The frequency band between the infrared and the microwave seems to be ignored compared to the other bands of the terahertz electromagnetic spectrum. According to a report by Mammus Consulting, a research team from the Chinese University of Hong Kong and The University of Warwick recently published research showing that wide bandwidth, large and fast modulation of terahertz beams is possible, even Very simple devices can be implemented.
Modulator structure and its interaction with terahertz light
In order to design cameras and spectrometers operating in the terahertz band, researchers have put a lot of effort into it. It has been proven to be useful in airport security scanners and old-picture recognition applications.
An important component of these devices is the modulator, which controls the amplitude or phase of the terahertz beam. The modulator must operate quickly and with low power consumption, giving consistent modulation over a wide frequency range, maximizing the intensity or phase of the terahertz beam. To date, alternative methods have included metamaterials, semiconductors, and liquid crystal devices, but none of them have met all of them.
Mr. Brewster is here.
In 1815, David Brewster published a paper describing the angle of incidence required to achieve zero reflection from transparent objects. More than two hundred years later, the team of scientists led by Xu Jianbin of the Chinese University of Hong Kong and Emma Pickwell-MacPherson of the University of Warwick applied this knowledge and the latest technology to create a record-breaking terahertz modulator.
Pickwell-MacPherson commented, "Our first step is to demonstrate broadband terahertz modulation by using a total internal reflection (TIR) ​​geometry rather than a transmission geometry to achieve a lower conductivity variation. Using the latest Brewster This has become the way to implement several new device designs."
The device was realized by performing a single layer stack of graphene, aluminum oxide (Al 2 O 3 ) and titanium oxide (TiO x ) on a quartz substrate. A bundle of p-polarized terahertz beams is reflected from the stack, and when the Brewster angle is reached, the reflection becomes zero. The addition of a layer of graphene allows the introduction of tunable elements. When a voltage is applied across the graphene between the two gold contacts, the conductivity changes. This changes the Brewster angle of the stack so that for a given angle of incidence, the reflected terahertz can be "on or off" by controlling the voltage.
Select mode of operation
The p-polarized terahertz beam is irradiated onto the device at an angle of 65°, and the voltage applied to the graphene is changed from -12V to +14V, and the terahertz amplitude can be achieved from 99.3% to 99.9% in the frequency range of 0.5 to 1.6 THz. Adjustment. The amplitude adjustment range is limited by experimental conditions and theoretically allows for greater bandwidth.
But this is not the only option. The researchers used the fact that the reflected beam produced a 180° phase transition when it was greater than the Brewster angle. When the voltage is changed from -12V to +16V, a terahertz beam incident at an angle of 68° will undergo a phase change of not less than 140° in the same frequency range. In this voltage range, the Brewster angle varies between 72° and 64°.
Modulation of terahertz time domain waveform (red) and modulation depth response (blue) for 1 kHz square wave electrical signals
Speed ​​requirement
The rise time of the modulation is about 1 ms, so it is easy to achieve a modulation frequency of 1 kHz. However, frequencies up to 10 kHz can be achieved if the modulation depth can be sacrificed. While other solid-state terahertz modulators operate at higher frequencies of approximately 2.4 MHz, small adjustments can be made to increase the modulation frequency of the device. Currently limited by the resistance and capacitance between the gold contact layers, the modulation speed is comparable to that of other devices by reducing the size to about 1 mm and using graphene instead of TiOx.
Xu Jianbin, director of the Materials Science Research Center at the Chinese University of Hong Kong, explained, "Another benefit of this device is that it can be retrofitted into an existing commercial terahertz spectrometer." The graphene-controlled Brewster angle terahertz modulator will really take us into too Hertz technology enters the future of real-world applications.
Is it Time to Change Your Windshield Wiper Arm?
All windshield wiper arms have a hinge at the base that allows the arm to flex as it follows the curvature of the window. If the wiper skips over certain spots, even with a new blade, chances are the hinge is binding from corrosion. It`s most common on rear window wipers since they`re used less often.
You can oil the hinge, but that`s just a temporary fix-the corrosion and binding usually return. To fix the problem permanently, replace the Wiper Arm (available at an auto parts store).
What you`ll need to replace your windshield wiper arm:
- Socket/ratchet set
- Flat-blade screwdriver
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