Continue Sensors Story

      Sensors are classified due to the nature of the quantities they measure:

1. Acoustic & Sound sensors, detect sound via means of using microphones, or other types of filters.

2. Automotive sensors, capture data about an automobile such as pressure, air and coolant temperature, speed, acceleration, linear motion, timing, and convert them to electrical signals, then interpreted by the automobile's ECU.

3. Chemical Sensors, changes chemical information (composition, presence of a particular element or ion, concentration, chemical activity, partial pressure…) into an analytically useful signal.
4. Electric & Magnetic Sensors, examine the changes in electrical or magnetic signals based on an environmental input.

 5. Environmental Sensors, measure the presence and quantity of a specific chemical in an environment.

 6. Optical Sensors, use principles of light to quantify object characteristics.7. Mechanical Sensors, measure the change in a mechanical property of an object or system.

8. Thermal & Temperature sensors, report the temperature of a part or environment.

9. Proximity & Presences sensors, sensor able to detect the presence of nearby objects without any physical contact.

Sensors Story

 Sensor is an object that can detect changes in its surrounding environment and provide this change as an output. Sensors are devices that can convert one form of energy to another (i.e. converts a signal in one form of energy to another), thus sensors are known as transducer. There are two basic types of sensors: analog and digital. The two are quite different in function, in application. An analog sensor produces a continuously varying output value over its range of measurement. Digital sensors, on the other hand, have only two states, often called "on" and "off." Sensor's sensitivity indicates how much the sensor's output changes when the input quantity being measured changes (i.e. ratio between output signal (from sensor) and its measured property. A good sensitive sensor is the one that is sensitive to its measured property, on the other hand, it is not sensitive to any other property, and it doesn’t influence the measured property.

Sensors has another quantity known as the resolution, which is defined as the smallest change in the measuring property the sensor can detect, the resolution is related to the precision with which the measurement is made. Sensors are chosen depending upon criteria, given as follows:
1. Sensor Accuracy
 2. Environment surrounding the sensor
 3. Measurement limit of the sensor
 4. Calibration
 5. Resolution
 6. Repeatability

Optical Resonator

    In recent years, high optical quality factor resonators have been used for many applications.
Some of these include those in optical telecommunication biological and mechanical sensing. References describe a detailed review of recent morphology dependent resonances (MDR) applications. The MDR are optical OPEN ACCESS Sensors 2014, 14 7042 modes that are observed in dielectric resonator, and are excited by coupling light from a tunable laser into the resonator using a single mode optical fiber. A simplified description of the MDR phenomenon can be obtained by using geometric optics.
This description is valid when the wavelength of the light used to excite the optical modes is much smaller than the size of the optical cavity. In this geometric view, light coupled into the microsphere (for example using a single mode optical fiber) circles the interior of the sphere through total internal reflection as long as the refractive index of the sphere is larger than that of the surrounding medium. There are many experiments to investigate the effect of angular velocity on the MDR shifts of 60:1 and 10:1 polydimethylsiloxane (PDMS). The opto-electronic setup that the scientists used to excite and monitor the MDR is the same as described in this figure:

Briefly, the output of a distributed feedback (DFB) laser (nominal central wavelength 1.312 μm) was coupled at one end of a single mode optical fiber, while the other end was terminated to a photodiode to monitor the transmission spectrum. The DFB laser was currenttuned to excite the optical resonances. The light was coupled evanescently into the microsphere using a tapered section of a single mode optical fiber. The optical fiber was brought in contact with the resonator using a micro translation stage. Once resonances were observed trough the transmission spectrum, the fiber holder was glued to the disk.

While this design is rotational stage in one axis only but there is a design in 3 axis, this design is rotation Stage provides ±5° uncoupled tilt adjustment in pitch and roll, together with ±10° rotation (yaw) adjustment. 

These adjustments allow optical components and fixtures to be aligned with a plane, and then rotated within that plane.

But we found that this design is not enough because it is only manual and not has enough accuracy so we have been modified this design to increase its accuracy and to be manual and motorized at the same time.

Motor Selection

General Motor Principles Motors convert electrical energy into mechanical energy using electromagnetic principles. 

The energy conversion method is fundamentally the same in all electric motors. 

• Magnetic Force:

 Magnetic poles generate invisible lines of magnetic force flowing from the North Pole to the South Pole as shown in This Figure . When magnetic poles of opposite polarity face each other, they generate an attractive force, while like poles generate a repulsive force.

• Left-Hand Rule:

Current in a conductor generates a magnetic field. Placing a conductor in the vicinity of a separate magnetic can generate a force that reaches its apex when the conductor is at 90° to the external field. The left-hand rule can help the user determine the direction of the force, as shown in this Figure

• Right-Hand Rule:

The movement of the conductor in the magnetic field induces an electromotive force known as the BEMF. The right-hand rule can determine the direction of the force as shown in this Figure. The Right-Hand Rule: Stretch out the right hand with the four fingers and the thumb on the same plane, the palm facing the north pole of the external magnetic field, and the thumb pointing in the direction of the velocity of v. The four fingers point in the direction of the induced electromotive force. The magnitude of the induced electromotive force can be calculated as: E BLv sin = θ

Where: E is the induced electromagnetic force (V). v is the velocity of the conductor (m/s). θ is the angular difference between B and L (rad).

When the motor rotates at an angular velocity of ω (rad/s) and there are N coil turns, the total electromotive force is: E 2BLvN 2BL rN K = = ω=ω Where: ω is the angular velocity (rad/s). r is the internal radius of the motor (m). KE=2rBLN is the electromotive force constant (V·s/rad).
Based on the parameters from This Figure:

The Brushless motor DC (BLDC)

It is widely used in applications including appliances, automotive, aerospace, consumer, medical, automated industrial equipment and instrumentation. The BLDC motor is electrically commutated by power switches instead of brushes. Compared with a brushed DC motor or an induction motor, the BLDC motor has many advantages like :
 Higher efficiency and reliability
 Lower acoustic noise
 Smaller and lighter
 Greater dynamic response
 Better speed versus torque characteristics
 Higher speed range
 Longer life Operation BLDC theory Motor operation is based on the attraction or repulsion between magnetic poles. Using the three-phase motor shown in Figure 9, the process starts when current flows through one of the three stator windings and generates a magnetic pole that attracts the closest permanent magnet of the opposite pole. The rotor will move if the current shifts to an adjacent winding. Sequentially charging each winding will cause the rotor to follow in a rotating field. The torque in this example depends on the current amplitude and the number of turns on the stator windings, the strength and the size of the permanent magnets, the air gap between the rotor and the windings, and the length of the rotating arm.

DC Motors

DC motors consist of one set of coils, called armature winding, inside another set of coils or a set of permanent magnets, called the stator. Applying a voltage to the coils produces a torque in the armature, resulting in motion. Stator
 The stator is the stationary outside part of a motor.
 The stator of a permanent magnet dc motor is composed of two or more permanent magnet pole pieces.
 The magnetic field can alternatively be created by an electromagnet. In this case, a DC coil (field winding) is wound around a magnetic material that forms part of the stator. Rotor
 The rotor is the inner part which rotates.
 The rotor is composed of windings (called armature windings) which are connected to the external circuit through a mechanical commutator.
 Both stator and rotor are made of ferromagnetic materials. The two are separated by air-gap. Winding A winding is made up of series or parallel connection of coils.
 Armature winding - The winding through which the voltage is applied or induced.
 Field winding - The winding through which a current is passed to produce flux (for the electromagnet)
 Windings are usually made of copper. Principle of operation of DC motor Consider a coil in a magnetic field of flux density B. When the two ends of the coil are connected across a DC voltage source, current I flows through it. A force is exerted on the coil as a result of the interaction of magnetic field and electric current. The force on the two sides of the coil is such that the coil starts to move in the direction of force.