A Wireless-Implantable Microsystem for Continuous Blood Glucose Monitoring

Abstract

A remotely powered implantable microsystem for continuous blood glucose monitoring is presented. The microsystem consists of a microfabricated glucose biosensor flip-chip bonded to a transponder chip. The transponder chip is inductively powered by an external reader with a 13.56-MHz carrier. It then measures the output signal of the glucose biosensor and transmits the measured data back to the external reader using load-shift keying (LSK). The microsystem has a volume of 32 mm(3). The procedures for the microfabrication of the glucose sensor and the assembly of the microsystem are described along with the description of the circuit blocks of the transponder chip. The transponder chip has been fabricated with the TSMC 0.18-mum CMOS process and has a total area of 1.3 x 1.3 mm(2). The chip can measure the sensor output current ranging from 1 nA to 1 muA with less than 0.3% nonlinearity error, provided that the amplitude of the received RF signal is higher than 2.6 V; the circuit consumes a total current of about 110 muA.

Energy Harvesting and Remote Powering for Implantable Biosensors

“…As previously mentioned, almost all the works reported in the literature utilize frequencies in the order of a few megahertz or lower [53]- [61] since this range of frequencies minimizes the power absorbed by the tissues, yielding a higher transmission efficiency. A recent work [65] has questioned this choice: the tissue absorption increases with the frequency only if the displacement current is omitted into the Maxwell equations (quasi-static assumption).…”

“…Almost all of the works reported in the literature utilize frequencies in the order of a few megahertz or lower [53]- [61]. The reason behind this choice is that this range of frequencies minimizes the power absorption by the tissues, yielding a higher transmission efficiency.…”

Disposable Wireless Immuno-Sensing Chips

“…Wireless data transfer is also required to reduce costs. Many wireless data transmission methods have been developed such as electric field coupling [4], magnetic field coupling [5,22] and light emission [21]. Electro-magnetic waves cannot propagate through the electrolyte and thus cannot be used in this system.…”

Precision in harsh environments

“…However, use of silicon allows a number of sensors to be included on a single chip 100,101 . As stated above, catheters are generally used over periods of o 72 h and maintain direct wired contact to the outside world, but implanted sensors often must remain in the body for longer periods and use wireless communication 102,103 . In addition, power for the devices must be considered.…”