully inte-
grated high volume MEMS product). The transduction approach taken to
measure membrane deflection under pressure loading is somewhat unusual
since it uses a single piezoresistor element to measure strain, as opposed to
the conventional approach of using multiple, distributed piezoresistors (e.g.,