Haiyu Huang’s research while affiliated with Maxim Integrated and other places

Cough detection has aroused great interest because the assessment of cough frequency may improve diagnosis accuracy for dealing with several diseases, such as chronic obstructive pulmonary disease (COPD) and the recent COVID-19 global pandemic crisis. Here, we propose and experimentally demonstrate a wireless smart face mask based on a passive harmonic tag for real-time cough monitoring and alert. Our results show that the cough events can be successfully monitored through non-contact track of the received signal strength indicator (RSSI) at the harmonic frequency. Owing to the frequency orthogonality between the launched and backscattered radio-frequency (RF) signals, the harmonic tag-based smart mask can well suppress the electromagnetic interferences, such as clutters and crosstalks in noisy environments. We envision that this zero-power and lightweight wireless wearable device may be beneficial for cough monitoring and the public health condition in terms of tracking potential contagious person and virus-transmissive events.

In this article, we design and experimentally demonstrate a flexible, low-profile harmonic transponder sensor, capable of performing multiplexed fluidic sensing. The harmonic transponder comprises multiple reconfigurable electrically small antennas (ESAs) integrated with microfluidic channels for receiving radio frequency (RF) signals at the fundamental frequencies ( $f_{0}$ ), as well as a broadband microstrip monopole for retransmitting the second-harmonic signal ( $2~f_{0}$ ) to a sniffer. Such a frequency orthogonality can help suppressing possible echoes, clutters, and crosstalks in the rich-scattering environment. We show that injection of different liquid samples into a microfluidic channel, which tunes the operating frequency of an ESA, can be precisely recognized by analyzing the shift of peak second-harmonic received signal strength indicator (RSSI) in the frequency-hopping spread spectrum (FHSS). We also demonstrate the possibility of performing rapid and multiplexed noncontact detection with the proposed harmonic transponder sensor. We envision that this battery-free and lightweight multiplexing wireless sensor may benefit various Internet-of-Things (IoTs) and healthcare applications, such as rapid contactless point-of-care (POC) and drive-through tests.

We present here new types of self-powered, low-interference wireless sensors based on graphene circuits, which can have dual functions: chemical sensing at the molecular level and radio-frequency (RF) modulation. We demonstrate that a fully-passive, graphene-based harmonic (transponder) sensor can display a chemically-sensitive frequency multiplication effect, which, when linked to a hybrid-fed small antenna, can realize an ultrasensitive, low-profile, light-weight, and potentially flexible RF sensor. We have designed two different types of circuits comprising back-gate graphene field-effect transistors (GFETs) and compared in detail their performance and implementation complexity. We have also proposed a reliable readout method based on the machine learning for extracting the mean value and the fluctuation of chemical doping levels in GFETs. The proposed graphene-based harmonic sensor may potentially benefit a wide range of sensing applications, including, but not limited to, power-efficient, real-time monitoring of chemical/gas exposures and biological agents, as well as emerging wearable and implantable devices.

Modern internet of things (IoTs) and ubiquitous sensor networks could potentially take advantage of chemically sensitive nanomaterials and nanostructures. However, their heterogeneous integration with other electronic modules on a networked sensor node, such as silicon-based modulators and memories, is inherently challenging because of compatibility and integration issues. Here we report a novel paradigm for sensing modulators: a graphene field-effect transistor device that directly modulates a radio frequency (RF) electrical carrier signal when exposed to chemical agents, with a memory effect in its electrochemical history. We demonstrated the concept and implementation of this graphene-based sensing modulator through a frequency-modulation (FM) experiment conducted in a modulation cycle consisting of alternating phases of air exposure and ethanol or water treatment. In addition, we observed an analog memory effect in terms of the charge neutrality point of the graphene, V cnp, which strongly influences the FM results, and developed a calibration method using electrochemical gate-voltage pulse sequences. This graphene-based multifunctional device shows great potential for use in a simple, low-cost, and ultracompact nanomaterial-based nodal architecture to enable continuous, real-time event-based monitoring in pervasive healthcare IoTs, ubiquitous security systems, and other chemical/molecular/gas monitoring applications.

We propose the concept and design of a transparent, flexible, and self-powered wireless sensor comprising a graphene-based sensor/frequency-modulator circuitry and a grapheneantenna. In this all-graphene device, the multilayered-graphene antenna receives the fundamental tone at C band and retransmits the frequency-modulated sensed signal (harmonic tone) at X band. The frequency orthogonality between the received/re-transmitted signals may enable high-performance sensing in severe interference/clutter background. Here, a fully passive, quad-ring frequency multiplier is proposed using graphene field-effect transistors, of which the unique ambipolar charge transports render a frequency doubling effect with conversion gain being chemically sensitive to exposed gas/molecular/chemical/infectious agents. This transparent, light-weight, and self-powered system may potentially benefit a number of wireless sensing and diagnosis applications, particularly for smart contact lenses/glasses and microscope slides that require high optical transparency.

Autonomous liquid-volume monitoring is crucial in ubiquitous healthcare. However, conventional approach is based on either human visual observation or expensive detectors, which are costly for future pervasive monitoring. Here we introduce a novel approach based on passive harmonic transponder antenna sensor and frequency hopping spread spectrum (FHSS) pattern analysis, to provide a very low cost wireless μL-resolution liquid-volume monitoring without battery or digital circuits. In our conceptual demonstration, the harmonic transponder comprises of a passive nonlinear frequency multiplier connected to a metamaterial-inspired 3-D antenna designed to be highly sensitive to the liquid-volume within a confined region. The transponder first receives some FHSS signal from an interrogator, then converts such signal to its harmonic band and re-radiates through the antenna sensor. The harmonic signal is picked up by a sniffer receiver and decoded through pattern analysis of the high dimensional FHSS signal strength data. A robust, zero power, absolute accuracy wireless liquid-volume monitoring is realized in the presence of strong direct coupling, background scatters, distance variance as well as near-field human-body interference. The concepts of passive harmonic transponder sensor, metamaterial-inspired antenna sensor, and FHSS pattern analysis based sensor decoding may help establishing cost-effective, energy-efficient and intelligent wireless pervasive healthcare monitoring platforms.