Dohyuk Ha

Selective Wireless Power Transfer for Smart Power Distribution in a Miniature-Sized Multiple-Receiver System

In a multiple-receiver wireless power transfer (WPT) system, determining the condition for uniform power distribution at a high transfer efficiency is a challenging issue. In this paper, a selective WPT technique using magnetic resonance coupling (MRC) is introduced for smart power delivery in a multiple-receiver system. The proposed method selectively and exclusively delivers power to only one designated receiver among multiple receivers, eliminating the cross-coupling effect and unbalanced power division problem across the receivers. This is achieved by separating the resonant frequencies of the receivers to isolate the coupling effects between coils. The power division ratio of the receivers is controlled by changing the duration time ratio for power transfer. In this paper, a one-transmitter three-receiver selective MRC system is designed and fabricated. The power distribution is demonstrated under impedance matched condition, showing a power transfer efficiency of 24%-29% at a very small coupling coefficient of 0.01 with a 12-mm-diameter receiver coil. Distance compensation and a one-way communication of time division multiple access are demonstrated for a multiple-receiver system, using the proposed method.

3D packaging technique on liquid crystal polymer (LCP) for miniature wireless biomedical sensor

This paper presents a novel 3D packaging technique for a miniature wireless biomedical sensor. The end goal of this sensor is for implantation into the eye of a mouse, therefore size is extremely limited. The application makes the packaging of the sensor and control of IC a difficult challenge. The thickness of the unit must be less than 300 microns total. It is demonstrated in this paper that the thickness requirement can be met using novel epoxy interconnects and that micro-vias can be implemented in the package to distribute signals vertically to limit the eventual area of the device. First, the layer-to-layer interconnection between silicon and liquid crystal polymer (LCP) layers is demonstrated using a magnetically aligned Z-axis anisotropic conductive adhesive (ACA). The total thickness of the IC and the packaging layer is less than 150 microns. The resistance through Z-axis ACA represented 1.15 Ω on average for 75 micron pads. Second, 3D transitions through LCP via holes of 20 µm are demonstrated, which are suitable to distribute signals through the small form factor unit. In this paper, we demonstrate transition from an antenna layer through the LCP to a layer above where a rectifier resides. RF power received by a loop antenna on the bottom LCP layer is transferred to the rectifier on the top layer and generates 5 volts of DC voltage. These miniature 3D packaging techniques could make it possible to integrate all components in the small area (500 µm × 500 µm) to implement an implanted wireless biomedical micro-sensor.

Ultra-thin tag fabrication and sensing technique using third harmonic for implantable wireless sensors

This paper presents the fabrication of an ultra-thin tag for identification and sensing applications in extremely small implantable regions. Particularly, we are demonstrating the capability to create a telemetry system which is implantable in a mouse eye. This system will eventually be able to monitor intraocular pressure (IOP). The small size of the mouse eye presents challenges for surgery and the integration of components. Therefore, there is a need for a device which is biocompatible, flexible, compressible, self-expandable, and thin enough for implantation. This paper demonstrates the fabrication of a thin tag with a self-expandable Nitinol antenna, polymer based embedded components, and high density routing. Telemetry with a small tag implanted inside of the eye is established for the first time using the 3rd order harmonic response from the implanted device.

Parylene Interposer as Thin Flexible 3-D Packaging Enabler for Wireless Applications

This paper presents a novel, all-Parylene, thin, flexible 3-D packaging technology with an application demonstration of wireless powering. Parylene is utilized as a base substrate of a packaging interposer, and multilayer thin films are conformally stacked on the Parylene substrate. High-density (450 pF/mm2) metal-insulator-metal capacitors are implemented with an ultrathin (~47 nm) deposition of Parylene-N. The energy storage capabilities as well as RF characteristics are characterized. To demonstrate interposer applicability, an RF energy-harvesting study is performed by implementing a rectifier circuit on the Parylene interposer utilizing embedded capacitors of wide-ranging values and an antenna. Finally, substrate folding tests are performed to verify the applicability of the Parylene interposer in a flexible form factor without undergoing degradation in energy-harvesting capability. The thin-film flexible capacitors are demonstrated to not short-circuit even under the stress of folding the interposer.

Sub-cubic millimeter intraocular pressure monitoring implant to enable genetic studies on pressure-induced neurodegeneration

There is often a strong correlation between elevated levels of intraocular pressure (IOP) and glaucoma; however, the underlying mechanisms that lead to blindness are not well understood. The key may lie in the study of genetic factors which determine IOP and lead to glaucoma-related blindness. Mice are typically used for genetic research due to their short generation time and accelerated lifespan, manageability, the availability of established and pure lines, and the ability to manipulate the genome. Post genetic manipulation, IOP monitoring at regular intervals is needed and for large scale testing, on the order of thousands of mice, it is crucial to have at least a partially automated data collection scheme. This work presents a fully wireless system on a chip that measures 300 µm in its widest dimension, has a wireless microwave-based data and power link, and is capable of relaying digitized pressure recordings to a nearby base-station.

A planar parasitic array antenna for tunable radiation pattern

A planar cross-type parasitic patch array antenna has been successfully demonstrated to give tunable radiation patterns. Even with readily available commercial varactors, approximately 30 degrees of tunability is achieved. The simulated result is well matched to the measured result. If different varactors were used with an increased capacitance range then the antenna pattern could be tuned more, however more side lobes would also be introduced.

Thin-film multilayer Parylene interposer for high-density 3D packaging with embedded capacitors

A novel all-Parylene based multilayer organic interposer for high-density 3D packaging is presented. The multilayer interposer consists of both a thick 50µm Parylene substrate layer as well as thin layers, down to ∼50 nm, which are formed by successive conformal thin-film deposition. The processing of the layers utilizes standard thin film techniques such as photolithography, dielectric/metal deposition, and dry/wet etching. This allow excellent control over feature dimension both vertically (<0.1 µm) and horizontally (< 10 µm). On a multilayer design platform, high-density (∼ 450 pF/mm2) metal-insulator-metal capacitors are implemented with an ultra-thin (47 nm) deposition of Parylene-N as a capacitor dielectric. Capacitances and breakdown voltages are characterized over fabricated capacitors of various sizes. To demonstrate the Parylene stack-up is designed and implemented. For directly transmitted RF power, the rectifier generates 6.35 Volts of DC voltage. This shows the embedding of both the RF capacitors as well as the high valued storage capacitors is successful and applicable to RF power delivery.

A compact-size packaged third-order harmonic tag for intraocular pressure (IOP) monitoring inside a mouse eye

This paper shows measurement of intraocular pressure (IOP) within a mouse eye. Three main challenges faced the development of a device for the measurement: the size of the mouse eye, the depth of the anterior chamber where the device will be implanted, and the maximum allowable incision size. These factors all limit the size of the device. In addition, a novel detection scheme is required which enables detection of changes in IOP with high resolution. This paper presents the fabrication process of an ultra-small size Parylene tag in which a micro-electromechanical systems (MEMS) capacitive pressure sensor is packaged with a self-expandable Nitinol antenna and a diode. From the device implanted inside the mouse eye, a resonance frequency shift of the third-order harmonic signal was detected with a sensitivity of approximately 1.5 MHz/mmHg at an 11.5 cm distance from the sensor as the pressure inside the mouse eye changed. This work thus shows the feasibility of IOP monitoring using the third order harmonic from a device implanted inside the mouse eye.

Power distribution to multiple implanted sensor devices using a multiport bandpass filter (BPF) approach

This paper presents a magnetically coupled bandpass filter (BPF) approach for power distribution to multiple implanted devices. The BPF design approach accounts for the multiple loads and enables maximum power transfer into each individual receiver for given coupling coefficients between the coils. The proposed concept is demonstrated by showing power distribution to two identical receivers below biological tissue through an external repeater on the tissue surface. In order to mimic biomedical implants, the test structure is fabricated using 25 μm thick liquid crystal polymer (LCP) substrates covered with a surrogate for biological tissue. The power transfer efficiency (PTE) distributed to each receiving unit is measured as 20.7 % for each of two devices while the total power transfer to a single receiver shows an efficiency of 42.2 % indicating that the power distribution only causes a power loss of 0.8 %. Therefore, the results imply the utility of the proposed design approach for power distribution to a network of biomedical implants.

A cavity-backed slot antenna with high upper hemisphere efficiency for sewer sensor network

A wireless sewer sensor network has been widespread to monitor combined sewer overflow (CSO) causing human health and environmental hazards. To enable the wireless interconnection between sensor nodes, a radiator needs to be embedded into a manhole cover with sufficient mechanical strength. In addition, the high efficiency in upper hemisphere is essential for successful communication to above-ground sensor nodes. In order to meet these requirements, a full wavelength slot antenna embedded in a shallow cavity inside a cast-iron manhole cover is designed. An electromagnetic analysis is conducted to verify the antenna design. Simulation and measurement show a good agreement. The result shows 2.5dB higher total radiated power in three-dimensional upper hemisphere, compared to a half wavelength slot on the same substrate without a cavity.