Wireless power transfer (WPT) provides a convenient method of delivering energy to multiple devices. With the increasing use of WPT, safety concerns inevitably create the need for a reliable control mechanism. Previous approaches in advanced WPT or metamaterial-enhanced WPT, however, have the limitation that neither the intensity nor the shape of the field-localizing area can be dynamically controlled. To address this limitation, we introduce the novel concept of a hotspot or power-focused region using field-localizing WPT. Using the proposed method, we provide experimental evidence demonstrating that the location, shape, and intensity of the hotspot can be manipulated as desired. The hotspot effectively enhances power delivery to the intended device while reducing leakage to unwanted areas. To dynamically reconfigure the hotspots, we propose an active metasurface with multi-functionality due to its frequency switching and tuning capability. The dynamic reconfiguring capability provides a wide range of versatile practical applications, overcoming the limitations associated with passive metamaterials. Because the location, shape, and intensity of hotspots can readily be controlled, the proposed method is not limited to WPT applications. It can also be used for a broad range of applications that require precise control of power delivery.

To enable the geometrical freedom envisioned for wireless power transfer (WPT), fast dynamic adaptation to unpredictable changes in receiver position is needed. In this paper, we propose an adaptive impedance-searching system that achieves good impedance matching quickly. For fast and robust operation, the proposed method consists of three steps: system calibration, coarse search, and fine search. The proposed WPT system is characterized using distance variation and lateral and angular misalignment between coils. The measured results indicate that the proposed method significantly reduces searching time from a few minutes to approximately one second. Furthermore, the proposed system achieves impedance matching with good accuracy. The robust impedance-searching capability of the proposed system significantly improves power transfer efficiency. At 6.78 MHz, we achieve a maximum efficiency of 89.7% and a high efficiency of >80% up to a distance of 50 cm. When the center-to-center misalignment is 35 cm, the efficiency is improved from 48.4% to 74.1% with the proposed method. At a distance of 40 cm, the efficiency is higher than 74% for up to 60° of angular rotation. These results agree well with the simulated results obtained using a lumped-element circuit model.

In a wireless power transfer (WPT) system, misalignment between transmitter and receiver coils is one of the key factors affecting efficiency. Recently, metamaterials have shown great potential to enhance electromagnetic propagation in various environments. In this work, we apply a metamaterial to enhance the WPT in a more general environment where misalignment is considered. Using an anisotropic metamaterial, we obtain a significant efficiency enhancement. Therefore, we propose that the metamaterial is an effective means to mitigate the decreased efficiency caused by misalignment. In addition, we investigate the effect of coil misalignment on the threshold distance beyond which the metamaterial enhances the performance of WPT.

Computing-in-memory (CIM) is a promising approach to reduce latency and improve the energy efficiency of the multiply-and-accumulate (MAC) operation under a memory wall constraint for artificial intelligence (AI) edge processors. This paper proposes an approach focusing on scalable CIM designs using a new ten-transistor (10T) static random access memory (SRAM) bit-cell. Using the proposed 10T SRAM bit-cell, we present two SRAM-based CIM (SRAM-CIM) macros supporting multibit and binary MAC operations. The first design achieves fully parallel computing and high throughput using 32 parallel binary MAC operations. Advanced circuit techniques such as an input-dependent dynamic reference generator and an input-boosted sense amplifier are presented. Fabricated in 28 nm CMOS process, this design achieves 409.6 GOPS throughput, 1001.7 TOPS/W energy efficiency, and a 169.9 TOPS/mm ² throughput area efficiency. The proposed approach effectively solves previous problems such as writing disturb, throughput, and the power consumption of an analog to digital converter (ADC). The second design supports multibit MAC operation (4-b weight, 4-b input, and 8-b output) to increase the inference accuracy. We propose an architecture that divides 4-b weight and 4-b input multiplication to four 2-b multiplication in parallel, which increases the signal margin by 16× compared to conventional 4-b multiplication. Besides, the capacitive digital-to-analog converter (CDAC) area issue is effectively addressed using the intrinsic bit-line capacitance existing in the SRAM-CIM architecture. The proposed approach of realizing four 2-b parallel multiplication using the CDAC is successfully demonstrated with a modified LeNet-5 neural network. These results demonstrate that the proposed 10T bit-cell is promising for realizing robust and scalable SRAM-CIM designs, which is essential for realizing fully parallel edge computing.

In this letter, we propose a magneto-inductive wave (MIW) metamaterial cavity for enhanced mid-range wireless power transfer (WPT) applications. Cavity operation is achieved by controlling the propagation of MIWs at lower megahertz frequencies. The cavity is realized by omitting a cell and thereby breaking the periodicity of the closely coupled metamaterial slabs. The cavity in the proposed metamaterial effectively confines the MIWs into a subwavelength region. Consequently, it localizes the magnetic field in the WPT region and provides enhanced power transmission. When the proposed MIW metamaterial cavity is used, the measured efficiency improves significantly from 8.7 to 54.9%.

This letter presents a compact (0.12 x 0.14lambda) RFID tag antenna which has near-isotropic radar cross-section (RCS) patterns and easy conjugate impedance matching property by virtue of an inductively coupled feeding. Its measured maximum and minimum RCS' are -17.3 dBm2 and -20.4 dBm2, respectively, with a difference of only 3.1 dB in all incident angles. The measured RCS' have been found to be in good agreement with simulation.