A Review of Emerging Electromagnetic-Acoustic Sensing Techniques for Healthcare Monitoring.

Conventional electromagnetic (EM) sensing techniques such as radar and LiDAR are widely used for remote sensing, vehicle applications, weather monitoring, and clinical monitoring. Acoustic techniques such as sonar and ultrasound sensors are also used for consumer applications, such as ranging and in vivo medical/healthcare applications. It has been of long-term interest to doctors and clinical practitioners to realize continuous healthcare monitoring in hospitals and/or homes. Physiological and biopotential signals in real-time serve as important health indicators to predict and prevent serious illness. Emerging electromagnetic-acoustic (EMA) sensing techniques synergistically combine the merits of EM sensing with acoustic imaging to achieve comprehensive detection of physiological and biopotential signals. Further, EMA enables complementary fusion sensing for challenging healthcare settings, such as real-world long-term monitoring of treatment effects at home or in remote environments. This article reviews various examples of EMA sensing instruments, including implementation, performance, and application from the perspectives of circuits to systems. The novel and significant applications to healthcare are discussed. Three types of EMA sensors are presented: (1) Chip-based radar sensors for health status monitoring, (2) Thermo-acoustic sensing instruments for biomedical applications, and (3) Photoacoustic (PA) sensing and imaging systems, including dedicated reconstruction algorithms were reviewed from time-domain, frequency-domain, time-reversal, and model-based solutions. The future of EMA techniques for continuous healthcare with enhanced accuracy supported by artificial intelligence (AI) is also presented.

A Silicon-Based Adaptable Edge Coherent Radar Platform for Seamless Health Sensing and Cognitive Interactions With Human Subjects.

Empowered by the rapid advancements of semiconductor techniques, emerging areas such as industry 4.0, precise healthcare, pervasive communications, intelligent robots, and smart buildings are to be realized, which put substantial demands on low-power and high-performance cognitive edge sensors. Capabilities of precise sensing and seamless interactions with human subjects are pivotal to boosting versatile Internet of Everything (IoE) applications. However, it is challenging to attain various kinds of intuitive sensing based on one edge sensor. A novel silicon-based phased-array coherent radar sensing platform is proposed to attain versatile application-driven capabilities by focusing the wideband radar beams accurately at the target's direction to attain precise sensing. The coherent radar platform can support a maximum 60° field-of-view sensing range with smaller than 2° optimum steering step resolution and -70-dBm sensitivity. The silicon-based mixed-signal coherent radar chip platform is fabricated by a 65-nm CMOS process and owns the convenience for massive deployments at the edge. A series of experiments were conducted to validate the integrated radar platform's adaptable capabilities and salient performances on human subject detection, vital signs monitoring, and motion recognition. Notably, the adaptable multifunction integrated radar platform opens up the enticing possibility for next-generation monolithic edge devices supporting seamless health sensing and cognitive interactive functions with human subjects.

A Super-Sensitivity Photoacoustic Receiver System-on-Chip Based on Coherent Detection and Tracking.

Photoacoustic (PA) imaging is becoming more attractive because it can obtain high-resolution and high-contrast images through merging the merits of optical and acoustic imaging. High sensitivity receiver is required in deep in-vivo PA imaging due to detecting weak and noisy ultrasound signal. A novel photoacoustic receiver system-on-chip (SoC) with coherent detection (CD) based on the early-and-late acquisition and tracking is developed and first fabricated. In this system, a weak PA signal with negative signal-to-noise-ratio (SNR) can be clearly extracted when the tracking loop is locked to the input. Consequently, the output SNR of the receiver is significantly improved by about 29.9 dB than input one. For the system, a high dynamic range (DR) and high sensitivity analog front-end (AFE), a multiplier, a noise shaping (NS) successive-approximation (SAR) analog-to-digital convertor (ADC), a digital-to-analog convertor (DAC) and integrated digital circuits for the proposed system are implemented on-chip. Measurement results show that the receiver achieves 0.18 µVrms sensitivity at the depth of 1 cm with 1 mJ/cm2 laser output fluence. The contrast-to-noise (CNR) of the imaging is improved by about 22.2 dB. The area of the receiver is 5.71 mm2, and the power consumption of each channel is about 28.8 mW with 1.8 V and 1 V power supply on the TSMC 65 nm CMOS process.

A Mixed-Signal Chip-Based Configurable Coherent Photoacoustic-Radar Sensing Platform for In Vivo Temperature Monitoring and Vital Signs Detection.

For precise health status monitoring and accurate disease diagnostics in the current COVID-19 pandemic, it is essential to detect various kinds of target signals robustly under high noise and strong interferences. Moreover, the health monitoring system is preferred to be realized in a small form factor for convenient mass deployments. A CMOS-integrated coherent sensing platform is proposed to achieve the goal, which synergetically leverages quadrature coherent photoacoustic (PA) detection and coherent radar sensing for achieving universal healthcare. By utilizing configurable mixed-signal quadrature coherent PA detection, high sensitivity and enhanced specificity can be achieved. In-phase (I) and quadrature (Q) templates are specifically designed to accurately sense and precisely reconstruct the target PA signals in a coherent mode. By mixed-signal implementation leveraging an FPGA to generate template waveforms adaptively, accurate tracking and precise reconstruction on the target PA signal can be attained based on the early-late tracking principle. The multiplication between the received PA signal and the templates is implemented efficiently in analog-domain by the Gilbert cell on-chip. In vivo blood temperature monitoring was realized based on the integrated PA sensing platform fabricated in a 65-nm CMOS process. With an integrated radar sensor deployed in the indoor scenario, noncontact monitoring on respiration and heartbeat rates can be attained based on electromagnetic (EM) sensing. By complementary usage of PA-EM sensing mechanisms, comprehensive health status monitoring and precise remote disease diagnostics can be achieved for the currentglobal COVID-19 pandemic and the future pervasive healthcare in the Internet of Everything (IoE) era.

A Digital-Enhanced Chip-Scale Photoacoustic Sensor System for Blood Core Temperature Monitoring and In Vivo Imaging.

Monolithic integration of photoacoustic (PA) sensor with compact size, lightweight, and low power consumption is attractive to be implemented on wearable medical devices for in vivo blood metabolic sensing and imaging. This work presents a miniaturized chip-scale mixed-signal photoacoustic sensor system which can achieve coherent lock-in function to detect weak target PA signals noninvasively at in vivo scenarios of poor signal to noise ratio (SNR) and strong interferences. A low-noise amplifier (LNA), a 3rd order Butterworth low-pass filter (LPF), and a variable-gain amplifier (VGA) chain with 10 MHz cutoff frequency are implemented on-chip to attain a high-quality sensing performance with 50-dB dynamic range. A Gilbert-cell type multiplier is integrated on-chip to fulfill the coherent lock-in process on acquired PA signals in a closed-loop process with an embedded FPGA system. Fabricated in 65-nm CMOS technology, the prototype PA sensor system demonstrated 50 µV sensitivity. The functions of the chip-scale PA sensor system enhanced by coherent lock-in process were validated through the experiments on temperature monitoring and vessel imaging. The PA receiver chip occupies an area of 0.6 mm2 and consumes 20 mW at a 1.8-V supply.