Allan T. Evans

A piezoelectric microvalve for cryogenic applications

This paper reports on a normally open piezoelectrically actuated microvalve for high flow modulation at cryogenic temperatures. One application envisioned is to control the flow of a cryogen for distributed cooling with a high degree of temperature stability and a small thermal gradient. The valve consists of a micromachined die fabricated from a silicon-on-insulator wafer, a glass wafer, a commercially available piezoelectric stack actuator and Macor TM ceramic encapsulation that has overall dimensions of 1 × 1 × 1c m 3 .A perimeter augmentation scheme for the valve seat has been implemented to provide high flow modulation. In tests performed at room temperature the flow was modulated from 980 mL min −1 with the valve fully open (0 V), to 0 mL min −1 with a 60 V actuation voltage, at an inlet gauge pressure of 55 kPa. This range is orders of magnitude higher flow than the modulation capability of similarly sized piezoelectric microvalves. At the cryogenic temperature of 80 K, the valve successfully modulated gas flow from 350 mL min −1 down to 20 mL min −1 with an inlet pressure of 104 kPa higher than the atmosphere. The operation of this valve has been validated at elevated temperatures as well, up to 380 K. The valve has a response time of less than 1 ms and has operational bandwidth up to 820 kHz. (Some figures in this article are in colour only in the electronic version)

A Microvalve With Integrated Sensors and Customizable Normal State for Low-Temperature Operation

This paper reports on design, fabrication, and testing of a piezoelectrically actuated microvalve with integrated sensors for flow modulation at low temperatures. One envisioned application is to control the flow of a cryogen for distributed cooling with a high degree of temperature stability and a small thermal gradient. The valve consists of a micromachined die fabricated from a silicon-on-insulator wafer, a glass wafer, a commercially available piezoelectric stack actuator, and Macor ceramic encapsulation that has overall dimensions of 1.5 x 1.5 x 1.1 cm3. A piezoresistive pressure sensor and a thin-film Pt resistance temperature detector are integrated on the silicon die. The assembly process allows the implementation of normally open, partially open, and normally closed valves. At room temperature, gas flow modulation from 200 to 0 mL/min is achieved from 0- to 40-V actuation. Flow modulation at various temperatures from room temperature to 205 K is also reported. The pressure sensor has sensitivity of 356 ppm/kPa at room temperature, with temperature coefficient of sensitivity of -6507 ppm/K. The temperature sensor has sensitivity of 0.29 %/K. The valve and the sensors are tested across a wide range of temperatures, and the effect of temperature on performance is discussed.

A Multidrug Delivery System Using a Piezoelectrically Actuated Silicon Valve Manifold With Embedded Sensors

This paper describes a drug delivery system for chronic pain that can accommodate multidrug protocols. An element that is important to the function of the system is a customized silicon micromachined valve manifold. Each valve is piezoelectrically actuated and operates by pressing an elongated valve seat against a shared glass substrate. The dual-valve substrate has two inlets and one outlet; a piezoresistive pressure sensor is embedded in the Si structure near each of these three ports. The sensors, which permit closed-loop control and error monitoring of the flow rate, have a typical sensitivity of 698 ppm/kPa. The 1 × 1.5 × 3 cm3 manifold provides modulation and mixing capabilities. The manifold is integrated into a stainless steel housing with a total volume of 130 cm3 and a reservoir volume of 40 cm3. Two spring-loaded polyethylene reservoirs feed the valve manifold at pressures up to 0.52 kPa/mL. Benchtop tests of bolus and continuous flow delivery demonstrate flow rates ranging from 2.30 to 0.51 mL/h. (Both larger and smaller rates can be achieved by adjusting the parameters of the manifold valves or reservoir springs.) Additional tests suggest that the system can compensate for changes in spinal fluid pressure and that pressure profiles can be used to detect catheter occlusions and disconnects.

Compact, power-efficient architectures using microvalves and microsensors, for intrathecal, insulin, and other drug delivery systems☆

This paper describes a valve-regulated architecture, for intrathecal, insulin and other drug delivery systems, that offers high performance and volume efficiency through the use of micromachined components. Multi-drug protocols can be accommodated by using a valve manifold to modulate and mix drug flows from individual reservoirs. A piezoelectrically-actuated silicon microvalve with embedded pressure sensors is used to regulate dosing by throttling flow from a mechanically-pressurized reservoir. A preliminary prototype system is demonstrated with two reservoirs, pressure sensors, and a control circuit board within a 130cm(3) metal casing. Different control modes of the programmable system have been evaluated to mimic clinical applications. Bolus and continuous flow deliveries have been demonstrated. A wide range of delivery rates can be achieved by adjusting the parameters of the manifold valves or reservoir springs. The capability to compensate for changes in delivery pressure has been experimentally verified. The pressure profiles can also be used to detect catheter occlusions and disconnects. The benefits of this architecture compared with alternative options are reviewed.

Dual drug delivery device for chronic pain management using micromachined elastic metal structures and silicon microvalves

This paper describes a dual-chamber drug delivery microsystem that provides regulated flow from two spring- pressurized balloon reservoirs using independent microvalves. A preliminary prototype has been constructed with the primary components. Micromachined bulk metal springs (Co-Ni-Cr alloy), with an in-plane spring constant exceeding 300 N/m, are used in conjunction with 18.8 mL reservoirs, and provide 15 kPA pressure when the balloons are fully inflated. A piezoresistive pressure sensor that is embedded in the microvalves monitors reservoir pressure with a sensitivity of 250 ppm/kPa, and is used to regulate bolus delivery. Two control plans for the valve and their respective limitations are presented. In a demonstration of regulated bolus delivery, 1.5 mL bolus doses are delivered at different rates.

A piezoelectric microvalve with integrated sensors for cryogenic applications

This paper describes a normally open, self-encapsulated, gas valve that has embedded sensors for pressure and temperature monitoring. The valve has been validated at operating temperatures over 80-380 K, and at pressures up to 130 kPa. A perimeter augmentation scheme for the valve seat has been implemented to provide higher flow modulation. Two kinds of suspensions are described for the valve seat. In tests performed at room temperature, the flow was modulated from 980 mL/min. with the valve fully open (0 V), to 0 mL/min. with 60 V actuation, at an inlet pressure of 55 kPa. Cryogenic flow rate tests show similar modulation with flow from 166 mL/min. with the valve fully open, to 5.3 mL/min. with 120 V actuation voltage, at an inlet pressure of 70 kPa. The platinum RTD temperature sensor is independently tested from 40-450 K with sensitivity of 0.23 %/K in its operational range of 150- 450 K. The pressure sensor has sensitivity of 250 ppm/kPa at room temperature.

A Low Power, Microvalve-Regulated Drug Delivery System using a SI Micro-Spring Pressurized Balloon Reservoir

This paper reports on a drug delivery system that provides modulated delivery of liquid-phase chemicals. The device uses silicon torsion springs on a 2times3 cm2 chip to pressurize a soft polymeric reservoir and regulate flow with a piezoelectricaly actuated silicon microvalve that is 1.5times1.5times1 cm3. Using the finished device, regulated diffusion of a fluorescent dye into agar gel was demonstrated. Fluid flow out of the 500 muL reservoir could be regulated from 10-500 muL/min with up to 80 kPa of delivery pressure. Typical regulation consumes 0.136 muW of power. Analysis of the valve, reservoir springs, and a model based on pressure-enhanced diffusion are presented and are validated by experimental data.

Note: A low leakage liquid seal for micromachined gas valves

We report a method for addressing gas leakage in micromachined valves. The valves used for evaluating the proposed concept utilize a silicon valve seat that is bonded to a glass substrate and actuated by a piezoelectric stack, all of which are assembled within a ceramic package. The sealing method uses the capillary forces of a liquid sealant on the valve seat to reduce gas leakage below measurable limits. The gas leak rates are compared in valves with and without the seal enhancement. For example, a valve closes against 13.5 kPa with 10 V actuation, compared to 40 V required without the enhancement. Leakage is also evaluated for liquid flow.

Transdermal Power Transfer for Implanted Drug Delivery Devices using a Smart Needle and Refill Port

This paper describes a pair of micromachined components that work together for transdermal power (and data) transfer into implantable drug delivery devices. In particular, it describes a smart refill port that is electrically accessed with a mating, multi-pole, plug-in needle. These components are fabricated entirely from molded PDMS, Parylene, Kapton, and micro-electro-discharge machined stainless steel. The component pair demonstrates power transfer with low current leakage into both dry and saline ambient, and it has been used to recharge batteries with currents ranging from 10 mA up to 500 mA while temperature change is monitored.

A piezoelectric valve manifold with embedded sensors for multi-drug delivery protocols

This paper describes a two-valve manifold for use in a dual chamber drug delivery device for pain therapy. The scalable manifold is hybrid assembled with piezoelectric stacks to actuate Si valve seats against a glass substrate. The substrate has two inlets and one outlet; a piezoresistive pressure sensor is embedded in the Si near each of these three ports. The sensors, which permit closed loop control and error monitoring of the flow rate, have a typical sensitivity of 647 ppm/kPa. The 1×1.5×3 cm3 manifold provides modulation and mixing capabilities. In laboratory tests, flow of isopropyl alcohol was regulated from 1.77 mL/hr to 0.028 mL/hr. The manifold design achieves the desired dynamic range for intrathecal drug delivery and can also be used for gas modulation in other contexts.