How Do Ultrasonic Distance Sensors Work? - The Learning Circuit

Summary

In this 'Learning Circuit' episode, Karen discusses ultrasonic distance sensors, explaining how they function similarly to echolocation in nature. She covers the science behind calculating distance using the time it takes for sound to reflect off objects and return, the role of transducers, and the differences between piezoelectric and capacitive types. Karen also touches on the practical applications, limitations, and the future of these sensors in compact electronics.

Takeaways

• 🐬 Ultrasonic sensors work on the principle of echolocation, similar to how dolphins and bats detect their surroundings.
• 🛰 The distance is calculated using the formula (1/2 * t * c), where t is the time for the sound to travel and c is the speed of sound.
• 🔊 The speed of sound varies by medium, being approximately 767 miles per hour in air and 4.3 times faster in water.
• 👂 Ultrasonic sensors operate beyond the audible range for humans, which is above 20 kHz.
• 🔌 These sensors are transducers, converting electrical signals into sound waves and vice versa.
• 💠 Piezoelectric and capacitive are the two types of ultrasonic transducers, each with different mechanisms for generating and detecting sound.
• 📡 Capacitive transducers can be micro-machined, allowing for compact and integrated designs.
• 📊 The detection range and area of an ultrasonic sensor depend on its frequency and the angle at which sound is emitted.
• 🚫 Factors like object size, distance, material, and shape can affect the sensor's ability to detect objects.
• 💧 Ultrasonic sensors are not affected by visual characteristics and can even detect clear plastic and water surfaces.
• 🔩 Commonly used ultrasonic sensors for hobbyist projects come pre-built into boards with pins for easy integration.

Q & A

What is an ultrasonic sensor and how does it function?

An ultrasonic sensor detects the distance of an object without physical contact by emitting ultrasonic sound waves and measuring the time it takes for the sound to return after bouncing off the object.

What natural examples of echolocation are mentioned in the video?

Dolphins and bats are examples of animals that use echolocation to detect their surroundings by emitting sound waves and interpreting the echoes that bounce back.

What is the formula used to calculate distance in ultrasonic sensors?

The formula is ½ * t * c, where 't' is the time it takes for the ultrasound to travel to the object and back, and 'c' is the speed of sound.

Why is the distance formula multiplied by ½ in ultrasonic sensor calculations?

The distance formula is multiplied by ½ because the sound wave travels to the object and back, so the actual distance is only half of the total travel time.

How do piezoelectric ultrasonic transducers work?

Piezoelectric transducers use a crystal that flexes back and forth when an electric charge is applied, generating ultrasonic waves or detecting incoming waves by converting the vibration into electrical signals.

What is the difference between piezoelectric and capacitive ultrasonic transducers?

Piezoelectric transducers rely on a vibrating crystal to generate sound, while capacitive transducers use a diaphragm membrane that moves in response to electric charges, causing the membrane to vibrate and produce sound.

What are capacitive transducers (CMUTs), and why are they important?

Capacitive transducers (CMUTs) are micro-machined devices that operate similarly to piezoelectric transducers but are cheaper and easier to manufacture. They can be packed into arrays for larger bandwidth and integrated into circuits.

What factors can prevent an object from being detected by an ultrasonic sensor?

Objects may not be detected if they are too small, too close (in the blind zone), have a shape that reflects sound away from the sensor, or are made of materials that absorb sound.

How does the frequency of an ultrasonic sensor affect its range?

Higher frequency sensors work best for detecting objects at short distances, while lower frequency sensors are more suitable for long-range detection.

What advantages do ultrasonic sensors have in detecting objects, regardless of material?

Ultrasonic sensors are not affected by the color, transparency, or visual characteristics of an object, making them suitable for detecting clear plastic and even the surface of water.

Outlines

00:00

🔊 Introduction to Ultrasonic Sensors

The script introduces ultrasonic distance sensors, explaining how they function similarly to echolocation used by dolphins and bats. It details how these sensors emit sound waves that reflect off objects and return to the sensor, allowing for distance calculation using the formula (1/2) × t × c, where t is the time for the sound to travel and c is the speed of sound. The script also covers the difference between ultrasonic and audible frequencies, the use of ultrasound in medical imaging, and the two types of ultrasonic transducers: piezoelectric and capacitive. Piezoelectric transducers use a crystal that flexes when charged, while capacitive transducers use a vibrating membrane to generate and detect sound waves. The script concludes with a brief mention of how these sensors can be integrated into electrical circuits.

05:02

📡 Applications and Limitations of Ultrasonic Sensors

This section discusses the practical applications of ultrasonic sensors, including their use in detecting objects at various distances and sizes. It explains the concept of a detection cone and how the frequency of the transducer affects the sensor's range, with lower frequencies being better for long-range detection and higher frequencies for short-range. The script also addresses potential issues such as blind zones, false positives from mounting positions, and the difficulty in detecting objects that are too close or made of sound-absorbing materials. Additionally, it highlights the advantage of ultrasonic sensors being unaffected by color or visual characteristics and their ability to detect clear plastic and water surfaces. The section concludes with a mention of hobbyist-friendly ultrasonic sensor boards and a teaser for a future video demonstrating a project using these sensors.

Keywords

💡Ultrasonic Sensor

An ultrasonic sensor is a device that uses high-frequency sound waves to detect and measure the distance of objects. In the video, it is explained that these sensors operate without physical contact and are used in various applications, such as by dolphins and bats for echolocation and by ships for underwater detection with sonar. The sensor emits a sound wave and measures the time it takes for the echo to return, which is then used to calculate the distance to the object.

💡Echolocation

Echolocation is a biological sonar system used by animals like dolphins and bats to navigate and locate objects by emitting sounds that reflect off objects and return to the emitter. The video script mentions that these animals use echolocation to detect their surroundings, which is analogous to how ultrasonic sensors work, emitting sound waves that echo off objects to determine their distance.

💡Sonic Speed

Sonic speed, also known as the speed of sound, is the rate at which sound waves travel through a medium. The video explains that the speed of sound is approximately 767 miles per hour at sea level, and it varies depending on the medium, traveling 4.3 times faster in water than in air. This speed is crucial for ultrasonic sensors as it is used in the formula to calculate the distance of objects based on the time it takes for the sound to reflect back.

💡Transducer

A transducer is a device that converts one form of energy into another. In the context of the video, ultrasonic sensors act as transducers by converting electrical signals into sound waves and vice versa. The script explains that ultrasonic sensors use either piezoelectric or capacitive transducers to generate and detect ultrasonic waves, which are used to measure distance.

💡Piezoelectric

Piezoelectric refers to the property of certain materials that generate an electric charge in response to applied mechanical stress. The video script describes how piezoelectric devices, such as those used in ultrasonic sensors, use a crystal substance that flexes back and forth quickly when a charge is introduced, generating ultrasonic waves or vibrating in response to received waves.

💡Capacitive Transducer

A capacitive transducer is a type of sensor that uses the principle of a capacitor, which consists of two conductive plates separated by a dielectric material. The video explains that in a capacitive ultrasonic sensor, one plate sits on a dielectric membrane above a cavity, and when current is applied, it causes the membrane to vibrate, generating ultrasonic waves. This type of transducer can be integrated into electrical circuits, making them compact and suitable for miniaturization.

💡Frequency

Frequency in the context of the video refers to the rate of vibration of the ultrasonic sensor's membrane, which determines the pitch of the sound waves it emits. Higher frequencies result in shorter transmission distances, while lower frequencies are better for long-range detection. The script mentions that ultrasonic sensors work best at specific frequencies, depending on whether they are designed for short or long-range sensing.

💡Blind Zone

The blind zone is a term used in the video to describe the area too close to the ultrasonic sensor where objects cannot be detected. If an object is within this zone, the sensor will not be able to register it because the sound reflects back too soon after being emitted. This concept is important for understanding the practical limitations of ultrasonic sensors in close proximity detection.

💡Detection Range

Detection range is the distance within which an ultrasonic sensor can effectively detect objects. The video script explains that this range is influenced by the frequency of the transducer's vibration and the size of the object. Larger objects can be detected from farther away compared to smaller ones, which may only be detectable within a limited distance.

💡Hobbyist Sensors

Hobbyist sensors refer to pre-built ultrasonic sensors that are designed for use by hobbyists and makers. These sensors often come with a board that helps process the data and have pins for power, ground, and signal transmission. The video mentions that these sensors are commonly used in projects to measure distance, offering a practical application of the technology discussed.

Highlights

Ultrasonic sensors detect object distances without physical contact.

Dolphins and bats use echolocation, similar to how ultrasonic sensors work.

Ships and submarines use sonar to detect underwater objects, similar to how ultrasonic sensors function.

The formula for calculating distance with ultrasonic sensors is 1/2 * t * c, where t is the time and c is the speed of sound.

Sound travels faster in water, about 4.3 times faster than in air.

Ultrasonic sensors generate and detect sound waves through a vibrating membrane.

Humans can hear sounds between 20 Hz and 20 kHz, but ultrasonic sensors operate above 20 kHz.

Ultrasound is used in medical imaging, and ultrasonic sensors use sound waves to measure distance.

Ultrasonic transducers can be piezoelectric or capacitive.

Piezoelectric devices use a crystal substance that flexes to generate ultrasonic waves.

Capacitive transducers are built similarly to capacitors with charged plates that move to generate ultrasonic waves.

Capacitive transducers are micro-machined and can be used in arrays to increase bandwidth.

Most commercial ultrasonic sensors currently use piezoelectric technology, but capacitive technology is emerging.

Ultrasonic sensors detect objects within a cone-shaped detection area.

Objects need to be large enough and close enough to be detected by ultrasonic sensors; materials that absorb sound may be difficult to detect.

Transcripts

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join now at element14.com presents

hi i'm karen and welcome back to the

learning circuit in this lesson i'm

going to talk about ultrasonic distance

sensors

let's do it

[Music]

an ultrasonic sensor can detect the

distance of an object within its range

without requiring physical contact in

nature

dolphins and bats are two animals that

can detect their surroundings by using

echolocation

both creatures emit sound waves which

echo off nearby objects

bouncing waves back towards the animals

the animals use these echoes to locate

and identify objects in their

surroundings

ships and submarines use the same

technique to detect objects under water

with sonar

the time it takes for the sound to

reflect back to the sonar is used to

calculate the distance of the objects

the formula for calculating distance is

one half t

times c t is the time it takes for the

ultrasound to travel to the object

and return to the sensor since that's

twice the distance between the sensor

and the object

we multiply by half so that the distance

is only counted once

then times c the speed of sound or sonic

speed

the speed of sound is about 767 miles

per hour at sea level

but sound can travel 4.3 times faster in

water than in air

ultrasonic sensors use a vibrating

membrane to both generate

and detect the sound used to determine

distance

humans can typically hear sounds within

the acoustic frequency range of 20 hertz

up to 20 kilohertz above 20 kilohertz is

the ultrasonic range

ultrasonic sounds are those with waves

with a frequency above the upper limit

of human hearing

ultrasound is used in medical imaging

the faster the membrane vibrates the

higher the frequency

ultrasonic sensors convert energy

between electrical signals and sound

waves

making them transducers a transducer

is a device that converts a signal from

one form of energy to

another in this case electric current

and sound waves

ultrasonic transducers typically

function in one of two ways

piezoelectric or capacitive i've talked

about piezoelectric devices before in

previous learning circuit videos

like with microphones and speakers and

accelerometers

you can find the links to those videos

in the description below

piezoelectric devices use a crystal

substance that when a charge is

introduced

the particles rearrange causing a

membrane or diaphragm to flex back and

forth very quickly

in ultrasonic sensors the diaphragm

movement can either generate ultrasonic

waves

or will vibrate in response to received

waves

and translate that energy into

electrical signals

the other type of transducer is

capacitive

let's look back at what we learned about

capacitors in a previous video

capacitors have two conductive plates

separated by a dielectric material

when connected to power one plate gains

electrons

becoming negatively charged while the

second plate loses electrons

becoming positively charged in a

capacitive transducer

one plate or electrode sits on a

dielectric membrane

which is suspended above a cavity in its

silicon substrate

the substrate acts as the second

electrode

when current is applied to the

transducer the electrodes become

charged and the top plate is attracted

to or repelled by

the lower plate moving the membrane

applying an alternating current can

cause this to happen quickly

making the membrane vibrate and act as a

diaphragm generating ultrasonic waves

it's helpful to understand that sound

waves are just moving air

when a diaphragm vibrates air is pushed

out in waves at the same frequency as

the vibration

when the sound reflects off nearby

objects and bounces back

it is again airwaves of a certain

frequency that cause the diaphragm to

vibrate

and the transducer converts this energy

to electrical signals in the form of

alternating current

each ultrasonic sensor emits sounds in a

specific frequency

so whatever frequency it emits is the

same frequency it is looking to detect

this is why sounds of other frequencies

don't affect the sensor's readings

capacitive transducers often abbreviated

to cmut

are micro machined the micro machine man

hey presenting the genuine original

closely collectable most mighty

miniature episodes of the real things

micro machines i'm not talking about the

tiny toy cars from the 80s

more like men's technology unlike

piezoelectric transducers

siemens can be manufactured using

methods similar to mems

and integrated directly into electrical

circuits

not only does this make them cheap and

easy to manufacture but they can be

tightly packed into arrays

with seamlets that use a variety of

frequencies yielding an overall larger

bandwidth

this is still a relatively new concept

in the field of ultrasonic transducers

so most commercial ultrasonic sensors

still use piezoelectric technology

but since humans are obsessed with

making our electronics as small and

compact as possible

i'm guessing that will change pretty

quickly in the years to come

while some sensors use a separate sound

emitter and receiver

it's also possible to combine them into

a single device

having an ultrasonic element alternate

between emitting

and receiving signals the sound from the

emitter comes out at an angle

resulting in a cone-shaped detection

area

this shape will vary slightly depending

on the model

notice that most of these models can

detect up to between 5 and 15 feet away

and in particular on these hrlv models

the different fields show the detection

of various diameter objects

a smaller object like a one-quarter inch

dowel can only be detected for a limited

distance

while a larger object can be detected

from farther away

the range of an ultrasonic sensor is

determined by the frequency of vibration

of the transducer

as the frequency increases the sound

waves transmit for progressively shorter

distances

so long-range ultrasonic sensors work

best at lower frequencies

and short-range ultrasonic sensors work

best at higher frequencies

detection is dependent on the ultrasound

reflecting off the objects

and back to the sensor there are a

variety of factors that can prevent an

object from being detected

as stated the object has to be close

enough and large enough

if an object is too close to the sensor

it may be in what is known as the blind

zone

single unit sensors can only emit or

detect at any given time

if it is emitting it cannot detect

objects that are too close

will reflect sound too soon to be

detected

if the sensor is mounted too low the

floor may give off false positives

the object also needs to be shaped in a

way that the waves are reflected back

and not in a direction away from the

sensor

materials that absorb sound don't

reflect it well

so they may be difficult to detect

a fortunate feature is that ultrasonic

sensors are not affected by color

or other visual characteristics of the

detected object

and can even detect clear plastic and

the surface of water

some units are even fully enclosed and

waterproof in order to be used for water

level sensing

the ultrasonic sensors most commonly

used by hobbyists

come pre-built into boards that help

process the data

these will have pins for power and

ground and either one or two pins

used to trigger the signal emitted out

and detect the echo signal that is

received

while there are a variety of sensors

that can simply detect movement or an

object in its range

ultrasonic distance sensors are special

in that they can tell just how far away

that object

is be sure to check out my next video

where i show how to use one of these

handy devices

in a project in the meantime as usual if

you have any comments or questions about

what i talked about in this video

you can find me maker karen by posting

on the element 14 community on

element14.com forward slash

the learning circuit happy learning

you