Have you ever wondered where the term "MEMS" came from?

Read J.E. Wood's account:

Click Here:  A brief history of the term Micro Electro Mechanical Systems (MEMS)

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Modeling a Micro Pressure Sensor Kit

(Formerly Pressure Sensor Model Kit)

Description

This kit supports the Wheatstone Bridge Learning Module.

The Modeling a Micro Pressure Sensor Kit provides participants an opportunity to understand how a micro pressure sensor works. Participants build a macro-size model of a micro pressure sensor that uses a Wheatstone bridge. After learning about how the Wheatstone bridge functions as a sensing circuit, participants apply this knowledge to an analysis of their own pressure sensor model. Participants test its operation by measuring the resistance and voltage outputs of the Wheatstone bridge as pressure is applied to the surface of the diaphragm. For further exploration of the sensor's operation, participants create a calibration curve that shows the sensor changes in voltage due to changes in applied pressure.

The kit contains the Wheatstone Bridge Learning Module plus the majority of supplies needed to build two models. The instructor must provide safety glasses, a multi-meter for testing the circuit, rubber cement, and some common office supplies.

Download Learning Module

 
 

Where can I use this kit?

This is one of SCME's most popular kits!  The students make an actual WORKING pressure sensor transducer.  They not only learn the theory behind the Wheatstone bridge circuit but apply this knowledge to the building and characterization of a sensor.

The thin film pressure sensor transducer is one of the oldest MEMS commercial devices and were first made commercially in the 60's and 70's. 

The following courses can all benefit from the inclusion of this hands-on classroom kit:

Electronics - Fundamentals of analog electronics classes all teach Ohm's and Kirchkoff's circuit laws.  These can be used to derive the Wheatstone bridge equation.  The Wheatstone bridge, being the most essential and basic of  transducer circuits, converts the change in resistance due to stress (piezoresistor) to a voltage output.  The voltage varies as a function of the changing stress.  The resistors are stressed (stretched) due to the flexing of a membrane which is a function of the difference in pressure from one side of the membrane to the other.  The output voltage can be amplified, input into a A/D converter and read by a computer (LabView) system.  Students can learn the fundamentals of fabricating a sensor, designing a circuit to manipulate the voltage and apply logic resulting in the creation of a measurement system.

Physics - Pressure is defined as force per unit area.  Once this sensor is built, students stack known unit masses (e.g., coins) and monitor changes in voltage.  Since F=mg, (g=acceleration due to gravity), and we know the area of the membrane, one can create a calibration curve of Voltage Vs. Pressure.  Once a calibration curve is made, the students determine the pressure of an unknown source.  They can also heat the can and monitor the change in pressure.

Nano/Materials Science/Chemistry - The resistors themselves are made by grinding pencil lead (graphite/graphene) into a fine powder and mixing it with rubber cement in the correct proportions.  The Wheatstone bridge circuit is applied using this mixture to the surface of the membrane (balloon).  One can change the properties of these resistive elements by varying the proportions of the mixture (graphene/rubber cement), grinding the graphene to different particle sizes, and by varying the thickness and the consistency of the applied graphite mixture.  Students compare their results and find the best process based on the performance of the device. 

Just a side note:  Graphene is considered a nano material because it is made out of sheets of carbon atoms and is conductive. 

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