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Haptic technology involves the use of electrical or mechanical means to stimulate afferent nerves or mechanoreceptors in the skin as the basis for creating sensations of physical touch that can qualitatively expand virtual or augmented reality experiences beyond those supported by visual and auditory cues alone. An emerging direction in this field involves the development of platforms that provide spatiotemporal patterns of sensation to the skin across not only the fingertips, but to any and all regions of the body, using thin, skin‐like technologies that impose negligible physical burden on the user. This review highlights the biological basis for skin interfaces of this type and the latest advances in haptics in the context of this ambitious goal, including electrotactile and vibrotactile devices that support perceptions of touch in form factors that have potential as skin‐integrated interfaces. The content includes a discussion of schemes for integrating these stimulators into programmable arrays, with an emphasis on scalable materials and designs that have the potential to support soft interfaces across large areas of the skin. A concluding section summarizes the potential consequences of successful research efforts in this area, along with key multidisciplinary challenges and associated research opportunities in materials science and engineering. [ABSTRACT FROM AUTHOR]

Electronic systems built on flexible plastic films and stretchable rubber sheets have attracted new applications in many emerging fields. Integration of high-speed electronics such as microwave power amplifiers and switches can extend the applications even further with wireless capabilities. As such, flexible and stretchable microwave electronics represent opportunities for future electronics where remote capabilities are desired. Here, we review advances in numerous types of microelectronic devices used for fast, flexible, and stretchable electronic devices, as well as flexible and stretchable passive elements and circuitries. We first introduce the challenges associated with design and fabrication, and the characteristics required for high-frequency operation of the devices on foreign substrates. Second, we review the recent efforts that were made utilizing different types of high-performance semiconductors, which are ideal for high-speed flexible and stretchable electronics, such as silicon, compound semiconductors, and 1-D and 2-D materials. Third, passive electronic components fabricated on such substrates, including inductors, capacitors, and transmission lines, are reviewed. Finally, we discuss the flexible and stretchable microwave electronics at the circuit level and review the recent advances in making numerous types of flexible and stretchable microwave circuits for diverse applications. [ABSTRACT FROM AUTHOR]

Stretchable electrical interconnects based on serpentines combined with elastic materials are utilized in various classes of wearable electronics. However, such interconnects are primarily for direct current or low-frequency signals and incompatible with microwave electronics that enable wireless communication. In this paper, design and fabrication procedures are described for stretchable transmission line capable of delivering microwave signals. The stretchable transmission line has twisted-pair design integrated into thin-film serpentine microstructure to minimize electromagnetic interference, such that the line's performance is minimally affected by the environment in close proximity, allowing its use in thin-film bioelectronics, such as the epidermal electronic system. Detailed analysis, simulations, and experimental results show that the stretchable transmission line has negligible changes in performance when stretched and is operable on skin through suppressed radiated emission achieved with the twisted-pair geometry. Furthermore, stretchable microwave low-pass filter and band-stop filter are demonstrated using the twisted-pair structure to show the feasibility of the transmission lines as stretchable passive components. These concepts form the basic elements used in the design of stretchable microwave components, circuits, and subsystems performing important radio frequency functionalities, which can apply to many types of stretchable bioelectronics for radio transmitters and receivers. [ABSTRACT FROM AUTHOR]

The miniaturization and flexibility of wearable and implantable devices allow humans to carry them directly on or in their bodies, thus enabling these devices to measure biometric signals in real‐time anywhere. However, as they are embedded or implanted into an actively moving human interface, motion artifact noise inevitably occurs. Typically, devices are laminated or implanted on body surfaces, but the positions of such devices cannot be designed without any discussion of the noise. Thus, this paper investigates an approach that minimizes the noise to achieve negligible motion artifacts in implantable micro‐devices that have a specific angle on the surface of the body, while maintaining the function of sensor. The device with a specific angle successfully detects the target signal, while motion artifacts—such as tension, compression, and bending—disturb the measurement. The pulse signal on a wrist is well measured while the hand is rotating, and artificial skin implanted on a rat can distinguish external pressure from the movement noise. A thermometer sensor that follows the same rule is further examined. Therefore, this approach is expected to be useful in numerous areas including human interface‐based medical devices, virtual reality, and health aids to improve quality of life. [ABSTRACT FROM AUTHOR]

Electrotactile devices, flexible electronics, haptic interfaces, vibrotactile devices, virtual reality Skin-Integrated Vibrohaptic Interfaces for Virtual and Augmented Reality (Adv. Funct. Keywords: electrotactile devices; flexible electronics; haptic interfaces; vibrotactile devices; virtual reality EN electrotactile devices flexible electronics haptic interfaces vibrotactile devices virtual reality 1 1 1 09/28/21 20210923 NES 210923 B Skin-Integrated Vibrohaptic Interfaces b Haptic technologies add a sense of touch to visual and auditory queues, as the basis for advanced forms of virtual and augmented reality experiences. [Extracted from the article]

A compact broadband flexible antenna is proposed for applications in wireless local area network (WLAN) and upper ultra‐wideband (UWB) systems, which can operate in the bandwidths of 2.4–2.484 GHz and 3.5–10.6 GHz with a reflection coefficient of <−10 dB. The presented antenna coated with bio‐compatible ultra‐thin parylene‐c is fabricated on a thin polyimide substrate with a thickness of 127 μm. The characteristics of the proposed antenna are measured under bending and flat conditions. The measured results showed that the antenna is suitable for integration with flexible electronic devices. [ABSTRACT FROM AUTHOR]

Keywords: anisotropic thermal conduction; boron nitride nanocomposite; flexible and stretchable heat sink; networked assembly; tetrahedral structures The structured boron nitride layer in the composites induces high thermal conductivity in through- as well as in-plane directions even with a low boron nitride fraction. Anisotropic thermal conduction, boron nitride nanocomposite, flexible and stretchable heat sink, networked assembly, tetrahedral structures. [Extracted from the article]

Owing to the growing demand for highly integrated electronics, anisotropic heat dissipation of thermal management material is a challenging and promising technique. Moreover, to satisfy the needs for advancing flexible and stretchable electronic devices, maintaining high thermal conductivity during the deformation of electronic materials is at issue. Presented here is an effective assembly technique to realize a continuous array of boron nitride (BN) nanosheets on tetrahedral structures, creating 3D thermal paths for anisotropic dissipation integrated with deformable electronics. The tetrahedral structures, with a fancy wavy shaped cross‐section, guarantee flexibility and stretchability, without the degradation of thermal conductivity during the deformation of the composite film. The structured BN layer in the composites induces a high thermal conductivity of 1.15 W m−1 K−1 in the through‐plane and 11.05 W m−1 K−1 in the in‐plane direction at the low BN fraction of 16 wt%, which represent 145% and 83% increases over the randomly mixing method, respectively. Furthermore, this structured BN composite maintains thermal dissipation property with 50% strain of the original length of composite. Various electronic device demonstrations provide exceptional heat dissipation capabilities, including thin film silicon transistor and light‐emitting diode on flexible and stretchable composite, respectively. [ABSTRACT FROM AUTHOR]

Stretchable high‐frequency transmission lines with twisted‐pair geometry integrated into stretchable serpentines for wearable electronics are presented by Z. Ma and co‐workers on page 4635. This shielded transmission line that is in the form of an ultrathin, conformal structure can effectively confine microwave frequency signals and transmit them with ultra‐low radio‐frequency radiation losses, which enables electrical interconnects for epidermal electronic systems requiring high‐speed wireless communication capabilities. [ABSTRACT FROM AUTHOR]

Conventional implantable electrocardiogram monitors are impenetrable to electromagnetic radiation, posing challenges in imaging (i.e. X-rays). In this study, we demonstrate a radiolucent implantable electrocardiogram (ECG) device using graphene sheets and Parylene substrate which allows bypassing of electromagnetic radiation through the implanted device. Evaluated on a canine model, the graphene electrodes detect signals comparable to those recorded using surface electrodes, presenting a valuable and novel modality for medium and long-term monitoring of cardiac rhythm. When compared with current technology, the new system has the distinct advantages of being flexible and radiolucent, thereby improving patient comfort, and avoiding device artifact and shadowing on clinical radiographic imaging. Image 1 [ABSTRACT FROM AUTHOR]

The ineffective p-type doping of nitrides using magnesium (Mg), the best available dopant, has limited the development and performance of all III-nitride-based devices, including bipolar junction transistors and light emitting diodes (LEDs). For nitride-based ultraviolet (UV) LEDs, as the Al composition increases for achieving shorter wavelengths (e.g. <280 nm) into the UVC spectral range, the p-type doping issue, which causes very inefficient hole injection, becomes more severe than ever. In this work, we report the detailed study of using p-type Si as a hole supplier for high-Al composition UVC LEDs. We first describe the method of Si/GaN junction formation, where the lattice-mismatch challenge between Si and GaN is overcome by using a 0.5 nm thick Al2O3 layer at the interface. This serves as a physical separation layer between the two materials as well as a passivation, tunneling, and thermal buffer layer. High-resolution transmission electron microscope image illustrates the high-quality interface between Si and GaN. We further detail the hole transport mechanism of the p–p Si/GaN isotype junction through both simulations and experiments. The enhanced hole concentration in the AlGaN/AlN multiple quantum wells (MQWs) due to the use of p-type Si as the hole supplier is verified through comparison with conventional UVC LEDs. Finally, high-performance UVC LEDs made with AlN/AlGaN (Al: 72%) MQWs employing p-type Si as their hole suppliers are demonstrated experimentally to serve as an example of the novel hole injector strategy. [ABSTRACT FROM AUTHOR]

• Fabrication methodology for creating thin-film peripheral nerve interfaces. • Combining both traditional cuff and sieve electrode (CASE) interfaces. • Surgical implantation methodology for thin-film CASE interfaces. • Acute somatosensory evoked potentials (SSEPs) via the CASE interface. A number of peripheral nerve interfaces for nerve stimulation and recording exist for the purpose of controlling neural prostheses, each with a set of advantages and disadvantages. The ultimate goal of neural prostheses is a seamless bi-directional communication between the peripheral nervous system and the prosthesis. Here, we developed an interfacing electrode array, the "cuff and sieve electrodes" (CASE), integrating microfabricated cuff and sieve electrodes to a single unit, to decrease the weaknesses faced by these electrode designs in isolation. This paper presents the design and fabrication of CASE with ex vivo and in vivo testing towards chronic application. Electroplating on electrode sites was performed to improve electrical properties of CASE. The surface morphology and chemical compound were characterized using scanning electron microscopy and energy-dispersive spectroscopy, respectively. Electrochemical impedance spectroscopy and cyclic voltammetry were performed to evaluate the electrical properties of CASE and determine viability for in vivo applications. Terminal CASE implantations were performed in a rat sciatic transection model to test the ease of implantation and capacity to write sensory information into the biological system. The modified platinum film resulted in reducing impedance magnitude (9.18 kΩ and 2.27 kΩ) and increasing phase angle (over 70°). CASE stimulation of the sciatic nerve at different amplitudes elicited significantly different cortical responses (p < 0.005) as demonstrated by somatosensory evoked potentials, recorded via micro-electrocorticography. Conclusions: The ability to elicit cortical responses from sciatic nerve stimulation demonstrates the proof of concept for both the implantation and chronic monitoring of CASE interfaces for innovative prosthetic control. [ABSTRACT FROM AUTHOR]