Locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation using piezoceramic microheaters

This paper reports the locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation. A finite element model has been developed to predict the variation of insect–stimulator interface temperature with input power. Piezothermal stimulators have been fabricated from lead zirconate titanate (PZT) using a batch mode micro ultrasonic machining process. Typical sizes range from 200 µm to 3.2 mm. For PZT stimulators, the temperature and thermal efficiency reach the maximum value around the resonance frequency which is typically in the range of 650 kHz to 47 MHz. Experiments have been conducted on green June beetles (GJBs), Madagascar hissing roaches and green diving beetles (GDBs) in order to show the versatility of the proposed technique. The stimulators have been implanted near the antennae of the GJBs and on either side of the thorax of the Madagascar hissing roaches and GDBs, respectively. In all cases, the insects move away from the direction of the actuated stimulator. The left and right turns are statistically similar. Thermal stimulation achieves an overall success rate of 78.7%, 92.8% and 61.6% in GJBs, roaches and GDBs, respectively. On average, thermal stimulation results in an angle turn of about 13.7°–16.2° on GJBs, 30°–45° on the roaches and 30°–50° on GDBs. The corresponding average input power is 360, 330 and 100 mW for GJBs, roach and GDBs, respectively. Scaling limits of the PZT stimulators for operating these stimulators are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90797/1/0960-1317_21_12_125002.pd

A non-contact method for spatially localized sedimentation of particles from liquid suspensions using Marangoni forces

This paper presents the directed sedimentation of suspension particles in a thin layer of liquid (≤1 mm) onto a featureless glass substrate by Marangoni flows. A programmable 16 _ 8 array of surface mount resistors suspended 0.1–2 mm above the liquid provides dynamic millimeter-sized heat sources to locally heat the liquid surface to temperatures from approximately 28.5 to 36.5 °C. The heaters in this array can be activated independently by a graphical user interface, creating surface tension gradients along the liquid surface. The resulting Marangoni flows direct spatially localized particle sedimentation on the substrate. The resultant sedimentation patterns and accumulation levels depend on factors such as the temperature gradient at the liquid surface, number of active heaters and type of liquid used. For example, when a single heater is activated, a liquid surface temperature elevation of 6.9 °C results in a localized sedimentation of suspended weed pollen Kochia scoparia (_ = 25 µm) in silicone oil DC-704 over a region of 2.9 mm 2 that is centered directly beneath the active heater. This sedimentation method is a contactless technique, which reduces the likelihood of sample contamination.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90796/1/0960-1317_21_11_115028.pd

Microheaters based on ultrasonic actuation of piezoceramic elements

This paper describes the use of micromachined lead zirconate titanate (PZT) piezoceramic elements for heat generation by ultrasonic energy dissipated within the elements and surrounding media. Simulations based on three-dimensional finite-element models suggest that circular disk-shaped elements provide superior steady-state temperature rise for a given cross-sectional area, volume of the PZT element and drive voltage. Experimental validation is performed using PZT-5A heaters of 3.2 mm diameter and 0.191 mm thickness. Single-element heaters and dual-element stacks are evaluated. Although the steady-state temperature generated by these heaters reaches the maximum value at the frequency of maximum electromechanical conductance, the heating effectiveness is maximized at the frequency of maximum electromechanical impedance. Stacked PZT heaters provide 3.5 times the temperature rise and 3 times greater heating effectiveness than single elements. Furthermore, the heaters attain the maximum heating effectiveness when bonded to highly damping and non-conducting substrates. A maximum temperature of 120 °C is achieved at 160 mW input power. Experiments are performed using porcine tissue samples to show the feasibility of using PZT heaters in tissue cauterization. A PZT heater probe brands a porcine tissue in 2–3 s with 10 V RMS drive voltage. The interface temperature is ≈150 °C.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90803/1/0960-1317_21_8_085030.pd

Porous ceramics for multistage Knudsen micropumps—modeling approach and experimental evaluation

This paper describes the evaluation of four types of porous ceramics for use as thermal transpiration materials in Knudsen pumps that operate at atmospheric pressure. Knudsen pumps are motionless gas pumps that utilize thermal transpiration along a channel or a set of channels; the channels must have a temperature gradient and must constrain the flow to remain within the free molecular or transitional flow regimes. Of the ceramics evaluated, a clay-based, 15 bar synthetic ceramic (15PC) presents the most favorable properties for Knudsen pumps. For an input power of 3.4 W, a 25 _ 25 mm 2 nine-stage Knudsen pump that uses this material provides a maximum pressure head of 12 kPa and a maximum gas flow rate of ≈3.7 µL min _1 . Reliability tests demonstrate more than 11 750 h of continuous operation without any deterioration in their gas pumping capabilities. A fitted model suggests that the temporal evolution of pressure at the sealed outlet of a Knudsen pump can be captured adequately using four parameters. These parameters correspond to various nonidealities that play dominant roles in the transient response of these pumps.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90805/1/0960-1317_21_9_095029.pd

Tailored magnetoelastic sensor geometry for advanced functionality in wireless biliary stent monitoring systems

This paper presents three types of wireless magnetoelastic resonant sensors with specific functionalities for monitoring sludge accumulation within biliary stents. The first design uses a geometry with a repeated cell shape that provides two well-separated resonant mode shapes and associated frequencies to permit spatial localization of mass loading. The second design implements a pattern with specific variation in feature densities to improve sensitivity to mass loading. The third design uses narrow ribbons joined by flexible couplers; this design adopts the advantages in flexibility and expandability of the other designs while maintaining the robust longitudinal mode shapes of a ribbon-shaped sensor. The sensors are batch patterned using photochemical machining from 25 µm thick 2605SA1 Metglas™, an amorphous Fe–Si alloy. Accumulation of biliary sludge is simulated with paraffin or gelatin, and the effects of viscous bile are simulated with a range of silicone fluids. Results from the first design show that the location of mass loads can be resolved within ~5 mm along the length of the sensor. The second design offers twice the sensitivity to mass loads (3000–36 000 ppm mg−1) of other designs. The third design provides a wide range of loading (sensitive to at least 10× the mass of the sensor) and survives compression into a 2 mm diameter tube as would be required for catheter-based delivery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85405/1/jmm10_7_075040.pd

A microfabricated steel and glass radiation detector with inherent wireless signaling

This paper describes an investigation of the performance compromises imposed by a manufacturing approach that utilizes lithographic micromachining processes to fabricate a wireless beta/gamma radiation detector. The device uses in-package assembly of stainless steel electrodes and glass spacers. These elements are micromachined using photochemical etching and powder blasting, respectively. The detector utilizes a commercial, TO-5 package that is hermetically sealed at 760 Torr with an Ar fill-gas. Gas microdischarges between the electrodes, which are initiated by the radiation, transmit wideband wireless signals. The detector diameter and height are 9 and 9.6 mm, respectively, and it weighs 0.97 g. The device performance has been characterized using various sealed, radioisotope sources, e.g., 30–99 µCi from 137 Cs (which is a beta and gamma emitter) and 0.1 µCi from 90 Sr (which is a pure beta emitter). It has a measured output of >15.5 counts s _1 when in close proximity to 99 µCi from 137 Cs. The wireless signaling spans 1.25 GHz at receiving antenna-to-detector distances >89 cm, when in close proximity to a 0.1 µCi 90 Sr source. The estimated intrinsic detection efficiency (i.e. with the background rate subtracted) is 3.34% as measured with the biasing arrangement described in the paper.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90792/1/0960-1317_21_1_015003.pd

High-resolution scanning thermal probe with servocontrolled interface circuit for microcalorimetry and other applications

This article presents a scanning thermal microscopy sensing system equipped with a customized micromachined thermal imaging probe and closed loop interface circuit. The micromachined thermal probe has a thin film metal bolometer sandwiched between two layers of polyimide for high thermal isolation and mechanical flexibility, and a tip with a diameter of approximately 50 nm which provides fine spatial resolution. The circuit includes a proportional-integral (PI) controller which couples to a Wheatstone bridge circuit in which the bolometer forms one leg. The PI controller adjusts power supplied to thermal probe, compensating change in heat loss from probe tip to sample and keeping the resistance bridge balanced. It permits precise control of probe temperature to within 2.3 mK, and widens its applications to microcalorimetry. The probe is used in thermal mapping and microcalorimetry applications. A calibration method based on microcalorimetric measurements of melting temperature is presented for the probe. Scanning thermal images show a high signal-to-noise ratio of 15.7 for 300 nm thick photoresist in which the minimum detectable thermal conductance change is <23 pW/K<23pW/K (which corresponds to a topographic change of 7.2 nm). Subsurface scans show a signal-to-noise ratio of 15.5 for variation of 1.0% in thermal resistance for a topographically smooth surface.© 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69814/2/RSINAK-75-5-1222-1.pd

Virtual microfluidic traps, filters, channels and pumps using Marangoni flows

"This paper describes how Marangoni flows of various forms can be generated in thin liquid films for the purposes of microfluidic manipulation. Several microfluidic components, including traps, channels, filters and pumps, for manipulating aqueous droplets suspended in a film of oil on blank, unpatterned substrates are demonstrated. These are 'virtual' devices because they have no physical structure; they accomplish their function entirely by localized variations in surface tension (Marangoni flows) created in a non-contact manner by heat sources suspended just above the liquid surface. Various flow patterns can be engineered through the geometric design of the heat sources on size scales ranging from 10 to 1000 um. A point source generates toroidal flows which can be used for droplet merging and mixing. Virtual channels and traps, emulated by linear and annular heat fluxes, respectively, demonstrate nearly 100% size selectivity for droplets ranging from 300 to 1000 um. A source of heat flux that is parallel to the surface and is triangular with a 10deg taper serves as a linear pump, translating droplets of about the same size at speeds up to 200 um s[?]1. The paper includes simulations that illuminate the working principle of the devices. Models show that Marangoni flows scale favorably to small length scales. By using microscale thermal devices delivering sharp temperature gradients, it is possible to generate mm s[?]1 flow velocities with only small increases (<1deg) in liquid temperature."http://deepblue.lib.umich.edu/bitstream/2027.42/64184/1/jmm8_11_115031.pd

A Si-micromachined 48-stage Knudsen pump for on-chip vacuum

This paper describes a thermal transpiration-driven multistage Knudsen pump for vacuum pumping applications. This type of pump relies upon the motion of gas molecules from the cold end to the hot end of a channel in which the flow is restricted to the free molecular or transitional regimes. To achieve a high compression ratio, 48 stages are cascaded in series in a single chip. A five-mask, single silicon wafer process is used for monolithic integration of the designed Knudsen pump. The pump has several monolithically integrated Pirani gauges to experimentally measure the vacuum pumping characteristics of the pump. It has a footprint of 10.35 × 11.45 mm 2 . For an input power of 1350 mW, the fabricated pump self-evacuates the encapsulated cavities from 760 to ≈50 Torr, resulting in a compression ratio of 15. It also pumps down from 250 to ≈5 Torr, resulting in a compression ratio of 50. Each integrated Pirani gauge requires ≈3.9 mW of power consumption, and its response is sufficiently sensitive in the operating pressure range of 760–1 Torr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98610/1/0960-1317_22_10_105026.pd

MICROMACHINED INTRALUMINAL DEVICES FOR ACTIVE AND PASSIVE ELECTROMAGNETIC MEASUREMENTS OF FLOW

ABSTRACT This paper outlines architectures for implantable (active and passive) sub-systems intended for monitoring of intraluminal blood flow by electromagnetic transduction, and presents the fabrication and test results of select components within these sub-systems. Central to both schemes is a ringshaped intraluminal stainless steel cuff with two electrodes. In the presence of a magnetic field, it produces a voltage proportional to the flow velocity. It is fabricated by microelectro-discharge machining and deployed by an angioplasty balloon. Cuffs deployed within 3-mm i.d. silicone tubes demonstrate linear and symmetric responses of 3.1-4.3 µV per cm/sec over 180 cm/sec with magnetic fields of about 0.25 T. In the passive monitoring scheme, voltage from the cuff modulates a varactor that is also connected to an antenna stent (stentenna). This approach is explored using a hybrid diode for the varactor and a stentenna deployed within a mock artery. Preliminary tests in saline indicate that an external transmitting coil will experience shifts in phase spectrum of 2.0-3.3 KHz/mV of output from the cuff