Ultra-miniature wireless temperature sensor for thermal medicine applications

Abstract

This study presents a prototype design of an ultra-miniature, wireless, battery-less, and implantable temperature-sensor, with applications to thermal medicine such as cryosurgery, hyperthermia, and thermal ablation. The design aims at a sensory device smaller than 1.5 mm in diameter and 3 mm in length, to enable minimally invasive deployment through a hypodermic needle. While the new device may be used for local temperature monitoring, simultaneous data collection from an array of such sensors can be used to reconstruct the 3D temperature field in the treated area, offering a unique capability in thermal medicine. The new sensory device consists of three major subsystems: a temperature-sensing core, a wireless data-communication unit, and a wireless power reception and management unit. Power is delivered wirelessly to the implant from an external source using an inductive link. To meet size requirements while enhancing reliability and minimizing cost, the implant is fully integrated in a regular foundry CMOS technology (0.15 μm in the current study), including the implant-side inductor of the power link. A temperature-sensing core that consists of a proportional-to-absolute-temperature (PTAT) circuit has been designed and characterized. It employs a microwatt chopper stabilized op-amp and dynamic element-matched current sources to achieve high absolute accuracy. A second order sigma-delta (Σ-Δ) analog-to-digital converter (ADC) is designed to convert the temperature reading to a digital code, which is transmitted by backscatter through the same antenna used for receiving power. A high-efficiency multi-stage differential CMOS rectifier has been designed to provide a DC supply to the sensing and communication subsystems. This paper focuses on the development of the all-CMOS temperature sensing core circuitry part of the device, and briefly reviews the wireless power delivery and communication subsystems.

Temperature-field reconstruction for the application of prostate cryosurgery

“…Our research team has developed a new concept for realtime monitoring of cryosurgery with the development of miniature, implantable, wireless temperature sensors [2]. In particular, the current study is aimed at examining the feasibility of temperature-field reconstruction from an array of wireless temperature sensors.…”

Temperature field reconstruction for minimally invasive cryosurgery with application to wireless implantable temperature sensors and/or medical imaging

“…The current project is focused on developing miniature, wireless, implantable temperature sensors to reconstruct the temperature field in real time—a capability which is yet unavailable for routine practice. This project combines two parallel efforts: (i) to develop the hardware necessary for implantable sensors [11,23], and (ii) to develop a method for temperature-field reconstruction in real time, which is the subject matter of the current study. This is a proof-of-concept level study, which uses prostate cryosurgery as a developmental model.…”

“…While hardware development is the subject matter of a parallel effort [11,23], its current state of development is overviewed here in brief, for the completeness of presentation only. Hardware development is aimed at an ultra-miniature, wireless, battery-less, implantable temperature-sensing device, having a diameter of 1.5 mm and a length of 3 mm to enable minimally invasive deployment through a hypodermic needle.…”