Photoconductive Wide-Bandgap Resistors for Linear Signal Modulation
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Solution Overview
Problem
Existing photoconductive wide bandgap semiconductor materials used in high-power applications require operation in avalanche mode, leading to non-real-time adaptability and low spectral energy content, causing communication interference and inefficiencies in high-frequency modulation applications like microwave transmission.
Innovation Solution
Utilizing photoconductive wide bandgap semiconductor materials to modulate electrical signals by varying their conduction response through transconductance-like properties, allowing for high-frequency modulation without bi-stable operation, using compact structures and radiation-controlled resistors that respond to visible optical energy or other radiation types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If photoconductive wide bandgap semiconductor materials are operated in avalanche mode to generate high-power microwave signals, then the radiated energy level is improved, but the spectral bandwidth increases causing communication fratricide and the system loses real-time adaptability
Solution Approach 1:
The patent changes the operational parameters of the photoconductive semiconductor switch from avalanche mode to non-avalanche mode, specifically operating at lower electric fields and currents. This parameter change reduces the spectral bandwidth and eliminates communication fratricide while maintaining sufficient radiated energy for the application.
2Power
If vacuum electronic devices are used for high-power microwave generation, then the radiated energy is improved, but the device size and complexity increase
Solution Approach 1:
The patent replaces vacuum electronic devices (mechanical/electromagnetic tube-based systems) with solid-state photoconductive semiconductor switches. This substitution eliminates the need for bulky vacuum tubes, magnetic fields, and complex mechanical structures, resulting in a compact, solid-state system that maintains high-power microwave generation capability.
3Power
If nonlinear transmission lines are used for microwave generation, then the radiated energy is improved, but the manufacturing difficulty and material availability worsen
Solution Approach 1:
The patent changes the operational regime from requiring specialized nonlinear transmission line materials to using conventional photoconductive semiconductor materials operated in non-avalanche mode. This parameter change enables the use of well-characterized, readily available semiconductor materials such as gallium nitride and silicon carbide, greatly improving ease of manufacture and material availability.
4Power
If photoconductive materials are operated in avalanche mode to achieve high current capacity, then the power output is improved, but the switching speed and real-time adaptability are reduced
Solution Approach 1:
The patent employs periodic optical modulation of the photoconductive switch at microwave frequencies, enabling real-time adaptive control of the output signal. This periodic action allows the system to achieve both high current capacity and fast switching speed by modulating the switch state in response to the desired output waveform.
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
Enables efficient, real-time adaptive modulation of high voltage electrical signals and energy modulation of charged particle beams, achieving high current capabilities and linear response, reducing communication interference and improving energy efficiency in applications like high power microwave generation.
Implementation Method 1
Wide bandgap semiconductor materials are known to be photoconductive, i.e. characterized by increased electrical conductivity in response to illumination.
Data Source
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Figure 6A~7
AI summary
A system and method for producing modulated electrical signals. The system uses a variable resistor having a photoconductive wide bandgap semiconductor material construction whose conduction response to changes in amplitude of incident radiation is substantially linear throughout a non-saturation region to enable operation in non-avalanche mode. The system also includes a modulated radiation source, such as a modulated laser, for producing amplitude- modulated radiation with which to direct upon the variable resistor and modulate its conduction response. A voltage source and an output port, are both operably connected to the variable resistor so that an electrical signal may be produced at the output port by way of the variable resistor, either generated by activation of the variable resistor or propagating through the variable resistor. In this manner, the electrical signal is modulated by the variable resistor so as to have a waveform substantially similar to the amplitude-modulated radiation.