Patterned graphene and terahertz metasurface-enabled multidimensional ultra-sensitive flexible biosensors and bio-assisted optical modulation amplification
Haiyun YaoMaosheng YangXin YanLanju LiangZhaoqing SunQili YangTongling WangXiaofei HuZiqun WangZhenhua LiMeng WangKaikai LvYaru WangJianquan Yao
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Although terahertz metasurface-enabled biosensors focus on current research, reports of multidimensional ultra-sensitive detection in the terahertz (THz) regime are rare. Here, we present a novel flexible THz biosensor that consists of electromagnetic-induced transparency-like metasurfaces and patterned graphene, which is used for the multidimensional ultra-sensitive detection of plant protein. Based on changes in frequencies and amplitude, the proposed biosensor could detect plant protein molecules with a 42.3 pg/ml limit. The internal mechanism can be explained by the positive impact of plant proteins on the dielectric environment. As plant protein concentration increases and covalent bonding of the patterned graphene strengthens, the Fermi level of graphene moves to the Dirac point, and the conductivity of graphene correspondingly decreases. As a result, we observed marked enhancement of the transmission amplitude and all frequency point shifts. We also show results for fitting the coupled harmonic oscillator model and theoretical analysis of the changes of graphene Fermi level to explain the sensing mechanism. In addition, we successfully achieved biological-assisted optical modulation amplification under laser excitation. This work may provide a new strategy for applying terahertz metasurfaces in the field of biosensing.Keywords:
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A feedforward modulation technique is used to suppress amplitude modulation associated with 40-GHz pulses generated from a subharmonically mode-locked semiconductor laser. It is shown that the amplitude modulation can be suppressed by as much as 20 dB. The improvement of amplitude modulation is shown for different subharmonic numbers.
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Psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies (fc) were 125, 1000, and 6000 Hz, and modulation rates (g) were 2, 5, and 10 Hz. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For fc=125 and 1000 Hz and g=10 Hz, some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low. For g=2 Hz, some subjects identified the type of modulation as well as they detected the modulation. For a carrier frequency of 6000 Hz, the effect of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. We suggest that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM.
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Terahertz technology provides wide range applications and graphene has appeared as a highly promising material to control terahertz wave. Here we propose a terahertz amplitude modulator which consists of a single-layer graphene and subwavelength metal structure surface (SMSS). Graphene is core regulatory elements which controls the terahertz wave by means of tuning Fermi level in graphene. SMSS acts as the gate electrode and meanwhile plays a role of frequency selection that the appropriate modulation frequency bandwidth can be chosen.
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The main objective of this study was to determine the detection thresholds of random amplitude modulation (RAM) as a function of modulation and carrier frequency. Two experiments were performed. Experiment 1 concerned the detection thresholds of AM stimuli for only random amplitude changes at constant modulation frequency. Experiment 2 dealt with detection thresholds for simultaneous, random changes in amplitude and modulation frequency. The data obtained showed that for low modulation frequency, the detection thresholds for sinusoidal amplitude modulation (SAM), random amplitude modulation at constant modulation frequency [RAM(fm const)], and random amplitude and modulation frequency [RAM(fs random)] overlapped one another in the limit of SD. However, for higher carriers and modulation frequencies the RAM(fm const) thresholds were, in a limited range offm , much lower than the SAM ones. When random changes in modulation frequency were combined with random changes in amplitude, the RAM(fm random) thresholds decreased relative to the RAM(fm const) thresholds. a)Permanent address: Institute of Acoustics, Adam Mickiewicz University, Poznan ul. Matejki 48/49, Poland.
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We present a concept for all optical Terahertz (THz) amplitude modulators based on a Fabry-Pérot (FP) filter design. By trapping the THz wave inside a cavity, an enhanced modulation can be achieved. The easy-to-handle and easy-to-fabricate design renders this concept very auspicious.
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Simulations of weak-strong pp collisions with a periodic tune modulation show the possiblity of beam blowup at sufficiently strong modulation amplitudes. This beam blowup is associated with the appearance of nonrepeatable "chaotic" trajectories and occurs when low order resonances are crossed by the modulation. In this paper we also report results of an investigation of the dependence of this blowup upon the modulation frequency, with the modulation amplitude fixed. It is determined that a threshold freqency exists, modulations at frequencies greater than the threshold do not lead to beam blowup.
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Modulation is the transmission of information to be loaded onto a high-frequency(carrier) signal in the process.Amplitude modulation using signal to control the rate of carrier,with its linear modulation signal changes,and maintain the same carrier frequency.In the amplitude modulation,in accordance with the strength of signals in the spectrum of different components,it is divided into ordinary AM(amplitude modulation standard AM),with inhibition of bilateral carrier AM(DSB),the carrier single sideband suppression AM(SSB).The main difference is the different methods and structure of the spectrum.
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Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d′ of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d′ up to about 2), some subjects discriminated the type of modulation as well as they detected the modulation. For a carrier frequency of 6000 Hz, the effect of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of phase-locking information depends on the time that the stimuli spend at frequency extremes.
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