Utilizing injectable devices for monitoring animal health offers several advantages over traditional wearable devices, including improved signal-to-noise ratio (SNR) and enhanced immunity to motion artifacts. We present a wireless application-specific integrated circuit (ASIC) for injectable devices. The ASIC has multiple physiological sensing modalities including body temperature monitoring, electrocardiography (ECG), and photoplethysmography (PPG). The ASIC fabricated using the CMOS 180 nm process is sized to fit into an injectable microchip implant. The ASIC features a low-power design, drawing an average DC power of 155.3 μW, enabling the ASIC to be wirelessly powered through an inductive link. To capture the ECG signal, we designed the ECG analog frontend (AFE) with 0.3 Hz low cut-off frequency and 45-79 dB adjustable midband gain. To measure PPG, we employ an energy-efficient and safe switched-capacitor-based (SC) light emitting diode (LED) driver to illuminate an LED with milliampere-level current pulses. A SC integrator-based AFE converts the current of photodiode with a programmable transimpedance gain. A resistor-based Wheatstone Bridge (WhB) temperature sensor followed by an instrumentation amplifier (IA) provides 27–47 °C sensing range with 0.02 °C inaccuracy. Recorded physiological signals are sequentially sampled and quantized by a 10-bit analog-to-digital converter (ADC) with the successive approximation register (SAR) architecture. The SAR ADC features an energy-efficient switching scheme and achieves a 57.5 dB signal-to-noise-and-distortion ratio (SNDR) within 1 kHz bandwidth. Then, a back data telemetry transmits the baseband data via a backscatter scheme with intermediate-frequency assistance. The ASIC’s overall functionality and performance has been evaluated through an in vivo experiment.

Obtaining physiological data from animals in a non-obtrusive and continuous manner is important to veterinary science. This paper demonstrates the design and deployment of a miniaturized capsule-based system for subdermal injection to provide real-time and continuous heart-rate, movement, and core-body-temperature measurements. The presented device incorporates sensors for photoplethysmography, motion detection, and temperature measurements. A Bluetooth-Low-Energy enabled microcontroller configures the sensors, digitizes the sensor information, and wirelessly connects with external devices. The device is powered by a CR425 battery for this paper, and various other battery solutions are available based upon the use case. The design uses only commercially available integrated circuits in order to reduce the development cost and be modular. The encapsulation is a combination of medical epoxy and poly(methyl methacrylate) that fits within a 6-gauge hypodermic needle. The preliminary evaluation of the device included an in vitro assessment of its thermal response and measurement accuracy, the impact of one-month implantation on surrounding tissue, the power consumption with duty-cycling of various sensors, and a measurement of physiological signals in a rat and a chicken. Having a form factor and implantation method similar to existing devices for animals, this novel system is a useful platform for both scientists and veterinarians to better study a diverse range of animals.

Identification and quantification of stress and stress inducing factors are important components of animal welfare assessment and essential parts of poultry management. Measurement of the autonomic nervous system's influence on cardiac function using heart rate and heart rate variability (HR/HRV) indices can provide a non-invasive assessment of the welfare status of an animal. This paper presents a preliminary study showing the feasibility of continuous long-term measurement of HR/HRV indices in freely moving chicken. We developed and evaluated an electrocardiography (ECG) based HR/HRV recording system that can be used as a poultry wearable backpack for research studies. The backpack system was first validated against a commercial ECG amplifier, and the corresponding estimations of HR values matched well with each other. Then, an in vivo proof-of-concept experiment was conducted on floor-reared chickens to collect ECG data for 2 weeks. The extracted HR/HRV values show strong alignment with circadian patterns and well-defined sleep cycles. Wearable devices, like the backpack ECG system used in this study, may be best suited for application in freely moving poultry to get an insight into circadian abnormalities and sleep quality for stress and welfare management.

Photoplethysmography (PPG) has emerged as a highly convenient and non-invasive technique for assessing heart rate and its variability in wearable health monitoring devices. However, a drawback lies in the energy demand of PPG systems which consequently increases the average power consumption of the wearable devices integrated with PPG sensors. In this paper, we present our efforts towards packaging a novel compressed-sensing (CS) based ultra-low power PPG application-specific integrated circuit (ASIC) into a wearable device and testing it through a preclinical human study. The system comprises a custom-designed PPG analog front-end circuit, integrated with a digital back-end to implement CS, a light source-detector pair, and a commercial off-the-shelf microcontroller for Bluetooth Low Energy (BLE) based wireless data transfer. Two circular PCBs, a general-purpose main board containing the microcontroller and a plugin board housing the ASIC interfacing components, fit into a wristband form factor. This modular architecture of the wristband platform allows for the incorporation of other environmental sensors for future correlated sensing studies between health and the environment. The PPG ASIC consumes 172 $\bm {\mu }$ W power to extract heart rate from the sparse PPG signal whereas the whole system consumes 1.66 mW power for continuous streaming of heart rate data over the BLE radio which can be further duty cycled. The preclinical trial of the platform demonstrated its efficacy in assessing accurate heart rate in comparison to commercial PPG and electrocardiography systems. This work presents the first-ever demonstration of a wearable wristband with CS based PPG performed on a chip.

In this paper, we present our efforts towards packaging of a novel compressive sampling (CS) based ultra-low power photoplethysmography (PPG) application-specific integrated circuit (ASIC) into a wearable form factor. The system comprises of a custom PPG analog front-end circuit, integrated with a digital back-end to enable CS, and a commercial off-the-shelf (COTS) system-on-chip (SoC) for Bluetooth Low Energy (BLE) based wireless data transfer. The ASIC consumes 172 μW power to extract heart rate from the sparse PPG signal where the whole system consumes 1.66 mW power for continuous streaming of heart rate data over the COTS BLE radio. This work presents the first ever demonstration of a CS based PPG ASIC in wrist-band form factors and paves our way towards deploying and evaluating this custom PPG ASIC in future clinical studies. The modular architecture of the wristband platform allows for incorporation of other sensors for future correlated sensing studies between health and environment.

Unobtrusive acquisition of physiological and behavioral data from freely moving animals is important to many applications including animal research, veterinary science, animal husbandry, pet monitoring, etc. This paper reports a miniaturized, injectable, and multimodal implant for real-time measurements of heart rate, breathing rate, movement, and subcutaneous temperature with future extensions to blood pressure and oxygen saturation. To estimate these vital signs, the presented device incorporates sensors of various modalities: photoplethysmography, electrocardiography, accelerometry, magnetometry, and thermometry. A rechargeable battery drives the system containing a system-on-chip with Bluetooth low energy capability and multiple sensor front-end circuits. The implant electronics are isolated from the animal’s extracellular fluid by a dual-layer encapsulation of biomedical epoxy and poly(methyl methacrylate) that fits into a 6-gauge surgical needle to allow for subcutaneous injection. Electrically conductive epoxy is used to create electrodes on the surface of the encapsulation for biopotential measurements. With a 3-meter wireless range from a custom receiver, this implant can continuously transmit data from all the sensors for 20 hours, which can support 2-3 months of duty-cycled and intermittent recording between battery recharges. The system was tested in vivo where the acquired heart rate and breathing rate estimations showed an error of less than 2 beats per minute compared to the gold standard. Longer-term evaluation of tissue reaction showed an acceptable level of immune responses with minimal effect on the sensing performance. This novel system has the potential to provide new insights with greater depth in veterinary research and practice, and animal welfare management.