1. Transducers Measurement/Information Processing System or
Nano/Microelectromechanical System (N/MEMS)

2. N/MEMS: Basic Components
Measurand: input signal which is the physical or chemical quantity to be measured.
Sensor (input transducer): it is a device that converts a non-electrical physical or chemical quantity into an electrical signal. Sensor detects the measurand.
Preprocessor/processor: is a device(s) that modifies the signal from the sensor without changing the form of energy that describes the signal.
Actuator (output transducer): is a device that converts an electrical signal into a physical or chemical quantity.

3. Classification of Sensors by Signal Form
Form of Signal
Measurand
Thermal
Temperature; heat; heat flow; heat capacity…etc.
Mechanical
Distance; velocity; acceleration; force; pressure; flow;….etc.
Radiation
Infra Red; x-rays; visible; radio waves;….etc.
Chemical
Methane gas; humidity; pH level; water vapor;…etc.
Magnetic
Flux; magnetic field; magnetic moment; magnetization;…..etc.
Biological
Proteins; sugar; hormones; antigens;….etc.
Electrical
Voltage; current; charge; resistance; capacitance;…etc.

4. Classification of Common Actuators
Actuation Type
Actuator
Quantity
Principle of Operation
Display
Light emitting diode
Visual display unit
Liquid crystal display
Radiation
Current to photons
Fluorescent screen
Transmittance by molecular crystal
Recording
Thermal printing
Magnetic recording head
Laser
Thermal
Magnetic
Melted ink
Magnetization of thin films on computer disc
Ablation of material on optical disc
Transmission
Loudspeaker
Electric motor
Mechanical
Sound generation
Generation of motion

5. Ideal Transducer Characteristics
Definitions
Self-exciting transducer: is one which does not need an external poser supply to work (e. g., thermocouple).
Modulating transducer: is one which needs an external modulating source (e. g., photodiode is a radiant sensor whose forward current is modulated by photo-induced electrons)
A transducer may be regarded as a system with an input x(t) and output y(t).
In case of a modulating transducer xo(t) is the external supply signal which should ideally be stationary and noise free. yo(t) is zero-signal output.

6. Self-exciting:
Modulating:
Ideal input-output relationships for linear transducers

7. Non-Ideal Linear Transducer Characteristics
In general for a time-dependent linear transducer we have:
For a first order case:
Where for a self-exciting transducer y(t)=0 and x(t)=0 at all t, and y(t)=yo(t) at x(t)=0 for all to for a modulating transducer. ao relates to the transducer gain, and a1 relates to its characteristic time response.
(a)

8. In the case of instantaneous change in the measurand from zero to xo: i. e., a step change in input signal:
Taking the Laplace transform of both sides of (a)
y(0) is zero for a self exciting transducer and is yo for a modulating transducer.
The transfer function for self-exciting transducer G(s)=Y(s)/X(s) is
1/ao = Gain and t=a1/ao is the characteristic response time.

9. The output of the transducer Y(s) in Laplace space to the step input of height xo is
Taking the inverse Laplace transform, one obtains for self-exciting transducer
For a modulating transducer we have;

10. Important Parameters Response: Gain (A): Sensitivity Band-width 1/t
Baseline Signal (yb) is y(t) at x(t)=0

11. Transient response of linear first-order Transducer

12. Desirable Transducer Characteristics
Transducer Parameter
Optimum Output
Response, Dy
Linear and free of noise
Baseline, y
Zero
Response time, t
Zero for instantaneous response
Frequency bandwidth
Infinite for instantaneous response
Time to reach final value
Full scale reading, ymax
Calibrated maximum output
Working range, ymax – ymin
Infinitely wide
Sensitivity, S
High and constant over the entire working range
Resolution
High

13. Undesirable Transducer Characteristics
Non-linearity: response not proportional to input signal.
Slow response: output is slow to reach a steady state value.
Small working range: operating range is narrow.
Low sensitivity: can only respond to high input signal.
Sensitivity and baseline drifts: output varies with time.
Aging: output varies with age.
Noise: output contains unwanted random signal.
Hysteresis: non-reproducible readings.

14. Input-sensitivity relationship for ideal and real transducers

15. System Control: Open-Loop Process
Xin(s) = input signal to system
Ys(s) = Gs(s)Xin(s) = sensor’s output
Yp(s) = Gp(s)Ys(s) = processor’s output
Ya(s) = Ga(s)Yp(s) = actuator’s output = system output = Yout
Gs, Gp, and Ga are sensor’s, processor’s, and actuator’s transfer functions, respectively.
Overall
Go(s) = Gs(s)Gp(s)Ga(s), which is system’s transfer function, Yout(s) = Go(s)Xin(s)

16. System Control: Closed-Loop Process
The overall transfer function Gc(s):
H(s) is the transfer function for the control sensor