Methods for measuring phase dynamics and other properties
Inventors
Yost, William T. • Cantrell, John H. • Perey, Daniel F.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-11185232-B2
Publication Date
2021-11-30
Expiration Date
2036-03-09
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Abstract
Systems and methods for measuring phase dynamics and other properties (e.g. intracranial pressure) are disclosed. For example, the system may generate a reference waveform and a measurement waveform using digital synthesizers, each waveform having an identical constant frequency but also a relative phase shift. Next, system may send a tone-burst, via a transducer, into a sample (e.g. a skull or a bonded material), and then receive a reflected tone-burst in response. Then, a phase difference between the received tone-burst and the measurement waveform may be determined with a linear phase detector. Next, the phase shift of the measurement waveform may be adjusted, by the determined phase difference, such that there is no longer any phase difference between the received tone-burst and the adjusted measurement waveform generated by the appropriate digital synthesizer. A similar adjustment may occur after subsequent tone-bursts, allowing accurate monitoring of continuously variable phase relationships.
Core Innovation
The invention relates to systems and methods for measuring phase differences, variable phase relationships, and other properties such as intracranial pressure. The system includes at least one processor, a digital oscillator module with one or more direct digital synthesizers generating waveforms of constant frequency and relative phase shift, a linear phase detector, a tone-burst module, and a transducer configured to be attached to a sample. The system sends an ultrasonic tone-burst into the sample and receives a reflected tone-burst, determining the phase difference between the received tone-burst and the measurement waveform, then adjusts the phase shift to eliminate this difference for accurate continuous monitoring of phase changes.
The problem addressed is the inaccuracy, imprecision, noise, and instability in prior methods for non-invasive intracranial pressure evaluation, which relied on pulsed phase-locked loop technology using quadrature phase detectors that adjusted oscillator frequency to reestablish quadrature. This approach led to errors and uncertainties caused by other measurement path elements influencing the signal phase as frequency changes and reflections from the skull causing unintended phase shifts. The quadrature phase detector also prevented linear phase difference measurements, limiting numerical output capabilities.
The disclosed systems utilize constant frequency pulsed phase-locked loops with digital synthesizers and a linear phase detector to maintain phase measurement stability and accuracy. This allows continuous linear measurement of phase shifts without frequency changes, improving precision and bandwidth. The system generates a reference waveform and a measurement waveform at the same frequency but with an adjustable initial phase shift, detects phase differences from reflected tone-bursts, and adjusts the measurement waveform phase to maintain null phase difference, enabling robust and accurate measurement of dynamic phase relationships over time.
Claims Coverage
The patent includes multiple independent claims focusing on methods for phase measurement involving digital synthesizers, tone-bursts, and phase difference adjustments. Below are the main inventive features of the independent claims.
Generation of reference and measurement waveforms with initial phase shift
Generating, with a first direct digital synthesizer, a reference waveform having a constant frequency and, using a second direct digital synthesizer, a measurement waveform having the same constant frequency as the reference waveform but with an initial phase shift relative to it.
Sending and receiving tone-bursts based on reference waveform
Determining a tone-burst wave sequence based on the reference waveform, sending one or multiple tone-bursts into a sample using a transducer, and receiving corresponding reflected tone-bursts from the sample.
Determining and adjusting phase difference to maintain null difference
Determining a phase difference between the received tone-burst and the measurement waveform using a linear phase detector and adjusting the measurement waveform's phase shift by the determined phase difference such that there is no longer any phase difference between them.
Continuous phase adjustment across multiple tone-bursts
After each received tone-burst, further adjusting the phase shift of the measurement waveform before sending the next tone-burst, maintaining no phase difference at each step, and recording a plurality of phase differences from multiple tone-bursts.
Application of phase measurement to different sample types and frequencies
Using constant frequencies between 100 KHz and 15 MHz, applying the method to samples such as human heads for determining skull volume expansion, fluid volume, and intracranial pressure, or articles with bonded materials to determine bond characteristics.
The claims define methods utilizing direct digital synthesizers for generating phase-shifted waveforms, sending tone-bursts into samples, determining phase differences with reflected signals, adjusting phase shifts to eliminate differences, and applying continuous phase adjustments for accurate measurement of dynamic phase changes. These features enable precise monitoring of intracranial and bonded material properties at defined frequency ranges.
Stated Advantages
Provides more accurate and robust measurement capability with improved bandwidth compared to prior systems.
Achieves higher precision and lower noise levels in phase measurements through digital phase detection and adjustment.
Improves operational circuit stability, resulting in more stable and reliable data collection.
Enables continuous linear measurement of phase changes, allowing numerical output in phase rather than relying on quadrature detection.
Allows remote, non-invasive evaluation of physiological dynamics such as intracranial pressure and skull volume expansion.
Offers flexible phase adjustment for improved stability and removal of secondary effects from measurement outputs.
Documented Applications
Non-invasive measurement of intracranial pressure and related intracranial dynamics in humans, including assessment of skull volume expansion and total fluid volume in the skull.
Measurement and analysis of skull volume changes related to pulsatile cerebral blood flow and head injuries such as concussions, strokes, brain tumors, and meningitis.
Evaluation of bond characteristics between bonded dissimilar materials through detecting phase changes associated with bond stress, strain, and temperature.
Continuous monitoring of dynamic physiological phenomena related to cranial expansion over time for medical diagnostics and treatment monitoring.
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