1. Briefly define the following terms
1)Transducer
A transducer is  a  device  that  converts  a  signal from one physical form to a corresponding signal having a different physical form .
2)Sensor
A sensor converts a physical signal into an electrical signal (i.e., a microphone).
3)Actuator
An actuator is a device that converts electrical energy into physical energy (i.e., a loudspeaker).
4)Linearity
The linearity describes the closeness between the calibration curve and a specified straight line.
5)Sensitivity
The sensitivity is defined in terms of the relationship between input physical signal and output electrical signal. It is generally the ratio between a small change in electrical signal to a small change in physical signal. The sensitivity is the slope of the calibration curve.
6)Hysteresis
The hysteresis refers to the difference between two output values that correspond to the same input, depending on the direction (increasing or decreasing) of successive input values. That is, similarly to the magnetization in ferromagnetic materials, it can happen that the output corresponding to a given input depends on whether the previous input was higher or lower than the present one.
Some sensors do not return to the same output value when the input stimulus is cycled up or down. The width of the expected error in terms of the measured quantity is defined as the hysteresis.
7)Repeatability                                                                The repeatability is the closeness of agreement between successive results obtained with the same method under the same conditions and in a short time interval.                   
 
      δ—sample standard deviation
8)Strain (mechanical)
Fractional change in length ΔL/L.
9)Gage factor
The gage factor is defined as the fractional change in resistance divided by the        strain.
10)Piezoresistive effect
The change in resistivity as a result of a mechanical stress is called the piezoresistive effect.
11)direct piezoelectric effect. 
the phenomenon of generation of a voltage under mechanical stress is referred to as the piezoelectric effect.
12)converse piezoelectric effect.
The mechanical strain produced in the crystal under electric stress is called the converse piezoelectric effect.
13)Numerical Aperture
The "acceptance cone" defines how much light will be accepted into the fiber and ultimately how much remains in the fiber, and is referred to as the numerical aperture.
14)register的名词Extrinsic sensor
The optical fiber plays no part in achieving the modulating but simply acts as a transmission medium ; these are extrinsic sensors.
15)Intrinsic sensors (fiber optic sensor)
The optical fiber plays a major role in modulating the energy from the source; these are referred to as intrinsic sensors.
16)Humidity
a quantity representing the amount of water vapor in the atmosphere or a gas
17)Absolute humidity
Absolute humidity is the mass of water vapor per unit volume of air.
18)Relative humidity
The ratio of the actual vapor density  to the theoretical maximum (saturation) vapor densit
y at the same temperature, expressed as a percentage. The relative humidity is the ratio of the actual vapor pressure to the saturation vapor pressure at given temperature.
19)Peltier effect
When two dissimilar metals are connected together, a small voltage called a thermojunction voltage is generated at the junction. This is called the Peltier effect.
20)Law of Homogeneous Conductors
For a given pair of homogeneous conductors forming a closed loop, the Seebeck emf depends only on the temperatures of the junctions, and not on the temperature distribution along the length of the conductors.
21)Law of intermediate metals
A third (intermediate) metal wire can be inserted in series with one of the wires without changing the voltage reading (provided that the two new junctions are at the same temperature).
If there is a third metal introduced into the thermocouple circuit , it will not adversely effect the reading, if and only if the two junctions of the third metal are at the same temperatures .
22)Bernoulli’s theorem
Bernoulli’s equation states that energy is approximately conserved across a constriction in a pipe.
Bernoulli’s equation:  P/(ρ•g) + ½v2/g + y = constant  (ρ=density;      g=acceleration of gravity ;  v=fluid velocity;    y=elevation )
2. Describe the following devices and how they work
1)Strain gage
The strain gauge usually consists of  wire, baking, thinpaper, and lead welded. The wire is arranged in the form of a grid in order to obtain higher resistances.
2)Parallel plate Capacitive Sensor
The parallel plate Capacitive Sensor is a function of the distance d (cm) between the electrodes of a structure, the surface area A (cm2) of the electrodes, and the permittivity ε0 (for air) of the dielectric between the electrodes; therefore:

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