Phyllotactic Transducer Array for Grating Lobe Suppression
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Solution Overview
Problem
Ultrasonic phased arrays face challenges with grating lobes, which cause energy leakage in unintended directions, limiting steering capabilities and affecting mid-air haptics and parametric audio performance due to suboptimal spacing and geometry of transducers.
Innovation Solution
The use of an acoustic waveguide structure that transforms the geometry of transducer arrays from rectilinear to phyllotactic spiral or pseudo-random arrangements, approaching critical spacing to eliminate grating lobes and enhance steering capabilities, while optimizing material usage and manufacturing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If transducers are arranged in a rectilinear array with uniform spacing, then manufacturing is simplified and packing density is increased, but grating lobes appear and distort the output
Solution Approach 1:
The patent applies asymmetry by transforming the rectilinear array geometry into a phyllotactic spiral arrangement. This irrational spacing pattern eliminates the periodicity that causes grating lobes, while maintaining ease of manufacture through a systematic geometric construction method based on the golden angle (137.5 degrees). The spiral pattern can be generated algorithmically, making it practical for manufacturing.
Solution Approach 2:
The patent changes the spacing parameter from uniform rectilinear distances to variable phyllotactic distances determined by the golden angle. This parameter transformation eliminates grating lobes by ensuring no two transducers are spaced at integer multiples of the wavelength, while maintaining high packing density through optimal space utilization of the spiral pattern.
2Quantity of substance
If element spacing is increased above critical spacing, then more transducers can be packed in the array, but grating lobes appear and create unwanted extra output focus points
Solution Approach 1:
The phyllotactic spiral arrangement uses irrational spacing based on the golden angle to break the periodicity that causes grating lobes. This allows transducers to be spaced farther apart on average while preventing the constructive interference at specific angles that creates grating lobes in uniform arrays.
Solution Approach 2:
The patent converts the potential harm of increased spacing (which would normally create grating lobes) into a benefit by using the irrational phyllotactic pattern. The same increased spacing that would create problems in uniform arrays instead distributes energy more evenly when arranged in the golden spiral, eliminating grating lobes while maintaining high transducer count.
3Adaptability or versatility
If frequency is set independently of element size and spacing, then design flexibility is improved, but unwanted extra output focus points appear due to geometric uniformity
Solution Approach 1:
The phyllotactic spiral arrangement provides inherent geometric asymmetry through its irrational spacing pattern. This allows the array to operate at various frequencies without developing grating lobes, as the non-periodic spacing prevents resonant constructive interference at any particular frequency, granting design flexibility.
Solution Approach 2:
The patent creates a universal array design that functions effectively across multiple frequencies. The phyllotactic pattern's irrational spacing makes the array frequency-agnostic, eliminating the need to optimize spacing for a specific frequency and allowing independent frequency selection based on application requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses grating lobes, enabling precise steering of acoustic fields and parametric audio beams to arbitrary angles with improved packing density and reduced material waste, maintaining frequency response integrity.
Implementation Method 1
Steering via a phased array can encounter grating lobes when element spacing is above critical spacing. This results in sound energy being projected in unintended directions. To bring the array closer to critical spacing an acoustic waveguide structure can be used.
Implementation Method 2
By selecting specific signals or, in the case of a monochromatic array, phases and amplitudes, the group of transmitters can shape the emitted field. In the case of an ultrasound phased array in air, the sound field can be focused, made to diverge, shaped into beams, and generally rearranged into many other forms.
Implementation Method 3
Uses for shaped and steered ultrasonic fields include mid-air haptics, directional audio, and the imaging of physical materials and scenes.
Data Source
AI summary
Defining critical spacing is necessary for steering of parametric audio. Comparing steering measurements both with and without a waveguide leads to a conclusion that the diffuse phyllotactic grating lobe contributes audio and is to blame for poor steering. In addition, the waveguide needs to function with correct phase offsets to achieve the steering required for performance. Arranging tubes so that the array configuration changes from rectilinear to another distribution is useful when the waveguide is short of critical spacing or constrained for space. Array designs may also capitalize on rectilinear transducer design while having the benefits of a transducer tiling that has irrational spacing to promote the spread of grating lobe energy.