(i) MAP Sensor:

• The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an internal combustion engine's electronic control system. As the name suggests it is positioned in the inlet manifold.
• The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU).
• This sensor is typically a diaphragm type vacuum gauge where the vacuum is measured against a reference vacuum.
• The position of the diaphragm is sensed by a silicon chip and information is sent to the ECU which looks up a table and the pressure is identified.
• Figure shows positions of the sensor when there is a high pressure and low pressure in the intake manifold.

(ii) Lambda Sensor:

• The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.
• The Lambda sensor is positioned in the exhaust pipe and can detect rich and lean mixtures.
• The mechanism in most sensors involves a chemical reaction that generates a voltage.
• The engine's computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.

(iii) SAW Sensor:

• Surface acoustic wave (SAW) technology is used as a strain transducer that is lightweight, small, rugged and recyclable.
• SAW sensors can readily sense torque and temperature for steering EPS and powertrain applications as well as pressure and temperature for Tire Pressure Measurement System.

• The operation of the SAW device is based on acoustic wave propagation near the surface of a piezoelectric solid. This implies that the wave can be trapped or otherwise modified while propagating.

• Surface acoustic wave technology takes advantage of the piezoelectric effect in its operation. Most modern surface acoustic wave sensors use an input interdigitated transducer (IDT) to convert an electrical signal into an acoustic wave.

• The sinusoidal electrical input signal creates alternating polarity between the fingers of the interdigitated transducer. Between two adjacent sets of fingers, polarity of the fingers will be switched.
• As a result, the direction of the electric field between two fingers will alternate between adjacent sets of fingers. This creates alternating regions of tensile and compressive strain between fingers of the electrode by the piezoelectric effect, producing a mechanical wave at the surface known as a surface acoustic wave.