This study presents a new class of independently polarization manipulable liquid-crystal (LC)-based reflective metasurface antenna. To the best of the authors’ knowledge, this study first introduces independent polarization controllability of the LC-based reflective metasurface in mmWave. Two LC layers are embedded into the proposed structure for independent manipulation of the polarization. Isolation topologies, such as rectangular patch shape and metal strip ground, are utilized to enhance polarization purity, achieving compact bias configuration. The independent polarization controllability and antenna performance, such as aperture efficiency, sidelobe level, and beam coverage, are validated as a reflectarray. The proposed antenna has a maximum aperture efficiency of 22.5% and beam coverage of over 120°. In addition, the proposed metasurface is employed to achieve link connectivity as a reconfigurable intelligent surface (RIS) at millimeter-wave 5G. The demonstration confirms a small aperture RIS concept, considering spillover and taper efficiencies.

This letter presents an ultrathin transmitarray (TA) in the D -band (110–170 GHz) by utilizing the bonding layer effect of spatial filters. The standard printed circuit board process limits the performance of spatial filters, resulting in a poor phase-shifting range in the sub-terahertz. The proposed unit cells based on the frequency selective surfaces use only two substrates to be ultrathin. By attaching the additional metal layer on the other side of the bonding substrate, the bonding layer effect can be maximized. Consequently, the proposed unit cells achieved a 271° phase-shifting range without any additional substrates. The proposed TA is the first to attain a high gain of more than 40 dBi in the D -band by reducing the quantization loss. The TA is synthesized using ten types of unit cells that have a low insertion loss of less than 1.5 dB. A 25.5 dBi horn antenna was selected as the source. The focal-to-diameter ( F / D ) ratio is 1.686 for the TA. The proposed TA, which is comprised of 50 176 elements, attains a peak gain of 44.3 dBi, an efficiency of 24.1%, and a bandwidth of 6% (134.5–143.5 GHz).

In this paper, an affordable and miniaturized 140 GHz transmit/receive (TRX) array antennaon- package (AoP) is proposed through the conventional printed circuit board process employing a single substrate. The proposed design approach involved an in-depth analysis of the potential performance degradation of a D-band antenna operating within a coarse process and a practical design guide for the configuration of matching network packaging with robust wedge bonding. An asymmetric matching network design technique for 1×4 array antenna packaging considered the 1-bit digital beamforming capabilities of radio frequency integrated circuits (RFIC). In its unprecedented demonstration, an AoP with 1×2 transmitting and 1×4 receiving antennas was packaged with an RFIC. The measurements arrayed maximum gains of the transmit and receive antennas were 9.8 and 11.8 dBi, respectively. In addition, gain bandwidths of 12.6% and 20.4% were achieved for the transmit and receive antennas, respectively. This study marked the first instance of fabricating a TRX AoP using a single RF metal layer via a width/gap process condition of 100/80 μm in the D-band.

We propose a microwave signal generation system for brain stimulation. The existing brain stimulation system uses a signal of several tens of kHz, and the magnetic field distribution is wide. Microwave is used to locally limit the distribution of the electromagnetic field and to change the action potential of the cell with less power. The switch modulates the microwave signal to obtain a pulse envelope. The action potential of the cell can be controlled to the excitation/inhibition state by adjusting the repetition frequency. These results are confirmed by measuring the cell potential of the mouse brain.

This article, for the first time, presents the design, fabrication, and measurement results of a novel microwave brain stimulation system enabling efficient probe focusing of rectangular-pulse enveloped 6.5-GHz waves. While the conventional ON/OFF stimulation systems in literature employ low frequencies below 0.5 GHz, the proposed system employs 6.5 GHz that can achieve more spatial energy focusing and a moderate level of energy penetration depth. In the proposed system, the ON/OFF modulated microwave signal is generated by a single chip consisting of a voltage-controlled oscillator (VCO) and power amplifier (PA). The VCO is driven by a switch at the current source to generate modulated signals with over 20-dB isolation between the high and low states. The probe with a center-opened aperture surrounded by a symmetric loading enables low power reflection toward the brain and focuses the field in the square-shaped aperture of 1-mm ² area. Finally, it is demonstrated that the 20-min stimulation of an in vivo mouse brain using microwave signals with 1-Hz repetitive pulse envelopes and 1% duty cycle enables the normalized firing rate to reach up to 0.2 while the normalized firing rate stays just within ±0.05 under no stimulation. This suggests that the proposed brain stimulation system can achieve a dramatic change in the activity of individual hippocampal neurons.

This study proposes a novel brain-stimulated mouse experiment system which is insensitive to the variations in the position and orientation of a mouse. This is achieved by the proposed novel crown-type dual coil system for magnetically coupled resonant wireless power transfer (MCR-WPT). In the detailed system architecture, the transmitter coil consists of a crown-type outer coil and a solenoid-type inner coil. The crown-type coil was constructed by repeating the rising and falling at an angle of 15 for each side which creates the H-field diverse direction. The solenoid-type inner coil creates a magnetic field distributed uniformly along the location. Therefore, despite using two coils for the Tx system, the system generates the H-field insensitive to the variations in the position and angle of the receiver system. The receiver is comprised of the receiving coil, rectifier, divider, LED indicator, and the MMIC that generates the microwave signal for stimulating the brain of the mouse. The system resonating at 2.84 MHz was simplified to easy fabrication by constructing 2 transmitter coils and 1 receiver coil. A peak PTE of 19.6% and a PDL of 1.93 W were achieved, and the system also achieved an operation time ratio of 89.55% in vivo experiments. As a result, it is confirmed that experiments could proceed for approximately 7 times longer through the proposed system compared to the conventional dual coil system.