A Power-Efficient Bridge Readout Circuit for Implantable, Wearable, and IoT Applications.

A power-efficient bridge-to-digital sensing interface is proposed, which also offers immunity against power supply noise. The interface utilizes duty-cycling to reduce the static power consumption of resistive bridge sensors, which are commonly used in implantable, wearable, and internet of things (IoT) applications, such as intracranial pressure (ICP) sensing and blood pressure (BP) monitoring. The proposed interface uses a revised version of the pseudo-pseudo differential (PPD) topology with the ping-pong technique to reduce the complexity of traditional fully-differential counterparts. A proof-of-concept prototype has been fabricated in 0.35-µm CMOS and occupies an active area of 0.48 mm2. It achieves 9.13 effective number of bits (ENOB) at 3.72 kHz sampling rate and improvement of more than 50 dB in the power supply rejection ratio (PSRR) by employing the ping-pong technique. It reduces the power consumption of a 5-kΩ Wheatstone bridge by 99.6% compared to a traditional interface, down to 2.53 µw at 1.8 V supply. The functionality of the system has also been demonstrated in an experimental setup in conjunction with an embedded resistive bridge pressure sensor.

Sensitivity and phase response of FBG based acousto-optic sensors for real-time MRI applications.

Fiber Bragg grating (FBG) based sensors have recently been introduced to the field of magnetic resonance imaging (MRI). Real-time MRI applications demand highly amplitude and phase sensitive MRI compatible sensors. Thus, a model and detailed analysis of FBG based ultrasound detection are required for designing better performing sensors. A hybrid FBG model incorporating numerical and FEA methods was developed and used for sensitivity and linearity analysis. The transfer matrix method was used for the modeling of optical modulation whereas FEA was used for pressure field calculations within the grating. The model was verified through reflection spectrum and acoustic pressure sensitivity testing of two π-phase shifted FBGs in a side slope read-out configuration. The sensitivity curves with respect to the operation point on the side slope was characterized in terms of amplitude and phase, and nonlinearity of the phase response has been quantified. Lastly, the impact of phase linearity of the FBG based acousto-optic sensor was tested under MRI when the sensor was used as a position marker and an analog phase shifter based solution was demonstrated.

Acousto-Optic Catheter Tracking Sensor for Interventional MRI Procedures.

OBJECTIVE: The objective of this paper is to introduce an acousto-optic optical fiber sensor for tracking catheter position during interventional magnetic resonance imaging (MRI) to overcome RF induced heating of active markers. METHODS: The sensor uses a miniature coil coupled to a piezoelectric transducer, which is in turn mechanically connected to an optical fiber. The piezoelectric transducer converts the RF signal to acoustic waves in the optical fiber over a region including a fiber Bragg grating (FBG). The elastic waves in the fiber modulates the FBG geometry and hence the reflected light in the optical fiber. Since the coil is much smaller than the RF wavelength and the signal is transmitted on the dielectric optical fiber, the sensor effectively reduces RF induced heating risk. Proof of concept prototypes of the sensor are implemented using commercially available piezoelectric transducers and optical fibers with FBGs. The prototypes are characterized in a 1.5 T MRI system in comparison with an active tracking marker. RESULTS: Acousto-optical sensor shows linear response with flip angle and it can be used to detect signals from multiple coils for potential orientation detection. It has been successfully used to detect the position of a tacking coil in phantom in an imaging experiment. CONCLUSION: Acousto-optical sensing is demonstrated for tracking catheters during interventional MRI. Real-time operation of the sensor requires sensitivity improvements like using a narrow band FBG. SIGNIFICANCE: Acousto-optics provides a compact solution to sense RF signals in MRI with dielectric transmission lines.

Coagulation measurement from whole blood using vibrating optical fiber in a disposable cartridge.

In clinics, blood coagulation time measurements are performed using mechanical measurements with blood plasma. Such measurements are challenging to do in a lab-on-a-chip (LoC) system using a small volume of whole blood. Existing LoC systems use indirect measurement principles employing optical or electrochemical methods. We developed an LoC system using mechanical measurements with a small volume of whole blood without requiring sample preparation. The measurement is performed in a microfluidic channel where two fibers are placed inline with a small gap in between. The first fiber operates near its mechanical resonance using remote magnetic actuation and immersed in the sample. The second fiber is a pick-up fiber acting as an optical sensor. The microfluidic channel is engineered innovatively such that the blood does not block the gap between the vibrating fiber and the pick-up fiber, resulting in high signal-to-noise ratio optical output. The control plasma test results matched well with the plasma manufacturer's datasheet. Activated-partial-thromboplastin-time tests were successfully performed also with human whole blood samples, and the method is proven to be effective. Simplicity of the cartridge design and cost of readily available materials enable a low-cost point-of-care device for blood coagulation measurements.