Direct Field Acoustic Testing Spatial Uniformity
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Solution Overview
Problem
Existing direct field acoustic testing systems fail to accurately simulate the reverberant acoustic field across the entire frequency spectrum, particularly at high and low frequencies, leading to spatial variability and coherence issues, which limits their reliability in evaluating the impact of high-intensity vibrations on complex objects like satellites.
Innovation Solution
A direct field acoustic testing system utilizing multiple groups of acoustical transducers driven by separately controllable signals, combined with a microphone system converting acoustical signals to fixed band-width narrow-band power spectral densities, and integrated with a multiple-input-multiple-output mechanical vibration controller to achieve stable closed-loop control and spatial uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If commercially available sound equipment is used to generate high intensity acoustic fields, then the testing system can be assembled temporarily on site, but the acoustic field exhibits substantial spatial variability and high coherence
Solution Approach 1:
The system divides the acoustic field generation into multiple independently controllable transducer groups (at least four groups) positioned around the UUT. Each transducer group can be controlled separately to generate acoustic energy that contributes to a uniform, incoherent field, resolving the contradiction between portable assembly and reliable spatial uniformity.
Solution Approach 2:
The system employs microphones positioned around the UUT to monitor the acoustic field and feeds this information back to the control system. The control system uses this feedback to adjust the drive signals to transducer groups, creating a closed-loop control that maintains spatial uniformity and reduces coherence, thereby achieving reliable testing with temporary assembly.
2Reliability
If fixed band-width narrow-band control is used, then stable closed-loop control across the entire frequency range is achieved, but the system complexity increases
Solution Approach 1:
The control system segments the frequency spectrum into multiple narrow bands with fixed band-widths. Each band is controlled independently through separate control channels, allowing stable closed-loop control across the entire frequency range (20 Hz to 10 kHz) while managing complexity through modular, frequency-specific control units.
Solution Approach 2:
The system changes the control parameter from variable band-width (octave-based) to fixed band-width narrow bands. This parameter change enables consistent, stable control across all frequencies by using uniform frequency intervals, thereby achieving reliable closed-loop control without excessive complexity.
3Reliability
If reverberant chamber testing is used, then accurate control of acoustic fields is achieved, but the UUT must be transported to the chamber which is costly and risky
Solution Approach 1:
The system creates a portable replica of the reverberant chamber environment using direct field acoustic testing. By positioning multiple transducer groups around the UUT and controlling them to generate an incoherent acoustic field, the system copies the essential characteristics of a reverberant chamber without requiring the UUT to be transported to a fixed facility, thereby eliminating transportation costs and risks while maintaining reliable acoustic field control.
4Device complexity
If single-axis mechanical vibration testing is used, then the testing system is simple, but it cannot evaluate high intensity acoustic vibrational fields
Solution Approach 1:
The system segments the acoustic field generation into multiple transducer groups that can be independently controlled. This segmentation allows the system to generate high intensity acoustic vibrational fields with controlled spatial distribution, enabling reliable evaluation of acoustic effects on the UUT while maintaining manageable system complexity through modular transducer groups.
Solution Approach 2:
The system replaces single-axis mechanical vibration testing with direct field acoustic testing using electro-dynamic transducers. This substitution enables the evaluation of high intensity acoustic vibrational fields that cannot be achieved with mechanical vibration systems, thereby improving the reliability of acoustic field evaluation while using similarly controllable transducer-based systems.
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
The system provides a high degree of spatial uniformity and low spatial coherence, effectively replicating the results of reverberant chamber testing across the entire frequency range from 20 Hz to 10 kHz, reducing the risk of over-testing and damage to sensitive objects.
Implementation Method 1
at least four groups of acoustical transducers driven by separately controllable drive signals
Implementation Method 2
at least one microphone disposed in an appropriate location to provide at least one acoustical input signal
Implementation Method 3
The reverberant nature of the chamber ensures a uniform but highly uncorrelated acoustic field
Data Source
AI summary
A direct field acoustic testing system includes at least one control microphone, a controller operatively coupled to the control microphone such that the controller receives at least one input signal from the control microphone, and at least four acoustic transducers operatively coupled to the controller such that each transducer is separately controllable by the controller such that a separate output signal is received by each transducer from the controller. A setup is applied to each of the acoustical transducers. The acoustic output of each of the acoustical transducers is monitored using the at least one control microphone. The output signal of each control microphone with respect to each acoustical transducer is compared to a reference spectrum to create a matrix of error functions, and a corrected drive signal computed for each acoustical transducer is applied to the respective acoustical transducer.