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The arithmetic mean is usually skewed towards the larger values in the data set. Therefore, to avoid this inherent bias towards smaller values, the harmonic mean is used.
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Simple harmonic motion is the name given to oscillatory motion for a system where the net force can be described by Hooke's law. If the net force can be described by Hooke's law and there is no damping (by friction or other non-conservative forces), then a simple harmonic oscillator will oscillate with equal displacement on either side of the equilibrium position. To derive an equation for period and frequency, the equation of motion is used. The period of a simple harmonic oscillator is given...
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To determine the energy of a simple harmonic oscillator, consider all the forms of energy it can have during its simple harmonic motion. According to Hooke's Law, the energy stored during the compression/stretching of a string in a simple harmonic oscillator is potential energy. As the simple harmonic oscillator has no dissipative forces, it also possesses kinetic energy. In the presence of conservative forces, both energies can interconvert during oscillation, but the total energy remains...
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The key characteristic of the simple harmonic motion is that the acceleration of the system and, therefore, the net force are proportional to the displacement and act in the opposite direction to the displacement. Additionally, the period and frequency of a simple harmonic oscillator are independent of its amplitude. For example, diving boards move faster or slower based on their thickness. A stiff, thick diving board has a large force constant, which causes it to have a smaller period, while a...
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Related Experiment Video

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Reduced-gravity Environment Hardware Demonstrations of a Prototype Miniaturized Flow Cytometer and Companion Microfluidic Mixing Technology
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HIFU Drive System Miniaturization Using Harmonic Reduced Pulsewidth Modulation.

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    Summary
    This summary is machine-generated.

    Harmonic reduction pulsewidth modulation (HRPWM) offers a solution for high-intensity focused ultrasound (HIFU) systems, enabling smaller, filter-free circuitry. This method creates effective thermal lesions comparable to linear amplifiers without causing cavitation.

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    Area of Science:

    • Ultrasound Engineering
    • Biomedical Engineering
    • Acoustic Therapy

    Background:

    • Current high-intensity focused ultrasound (HIFU) systems rely on linear amplifiers, which are costly, inefficient, and bulky.
    • Existing switched excitation methods for HIFU suffer from high harmonic distortion or lack apodisation capabilities, necessitating complex power filters and adjustable supplies.
    • Multilevel pulsewidth modulation (PWM) offers a potential solution but faces limitations due to transistor switching speeds, restricting the number of available pulses per cycle.

    Purpose of the Study:

    • To propose and evaluate a novel algorithmic solution, harmonic reduction PWM (HRPWM), for designing switched waveforms in HIFU systems.
    • To assess the feasibility of HRPWM for HIFU by designing a high-power, five-level unfiltered amplifier.
    • To compare the efficacy of HRPWM-generated lesions with those produced by linear and bi-level excitation methods.

    Main Methods:

    • Designed and implemented a high-power, five-level unfiltered amplifier utilizing the HRPWM algorithm.
    • Generated three switched waveforms at different electrical powers (16, 26, 35 W) using HRPWM.
    • Conducted ex vivo thermal-only lesioning experiments on chicken breast, measuring lesion sizes and comparing them to linear and bi-level excitation methods.

    Main Results:

    • HRPWM successfully produced symmetric, thermal-only lesions comparable in size to those generated by linear amplifiers.
    • At 16 W, bi-level excitation resulted in smaller lesions.
    • At higher power levels, bi-level excitation induced significant transients, leading to undesired cavitation, while HRPWM did not.

    Conclusions:

    • HRPWM effectively minimizes the size of HIFU drive circuitry without requiring power filters for harmonic removal or adjustable power supplies for array apodisation.
    • HRPWM provides a viable alternative to linear amplification for HIFU, offering improved efficiency and reduced system complexity.
    • The HRPWM algorithm demonstrates suitability for generating precise thermal lesions in HIFU applications, avoiding cavitation issues associated with other switched methods.