How Do Ultrasonic Distance Sensors Work? - The Learning Circuit
Summary
TLDRIn 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
🔊 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.
📡 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.
Mindmap
Keywords
💡Ultrasonic Sensor
💡Echolocation
💡Sonic Speed
💡Transducer
💡Piezoelectric
💡Capacitive Transducer
💡Frequency
💡Blind Zone
💡Detection Range
💡Hobbyist Sensors
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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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
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