Which type of proximity sensor is not suitable of detecting ‘Glass Bottles’? 

Proximity sensor:

• It is a non-contact sensor that detects the presence of an object (often referred to as the “target”) when the target enters the sensor’s field.
• Depending on the type of proximity sensor, sound, light, infrared radiation (IR), or electromagnetic fields may be utilized by the sensor to detect a target.
• Proximity sensors are used in phones, recycling plants, self-driving cars, anti-aircraft systems, and assembly lines. ​

The most popularly used proximity sensors are the Inductive and Capacitive type proximity sensor.

Inductive proximity sensor:

• An inductive proximity sensor can only detect metal targets. 
• This is because the sensor utilizes an electromagnetic field.
• When a metal target enters the electromagnetic field, the inductive characteristics of the metal change the field’s properties 
• Thereby alerting the proximity sensor of the presence of a metallic target. 
• Depending on how inductive the metal is, the target can be detected at either a greater or shorter distance. 
• So, it 'cannot' be used for the detection of glass bottles.

Capacitive Proximity sensor:

• Capacitive proximity sensors, on the other hand, are not limited to metallic targets. 
• These proximity sensors are capable of detecting anything that can carry an electrical charge. 
• Capacitive sensors are commonly used in liquid-level detection. 
• Possible targets for capacitive sensors include but are but not limited to: glass, plastic, water, wood, metals, and a myriad of targets of other materials.
• So, it can be used for the detection of glass bottles.

​Photoelectric type sensor:

• There are two main types of photoelectric proximity sensors: reflective and through-beam. 
• Reflective proximity sensors detect objects when the light emitted from the sensor is reflected back at the photoelectric receiver. 
• Through-beam sensors detect targets when the target breaks the beam of light between the sensor’s emitter and receiver. 
• Used to discover the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver.
• They are largely used in industrial manufacturing.
• So, it can be used for the detection of glass bottles.

​Ultrasonic type sensor:

• It measures the distance of a target object by emitting ultrasonic sound waves and converts the reflected sound into an electrical signal.
• Ultrasonic waves travel faster than the speed of audible sound (i.e. the sound that humans can hear).
• Ultrasonic sensors have two main components:
  The transmitter (which emits the sound using piezoelectric crystals) and
  The receiver (which encounters the sound after it has traveled to and from the target).
• They can be found in automobile self-parking technology and anti-collision safety systems. 
• Ultrasonic sensors are also used in robotic obstacle detection systems, as well as manufacturing technology.
• So, it can be used for the detection of glass bottles.