Building Acoustic Levitators: Physics & Arduino

Learning Goal: Design, assemble, and calibrate a single-axis ultrasonic acoustic levitator using an array of 40 kHz transducers, a dual H-bridge driver circuit, and an Arduino to generate standing waves for suspending and manipulating micro-particles.

• Prerequisites: Basic knowledge of electronics (voltage, current, parallel circuits), familiarity with the Arduino IDE, and foundational physics (wave properties).
• Estimated Total Study Time: 14 Hours

Module 1: The Physics of Sound and Standing Waves

This module establishes the foundational acoustic physics required to understand levitation. You will learn how high-frequency sound waves travel through gaseous mediums, undergo constructive and destructive interference, and form stationary pressure profiles (standing waves). You will explore the physical characteristics of "nodes" (low-pressure points) and "antinodes" (high-pressure points) to understand how acoustic radiation pressure counteracts gravitational force.

Recommended Videos

How Does Acoustic Levitator Really Work?

@TheActionLab08:50306,479

How Does Acoustic Levitator Really Work?

Acoustic levitation works by creating standing sound waves between an ultrasonic transducer and a reflector, forming alternating regions of high and low pressure called nodes and antinodes; particles levitate at different points depending on their size—smaller particles (less than ~10 wavelengths) are pushed to antinodes by the ponderomotive force, while larger particles settle at nodes due to acoustic radiation pressure, which is why the phenomenon isn't as straightforward as commonly explained

@TheActionLab · 08:50

• Why this video is valuable: This video provides an intuitive physical visualization of acoustic standing waves. It breaks down the mechanical interaction between transducers and reflectors, showing how air molecules behave within the resonant cavity to form high-pressure "invisible shelves" that suspend matter.

I built an acoustic LEVITATOR! Making liquid float on air

@physicsgirl09:24689,718

I built an acoustic LEVITATOR! Making liquid float on air

Acoustic levitation uses standing waves created by multiple speakers emitting sound waves at specific frequencies and angles, which generate nodes (points of zero air movement) where objects can be suspended mid-air; the 3D printed bowl-shaped structure focuses acoustic power to create these stable nodes, allowing any material to levitate as long as its density remains below the acoustic pressure threshold.

@physicsgirl · 09:24

• Why this video is valuable: Physics Girl demonstrates a practical implementation of a single-axis levitator, linking acoustic wave theory to an actual physical build. She explains the necessity of using high-frequency (ultrasonic) sound to keep the physical apparatus compact and quiet enough for safe human environments.

Acoustic Standing Waves and the Levitation of Small Objects

@NatSciDemos00:562,819,939

Acoustic Standing Waves and the Levitation of Small Objects

Small objects can be suspended or levitated in mid-air when placed within regions of high pressure created by standing sound waves. The demonstration shows that small balls settle into and remain suspended in these high-pressure zones, demonstrating how acoustic radiation pressure can counteract gravitational forces acting on lightweight particles.

@NatSciDemos · 00:56

• Why this video is valuable: A short, high-fidelity demonstration showing the exact physical position of suspended beads within a standing wave pattern. It serves as an excellent reference for what a properly aligned standing wave looks like in practice.

Knowledge Checkpoint

• Explain the difference between an acoustic node and an antinode. Where exactly do levitated particles sit?
• Calculate the wavelength ($\lambda$) of a 40 kHz sound wave in air at room temperature ($20^\circ\text{C}$, speed of sound $\approx 343\text{ m/s}$).
• Describe how acoustic radiation pressure counteracts gravity to hold a particle stationary.

Module 2: Piezoelectric Transducers and H-Bridge Drivers

To build an acoustic levitator, you must generate high-intensity ultrasonic waves. This module covers the operation of 40 kHz piezoelectric transducers, which convert high-frequency electrical signals into mechanical vibrations. You will also study the H-bridge driver topology (specifically the L298N driver), which is used to amplify the weak digital signals of a microcontroller to drive capacitive transducer loads with high-voltage alternating current.

Recommended Videos

How to use inexpensive transducers for ultrasonic measurement

@TexasInstruments00:4172,808

How to use inexpensive transducers for ultrasonic measurement

Piezoelectric transducers are ceramic crystals that exhibit the piezoelectric effect: when voltage is applied, the crystal contracts; when voltage is removed, it expands. This expansion creates pressure waves in the connected material. The TDC 1000 device can detect these echoes by being connected to a transducer, producing start and stop signals that indicate the beginning and reception of the echo pulse.

@TexasInstruments · 00:41

• Why this video is valuable: This brief technical explanation from Texas Instruments shows how piezoelectric crystals contract and expand in response to an applied voltage, creating the microscopic high-frequency pressure waves required for ultrasonic output.

Control DC Motors with L298N H-Bridge & Arduino Tutorial

@Dronebotworkshop05:341,356,543

Control DC Motors with L298N H-Bridge & Arduino Tutorial

An H-bridge uses four switches arranged in an H-shape with the motor at the center. Positive voltage connects to the top, negative to the bottom. Closing specific switch pairs reverses motor polarity: top-left and bottom-right switches cause clockwise rotation, while reversing these causes counterclockwise rotation. The L298N module implements this with motor power input (5-35V), common ground, and 5V logic supply. Enable lines control motor activation and accept PWM for speed control. Direction

@Dronebotworkshop · 05:34

• Why this video is valuable: While typically used for DC motors, the L298N H-bridge driver is perfect for acoustic levitation because it can rapidly switch polarities. This video explains the internal logic, pinouts, and switching characteristics of the L298N module, helping you understand how it processes drive signals.

Inside an invigorating electro-health device - with schematic

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Inside an invigorating electro-health device - with schematic

The H-bridge circuit enables polarity reversal by using diagonal pairs of transistors controlled by the microcontroller. When one pair of transistors is turned on, one output goes positive while the other goes negative; when the other pair is activated, the polarity reverses. This configuration allows the device to alternate between positive and negative outputs, creating the pulsing sensation characteristic of these devices. The transistors are driven by the microcontroller through high-value r

@bigclivedotcom · 01:25

• Why this video is valuable: This video breaks down a schematic of an H-bridge circuit, explaining how alternating diagonal pairs of transistors switch current direction through a load. This provides excellent foundational knowledge for understanding signal inversion in driver circuits.

Independent Search & Exploration

• Gap Note: Standard H-bridge tutorials focus primarily on low-frequency inductive loads (DC motors). For ultrasonic levitation, the L298N must drive highly capacitive 40 kHz transducer arrays.
• Recommended Search Query: DIY ultrasonic levitator L298N driver circuit schematic to study how to bypass standard motor driver filtering for high-frequency output.

Knowledge Checkpoint

• How does a piezoelectric crystal behave when an alternating current (AC) is applied across its terminals?
• Draw a simple schematic of an H-bridge circuit and identify which diagonal transistor pairs must be active to alternate current direction.
• What is "shoot-through current" in an H-bridge, and why must you prevent both high and low-side transistors on the same half-bridge from turning on simultaneously?

Module 3: Arduino Programming: Generating 40 kHz Signals

A standard Arduino Uno’s analogWrite() function operates at a default frequency (~490 Hz or ~976 Hz) that is far too low for acoustic levitation. In this module, you will learn to bypass the standard Arduino library and write register-level code to configure the ATmega328P internal timers. You will generate a precise 40 kHz PWM output, configure complementary (out-of-phase) square waves to drive the H-bridge, and insert "dead-time" to prevent electrical damage.

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(2) Timer Interrupts-Registers

@homelabs439009:051,911

(2) Timer Interrupts-Registers

This video explains how to configure Arduino timer interrupts by understanding the Timer Control Registers (TCCRA and TCCRB), including the prescaler bits (CS0, CS1, CS2) for setting clock division ratios, the Waveform Generation Mode bits (WGM00, WGM01, WGM02) for selecting CTC mode, and the Timer/Counter Register (TCNT) and Output Compare Register (OCRA) for controlling timer behavior. The video demonstrates how to use bitwise operations (OR, AND, left shift, right shift) to set specific bits

@homelabs4390 · 09:05

• Why this video is valuable: This video offers a clear, register-level explanation of how Arduino Timer Control Registers (TCCRA and TCCRB) and prescalers configure precise timer interrupts. Understanding these internal registers is critical for setting up the high-frequency clock cycles required for a 40 kHz output.

Arduino PWM Frequency Change Tutorial: Timer Prescaler Guide

@JulianIlett11:09156,370

Arduino PWM Frequency Change Tutorial: Timer Prescaler Guide

The Arduino's PWM frequency varies by pin: pins 5 and 6 operate at 976Hz using Timer 0, while pins 3, 9, 10, and 11 run at 490Hz using Timers 1 and 2; these frequencies can be modified by adjusting the timer prescalers in the TCCRnB register, though this may interfere with timing functions like millis() and delay().

@JulianIlett · 11:09

• Why this video is valuable: Julian Ilett provides a practical walkthrough on modifying the default PWM frequencies by directly manipulating the timer prescaler bits. This guide is essential for transitioning from low-frequency DC motor control to high-frequency ultrasonic signals.

Part 2: Arduino Nano 33 IoT - Complementary Pulse Width Modulation (PWM) pulses with Dead Time.

@ys_embedded25830:12525

Part 2: Arduino Nano 33 IoT - Complementary Pulse Width Modulation (PWM) pulses with Dead Time.

This tutorial explains how to generate complementary PWM pulses with dead time using the Arduino Nano IoT's TCC timer. The PWM frequency is calculated using the formula: F_PWM = F_CLK_TCC / (N × (TOP + 1)), where F_CLK_TCC is 48 MHz, N is the prescaler value, and TOP is the PR register value. For 33 kHz PWM with prescaler = 1, TOP = 1453. The dead time is inserted using the waveform extension control register, which prevents shoot-through in complementary PWM pairs (pins D2 and D6 are paired as

@ys_embedded258 · 30:12

• Why this video is valuable: This advanced tutorial explains how to generate complementary (180-degree out-of-phase) square waves with integrated dead-time using microcontroller timers. This concept is vital for safely driving the dual inputs of an H-bridge driver without causing short circuits.

Independent Search & Exploration

• Gap Note: Direct register programming varies significantly between Arduino architectures (e.g., ATmega328P on the Uno vs. SAMD21 on the Nano 33 IoT).
• Recommended Search Query: Arduino complementary PWM 40kHz acoustic levitator to find code templates written specifically for your hardware.

Knowledge Checkpoint

• Which Timer Control Registers on the ATmega328P are used to modify the frequency of Digital Pins 9 and 10?
• Why must the two signal lines driving a single H-bridge driver be exactly 180 degrees out-of-phase (complementary)?
• Define "dead-time" in H-bridge control and explain why it is essential for high-frequency switching applications.

Module 4: Mechanical Assembly and Transducer Alignment

This module covers the physical design, structural assembly, and electrical wiring of your acoustic levitator. You will learn to construct a physical frame (often 3D printed or laser-cut) that positions two opposing transducer arrays at a precise mechanical distance. You will also learn the practical steps of wiring multiple 40 kHz transducers in parallel with matched acoustic polarity (phase alignment).

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How to Make an Ultrasonic Levitator | Science Project

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How to Make an Ultrasonic Levitator | Science Project

This concluding section addresses power delivery and performance enhancement techniques. The Arduino's VIN pin provides raw voltage from external power supplies, enabling higher voltage operation for transducers. A jumper wire connects VIN to the power bus powering the H-bridge, providing higher voltages (e.g., 9V or 12V) while the Arduino maintains regulated 5V through USB. Arduino Uno R3 handles up to 12V on the barrel jack, while Uno R4 handles up to 20V. Higher voltages require external adap

@Science.Buddies · 10:07

• Why this video is valuable: This video is a step-by-step build guide for a dual-array acoustic levitator. It demonstrates physical assembly, wiring routing, external power connections via the Arduino's VIN pin, and basic testing.

How to Wire Two Single 4 ohm Subwoofers to a 2 ohm Final Impedance | Parallel Wiring

@SonicElectronix00:45529,389

How to Wire Two Single 4 ohm Subwoofers to a 2 ohm Final Impedance | Parallel Wiring

To wire two single 4-ohm subwoofers in parallel to achieve a 2-ohm final load, connect all positive terminals together and all negative terminals together. Use speaker wire (e.g., blue for positive, gray for negative) to join corresponding terminals. The combined wire then connects to the box terminal inside the enclosure, which links to the amplifier outputs. This parallel configuration reduces total impedance by half when using identical speakers.

@SonicElectronix · 00:45

• Why this video is valuable: This video clearly explains the principles of parallel wiring: connecting all positive terminals together and all negative terminals together. This same wiring technique is used to connect multiple 40 kHz ultrasonic transducers in parallel to ensure they operate in phase.

AVRant Podcast #736.0 - Series-Parallel Driver Configurations

@Avrant02:451,043

AVRant Podcast #736.0 - Series-Parallel Driver Configurations

Tactile transducers (bass shakers) can be wired in series-parallel configurations to increase power handling. For four transducers: 1) Wire transducers 1 and 2 in series (red from amplifier to red of transducer 1, black from amplifier to black of transducer 2, then connect black of transducer 1 to red of transducer 2), creating an 8-ohm load. 2) Wire transducers 3 and 4 in series using the same method, creating another 8-ohm load. 3) Connect both series pairs in parallel to the amplifier outputs

@Avrant · 02:45

• Why this video is valuable: This video explains how to wire multiple elements in series-parallel configurations to manage power distribution. This is highly useful if you want to scale up your levitator into a larger transducer array.

Independent Search & Exploration

• Gap Note: Ensuring all parallel transducers are wired with matched physical polarity is crucial; if some transducers are wired backwards, their acoustic waves will cancel each other out, ruining the standing wave.
• Recommended Search Query: how to wire 40kHz ultrasonic transducers parallel phase to find detailed visual guides on identifying the positive and negative terminals on bare piezoceramic transducers.

Knowledge Checkpoint

• Why must the distance between the top and bottom transducer arrays be a precise multiple of the acoustic half-wavelength ($n \cdot \frac{\lambda}{2}$)?
• If you wire two transducers in parallel with opposite polarity, what happens to the resulting acoustic wave?
• How do you identify the positive and negative terminals of a 40 kHz piezoelectric transducer?

Module 5: Calibration, Testing, and Particle Manipulation

Once assembled, your levitator must be carefully calibrated. This final module covers how to use an oscilloscope to check the output voltage of your H-bridge driver, tune the frequency to match the transducers' resonant frequency (~40 kHz), and mechanically align the acoustic axes to maximize standing wave pressure. You will also learn techniques for introducing and manipulating micro-particles (such as expanded polystyrene beads).

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Oscilloscope Basics: Y-Axis & Probe Calibration

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Oscilloscope Basics: Y-Axis & Probe Calibration

This video teaches beginners how to operate an analog oscilloscope's Y-axis (vertical) controls for voltage measurement, including probe calibration using the onboard square-wave generator. Key concepts include: (1) The oscilloscope probe has an x1/x10 switch that attenuates the signal by 10x, requiring corresponding adjustment of the vertical deflection knob to maintain proper waveform height; (2) Calibration involves connecting the probe to the probe adjust output (which provides a known 0.5V

@UncleDoug · 32:57

• Why this video is valuable: To calibrate your acoustic levitator, you must measure your drive signal. This video teaches you how to use an oscilloscope to measure voltage amplitudes and calibrate probes using a square wave generator.

Ultrasonic Transducers - Measurements and Calibration

@imajeenyus4230:32229,880

Ultrasonic Transducers - Measurements and Calibration

To measure the resonant frequency of an ultrasonic transducer, connect a sine wave signal generator to the transducer with a 100 ohm resistor in series, using an oscilloscope to monitor voltage and current; the resonant frequency occurs where current draw is maximum and current and voltage are in phase. When designing a horn, calculate the half-wavelength using the speed of sound in the material (approximately 5,800 m/s for aluminum) divided by the resonant frequency, then iteratively shorten th

@imajeenyus42 · 30:32

• Why this video is valuable: This deep dive shows how to measure the exact resonant frequency of an ultrasonic transducer using an oscilloscope and signal generator. It provides the technical foundation needed to tune your Arduino code to match your transducers' resonant frequency.

A Volumetric Display using an Acoustically Trapped Particle

@abitembedded10:191,726,759

A Volumetric Display using an Acoustically Trapped Particle

A volumetric display can be created by using a phased array of ultrasonic transducers to levitate and move a small particle (such as a 1mm foam ball) through the air at speeds exceeding 1m/s, creating the illusion of drawing in mid-air through the persistence of vision effect; the system works by calculating the phase shift for each transducer based on the distance from the focus point, with the wave number converting distance into phase, and using an FPGA to generate the precise 40kHz signals n

@abitembedded · 10:19

• Why this video is valuable: A demonstration of particle trapping, physical manipulation, and spatial control within a phased ultrasonic array. It shows how precision phase shifts can move particles along an acoustic axis.

Independent Search & Exploration

• Gap Note: Budget levitator builds often lack an oscilloscope. You can calibrate your setup physically by tuning a variable resistor or adjusting the mechanical distance until particles successfully suspend in mid-air.
• Recommended Search Query: oscilloscope calibration acoustic levitator standing wave or acoustic levitation troubleshooting guide particles drop for specific step-by-step physical alignment procedures.

Knowledge Checkpoint

• How do you use an oscilloscope to verify that your Arduino and H-bridge driver are outputting a clean 40 kHz square wave?
• What physical symptoms indicate that your upper and lower transducer arrays are out of alignment?
• Describe the technique for safely releasing a tiny polystyrene bead into an active acoustic node without disrupting the standing wave.

Course Map

Key People Index

• Dr. David Deak: Pioneer in acoustic wave chamber development and low-frequency resonant wave levitation systems.
• Asier Marzo: Leading researcher in acoustic holographic levitation and contactless robotic manipulation at the University of Bristol and UpnaLab.

Final Self-Assessment

• I can explain the physical principles of sound waves, standing waves, nodes, and antinodes.
• I can calculate the acoustic half-wavelength ($\frac{\lambda}{2}$) in air for any given ultrasonic frequency.
• I understand how a piezoelectric ceramic transducer converts electrical alternating voltage into mechanical vibrations.
• I can describe how an H-bridge driver (such as the L298N) functions to reverse polarity across a capacitive load.
• I can configure the Timer registers on an ATmega328P to change default PWM outputs to a precise 40 kHz frequency.
• I can write Arduino code that outputs dual out-of-phase (complementary) signals with necessary dead-time.
• I know how to wire multiple ultrasonic transducers in parallel with matched acoustic phase polarity.
• I have assembled a physical frame holding two opposing transducer arrays separated by a multiple of the acoustic half-wavelength.
• I can use an oscilloscope to verify output frequency, peak-to-peak voltage, and phase matching on my driver circuit.
• I can successfully calibrate, align, and troubleshoot my levitator to stably suspend small polystyrene beads in mid-air.