Magnetostrictive SAW RF Filter Tuning Without Complex Filter Banks
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Solution Overview
Problem
Current surface acoustic wave (SAW) filters in mobile devices lack tunability, requiring complex and cost-inefficient solutions for frequency adjustments, with existing tunable filters either being large, power-hungry, or computationally costly, and lacking a suitable replacement for acoustic filters.
Innovation Solution
A SAW device with interdigitated electrodes of unequal widths and a magnetostrictive film on a piezoelectric substrate, allowing for frequency tuning through magnetic fields or DC voltage application, enabling a compact, low-power, and wide-band pass configuration with minimal insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If fixed frequency SAW filters are used, then the filtering function is achieved, but the tuning capability is lost
Solution Approach 1:
The patent applies magnetostrictive materials that change their magnetic properties dynamically in response to external magnetic fields, enabling continuous frequency tuning of the SAW filter without requiring multiple discrete filter components. The magnetostrictive layer's saturation magnetization varies with applied magnetic field, directly controlling the filter's center frequency.
Solution Approach 2:
The invention changes the magnetic field parameter to control the filtering frequency. By adjusting the external magnetic field strength, the saturation magnetization of the magnetostrictive material changes, which in turn tunes the center frequency of the SAW filter across a wide range (e.g., 1.7 GHz to 2.2 GHz), eliminating the need for complex filter banks.
2Power
If mechanically-tuned filters are used, then high power handling is achieved, but the device size becomes large and response becomes slow
Solution Approach 1:
The patent replaces mechanical tuning mechanisms (motors, plungers) with a magnetic field control system. The magnetostrictive material responds to external magnetic fields, allowing electronic control of the filter frequency without any moving parts. This substitution dramatically reduces device size while maintaining power handling capabilities.
3Speed
If electrically-tuned filters with varactors are used, then fast tuning response is achieved, but isolation and selectivity deteriorate
Solution Approach 1:
The invention uses a composite structure combining piezoelectric substrate, SAW interdigitated electrodes, and magnetostrictive material. This composite approach leverages the fast response of electrical control (through magnetic field application) while maintaining the superior isolation and selectivity of acoustic wave filtering mechanisms, achieving both fast tuning and high performance.
4Adaptability or versatility
If wide-band SAW configurations are used, then the bandwidth is increased, but the filtering capability deteriorates
Solution Approach 1:
The patent makes the filter dynamically tunable by utilizing the magnetic field-dependent properties of magnetostrictive materials. The center frequency can be adjusted continuously across a wide bandwidth, allowing the filter to maintain high selectivity at any chosen frequency within the broad operating range, effectively combining wide bandwidth capability with excellent filtering performance.
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 solution provides a compact, frequency-tunable RF filter with low insertion loss and wide tuning range, addressing the need for efficient and cost-effective filtering in mobile devices while maintaining small size and low power consumption.
Implementation Method 1
The input transducer electrodes are to convert an incoming radio frequency (RF) electrical signal into surface acoustic waves
Implementation Method 2
a magnetostrictive film in the SAW propagation path to filter the surface acoustic waves that are at a ferromagnetic resonance frequency of the magnetostrictive film
Implementation Method 3
a magnetostrictive film in the SAW propagation path
Implementation Method 4
the output transducer electrodes are to convert the filtered surface acoustic waves into an outgoing electrical RF signal
Data Source
AI summary
A filter including a piezoelectric substrate; a surface acoustic wave (SAW) device on the piezoelectric substrate and including unequally spaced interdigitated input and output transducer electrodes of unequal widths, wherein the input transducer electrodes are to convert an incoming radio frequency (RF) electrical signal into surface acoustic waves; a SAW propagation path between the input and output transducer electrodes; and a magnetostrictive film in the SAW propagation path to filter the surface acoustic waves that are at a ferromagnetic resonance frequency of the magnetostrictive film, wherein the output transducer electrodes are to convert the filtered surface acoustic waves into an outgoing electrical RF signal. The SAW device may operate in a wide-band pass configuration. The wide-band pass configuration result in a transmission of frequencies up to −60 dB. The magnetostrictive film may include a ferromagnetic material. The interdigitated input and output transducer electrodes may include unequal widths between adjacent electrodes.