Steffen Krumbholz

Low profile power inductors based on ferromagnetic LTCC technology

Based on a compliant LTCC (low temperature co-fired ceramic) material system which allows the integration of soft magnetic NiCuZn ferrite layers in combination with Au and Ag thick film conductors, ultra low profile inductances of thickness between 200 and 400 mum have been developed and characterized. The designs of toroidal and spiral inductors of size between 2 and 6 mm were optimized. Inductance values in a range of between 1 and 10 muH at currents of up to 1 A and q-factors up to 30 at frequencies up to 1 MHz have been obtained. The DC resistance was between 40 and 200 mOhm depending on the number of windings. Inductance values and q-factors were measured as function of frequency, DC-bias and AC current. These inductors can be used for DC-DC converters for portable electronics or micro systems where the device height is of major concern

Optimization of efficiency and energy density of passive micro fuel cells and galvanic hydrogen generators

A PEM micro fuel cell system is described which is based on self-breathing PEM micro fuel cells in the power range between 1 mW and 1 W. Hydrogen is supplied with on-demand hydrogen production with help of a galvanic cell, that produces hydrogen when Zn reacts with water. The system can be used as a battery replacement for low power applications and has the potential to improve the run time of autonomous systems. The efficiency has been investigated as function of fuel cell construction and tested for several load profiles.

Development of micro fuel cells with organic substrates and electronics manufacturing technologies

A PEM micro fuel cell system is described which is based on self-breathing PEM micro fuel cells in the power range between 1 mW and 1 W. Micro patterned substrates were used as micro flow fields and replacement of gas diffusion layers (GDL). An analytical model was developed to estimate the losses in such structures and optimize channel design and current collector metallization. A detailed comparison was made between two different designs: pin structures and channel structures. A variety of micro fuel cells with variations of design parameters were tested to verify the model. As a result, micro fuel cell fabrication can be optimized in terms of cell performance and production costs. A maximum power density of 160 mW/cm2 has been achieved with the GDL-less design and a current collector pitch of 400 mum with commercial membrane electrode assemblies.