High frequency magnetostrictive transducers for waveguide applications
Inventors
Daw, Joshua Earl • Taylor, Steven Cheney • Rempe, Joy Lynn
Assignees
Publication Number
US-9960341-B1
Publication Date
2018-05-01
Expiration Date
2034-11-26
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Abstract
A high frequency magnetostrictive transducer includes a magnetostrictive rod or wire inserted co-axially into a driving coil, wherein the driving coil includes a coil arrangement with a plurality of small coil segments along the magnetostrictive rod or wire; wherein frequency operation of the high frequency magnetostrictive transducer is controlled by a length of the small coil segments and a material type of the magnetostrictive rod or wire. This design of the high frequency magnetostrictive transducer retains the beneficial aspects of the magnetostrictive design, while reducing its primary drawback, lower frequency operation.
Core Innovation
The invention describes a high frequency magnetostrictive transducer that includes a magnetostrictive rod or wire inserted co-axially into a driving coil composed of multiple small coil segments arranged along the rod or wire. The frequency operation of the transducer is controlled by the length of these small coil segments and the material type of the magnetostrictive rod or wire. This design enables operation at higher frequencies, demonstrated up to approximately 2 MHz with a 36% bandwidth, significantly increasing the frequency range compared to conventional magnetostrictive transducers.
The problem addressed is that conventional magnetostrictive transducers typically operate at lower frequencies, generally below 200 kHz, with a very narrow bandwidth, limiting their use in applications requiring higher frequency ultrasonic waves. Conventional transducers have coil arrangements tightly wound with little or no space between turns, limiting frequency capability and signal strength. Piezoelectric transducers, while capable of higher frequencies, are fragile and difficult to couple to metals, whereas magnetostrictive transducers are durable and easy to couple but frequency limited.
The invention solves this by introducing an advanced coil arrangement comprising a plurality of small coil segments spaced apart along the magnetostrictive rod or wire with open space between them. These coil segments can be wound in uniform or alternating directions and driven such that their magnetic fields collectively constructively interfere, enhancing signal strength. This arrangement allows the rod or wire to be driven at higher harmonics, producing higher frequency ultrasonic waves while maintaining good signal strength and bandwidth, thereby overcoming the frequency limitations of prior magnetostrictive transducers.
Claims Coverage
The patent includes two independent claims reciting a high frequency magnetostrictive transducer and a high frequency magnetostrictive transducer system. Each claim focuses on the novel coil arrangement and frequency control features.
Advanced coil arrangement with multiple small coil segments
The transducer comprises a magnetostrictive rod or wire co-axially inserted into a driving coil that includes a plurality of small coil segments electrically connected in series along the rod or wire. The coil segments are spaced apart with open spaces therebetween.
Frequency control by coil segment length and material type
The operating frequency is controlled by the length of the small coil segments and the material type of the magnetostrictive rod or wire, where the length of the coil segments and spacing are approximately defined by L = c/2·f (c = sound velocity, f = operating frequency).
Magnetic field orientations that constructively interfere
The plurality of small coil segments each form magnetic field orientations that collectively constructively interfere, resulting in greater signal strength.
High frequency and bandwidth operation
The transducer operates at a peak center frequency up to approximately 2 MHz, with an operating frequency range between about 1 MHz and 3 MHz, enabling operation at higher harmonics with greater than 50% signal amplitude.
Coil winding configurations
The small coil segments are configured to be wound either in a uniform direction or in alternating directions to achieve the desired magnetic field and frequency response.
System integration
A system comprising one or more such high frequency magnetostrictive transducers, a driving source configured to drive them, and a detection device coupled to the transducers to receive and process signals.
Signal excitation
The source produces a plurality of sinusoidal pulses with frequencies greater than 1 MHz and matched to the operating frequency of the transducer.
The claims focus on a high frequency magnetostrictive transducer with a novel coil arrangement of multiple small coil segments whose length and spacing control frequency, enabling operation at higher frequencies with greater signal strength and bandwidth, and the integration of such transducers into a system with corresponding excitation and detection elements.
Stated Advantages
Enables higher frequency operation of magnetostrictive transducers up to approximately 2 MHz, greatly exceeding conventional limits below 200 kHz.
Increases operational bandwidth substantially, supporting frequency ranges between about 1 MHz to 3 MHz compared to very narrow bandwidths in prior art.
Retains beneficial magnetostrictive properties such as durability and ease of coupling to metals while overcoming low frequency and narrow bandwidth drawbacks.
Improves signal strength through constructive interference of magnetic fields generated by multiple coil segments, despite operation at higher frequencies.
Allows excitation at higher harmonics of the magnetostrictive rod or wire, enabling better frequency response and resolution.
Documented Applications
Non-destructive evaluation to scan objects and identify defects using ultrasonic waves.
Core technology in sensor systems for measuring various parameters such as density, Young's Modulus, and others.
Ultrasonic cleaning and ultrasonic welding applications.
Material property testing including density and mechanical properties.
Enhanced ultrasonic sensors for Materials and Test Reactors (MTRs), commercial and naval fleets, and spent fuel casks.
Incorporation into thermometers for high temperature and high radiation conditions.
Use in liquid level sensors for accident-tolerant instrumentation in steam generators and pressurizers in nuclear reactors.
Flow meters, displacement sensors, and structural monitoring systems.
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